Thursday, September 10, 2009

Further Battles of the Spherical War Cows

In the comment thread to last week's post on lasers versus kinetics, Battle of the Spherical War Cows, I ventured a way to reduce that unending debate to a formula. Because calculus is above my math pay grade I worked it out using a spreadsheet, smashing up some lasers by throwing lots of kinetics at them. Among other things, I learned that the Killer Bus I proposed a couple of weeks ago is in fact a lousy way to deliver a kinetic punch.

As a service to bloodthirsty geekdom everywhere, I've refined the formula and now offer it to the world.

Suppose guided kinetics have faceplate armor of Super Nano Carbon Stuff (thermal properties like graphite, but strong), 1 meter thick. Mass of the faceplate depends on its shape, but as a broad guess this target seeker might have a ton of faceplate armor, plus another ton for the service module with guidance system, thrusters, and so on. The whole weapon is thus comparable in size and mass to a torpedo. It can be sent on its way by a rocket booster, a bus spacecraft (expendable or recoverable), or a mighty powerful coilgun.

The laser that engages it can be specified by average beam power (whether continuous or in pulses), wavelength, and size of the main mirror or other focusing optics. I use Luke's formula for continuous-beam heat damage, and follow Anthony Jackson's rule of thumb that drilling a laser hole becomes inefficient beyond a depth/diameter ratio of 50:1.

In ideal, spherical-cow conditions, how good a defense the laser puts up is given by this formula:


K = 1750 * P * D / (L * V)

Where

K = incoming kinetics destroyed

P = beam power (megawatts)
D = mirror diameter (meters)
L = wavelength (nanometers)
V = closing rate (km/s)


Example. A 25 MW, 1000 nm IR laser firing through a 3 meter mirror, against kinetics closing at 10 km/s:

1750 * 25 * 3 / (1000 * 10) = 13 (0.53 per MW)

So this laser will take out 13 target seekers with 1-meter faceplates before getting scragged by #14. The first incoming is taken out at nearly 1000 km range, half of them beyond 100 km.


Another example, higher techlevel. A 100 MW, 250 nm UV laser firing through a 10 meter mirror, against kinetics closing at 100 km/s:

1750 * 100 * 10 / (400 * 100) = 173 (1.73 per MW)

This powerful, long range laser will defeat an impressive 173 fast target seekers closing at 100 km/s. That is a lot, but dozens of aerial torpedoes were fired at Yamato and Musashi. This laser scores half its kills at ranges over 1400 km.


Now, a Ravening Beam of Death, a 1 gigawatt, 1 nanometer X-ray laser firing through a 1 meter telescope, against kinetics closing at 1000 km/s:

1750 * 1000 * 1 / (1 * 1000) = 1750 (1.75 per MW)

It seems that even kinetics thrown at Incredible Speed can't survive a Ravening Beam of Death, unless you throw a truly enormous number of them. A mere 1750 torpedoes aren't enough.


But all is not lost for kinetics. The key to successful kinetics turns out not to be huge ones, or even super duper fast ones, but lots and lots of small ones. Suppose that you can build a mini target seeker, with a face shield only 10 centimeters thick, but with the same proportions as the big ones. It might have a mass of a couple of kilograms, and be roughly the size and shape of a soft drink can ... a Soda Can of Death!

The number of these mini seekers you need to launch in a salvo goes up by a factor of 100 - but the total mass of your salvo goes down by a factor of 10.

To overwhelm the Ravening Beam of Death you need a staggering 175,000 Soda Cans of Death, but their combined mass of faceplate armor is now only 175 tons, for a total weight of ordnance of a few hundred tons. And if cost is proportional to mass - a fair first approximation, in most cases - the salvo will only cost a tenth as much as before. Is a few hundred tons of high-tech hardware, the equivalent of a single fairly small spaceship, too much to ask for taking out a Ravening Beam of Death?


A few lessons emerge from this. Unlike the World Wars image, laser defense against kinetics is not a task for 'secondary' armament - it is a job for your most powerful laser firing through your largest optics. The laser in our first example needed 5 minutes of steady zapping to defeat 13 target seekers. That same zap, directed against a single target, will burn through half a meter of Super Nano Carbon Stuff armor at 1000 km.

Kinetics should be fired in salvoes, enough to overwhelm the target. Launching them one at a time is like those bad guys who send in ninjas one at a time for the hero to defeat. (If you fire them sequentially from a coilgun, you'll need to bunch them up while enroute to the target.)

And if the salvo is enough to saturate a powerful laser defense, the target is unlikely to go staggering on its way from a few heavy hits. Overkill piles up quickly. If our second is attacked with a salvo of 200 target seekers, it will (ideally) stop the first 173 ... then get whacked by 26 tons of slugs, at least, hitting at 100 km/s. Kinetic salvoes almost always either fall short, or overkill the target.


As for the Purple-Green debate, the lesson is, it depends. If you want lasers to dominate the space battlefield, with kinetics not a factor, tweak laser performance so that no practical salvo can defeat it. (You can tweak the practical engineering as well as the physics; gigawatt lasers may just not be practical.) Vice versa if you want kinetics to dominate. If you want both beams and kinetics in play, tweak the factors so that the most powerful lasers can be defeated, but only by a massive and costly salvo.

So zap away or slug away as you please. Just make sure the parameters fit your desired result!


Related posts: Laser weapons, kinetic weapons (two parts), and my first on the battle of spherical war cows. Oh, and space fighters. And on all these subjects, always check out Nyrath the Nearly Wise's site about Atomic Rockets.

123 comments:

Eric said...

Does one really need to zap through a lot of armor to kill a KKV? Seems to me the outgassing from a laser zap is enough to deflect the kinetic from its course. In that case i don't need to destroy the slugs to defeat them.

pspinler said...

One other thought about the kinetics v. laser debate. If I recall correctly, one of Mechdan's/Isaac's favorite configurations over on sfconsim-l was 2 or more laser stars with some degree of separation. This would allow each to fire on the other's targets (e.g. incoming kinetic kill vehicles), but from an angle, and thus largely bypassing the targets' armor.

Thus, if you have n laserstars able to give each other fire support, the required kinetics per kill go up by some factor larger than n.

The interesting consequence of this is that soda cans of death become even more attractive - there's not much armor there to begin with, and it's easier to carry more throw weight of soda cans than any larger form of kinetics.

Anonymous said...

Hmm...giant shotguns (attached to spacecraft) that instead of firing buckshot, shoots 40mm 'pellets'...at 10 to 100 Km/s.

So...if by some stupendious blunder, the Kineticstar Elmer Fudd runs afoul of the Laserstars Buggs Bunny and Daffy Duck, would the Kineticstar be able to escape by saturating the Laserstars' rate of fire before getting out of range, or would the Laserstars fry it? Something to think about.

Ferrell

pspinler said...

I wish I thought of all this stuff at once, but, two other thoughts occurs to me. One favoring even more, smaller kkv's, and one arguing strongly against them.

The larger the kkv salvo is in number, the harder the job the tracking radar / lidar has to find and track all the targets. This job also gets harder the smaller the kkv. Finally, the laser's own defensive shots make its job worse yet - every kkv it fragments makes multiple more targets it has to find, track, and determine whether or not they are on a collision course (or might be able to thrust themselves into a collision course).

Once more, yet another argument toward massive amounts of smaller vehicles.

One counter argument to smaller kkv's - smaller == limited target seeking delta v.

Hmm, the delta v argument tips the balance back toward the laser star. Assume the two ton torpedo as a starting point. The initial parameters were 1 ton of armor (1000 kilos), and 1 ton of everything else (another 1000 kilos). Give that 1 ton of everything else an 85% fuel fraction, or 850 kilos of fuel, leaving 1150 kilos of total empty mass. That's a mass ratio of apx 2000 / 1150 =~ 1.74, and a propellent fraction of 42.5%.

According to atomic rockets, a solid fuel aluminum/oxy has a exhaust velocity of 2,800 m/s, or 2.5 km/s. That gives the killer torpedo a delta v of 2.8km/s * ln(.425) = 2.395km/s.

Compare that to a soda can of death. If I get the weight frm the original post correctly, 100 soda cans weigh 1/10 as much as a torpedo, so each torpedo = 1000 cans, and one can weighs 2 kilos. That right? Also, you state that 175,000 cans have a combined 175 tons of armor, yielding 1 kilo of armor per can, right?

If that's so, then each can has a pitiful 1 kilo for both guidance and fuel and thrusters. That's got to be a much smaller fuel fraction, if any at all, and thus much less delta v.

Ergo, the torpedo has a lot of jink in it, even with the crappy but logistically stable aluminum/oxy solid rocket. The can, on the other hand, likely has little or no jink, and a target could thrust out of a can swarm's way much more easily.

This gets even worse if one assumes ravening death beams, from which the cans are launched from far far away, out of the beam-o-death's practical range. Otherwise, were the can's buses hold on to the can inside the ravening death beams' range, then the buses would be killed before they could release.

So, there's a significant drawback to small kkv size, inadequate jink. Adequate jink, in this case, being defined as the distance the target laser star can jink while the kkv crosses it's kill zone. This would govern minimum effective kkv size. Any smaller, and the kkv misses regardless. But larger sizes limit total kkv numbers.

In summary, an interesting balance, and interesting bit of plot and game tension. Did the laserstar successfully conceal it's engine's last few milligee's of thrust capability? Is the kkv carrier's load out the right balance of jink and numbers? Can the laser star dump a tank, sacrificing total delta v to gain another milligee and dodge this wave, but leaving it at the mercy of the next? Can the kkv's be stacked, adding to total kkv delta v, and if so, did the tactical officer guess the right initial kkv configuration?

Hmm, drama. Not bad.

-- Pat

Rick said...

Eric - Interesting question. In the ideal, theoretical world of spherical cows, though, I ignore it, along with pesky details about how laser stars track thousands of incomings, or for that matter how you deploy them smoothly.


pspinler - Lasers defending each other is another little detail I ignored. But if you spin the kinetics, they don't need much sidewall armor, because a beam from the side has to function like a lathe rather than a drill, cutting through much more armor per cm of penetration.

On the delta v of mini-kinetics, the mass of propellant doesn't really matter, only the proportion of mass. Suppose you have a 2 kg kinetic with 1 kg of armor, 150 grams of 'everything else,' and 850 grams of fuel. It will have the same delta v as the big torpedo with the same proportions.

Miniaturizing the thrusters, guidance, and so forth into 150 grams is pretty demanding ... but we're getting pretty good at building small stuff, and I wouldn't want to bet against it 100 years from now.


Ferrell - Giant shotguns are devastatingly effective ... but only if the buckshot is 'smart.'

Kedamono said...

So basically, you use the old "Fuzzy Wuzzy" tactic with KKVs?

I just had a thought. What if in those 173 KKVs you're sending up against the target, you have one or two bomb-pumped x-ray laser warheads? It just waits to be targeted by a laser, and then it skews itself so that it is aligned with the attacking laser beam and then detonates, firing off the one-shot Ravening Beam of Death at the attacking laser's optics.

Even if it misses by a couple of meters, it's going to do a whole lotta hurt on the target ship.

Anonymous said...

Now forgive me if I sound a little off, atm I am writing this reply when it is currently two in the morning where I live.

Anyway, from what I am reading in this blog entry, there is an apparent limit to the number of KKVs (or AKVs, pick whatever acronym sounds right for one's Space Opera Universe) that a laser can take out before it becomes "saturated" with targets.

Even so, the launching of that many kinetic rounds, even ones small enough to require a Sabot to keep em all together while in the gun barrel, would seriously limit the number of salvos a Kinetistar could fire before it runs dry. Probably reason enough to deploy more than one Kinetistar in a Task Constellation, probably taking up a single Division of that constellation.

Either way, I like Rick's comment on the Purple vs. Green debate in that the answer depends upon the situation at hand. It doesn't really support either weapon system camp that satisfies (or dissatisfies, depending upon one's point of view) both parties. Might even be enough justification for a combat spacecraft to have a mixed layout of weapon systems similar to surface naval vessels of today for either offensive or defensive purposes.

Speaking of which, and correct me if this little issue has already been discussed, but in logistical terms what design strategy is considered easier in both construction and maintenance: Multiple-Mission Crafts or Singular Purpose Crafts such as Laserstars and Kinetistars?

- Sabersonic

Citizen Joe said...

I agree with Sabersonic. Rick's analysis of the war cows proves that either methodology could work and that it boils down to setting based numbers and tactics.

adam_grif said...

Can we get some comparitive masses for a "laserstar" verses a "kinetistar"?


Depending on the results, we may end up in situations where stationary "mines" and defenses will prefer one weapon system, with offensive craft favoring the other based on fuel ratios and the like.

ajackson said...

This largely ignores the role of countermissiles. If you put up a layer of beads, or sand, or sheet, or whatever, the total areal density required to stop a salvo passing through (assuming zero homing capability) is some multiple of the areal density of the projectiles; at extreme velocities the required mass ratio may be hugely in favor of defense (if we assume 1 MJ/kg to kill an impactor, at 10 km/sec the defense needs 2% of the areal density of the projectiles. At 100 km/sec that drops down to 0.02%). Since smaller projectiles have lower mass, they become easier to erode. The likely lesson here is that you use primary beams to kill stuff that will get through your kinetic shielding.

Kedamono said...

@ajackson: The problem with counter-missiles is that they breed counter-counter-missiles, which breeds counter-counter-counter-missiles, until you get a sky full of moving objects and debris and your ship has to move through all that crap.

A decently balanced warship would have missiles, coil-chainguns, AM lasers, and other things we haven't thought of yet. Like decoys. Each KKV can launch two dozen "decoys", highly reflective bags filled with fast expanding foam. They stand out both visually and on radar, and pose a risk because they have mass, perhaps around 5kg, and can do a hurt of the target ship if they hit.

I should have posted this in the other Spherical Cows post, but how does a foam react to a 25MW laser beam? The foam has all these cavities and each cavity is full of gas, what effect does that have on penetration? Would a light, silica foam be more resistant than a dense carbon armor?

Luke said...

Kedamono: A 25 MW laser would burn through a low density foam like a blow torch through tissue paper. All the cavities make it easier for the beam to penetrate, since the evaporate can expand sideways rather than just jetting out the front.

Mark said...

It seems that the math argues for long, small diameter KKVs to give as much mass as possible with the least exposed surface area, which is also good for penetrating the target's whipple shield. so instead of a coke can, a javelin, or at least a pringle's can.

maneuvering engines on the KKV are probably monopropellant, simple, fairly cheap, no need for an oxidizer, and already in use on satellites.

Rick said...

Kedamono - BPXLs could be salted in among big torpedo-size kinetics, not so easily among small ones. If they are effective enough they'd replace impact kinetics, but I admit a bias to the non-nuclear impact kind.


Sabersonic - For kinetic strikes against a first class laser star you may throw several busloads at it, so I think moderate size carrier buses are preferable.

And I am leaning toward recoverable buses. An expendable bus can use all its delta v for runup speed before launching kinetics, a recoverable bus only about a third. But the bus probably costs at least twice as much as the kinetics it carries, so most of the time you want it back. But the bus is probably unmanned, so if you need to expend it you can.

The bus itself does not need to 'shoot' the kinetics; it can simply release them at high relative speed, 'dive bombing' its target. That is lancer tactics. But a moderate powered coilgun providing a lateral kick can help the bus stay clear of the enemy, helpful if you want to recover it.


Adam - Comparative masses are very setting dependent, but in general I'd expect first class laser stars to be Big. As large as the technology, finance, and strategic situation allow.

If you are firing kinetics at multiple km/s from coilguns, you also need 'capital ships,' because in both cases the most powerful installations have a disproportionate advantage, particularly by outranging opponents. In space the shorter ranged weapon has very little chance to sneak up - except perhaps in cluttered orbital space.

If kinetics are launched from bus vehicles, on the other hand, there is no particular advantage in size, and flexibility in numbers. So I would tend to see kinetics based fleets as having lots of modest sized bus vehicles.

The analogy of battleships and destroyers is hard to resist, but don't take it too far. Kinetic buses may be fast, but they are not 'handy.'

Suppose a hostile expeditionary force is approaching from deep space. If kinetics need to be fast to be effective, much more than 10 km/s, you need buses with high Isp drives.

These may launch from parking orbit a couple of weeks in advance, with milligee drives putting on about 1 km/s per day, heading into the orbital track of the approaching constellation.

The buses put on maybe 15 km/s relative to Earth, head on at a constellation that has only just started to orbit match, and is going about 10 km/s relative to Earth coming the other way. (This simplifies orbital intercepts!)

But that is how you get 25 km/s kinetics in a midfuture setting with Realistic [TM] drives.


ajackson - Welcome to the discussion thread! A couple of thoughts on countermissiles. In the general case of a kinetic fight, the heavier throw weight wins.

In this case, on the one hand the defenders' Kirklin mines don't need armor; on the other hand, the defender is a big spacecraft with bulky fuel tanks and broad radiators, and a much larger target cross section than any of the kinetics in play. Call it a wash.

The upshot is that a Kirklin defense is only effective if its size and cost are comparable to the salvo it defends against. This doesn't rule it out, because Kirklins can be an added layer of defense, but carrying them is the homage that laser stars pay to kinetics.

Incidentally, coilguns could be an ideal weapon to launch Kirklins, which don't have to be sent off all that fast. Since a big laser star has plenty of onboard power, it can carry a couple of moderate power coilguns to boot Kirklin mines out at 1 km/s or so.


Kedamono - The regress of countermissiles is limited by the size/cost of guidance packages, which is independent of missile size. Smart soda cans are easy to imagine; smart bullets are a lot more demanding.

Rick said...

Mark - Side fire from another defending laser limits how spearlike the seekers can be. Even spinning, they'll need some side armor. Also they need to make lateral correction burns, so they need thrusters that kick them sideways. These can't be mounted very effectively at the back end of a long narrow projectile. But I haven't tried to work it out, so the above is an educated guess.

Well, so is this whole blog, really.

Citizen Joe said...

I think that you'll find that most strikes will occur on the forward or aft quarter of a target. Forward and aft refer to the direction of travel, not the actual ship locations. The reason is simple. If you are off by a millisecond on the forward quarter, you either hit a millisecond earlier or later, but you still hit. A millisecond of error perpendicular to the trajectory of the target means an error of tens of meters, likely producing a near miss. Rear quarter strikes are also easier, but rear quarter countermeasures are pathetically easy since closing velocities cancel each other out rather than stacking.

Since a ship traveling in deep space is going to encounter the occasional small bit of debris that would be mission kill at interplanetary velocities, it would have to be assumed that those ships have some sort of defensive countermeasure, which is deployed forward of the ship.

That could be some sort of auto targeting point defense lasers, but I wouldn't trust a system like that. Mostly because the lasers have to constantly stare into space and you need to keep the capacitors charged all the time. That means your defense system is always exposed and it is NOT regenerating.

Another option is to throw some sort of regenerative (recapturable) fluid forward of the ship. Small objects would hit that mass and detonate. Then your recover cycle recaptures the liquid and throws it forward again. It is sort of a long range regenerating whipple shield. The drawback is that throwing the shield out there is basically accelerating you backwards. Also if you change course, you'll lose your shield. And lastly, the shield will interfere with your lasers and sensors directly forward.

Never the less, any ship traveling at those speeds MUST be able to defend against something coming at Kinetistar speeds for simple navigational reasons. The only difference is that while navigating, kinetic impacts are random and sporatic, whereas combat kinetics are targeted and frequent.

Anonymous said...

Just a reminder, the results are for one laser acting as a counter. If the technology is such that they can pump multiple TW into the drive, then they should be able to direct that same power into other systems, including multiple laser banks. Which makes the mass required to get through this shoot up accordingly.

Also, does using a phased array change the formula much or at all? I've always imagined that for PD the ships would make use of phased array lidar systems by pumping more power into them, though against buses that are essentially miniature ships using the primary weapons makes more sense.

Are their any plausible figures for the soda cans of death, or are we looking more at them being unguided slugs? The volume constraints put some pretty strict limits on them.

Jean Remy said...

" [...] they should be able to direct that same power into other systems, including multiple laser banks."

Unlikely. I would assume Laserstars would be built in the same spirit as an A-10: You build the biggest baddest meanest laser you can, you slap it onto the largest mirror you can build, then you wrap the ship around that. To build more than one laser would require another mirror, and it's really the mirror that will determine the size of your ship. If you assume cigar-shaped vessel, its beam would be just a little more than the diameter of you laser. If you can build a 10m mirror, that gives you a ship of equivalent beam at the very least.

"Never the less, any ship traveling at those speeds MUST be able to defend against something coming at Kinetistar speeds for simple navigational reasons."

I would assume that's the role of an armored shutter. During normal travel it is kept close, once the kinetics start flying you open it and start shooting.

The fun part is this is also when the enemy Laserstars start trying to shoot your mirrors out from under you, so now you have to decide whether to shoot the enemy Laserstars or the incoming kinetics first. Because of that I would think you don't really need to throw as many kinetics as you have to in a strict kinetic v. laser fight, the game becomes launching enough kinetics that you force your adversaries to unshutter early so you can shoot their lasers. While they do the same to you. And you can't ignore either threats because without mirrors you Laserstars will be mauled by kinetics, but if you don't shoot the kinetics early enough a greater number of them will get through.

Messy messy messy.

Rick said...

Citizen Joe - Firing angles are complicated, because the way the ship points is usually different from its direction of travel. (And direction of travel depends on frame of reference!)

Spacecraft in battle probably try to keep the nose toward the most dangerous opponent at the moment, whether a hostile laser star or incoming kinetics.

I don't think natural collisions are a big concern unless you are going uber-fast, hundreds or thousands of km/s. There doesn't seem to be much talk about protection for civil spacecraft other than STL star probes.


Anon - There's a case to be made that onboard power probably won't go up as fast as drive power. In this century and maybe into the next we'll be using electric drives that need to plug into a reactor (or humongous solar wings). For these drives, onboard power is equal to drive power.

But the more advanced drives, such as fusion, generate thrust directly - instead of feeding energy into a plasma, the plasma generates its own energy. For these ships, onboard electrical power may only be a small percentage of drive power. And a good thing, too, for terawatt drives, because at torch level power density the waste heat is too hot to handle.

I don't know how phased arrays are treated optically - I'd guess just like a mirror, but that is only a guess.

Soda cans of death can have the same mass proportions as big seekers, just scaled down. Say the shield mass is 1 kg, 300 grams for the service section with control unit and microthrusters, and 700 grams propellant. That's enough for about 1.3 km/s of deflect delta v. And it can carry a mini drop tank for use during the long approach, before it gets into laser range.


Jean - I agree with your overall idea about how laser stars are built: around the laser installation; generator, laser, and mirror. Basically to turn it into a laser star you clap on a drive engine, propellant tankage, armor, and a control module (which may or may not have a crew).

But as someone said in comments a few weeks back, the lasers can be physically separate from the mirrors, with a beam path. I could see a bank of lasers mounted internally, all capable of firing through the main forward mirror, but some also having a beam path to secondary mirrors.

The mirrors* are your guns. The laser itself is really your magazine, except that it manufactures the rounds instead of just storing them.

* Or other focusing optics, as for X-ray lasers.

So the main mirror probably drives the design. But a deep space laser star needs lots of propellant, very bulky if it is hydrogen. So the fuel tanks probably determine hull diameter. But for orbital defense, designers might reduce the tankage for a more compact vehicle. For deep space service it would need to carry drop tanks.

I agree with you that it does not take a lot of kinetics to complicate a laser fight. If you have to turn and unshutter your main mirror to engage kinetics, exposing it to zaps it cannot reply to.

Which is why I can see a couple of secondary mirrors, to engage smaller scale kinetic attacks as well flexibility in a constellation engagement.

Rick said...

A general note. It is very natural to think of laser stars as 'battleships.' In some very important strategic ways they ARE battleships. They are big and impressive, and since they are built to keep the peace (on your terms), their peacetime mission of prestige and flag showing is arguably their primary mission, merely augmented by real fighting power.

But battleship analogies are misleading in the technical sphere, which is why I push back against them with ideas like keel mounted jumbo mirrors. The right set of technical circumstances could result in something quite different.

Still, the picture I am getting has a wonderfully predreadnought Belle Epoque flavor to it, with a forward mounted main mirror and a pair of wing mirrors. Mix with a little 18th century because of the gradual accelerations and the geometrical character of constellations.

What I picture is a setting of 'crises' and 'incidents,' with great powers dancing along the edge of war, and occasional flashes - so to speak - of combat.

Luke said...

Rick: For these purposes, a phased array can be treated as a mirror that can instantly re-direct its beam in any direction. And it automatically has adaptive optics for free.

Rick said...

Luke - Thanks for the explanation! That reduces the drawing-off effect of kinetics. You still have to divert enough zaps to stop them, but you don't have to physically pivot a big mirror, or the entire spacecraft.

Citizen Joe said...

I suspect that Laserstars are going to be much more spherical or possibly even disc shaped than other ship types. It could look very much like a gigantic gimballed eyeball.

Jean Remy said...

"I could see a bank of lasers mounted internally, all capable of firing through the main forward mirror, but some also having a beam path to secondary mirrors."

Sorry I wasn't specific. I envision modular solid-state laser arrays rather than one continuous chemical laser assembly, mostly because this is where military laser technology seems to want to be headed: chemical lasers have to pack a lot of noxious chemicals (strangely enough) liquid lasers are all but forgotten, and because solid cavities would be prone to shattering very easily if they were of one piece (not to mention massive, hard to handle, and hard to manufacture). They would be assembled as a series of discrete low power lasers that are then phased together to produce a laser of adequate power. Advantage: if you want to scare a smuggler, a quick low-power beam across his navigational telescope would be a very good illustration you are not kidding. The modules, then, can be combined with multiple pathing and very small auxiliary mirrors for last ditch defense from convergent attacks, or as in the above example to scare a smuggler.

"So the main mirror probably drives the design. But a deep space laser star needs lots of propellant, very bulky if it is hydrogen. So the fuel tanks probably determine hull diameter."

Good points with the fuel tanks dictating the size, however there is a caveat. Their size is flexible about the axes: you can have a long thin cylinder or a big sphere. The mirror is not: it's always a rough disk several meters in diameter, and is no work around. The remass tanks will of course primarily determine the overall volume of the ship, while the mirror would determine the minimum area of its smallest side. It depends on how important a small cross-section is for you, but that mirror would dictate the minimum dimension of the part of the ship it's built in. That said a 1m wide and 500m long hydrogen tank is probably not going to happen, so eventually, and depending on mirror technology, I'd say both mirrors and remass tanks will have a stake in determining the size of the ship's smallest face.

"But battleship analogies are misleading in the technical sphere, which is why I push back against them with ideas like keel mounted jumbo mirrors."

Ship classes are named for their roles, not their tactics. A Cruiser cruises around and shows the flag, a Destroyer defends against the battleship cannot defend against (so they might not be common since there's nothing they can destroy that the Battleship can't destroy faster in space) and Battleships whose task it was to project power across long distances, intimidate, and kill other Battleship. Hence the tactics will be completely UNLIKE naval tactics, the strategic roles (on which their names are based) will be similar. I wouldn't feel guilty then in using those names. Some of them have been in favor for over 500 years (Fregata) despite extremely varied changes in tactics so why would we simply forget them? Caveat: Ships of the Wall were actually named for their tactics. The term dropped out of use already, though.

Anonymous said...

"Mark - Side fire from another defending laser limits how spearlike the seekers can be. Even spinning, they'll need some side armor. Also they need to make lateral correction burns, so they need thrusters that kick them sideways. These can't be mounted very effectively at the back end of a long narrow projectile. But I haven't tried to work it out, so the above is an educated guess."

Actually, theres another problem with spinning as well - the centrifugal force alters the mass distribution of the fuel tanks, making them stop working. When Star Wars was first being considered, they looked at the Soviets spinning their ICBMs to get past beam weapons. It turns out that it changes the distribution of the oxidizer and fuel in SRBs, making them either sputter or blow up, and looked to do similar things to any liquid fueled rocket as well.

Anonymous said...

I had some thoughts about some things that would affect how these Laser vs Kinetics fights work out

Doctrine. If Nation A uses their Laserstars to primarily zap kinetics and as a secondary mission to zap enemy ships, with the Kineticstars primarily used to shoot ships and shooting at inbound kinetics an afterthought. Nation B, on the other hand, uses Kineticstars to target inbound kinetics and then to harrass enemy ships, while the Laserstars are used to zap at other ships and only zapping incoming rounds as needed. This would probably mean that Nation A's smallest Major Constellation would consist of two Laserstars and a Kineticstar; Nation B's smallest Major Constellation would be two Kineticstars and a Laserstar; the two ships providing defense and the single ship being used for offense. Of course, having a minimum of a pair of smaller Armed Space Cruisers in a Minor Constellation might be workable as well.

The largest combat spacecraft would most likely be at least as large as a supercarrier...90,000 to 110,000 tons at minimum, with the crusiers being a quarter of that, and the smaller patrol ships being 10,000 tons or less.

The ships themselves seem like they would resemble those Olympic-style throwing hammers; a massive faceplate with a long, thin trailling structure containing all the rest of the ship's systems. Both Laserstars and Kineticstars would look a lot like each other.

Ferrell

Rick said...

Citizen Joe - configuration will depend on lots of factors (which means it is not hard to get what you want). I think they will tend to be elongated, to minimize cross section across the main shield. But if 'melee' actions are the rule you want to minimize all round cross section, which favors a sphere.


Jean - You're picturing a laser installation much as I am, and power output is highly flexible.

Hydrogen tanks are really bulky. 1000 tons of H2 - which is nothing for the ships Ferrell suggested downthread! - requires a spherical tank 30 meters in diameter, or a cylindrical tank 15 meters in diameter and 100 meters long.

To add to the Belle Epoque flavor, there is something a bit zeppelin-esque about big ships that are mostly tanks of hydrogen (!), with gentle acceleration and necessarily stately motion.

I agree that functional names like 'battleship' can apply to very different types over time. (Or even merely evocative names like 'frigate.') A professional naval blog, Information Dissimenation, often refers to missile cruisers as 'battleships.'

My comment was much narrower. Surely there's a natural human tendency for us to start out imagining laser warcraft as like big-gun era battleships, festooned with turreted laser cannons. Which oddly enough makes us miss how big the main mirror may and probably will be.


Anon - I'm the one who mentioned spin, and yes, I glossed over the practical complications of spinning propellant tanks. A target seeker doesn't need the enormous delta v of an ICBM booster stage, giving the designer more options.

But really this is one of the many complications that can be used to tweak the formula to fit a desired setting. I called this series Spherical Cows because it deals with the idealized physics case. But engineering will have its say, and either kinetics or lasers may be much more limited than simple theory suggests.

My own guess is that kinetics are favored by the meta-point that Michael (was it Michael?) made in the first comment thread. Kinetics are mostly basic space technology, and benefit from constant commercial investment. Even if big industrial lasers are common, lasers firing through observatory mirrors are a specialized technology with mainly military applications.

Rick said...

Ferrell - I plugged your 100,000 ton figure into my rules of thumb for spacecraft, and this is what I got.

Main power plant/drive: 20,000 tons = 20 GW total output
Laser installation: 5000 tons = 5 GW maximum beam power (!)
Support pods (crew, etc.): 5000 tons
Armor: 10,000 tons
Structure and tankage: 10,000 tons

Total dry mass: 50,000 tons
Propellant: 50,000 tons

Full load mass: 100,000 tons

If you want to minimize frontal cross section, your main fuel tank may be 50 meters in diameter and 400 meters along, so the tank alone is the size of a supertanker. Overall length of the main structure could be 600 meters, with the drive engine pylon up to a kilometer long. The wingspan of the radiators is probably 400-500 meters. Faceplate armor may be up to 2.8 meters thick.

I'd give a laser star like this at least a 25 meter main mirror. The laser burns through armor at 4.4 mm/second at a light second, and through a meter in 25 seconds at 100,000 km.

Cost: $50 billion to $500 billion. Have your credit card number ready. :-)

pspinler said...

Just meditating on one other of Isaac/Mechdan's favorite laser multiplier back on sfconsim-l, mirror drones and/or fresnel lens drones. What are the engineering and economics behind this idea?

If it'd work, I can see a fleet of mirror drones being a huge asset to a laserstar - practically extending it's range by nearly double. However, I'm unconvinced they make either economical or engineering sense.

Consider - a mirror drone would be substantially similar to the laserstar itself, only sans laser, and likely with less total delta-v. Consider that one would want a mirror drone to have a substantially similar drive system to the base laser star, so it can meaningfully maneuver in formation with it. It would also have to have a similar sized mirror and/or fresnel lens. Further, as a first approximation, it'll have to carry about 1/4-1/3 the total delta-v of the laser star (e.g. the about same combat maneuver mass budget).

Since fuel tankage is the dominating size and mass factor for a ship, this means that as a back of the envelope estimate, a mirror drone would have to be about 1/4 the size of the laserstar itself, assuming both that the laserstar carried the drone to battle, and that the drone was considered expendable.

Why expendable? In battle, I'd expect such a drone to be shot off from the laserstar, and no one expected the laserstar to be able to catch up to it and recover it later. Also, it'd be the first target of the enemy lasers and kinetics. That's basically it's purpose in life, after all.

Unfortunately, at this size, that means any given laserstar is unlikely to carry more than one mirror drone.

Even leaving out the presumably expensive laser, that still leaves an expensive drive and expensive mirror to pay for, for something likely to not be able to be recovered after battle. Not sure it's worth that.

On the flip side, then, make the drone carry itself to battle - it only requires upsizing the tankage and drive. Problem is, if you're doing that, might as well pay the relatively small marginal cost to add the laser, and get yourself another laser star.

Ergo, my guess is that for all their tactical allure, mirror drones just won't be practical away from a few fixed installations, say, orbital defenses or the Lagrange points.

-- Pat

Jean Remy said...

"Faceplate armor may be up to 2.8 meters thick."

I am going to disagree with putting really heavy faceplates on Laserstars, actually. They make sense on missiles that will get close in with the Laserstars, however the vulnerability of a Laserstar lies in its mirror. Once battle is engaged, unless in a surprise attack at very short ranges, mirrors will be unshuttered at ranges that kill mirrors, not Laserstars. At those ranges the burn rate of carbon armor will be in the micrometers per second, being generous. Even if the mirror vaporizes at the same rate as carbon (I am feeling very generous) a one centimeter face plate would last 10 seconds, while the mirror would be disabled in one second--I can't imagine a mirror being functional with one micrometer of its surface irregularly melted, pitted, vaporized and otherwise damaged. I believe engagement ranges will be even greater than that. If you really want a safety margin, you can have armor a decimeter thick, and you'll still be perfectly safe.

Only in the unlikely case that an opponent wants to score a ship-kill rather than a mission-kill, and are willing to wade in while being shot at, to finally unshutter and shoot at point blank range, would armor of that thickness be needed.

Against kinetics, the armor, not matter how tick it is, will hardly matter: a kinetic kill is overkill.

Jean Remy said...

Oops BIG errata there, blame it on the time
"a one centimeter face plate would last 10 seconds"

That's the rate of burn at one MILLImeter per second. At my stated micrometer it is obviously 10,000 seconds. A "small" error huh?

Rick said...

Pat - I have the same feeling, that at least for deep space service, mirror drones probably are not cost effective.

If your mirrors are cheap, you aren't making them big enough.


Jean - I suspect you are right about the irrelevance of heavy armor.

I tried to work out just how vulnerable mirrors are, using Luke's sim and a great deal of guesswork. The key question is how well mirrors reflect the other guy's laser frequency. Military laser mirrors will be designed for robust broad spectrum reflectivity.

If you achieve 99.9 percent reflectivity against hostile frequencies, it will take the same time to scorch a mirror as to burn through a millimeter of armor. (0.001 of the energy absorbed, 0.001 as much thickness burned through.

But if the enemy mirror is large, you'll have to play your spot over the surface to scorch all of it. This might take a number of seconds, so mirror kill time might be equivalent to the time needed to burn through a few cm of armor.

So you might provide a laser star with 1-10 cm of armor, including a Whipple shield against stray kinetic fragments.

Daniel said...

Rick, will you be doing an update with your rules of thumb soon? Or at least one about estimating the cost of space craft? I've been trying to do some theoretical work on logistics lately and the cost would come into play.

Jean Remy said...

"But if the enemy mirror is large, you'll have to play your spot over the surface to scorch all of it."

I'd actually been thinking along those lines, along the idea of building Keck-like segmented mirrors so damage to one part wouldn't affect the mirror's overall effectiveness too rapidly.

Rick said...

Jean - One possible complication for segmented mirrors is light hitting the gaps. (There's a demi-philosophical question here - what makes all the segments contribute to one beam, for purposes of spot size calculation?)


Daniel - I'm thinking of doing just that. But I can give you the short form. Commercial jets today cost roughly $1 million per ton, 'dry weight' (the plane itself, fully equipped but without fuel, payload, etc.

So I use that same figure, $1 million per ton (or future money equivalent) for a mature tech and quantity production of fairly standard spacecraft, though probably with a lot of options you can specify.

Prototypes, or gold plated military stuff built in small runs with lots of specialized tech, could run $10 million per ton.

But I do plan to do a refined version, allowing that bulk structures such as propellant tanks are cheaper than drive engines or life support plants, etc.

Anonymous said...

A thought occures to me about trying to burn a mirror with a laser...how much of the reflected energy will come back into your mirror and/or other of your ship's structures? Is destroying the enemy's main mirror worth the possible damage to your own ship from a ricochet? After all, these mirrors will be parabolic. I have no idea if this is a valid concern or if it is a non-issue; any thoughts?

Oh, and Rick, since it probably will take a decade to build one of those $50 billion Laserstars, I'll put it on lay-away and make regular payments ;)

Ferrell

Luke said...

Rick: Multiple smaller mirrors joined together act as a larger mirror because the light they reflect is in phase. If you have gaps, the effect is of light diffracting around the gaps, much as it would diffract around a thin structural member in front of a monolithic mirror. This scatters some of the light, but if the gap (or structural member) is thin, most of your light will still be getting to your target. My web page on diffraction might be useful
http://panoptesv.com/SciFi/Diffraction.html .

Ferrel: Parabolic mirrors reflect light from a point into a parallel beam, and reflect light from a parallel beam to a point. When you illuminate the enemy mirror with your own beam, your beam is very nearly parallel, so it will be focused to very nearly the focal point of scope. The beam will spread out from there at the same angle it originally converged at, so by the time it gets to your spacecraft it will be very diffuse.

Anonymous said...

Luke: "Ferrel: Parabolic mirrors reflect light from a point into a parallel beam, and reflect light from a parallel beam to a point. When you illuminate the enemy mirror with your own beam, your beam is very nearly parallel, so it will be focused to very nearly the focal point of scope. The beam will spread out from there at the same angle it originally converged at, so by the time it gets to your spacecraft it will be very diffuse."
Actually, I knew that already; however, the beam will converge at the focal point of the mirror, not the original angle of the incoming beam. I worked with parabolic reflectors for over 20 years, so I'm pretty sure about that last point. Thanks for the input, however!

Ferrell

Daniel said...

RE: Cost

I haven't seen your numbers, but from some quick research I think you may be over estimating the numbers a bit. Looking at the 747, while you are right for todays prices, I think you are ignoring the effects of inflation and a broken market. A 747 clocks in at 276 tons and the first run of those cost 24 million, a far cry from today's 300 million. That would shift it down to $8,680 per ton. This is much more in line with the Areligh Burke and Nimitz class warships, who are about $8,700 and $4,000 per ton, respectively. Similarly, in 1998 prices the F-15 and F-16 were both $90,00 and $81,000 per ton. And I have a funny feeling that if I could find a source for what these cost in 1976 it would be more in line with the others.

When you look over history you see a sharp tick in the prices of hardware from those involved in the iron triangle. Without dragging to much of politics into it, it interestingly corresponds first with the RAND Corporation's Whiz Kids running the procurement show under McNamara, and then even worse with the shenanigans under Reagan.

It would be tempting to put the cost increases down to advancing technology and inflation, except the price spikes for the exact same product to a degree absurdly beyond what the market says it should. While the F-22, Predator, Zumwalft class, and F-35 may all be in the millions per ton, it appears this has less to do with what it really costs to make and more to do with Eisenhower's warning to us.

tl;dr; no politics version - over the longer history and comparing both air and sea craft, trend suggests mature tech should be more about $10^4/ton

Daniel said...

Addendum:

That's all kind of a sideshow really, the real cost to ships is yearly operating budget. A Nimitz class is about a billion per year (food alone each sailor is alloted $7.26 per day worth of food, as of 2005), it would have cost something like $600,000 a year per plane to keep the F-14 around as long as it was originally intended IIRC.

And people wonder where 800 billion a year goes.

Daniel said...

Addendum 2:

Yeah, brain juices are going now. This is what happens when an accounting student gets going :P

Les consider crew costs. Like I said, as of 2005 each sailor was alloted $7.26 worth of food per day by the US Navy. Additionally, once pro pay, hazard pay, BAH, BAS, time in service and tax free zone was factored in, an E-5 was making ~$48k a year.

The Zumwalt class will have 142 sailors and mass 14,100 tons, the Nimitz class has ~6000 squids with the aircrew embarked and masses 100,000 tons. So rule of thumb you are talking less than 1 spacer per 10 tons of dry mass. This 100,000 ton craft would have call it 1000 spacers on it, officers and enlisted, from admiral to recruit. At a mean pay rate equal to an E-5 with 5 years in and the above food consumption, the ship would cost ~$139,000 a day to operate, or north of $50 million a year.

This does not include bombs, fuel, replacement parts, cleaning supplies, docking and undocking tugs, etc. It also doesn't factor in that most of this stuff has to be lifted our of a gravity well. And it definitely doesn't factor in the costs of shipping it from, say, your home planet in the inner system to the gas giants where the ship is patrolling.

It gets pricey fast.

And to link this back in so I haven't gone to far afield, this deals with the spherical war cows on a strategic sense

Cost may be the biggest negative to a kkv. Laser systems are reusable, and judging by the work being invested in them for todays battlefields will be fairly durable. Missiles you have a limited supply of, so they will need to be shipped out, and will require a lot of manhours to keep those buses in the air (40-60 manhours per flighthour for the F-14 IIRC). That will be very, VERY expensive. If that ends up being the case, the combat effectiveness of kkvs may be become irrelevant as it may be too costly to field them.

Rick said...

Ferrell - Bear in mind that $50 billion is the estimated minimum price tag, achieved if giant laser stars are a production item the way 747s are, and (presumably) Imperial Star Destroyers.

The prototype will cost you $500 billion commercially, or a cool $1 trillion with gold plating and the typical changes of design halfway through. :-)

By rule of thumb, of course!


Luke - Thanks for the explanation and link!


Daniel - [On your first pair of comments; haven't read the latest yet.]

See, in part, my comment in reply to Ferrell! Modern military costs are pushed by a variety of factors, with different levels of culpability. My quick rule of thumb is that Iron Triangle production costs are about 2x commercial cost. Compare the C-17 to similar size commercial jets. Transports are handy because they broadly resemble a commercial type.

But we are getting some way different figures! According to Wikipedia, the original 747-100 was 172 tons empty, for a price in 1970 dollars of $140,000 per ton. By The Inflation Calculator, that is equivalent to $770,000 today, so still in the $1 million/ton range.

Wikipedia also has the empty weight of an F-16C as 8670 kg, with 1998 cost of $18.8 million, thus $2.17 million per ton.

But I agree that construction cost is not the real picture. What we are really concerned with is life cycle cost, basically operating cost plus the amortized construction cost spread over the life of the program.

So let's do some rough numbers. The direct operating cost of Nimitz is about $1 billion/year; procurement cost of USS Ronald Reagan in the 90s was $4.3 billion, call it $5 billion now. So operating cost is 20 percent of building cost. Applying my rule of thumb, direct operating cost is $200,000 per ton.

Paying off the building cost can be treated like a mortgage. At 5 percent for a 30 year service lifetime, payment on $1 million is $65,000 per year.

So life cycle cost is $265,000 per ton, and with overhaul cycles and various overhead, as a rule of thumb I'd say that the annual cost of keeping spacecraft in service is about a third of their building cost.

As a further rule of thumb, and anticipating a coming blog post, even with good commercial practices, prototypes will likely cost about 10x production cost, and if you only build a handful their unit cost will be about 3x ideal production cost.

This is what makes space exploration and development so expensive, even if you eliminate 'fraud, waste, and abuse.' I came up with about $200 billion (present day), over 30 years, to establish a Mars base late in this century, with 150 people going to Mars at each travel cycle (approx every other year), and 350 staying between travel cycles. That is after the general technology has been developed, e.g. multimegawatt electric deep space drive.

Space is not for shoestring budgets.

Rick said...

Daniel - Some apples and oranges in comparing costs and masses of spacecraft and naval ships. Naval ships are very heavily built, the main hull mostly steel. I expect spacecraft to be built, as now, much more the way aircraft are, with lightweight materials and structural fabrication to minimize mass.

Part of the reason they are so costly per ton is that they are big relative to their dry mass. The ship I outlined for Ferrell is 45,000 tons dry mass, half as much as Nimitz and is at least twice the overall bulk, not counting the long drive pylon and wide radiator wings.

So I would guess that a spacecraft with a main hull/fuselage about the size of a present day (10,000) ton cruiser would have a dry mass around 2000 tons and a departure mass around 5000 tons, half of it being propellant. Ideal cost on order of $2 billion. About 10x the mass and cost of a jumbo jet, or comparable cost but 20 percent the dry mass of a naval cruiser.

Crew size is a whole different matter. As a transport a ship of the size I just outlined might carry 200 people; as a 'warship' the crew might be anything from zero to about 50.

On kinetics. Apart from the cost of expending them when used, there are a couple of operating costs. There's the direct cost of keeping them operational, ready for use, and the indirect cost of operating the buses that deploy them.

A lot depends on your defense posture. Since surprise attack is unlikely, orbital defense kinetics can be kept in 'reserve' condition, basically stored. Even the buses can mostly be in a reserve posture.

If you are deploying kinetics actively into deep space the costs are similar to the costs of laser forces of similar size.

For this reason, if lasers and kinetics are in strategic balance, both viable weapons, you pretty much have to assume that a massive kinetic strike can take out even the most powerful laser star. Otherwise they probably aren't worth hauling around or even keeping in working order.

Daniel said...

Rick

Thank you for the prompt response!

Firstly, I suspect wiki may have been edited since you got your numbers, on the current page for the 747 (http://en.wikipedia.org/wiki/Boeing_747) it says in the data box that it cost 24 million in 1967. Similarly I used the F-16 A/B. I also used the total mass rather than the dry mass, as I didn't want to make any assumptions as to the particular engine type. I instead assumed that availability would determine energy source and economics would drive it from there. Since we don't field craft that carry their own reaction mass today, but do carry their own fuel, such a comparison would still be valid.

I think you far underestimate the markup that we have seen from the ironmongers. I am reminded of the quote from Larry Summers about “ketchup economists” who “have shown that 2 quart bottles of ketchup sell for exactly twice as much as 1 quart bottles of ketchup,” and conclude from this that the ketchup market has set the right price. For a more apolitical source, Dr. Zubrin has a rather excellent diatribe about how this has impacted the space lift industry in his book "Entering Space". I do think that using figures from the 50s and 60s or from groups like Mikoyan-i-Gurevich or Vickers-Armstrong would generate more accurate figures. But we may have to agree to disagree there.

On ships vs planes again we may have to disagree. I'm sure you will expand your reasoning in future blog posts, but I would point to the differences in operational philosophy. A plane leaves its support behind because it will be back soon, a ship must take everything with it. As to the armoring vs jinking defenses of both, well, thankfully there hasn't been a modern conflict that actually tested the design of any of the the hardware the big boys have. So the actual good design for modern combat may be completely unknown.

On operating costs there are to many variables to really distill it down like that, it depends heavily on those differences. A Nimitz class has an annual unit operating cost of ~$1 billion (~25% of construction cost) while a Los Angeles class has one of $21 million (~2% of construction cost).

As to the costs of kinetics, well my point was rather that the reserve and operating costs make it such so that they aren't worth hauling around. Logistics alone point to that - let's say I deploy my ship out there and it gets into battle. We win; hooray. The laserstar now keeps going. For the kinetic ship I must now launch or divert another ship to rearm it. Aside from slowing operating tempo, that's another ship I have to construct and pay the upkeep for. It's a simplified example, but it serves.

Rick said...

Daniel - Different benchmarks will get us in trouble for sure! I chose dry weight because I want what the vehicle itself costs per ton, and wasn't worried about finer points like which engine.

I only have one proviso about referencing 1950s practice in order to clear away contemporary goldplating, that you have to account for inflation.

Wikipedia says that a B-52D cost $6.5 millon in 1955, consistent with my memory of other sources. That's the unit flyaway cost, not counting development, and from a big production run.

$6.5 million in 1955 corresponds to $52 million in 2008 dollars. They don't give the empty weight of the B-52D, only the B-52H, 83 tons. The D was probably lighter, but taking the H weight, it comes to $630,000/ton.

That's markedly lower than my baseline, but not an order of magnitude lower. My $1 million figure is not meant to be precise, just a guideline on what to expect, and a measure of how space costs may relate to other costs.

I agree with you that the operation of spacecraft is much more like ships than planes, since their missions last for weeks or months.

I'm merely saying that 'spaceframes' will probably use lightweight construction, similar to airframes rather than the much heavier construction typical of ships, so their cost per ton will be similar to aircraft.

We are really talking about how big and impressive spacecraft are, not just how heavy the structure is. So volume comes into it.

Here is a handy reference point for hab pods. Wikipedia says the ISS has a mass of 304 tons, with 358 m3 living volume, while another source says 1200 m3 total volume.

That gives a density of about 0.25 tons/m3 for a hab assembly, fully equipped. Probably mature design would make them lighter, not heavier.

Hydrogen propellant tanks are big and lightweight. Based on the Shuttle external tank, a tank about 50 meters long and 10 meters in diameter should have a dry mass of about 30 tons, and hold 250 tons of H2.

Clap four of them onto the ISS, with an extended keel structure and long drive pylon, and the tanks are 120 tons; with keel, cryo plant, and other doodads perhaps 200 tons. Add drive unit with shadow shield, maybe another 200 tons, and you have a vehicle with a dry mass of 700 tons and full load mass of 1700 tons.

If you build one big hab pod instead of connecting a bunch, you might have a hab pod 15 meters long and 10 meters in diameter.

This gives you a main fuselage or hull structure at least 65 meters long, probably closer to 100 meters long, and about 25 meters around the assembly of 4 tanks. Volume of the tanks is 15,000 m3, of the hab pod 1200 m3.

In bulk this ship is comparable to a naval ship of about 5000-7000 tons.

I'm cutting this short to go eat dinner!

Rick said...

Daniel - On kinetics, I two thirds agree with you. But it all depends on how much of your magazine you have to expend to defeat a comparable laser armed opponent.

If a full magazine is enough to account for a couple of sizeable targets, kinetics can be worth carrying, and they are simpler to operate than lasers.

Deep space logistics will mainly be driven by propellant supply. A victorious laser star will probably also have to return to a friendly base, or get refueled from a tanker. I'll guess that for deep space craft, mass of propellant is about 5x the mass of kinetic ordnance, even for a ship armed purely with kinetics.

Short form: The better lasers are at zapping incoming kinetics, the less worth while it is to carry kinetics.

qwert said...

Space warfare economics. Seems interesting.

I would like to point out that unlike civilian uses, advanced tecnology tends to increase rather tha to decrease the price of military hardware.
A B-24 could be produced from Willow Run for some 2 million $ (2008). A modern F-16 however will cost you at least 20 million $, and its replacement, the F-35 is expected to cost some 83 million $ acording to wikipedia.
In other words, while we could expect spacefahring technologies to become cheaper, i wouldn´t expect that their high-perfomarmance military equivalents to be cheap.

I was also asking myself: With the need to send supplies to spacecraft patrolling deep space, may it be posible that anual operating cost of spaceships may even exceed building costs?

Rick said...

qwert - Yes, space war economics is interesting.

Your point relates to Daniel's. Obviously there is a great deal of bloat in the 'Iron Triangle' of US military procurement. Some of it is downright malfeasance. Some of it is political gamesmanship, like farming work out to subcontractors in 400 congressional districts. Some of it is accidental, as when a political compromise causes a weapon system to be procured, but barely, pushing up unit cost because of small production runs.

But I also suspect that the real cost of further improvements in aerospace tech has risen, because the technology is mature and we have already picked the low hanging fruit.

The 1950s and 1960s produced good basic solutions to long range high subsonic flight and shorter distance supersonic flight. Improving on those solutions requires extensive optimization and refinement, thus a costly development program. Unless you can sell a lot of planes/spacecraft, that means increased unit cost.

So I don't think the increase in aircraft cost is all due to poor practices; I think part of it is more demanding requirements.


On operating costs, in a way we are already at the scenario you describe. It costs more to recover spacecraft than to build them, which is why we use expendables.

A spacecraft in flight is relatively cheap to operate. You pay salaries for ground controllers or a crew, but otherwise it just hums along. (And if it doesn't, you probably lose the spacecraft.)

Where it gets expensive is between missions: refueling, checking out, preventive and corrective maintenance, mission planning.

qwert said...

I wasn´t saying that high costs were only due to ineficiencies. I mostly agree with wath you write here.
Bear in mind also that cost reduction has a lower priority to military users than commercial users. The result: new tecnologies are adopted as early as they become posible instead of waiting until they become cheaper (in other words when everibody can already acces them).

On other matter:
The Kinetics vs Laser debate is being reduced to: Are the kinetics spendt destroying a laserstar cheaper than the laserstar itself?
But how much cheaper would it be to destroy the same laserstar with another laserstar?
I suspect the main cost would be the risks that your laserstar is destroyed instead. The price of "zapping" one or more times may be negligible, or not?

Jean Remy said...

I think what should be taken into account as to the cost of kinetics v. lasers is the fact that a kinetic kill on a Laserstar kills the Laserstar and in fact overkills it. We're talking here about vaporizing at least 10 ktonnes of laser, engine, powerplant, structure, fuel, and crew. In Laserstar v. Laserstar we've established the most likely outcome to be an eyeball frying contest in most tactically viable situations. While frying mirrors will be very expensive, the most likely outcome would be for the loser to break contact and retreat, which scenario sees the above-mentioned 10 ktonnes of materiel and personnel intact and alive to fight another day--after mirror replacement. I assume a battle group, such as a carrier group today, would have a maintenance and supply ship on-hand with spare mirrors, thus the Laserstar might not even have to repair to "drydock" (!?) to switch mirrors and return.

Therefore, unless kinetics are completely outmatched by lasers, where the number of vehicles needed for an overkill is beyond any reasonable measure, then there will always be a place for them. At the very least they'd make a good Second Strike weapons against blinded Laserstars, because while a mission-kill is good enough tactically, a ship-kill is a lot better strategically.

qwert said...
This comment has been removed by the author.
qwert said...

Well, I supose, you can always shoot against your blinded oponent in order to destroy it before it escapes. Nothing says you have to stop firing as soon as they can´t fire back.
(Unless they surender, could it be posible to capture an enemy ship in space?)

Or are you expecting a stalemate, where both sides lose their mirrors?

Jean Remy said...

No I was expecting a situation where you can damage a mirror but your super carbon armor will be able to shrug it off long enough to make delta-v sideways and get out of the way. I'm expecting mirrors to be vulnerable at far longer ranges than the carbon armor. If that is not the case, than by all means keep shooting.

I'm also thinking that active pursuit is unlikely. At equivalent tech levels between both ships the chase would last far longer than either ship have remass for, and the winner has to make it back home.

Citizen Joe said...

If lasers are effective at 10,000 km, then they can probably wreck mirrors at 100,000 km. Assuming 40 km/s closing speeds, we're talking about a bit over half an hour to mission kill a laserstar and still give it time to change course. Then there is probably 5 minutes of laser ablation of armor followed by another five minutes of frantically destroying kinetics. Then the ships pass, kinetics are no longer useful because the ships are basically retreating from each other at 40 km/s. At that point, you've got 10 minutes of firing at each other destructively and then it is over. Yes, you could take pot shots at each other's mirrors, but there's no point risking your own.

Jean Remy said...

Qwert: I am not expecting prize crews to retrieve anything usable. The losing crew will have plenty of time (the winner has to match vectors) to dump their computers, fry the lasers, scrag what's left of their mirror, empty their fuel, remass, and coolants, and basically reduce anything valuable to scrap metal. And that's without the--unlikely--SF staple self-destruct.

CJ:

I find "jousting" to be likely only in extreme cases of desperation for both opponents. Most likely approach will be very oblique specifically for the purpose of generating sideways delta-v if things go very very wrong. I expect time in effective range to be minimized as much as possible. Not only that, but the defender will want to stay between his enemy and that which he is protecting, rather than flash past, because once he has done so, the enemy has a wide open window at that target. At this point, even if his mirror is scragged and his engines at half power and he's losing coolant, he is now 10 thousand tonnes of guided kinetic with no one in front. That would be filed under in the Bad Idea folder.

Also:
"Your job is not to die for your country, but to make sure the other bastard dies for his."

Anonymous said...

A couple thoughts on armor and multi-function war vessels:

Armor might be legitimate in a "police" style role. If the ship is expecting surprise attacks in cluttered orbital space, an extra layer of protection is probably in order. Laser attacks would be at close range (and if they are made with non-military grade equipment might not have instant eyeball frying capability), and kinetic attacks wouldn't be at the freaky instant kill velocity of military kinetic attacks. They might be more like some separatists that got their hands on a handful of anti-kinetic interceptors. Those sorts of missiles launched in a short range ambush would probably be mitigated by armor.


The eyeball frying contest does lead to a necessity for multifunction warships, even if the additional functions are limited. You don't want your multi-billion dollar ship that is far from home to be at the mercy of its enemies just because it loses a skirmish. You at least need accessible replacement mirrors, as has been mentioned. You also (badly) need back up point defense, because a laserstar with a confirmed mirror kill will be a target for every spare enemy missile within a couple day's flight time.

I'll argue that medium range backup weapons (probably kinetics) are also needed, either on the laser star itself or on a smaller support ship. The loser of the eyeball frying contest attempts to pull away, and the winner can't close fast enough to get into permanent kill range, or at least not fast enough to matter. The supporting kineticstar starts lobbing in high velocity seeker slugs to finish the target off, but non-main mirror point defense is holding them off.
The winning constellation then sends in a medium sized, high (relatively) acceleration craft to close distance with the wounded laser star and attack. It has heavier guns than are required for point defense (it's role during the main battle), and they can finish off the wounded laser star, or at least allow a supporting kineticstar to finish it off by attacking the laser star's point defenses.

Additionally it gets the winners close to examine enemy technology, take prisoners, seize data, etc (dependent on how effectively the enemy scuttles his/her laserstar before the winners get there).

Michael

Anonymous said...

Support craft mentioned in my above post might be equivalent in certain ways to cavalry in certain periods of history. It's really no threat to an organized defense, but it can make a broken force really pay for its loss.

Michael

qwert said...
This comment has been removed by the author.
qwert said...

Jean Remy:
Well, you would left the ship unusable (if that was not the reason of engaging it, it would definitvely be a bonus), and would get the most valuable part of it: it´s crew.
Your oponent may we willing to pay in order to get his personel back. (although the most probable payment wil be the release of your crew-menbers captured by him).

That situation you describe, where the ship transforms itself into a kinetik warhead, may need some way the crew can evacuate if (unless it´s a gigantic drone).

Anonymous said...

I didn't mean to imply that the support craft would hurl itself headlong into a wounded laser star. My intend was that one or more support craft, move in and engage the wounded laserstar with medium and short range weapons. The idea was that a laserstar sans main mirror(s) is susceptible to small, higher acceleration craft assuming it does not have secondary weapons of its own, or its own supporting defense craft. As previously illustrated, it seems unlikely that a laserstar or any long range combatant would be heavily armored, and as such even light, short range weapons could pose a problem if they were to get close.

Michael

Citizen Joe said...

I'm going to further add that nobody will fight over empty space. That leaves three possible situations:

1. Defender is at the guarded object, attacker is coming from deep space (another planet or something).
2. Both attacker and defender start in orbit of same planet (warring states).
3. No defender, two attackers moving to claim an unguarded object in space.

In scenario 1, attacker and defender have closing speeds in the tens of km/s range. Closing speed adds to the kill power of kinetics, but once you pass each other, kinetics become useless.

In scenario 2, closing speeds can be in the tens of km/s or virtually nil. However, range is limited by planetary eclipsing. Threats can come from the planet as well, which means potentially less than 100 miles before contact and planetary occlusion of incoming kinetics/lasers. This is very situational, but I believe kinetics have the advantage.

In scenario 3, closing speeds are negligible as both attackers need to match orbit with the destination. Until orbit is established, we're looking at an eyeball frying contest at extreme range. If you can toast the other guy's mirror, he won't be able to defend once he gets into orbit.

Anonymous said...

Scenario 4: Two powers have assets in a gas giant planetary system, and they're fighting over them.

I see this as the most likely scenario to bring about long range combat, as there are significant resources spread out over a huge volume of space, and occlusion is probably the exception, not the rule. All the while, it isn't strategically questionable empty space. If my guess is correct, it's something of a hybrid between planetary and empty space combat. Transfer speeds don't have to be great, but they might be, and combat can happen at great or close range.

Michael

Citizen Joe said...

Ooh, that adds something else to the mix. Most gas giants have some sort of ice balls floating around them. You can use those as a shield to soak the long range laser hits until you get close enough. Then the water vapor will just sort of re-condense eventually on some other ice ball.

Anonymous said...

Citizen Joe: "I'm going to further add that nobody will fight over empty space..." Nobody faught over empty ocean, but many battles happened in the middle of the ocean, so it seems that just because there is nothing of value with empty space, there is something OF value in empty space: transiting enemy ships. Intercepting an enemy convoy or combat constellation far from planet or station support.

Ferrell

qwert said...

What about the control of important orbits or transfer orbits between strategic points?
I suppose this may be important in a scenario where energy economics in space-travel is still important.

Rick said...

I can't even try to comment on all of this! But I'll take minor issue with Ferrell; most set piece naval battles have been near some point of land, such as Midway. OTOH 'The Glorious First of June' was named for its date because it did happen in the middle of nowhere.

If you are confined to Realistic [TM] drives, you have no choice but to make a gradual approach, because it takes you a day or so to put on or take off 1 km/s of speed.

If you are taking a fast orbit, like 30 km/s, you start your solar orbit matching / deceleration burn a month out and 0.3 AU from your destination. Deep space maneuvers with mere gigawatt drives are majestic in scale.

Approaching Earth to go into circular orbit, you'll pass lunar distance about two days out, and the closest orbit you can establish directly is around geosynch distance. To get closer you'll have to spiral down, about 5 days (?) to LEO.

My guess is that expeditionary forces will typically go into very high orbit. That establishes your presence. You could blockade a planet without getting closer. For a closer attack, go into a long ellipse, so you are passing through low orbital space at near escape velocity.

If you are going to use kinetics against an attacker, there's a good case to launch them very early, weeks ahead, to intercept the attacker in deep space at full transfer orbit speed. In orbital space the only way to put any speed is to sling them out of low orbit, preferably retrograde.

Important notice: All the rather cool stuff about orbital space only really applies at modest, Realistic [TM] tech levels. If you have torch drives, orbital space is effectively flat, and effective kinetics require torch buses.

Anonymous said...

Good point! Thanks, Rick.

Ferrell

wombatron said...

A little OT, but it strikes me that a good way to make kinetics dominate in a setting with torch-level drives is to have a drive tech that doesn't take much power (relatively speaking, of course) for confinement, like amat-initiated micro-fission/fusion or (maybe) nuclear saltwater rockets. That way, you can handwave high velocities for kinetics without having equally powerful lasers implied. A little convoluted, but it seems to be in the general spirit of things :-)

Jean Remy said...

Of course the Kinetistar itself will need engines commensurate with the Laserstar, and it shouldn't be too much of an issue anyway. I think the basic premise is that these would be ships of equivalent technologies flying in concert in constellations.

However it is quite impossible to power the submunitions, be they soda-cans-of-doom or even the heavier javelin-type penetrators, with anything other than SRB's in any realistic manner. The mass needed for a fusion reaction chamber (almost a given if dealing with a torchdrive) has to be in the hundreds of tonnes, if not nearly a ktonne to start with, not including the body, armor, and engine. Even an ICF system, where the engine's combustion chamber *is* the fusion reactor, would necessitate an onboard laser or particle beam generator--again, a lot more mass. A magnetic confinement system is even worse. As stated in Atomic Rockets: (horribly paraphrased) containing a fusion reaction in a magnetic field is like trying to hold jello with rubber bands. Making it into a drive is a hundred times worse.
AM has its own confinement issues, not to mention the need to generate magnetic nozzles which might require some serious hardware.

This might be the sticking point: The engines in the submunitions will not scale up as easily as the engines in the capital ships. This might force the Kinetistars to get closer to compensate, and the closer they get the less likely you are to retrieve them, and the more unbalanced the cost efficiency ratio becomes. The Kinetistars themselves costing a significant fraction of a Laserstar, it doesn't take long before the equations start to look ugly.

wombatron said...

@Jean: What I was thinking of was the kineticstar actually being a large missile consisting of a torch drive, remass, a kinetic bus (with however many soda cans of death can be packed in), and maybe some an armored faceplate. The torch missile would provide the main boost, and then release the soda cans, which only really need lateral maneuvering thrusters for some jink. The missile may or may not be recoverable (Rick's lancers); I see an advantage to both (recoverable, you can obviously use it again; non-recoverable, you have a fourfold advantage in delta-v, which can be used for either longer legs or more kinetics compared to a lancer of the same mass). So you are pretty much just putting a drive in harms way, rather than a full-fledged ship. The drive could also be built to a lower specification in non-recoverable torch missiles, since its just going to be used for a single burn.

Jean Remy said...

I agree with the idea, I was just trying to discuss whether or not it was even possible to recover the bus at all since at torch drive levels the soda can of death's (SCOD missile?... yeah yeah, bad joke) own lateral jink will be (comparatively to non-torch) quite a lot less effective, forcing the torch bus to get a lot closer than the non-torch, and therefore making the torch bus non-recoverable when a non-torch would be.

That was confusing.

Electric drive setting delta-v:
Capital ships: 30 km/s
SCOD: 2 km/s


Torch drive setting delta-v:
Capital ships: 300 km/s
SCOD: 2 km/s

(since you can't upgrade the drive to a torch on something the size of a soda can)

The larger difference of drive efficiency will force kinetic launchers to get closer, and therefore incur a far greater risk of being non-recoverable, namely because they get so close to the Laserstar that they won't survive. If I am correct Rick's formula supposes a recoverable bus, with SCODs being expendable. Once not only the SCODs but the bus itself are expendable, the formula would need an extra constant thrown in there proportional to salvo size (ie: if a bus carries 200 SCODs, in a setting where 200 SCODs are a kill, you need only add the cost of one bus. If 2000 SCODs are needed, you have to add the cost of 10 buses)

wombatron said...

Ok, I see what you are saying now. But wouldn't the fact that the kinetics themselves are coming in at a much higher relative velocity tend to even things out? The target ship can delta it's v faster, but it has less time to do so, relative to a gigawatt electric-drive setting.

Mark said...

my understanding is that seekers are only useful if their delta v for lateral maneuvers is comparable to how much the target can accelerate in the time it takes the seeker to hit.

so with milligee acceleration of nuclear electric the seekers can have days of flight time, so if the torch drive is doing 1 gee (for comfort's sake) and the seeker has 5m/s^2 delta v the seekers can only have about 1/2 second of flight, so at 300km/s they have to be launched from the bus at ~150km from the target. and if the bus is that close, at that speed, you might as well hit the target with the bus.

So nuclear electric propulsion means you have kinetic buses launching soda can seekers, and torch drives mean big well armored torch missiles that probably outmass the NEP bus and it's seekers. (That is unless the target has a laser that can take out multiple torch missiles, and while i haven't done the math i'm fairly sure it would require a ravening interplanetary death beam.)

Rick said...

Wombatron - Yes, the way to keep kinetics viable in a torch drive setting is to assume that the onboard power available for lasers is only a small fraction of the thrust power put out by the drive reaction. Essentially the drive gizmos just maintain a field to stabilize the torch reaction.

Note that onboard power is limited by radiators that have to operate at the cool end of the internal heat cycle. Even at 1500 K you need 1400 m2 of (double sided) radiators to dump 1 GW of waste heat. So you probably are not going to have multi-gigawatt lasers unless you can modify a torch drive to function as an X-ray laser. (And if you CAN, then forget about kinetics!)


Jean - Torch drives to reduce the flight time for kinetics, not so much because they have greater total delta v, but because they have greater sustained acceleration for evasion burns. If a torch can sustain 1 g, and the SCOD has 2 km/s of delta v, the target seeker only has 200 seconds before it runs out of fuel.

So the bus or lancer has to carry it to within 200 seconds' flight time. At 300 km/s this is 60,000 km - but the bus is headed straight at the target. If it then lights up its own torch for a 1 g lateral burn, opposite to the target's evasion burn, bus and target will flash past each other at a minimum distance of 400 km.

This is EXTREMELY close, and makes the bus very vulnerable ... but the target is very busy defending against the incoming SCODs.

That said, against strongly defended targets such as laser stars you probably will expend the bus as a torch missile. It is comparable in size and cost to a small torchship. But if it takes out a target 10 times bigger and more expensive, it can be worth it.

One small point. A recoverable bus can return on a slower orbit, so (simplifying) it can use about 1/3 of its delta v to launch a strike, another third to slow down, and the final third to return at half speed.

And any time you're attacking an approaching enemy on transfer orbit, the inbound speed of the target is added to the outbound speed of the kinetics.

Flip side, if you are an attacker and are going to launch a kinetic first wave against the defense, the kinetic buses can be sent in at transfer orbit speed - no reason to slow them down, when their whole point is high speed.

The upshot is that kinetics are most likely to be used in the opening rounds of an operation, the defender launching 'up the throat' of the approaching attacker, the attacker releasing them 'on the fly' before decelerating to match orbits.

Whoever is left can then fight it out with lasers.

Glenn said...

I'm wondering if the electric drive assumption might be a bit off. Considering that you need nuclear power to realistically generate the laser energy requirements (at least over a short time), and your electric propulsion is nuke powered, it seems that the 1963 Partial Test Ban is no longer in effect or being ignored (one could argue that the dissolution of the U.S.S.R. may technically allow the signers to ignore it anyway). If that is the case, then why bother with nuke-electric and just go for Orion Propulsion (and it's promised mass moving capabilities) or one of the derivatives such as mini-mag or advanced NERVA concepts? Seems to me that the discussed engine is setting limitations that might not really hold considering the the energy required to make a usable laser system as discussed. Or am I missing something blindingly obvious?

Jean Remy said...

Nuclear fission reactors and fission bombs work in completely different ways, and there is no way to use an electricity-generating nuclear reactor as a bomb. Even Chernobyl wasn't a nuclear explosion: it was a steam explosion. Unfortunately, it was a Heavy Water steam explosion that also melted the reactor core. That said, the nuclear treaties specifically limit the testing of nuclear weapons.

Powering a laser, or an electric engine, via a nuclear fission reaction cannot be construed as a violation of SALT since there is no nuclear weapon being tested.

Orion work by detonation nuclear bombs, which would be in violation of SALT and the test ban.

Rick said...

Plus the usual considerations with Orion - first, it might shake itself to pieces; second, it would be cheaper to burn money, except that money has a low specific impulse.

Mini-mag, like fusion drive, falls for practical purposes into the performance range of more advanced electric drives.

Glenn said...

Rick: lots of the discussion here hand-waves away engineering considerations to various levels (assuming the spherical cow holds up) and the engineering on Orion seems doable according to some pretty smart folks with classified information, so if the engineering aspect can be worked out so that it becomes another option, one that has many positive mass benefits, then how does it's inclusion impact on what's been discussed (tactics and strategy)? Does it change things or is nothing really altered? As for burning money all this discussion does that, but it's viable to expend resources of ridiculous measure for dominance. Sure the fuel might be expensive, but it still cheaper than being under the control of a nation you don't agree with.

Jeremy: I understand the nuclear differences, my point was to question the implications to this discussion if the bans were no longer enforced, withdrawn from, or altered thus freeing up this method. Additionally, what if in the future the term nuclear weapon in space is amended to count weapons or drive systems powered by nuclear power of any fashion - if it were (and there are plenty of greenie organizations that would love that) does that cripple manufacture of any nuke powered spacecraft (since the craft by itself could be construed a kinetic weapon that's nuclear powered under possible future legal circumstances), and if so then how does that impact the scenarios of Laser/Kinetic Stars? Would a clause such as this cause nations to withdraw from the ban or just provide political ammo for an "Earth Only" doctrine for spending money (except for those chemical boosted robot exploration probes)?

Jean Remy said...

Once again, let's examine the nuclear policies in place right now.

The reduction in terms of warheads so far has only made the US, the USS..er... Russian Federation and the French break down their oldest and least effective nukes, so while the accords *have* in fact reduced the number of weapon, its overall effect was more one of culling the herd to keep the best and most effective (notably submarine launched nuclear missiles).

The Partial Test Ban is... well, partial. The French continued underground testing under President Chirac, and the Bush administration had proposals to resume nuclear testing for his famous "Nuclear Bunkerbuster" program. Certain nations don't even think it applies to them, like the North Koreans who seem determined to violate every nuclear accord until they get sanctioned, then back off to get the sanctions lifted, to then resume testing... To say nothing of the Israelis (who maintain they don't have them) the South Africans (who maintain they destroyed theirs), India and Pakistan (and their somewhat-less-than-cordial relations) and whatever the Iranians are doing.

In the matter of nuclear-generated electricity: there are no bans in place besides the control of fissile by-products like plutonium. And while some countries have decided to avoid it altogether (like Italy, though they're considering relaunching it) other countries have embraced it thoroughly. The French power grid is fed at about 75 to 80% by nuclear power, In fact France has about as many nuclear generators as the whole of the United States for a far smaller population and a far smaller consumption per capita. The Russians themselves are not shy since almost a half-dozen Chernobyl-type reactors are still in existence, and of course a great many more of other types. The number of countries who have nuclear powered generators, or plan to build them, or at least have nuclear research reactors, is around fifty. An estimated 15% of all power generated in the world is nuclear generated.

Green movements notwithstanding, nuclear power is far too entrenched to simply vanish. Once they've lost that battle on Earth, which they pretty much have, it is unlikely they'll be any more successful in space. There are already nuclear-powered ships in the planning stages. To be honest, the green movements have never managed to shut anything down that governments weren't prepared to shut down for economic reasons. The infamous SuperPhenix, a fast-breeder testbed, was attacked by rockets. It was only shut down in 1997 when it was deemed the planned refit was too expensive, and that fast-breeders were not as efficient as expected in the first place. Once the space-faring nations decide to make a serious go at it, since nuclear power is central to any sustained duration flights, then the deal will be done.

On the matter of Orions: if the ban on nuclear weapons in space (as opposed to nuclear reactors) is lifted, if Orions are possible to engineer, if Orions are considered economically and tactically feasible, I still somehow doubt Orions can fly in constellations given all the, you know, nuclear explosions everywhere. Orion ships are fine with a nuke going off behind them, not so good with nukes going off in front. Anyone for some Bremsstrahlung? From your allies? I think that the engineering problems in building Orions, and the tactical issues surrounding their use, and the PR impact of nukes going off in orbit have an additive effect. "Conventional" nuclear-electric drives are far more likely in a near-future Realistic[TM] setting. That is not to say they cannot be built, only that the obstacles to overcome are bigger than those posed by electric drives, and therefore those are more likely to be achieved first.

Glenn said...

Jeremy, definitely agree that from a political spectrum that Orion style propulsion has allot going against them and also agree that given those current considerations that electric drives are far more likely to be developed first (if only for probe exploration that can later be adapted for military use). Given my understanding of nuke explosions in space, what people should mostly see are flashes - which I think would be quite a sight if they fought in Earth orbit. I understand if people want to limit the discussion to electric drives, I'm just wondering what the implications are to try to break the stalemate.

Couple of last thoughts though, in regards of tactics mentioned, I would expect the distance between constellations to be bigger, but not necessarily vast (10 to 100 KM maybe depending on the propulsion yields?). One thing I may have missed during this discussion that I will have to go back to read: What are the expected distances between units in a Laser/Kinetic Star Constellation formation?

Assuming that the Orion ship may be decelerating toward the target (pusher plate first), maybe the use of mirror drones becomes more viable (given greater potential for cargo mass, launch those ships/drones while decelerating from the sides and use a laser mounted near the front or sides of an Orion craft to shoot around the plate thus also providing limited mirror protection from straight vector closing). Could be that the plate could be armored to withstand several seconds of laser fire, or maybe the Orion unit just hangs back in the distance as a support ship that launched a small Laser/Kinetic Star constellation and is used for recovery missions if too much Delta-V is used up.

Or maybe it just doesn't work or change things, I dunno but was wondering.

Rick said...

Glenn - Orion never went past conceptual planning, so devils in the details (like the huge shock absorbers) were really never examined. Admittedly there are comparable handwaves to assuming that nuclear electric plants, with generators, shadow shield, and radiators, can achieve the ~1 kW/kg needed for fast orbits.

But what really kills Orion for any kind of general use is the security issues of handling so many nuclear charges, and - especially - fuel cost. Orion squanders nuclear fuel at an incredible rate.

As a benchmark, raw uranium cost 17.4 cents/gram in 2007, and contains 0.72 percent U-235. It takes about 5 kg of U-235 for a critical mass. So you need $120,000 worth of uranium per bomb, plus refinement of the U-235 (which, thank God, is a very demanding industrial process!) and fabrication of the device.

So perhaps $300,000 per bomb, with bombs set off at 1 per second to develop 1 g. That's $30 million per km/s, $1 billion for a 30 km/s burn. You'll get to the poorhouse even faster than you get to Mars.


Jean - One demurral, that solar electric is probably competitive with nuke electric for the inner system out to Mars, even the asteroids. You need humongous solar wings, but the drive is very elegant - no turbopumps or 1000+ K radiators, not to mention no radiation.

Of course, solar electric fades as you move outward, so you need some form of nuke propulsion for Jupiter or the outer planets.

And I agree that green movements are unlikely to prevent nuclear power in space. Unless governments want to kill it anyway because of cost, and a spacefaring future pretty much implies enough continuing public support to keep space programs going.

Rick said...

Glenn - We haven't really discussed constellation formations (yet). One consideration related to Jean's last point that also applies in lesser degree to nuke electric drive: Manned nuclear spacecraft of any sort need to keep widely separated - up to hundreds of km - when under power, because of radiation.

Tactically, I think even more spread-out formations will be preferred, because the objective is a mutually supporting formation at laser range, at least thousands of km. (Kinetics firing ranges are even longer.)

Classical Orion does not make a very good laser ship, because it does not have inherent onboard electrical power. If you have Orion craft, use them as fast kinetic buses. Orion can put on 30 km/s in an hour, where a nuke electric ship needs a month. Absent torch drives it is the only way to deliver a sudden, fast kinetic strike.

As I think Ian noted in an earlier thread, there is something ... odd ... about using nuclear bombs to accelerate a kinetic weapon!

Glenn said...

Interesting idea to use a bomb propulsion to send an expendable high-speed kinetic weapon, odd as it might seem.

Sorry if it sounds like I am beating a dead horse, but I'm intrigued by Orion's possibilities and what benefits/limitations there are in regards to the laser vs kinetic problem. George Dyson's book (http://www.space.com/spacelibrary/books/library_projectorion_020709.html)
and some trustees I talked to at the Nevada Atomic Testing Museum (http://www.atomictestingmuseum.org/ which I highly recommend to anyone to visit) seemed to think that Orion had moved quite bit beyond pie in the sky conception to at least work out some hard math numbers based on admittedly limited testing (sadly NASA apparently contacted George Dyson to buy government documents from him that he had collected to re-study the concept). Since large mirrors (15-50?) are mathematically possible, but remain unproduced (as far as I know of) in space for this discussion I've considered what should be physically possible rather than financially.

Not sure why an Orion type craft couldn't carry a nuclear plant or other generator type for powering a laser if the cargo mass capacity is supposed to be significant (not even getting into whether bomb pumped X-ray lasers will work or not and how that dovetails with Orion).

I understand the use of today's economics to try to cage the production problem of any space endeavor as a starting point, but spherical cows may be cheaper in the future if the economic model changes or necessity demands spending till you are past broke. Today's economics are most definitely a limiting factor I highly agree, but I'd also venture the discussion model needs to take in other economic scenarios other than a US/western style governing and commerce - while not in worldwide vogue now, one could for example use a slave labor force to produce food to feed laborers to build things (not saying that we should follow Roman or pre-USA Civil War textile production or Nazi Germany examples - just saying that people could be used in that way as little as 64 years ago and might again, with the V2 Mittelbau-Dora as a the only example I know of a high tech for the time system being assembled by slave labor), so while you could work out monetary costs for doing so, it doesn't correlate as directly as if you are spending those as financial dollars (people being considered cheap robots capable of highly complex tasks that replenish themselves even when you kill off the old broken ones). The use of time and resources that may or may not correspond to artificial inflation from today's economic standpoint will certainly play a big role in what is or isn't possible or viable in any endeaver. North Korea for example on the surface looks like it should be incapable of producing anything like a nuke given the economic isolation and reported starvation/severe living conditions among its population, but people find ways of doing things that economics will swear is unlikely or downright impossible impossible (likely given that there are so many variables and people don't always play by the rules). Hopefully Laser/kinetic Stars will be "civilized" weapons, but who knows?

Uranium for example (and this isn't just for Orion bomblets, but for producing needed power sources for long term space infrastructure where solar power is insufficient) has been discovered on the Moon and there are many refinement process in development that are looking to cheapen the process (which weren't developed previously due to technology limitations or just lack of need since reactors are not even being built to meet today's energy requirements much less the futures)

http://blogs.discovermagazine.com/badastronomy/2009/06/29/uranium-found-on-the-moon/

http://en.wikipedia.org/wiki/Enriched_uranium

(Normally I wouldn't use Wikipedia for information, it's just condensed conveniently in this case)

Glenn said...

Wahoo! Hit a word limit! Attach to previous post.

Back to the previous Laser/Kinetic electric drive discussion:

It seems based off the craft size discussions that the electric Laser/Kinetic Star constellations will have to be built in space (or assembled there after very expensive series of launches using the previously discussed economic model), likely after a significant infrastructure has been developed. This also gives some convenient targets/defensive locations for production yards/supply points:

Earth Orbit
Moon Orbit/Surface
Stable Lagrange Points
NEO Objects

Mars and beyond? What else?

Rick said...

Glenn - An Orion spacecraft can carry an onboard power reactor with no problem. It just doesn't come as factory equipment, the way it has to for electric drive.

Electric drive spacecraft are especially well suited to lasers or other onboard energy weapons, including coilguns, because the have onboard power equal to drive power. For Orion, like chemfuel, electric power is entirely separate from propulsion. Advanced torchlike drives are probably intermediate, bleeding some electric power off the drive.

Other economic arrangements than western and para-western ones are certainly possible, but they won't make order of magnitude changes in available resources.

This gets into the intersection of economics and politics. We could spend $1 trillion a year on space if we REALLY wanted to. But it would take something dramatic, like hostile aliens approaching, to make us spend that much.

Rick said...

Glenn - Oops, forgot your second comment.

Ceres, probably, and some other asteroids. The outer big moons of Jupiter; the inner ones are too deep in its radiation field.

It becomes hard to distinguish specific production centers from general centers of human interest. Rock is available all through the asteroid belt, and ice is available most everywhere beyond the snow line.

Anonymous said...

After watching the History Channel episode of The Universe about Space Wars, I heard an interesting idea use of the sci-fi staple of the cloking devise to which it can be used as an anti-laser defense since the cloak is able to bend electromagnetic radiation around the spacecraft in question. This would include lasers in the visible portion of the electromagentic spectrum, potentially even infrared and higher wavelengths such as ultra violet and X-rays. This could potentially give another reason to arm such battlestars with kinetic weaponry in addition to laser weapons to counter such defensive systems.

Granted, the cloaking devise as seen in numerous Science Fiction media is highly improbable at best, but when it comes to defenses against lasers, one only needs to warp the path of only a tiny wavelength band in order to protect the ship from that particular laser type.

- Sabersonic
Sabersonic@hotmail.com
jrposadas@gmail.com

babylonfreek said...

Exactly how do you deflect EM radiation? The only natural process we've seen so far that is able to bend light in a vacuum is gravity, from black holes to the "gravity lenses" that create mirage echoes of stars hidden behind massive objects. The point here is that is takes a massive object to create such an effect, in the multiples of solar masses, in fact.

The other way to deflect light is through medium changes: ie: a beam of light is diffracted when it hits glass, water, or the atmosphere. Certain media are more permeable to certain wavelengths than to others. But for this, you would have to vaporize a gas constantly around the ship, if that is even practical at deflecting highly energetic coherent beams, forcing you to embark that gas, vastly increasing your payload mass, and even then you'd likely only be able to maintain it for a very short period. Since fleet movements and maneuvers will be counted in days, that solution is at best a temporary shield.

Plasma windows would be hard to maintain, since the magnetic fields need to contain the plasma, requiring part of the magnetic coils to be on the other side of the plasma window. Think of it as a gas trapped between two panes of glass. If you have a pane of glass on only one side, you're not trapping anything.

In any case, light is hitting the ship and bouncing off it is not the major issue that prevents cloaking devices from existing. The issue is heat. If you could create a field that could bend light, it would deflect incoming light, fine, but it would also trap all light and EM emitted by the ship, including the infrared radiated from the heat sinks as a way to avoid cooking the crew, thereby negating the effect of the heat sinks since the heat is literally trapped, greenhouse style. I wonder if the crew tastes like chicken.

All of that said, generally speaking the scientific "speculation" episodes committed by channels like the Discovery Channel and the History Channel, at best fail to understand what exactly is going on (ie: calling the ability of a chimp to learn to use a robotic arm through a computer chip via trial and error and memorization "Mind Reading") and at worst are completely and wildly inaccurate. (ie: confusing quantum tunneling and quantum teleportation, and extrapolating those into Trek-like matter teleportation.) The Universe, for all its attempts to emulate Cosmos, does not have Carl Sagan on the writing staff.

Anonymous said...

The issue of heat to any theoretical and high improbable cloaking devise is a noteworthy problem if the field in question blocks ALL electromagnetic radiation including heat.

However, there have been some research in plasma-based and meta-materials technologies that can warp microwaves around an object yet heat and light can pass through without problems. The cloaking device, however it is made manifest, may not even need to block or warp infrared and other such thermal radiation. When it comes to a defense against weapon-grade laser projectors, it only needs to warp that particular part of the EM spectrum away from the spacecraft in question. However, this also means that its own laser weaponry would be affected as well if not only its own tracking and targeting sensors. This would also legitimize the need of not only having kinetic weaponry on board, but also tethered drones and/or sensors.

As for the documentary series and its accuracy, well one can take what one can get.

- Sabersonic
Sabersonic@hotmail.com
jrposadas@gmail.com

babylonfreek said...

Yes, but, which part of the spectrum, and how fine-tuned, and/or tunable? Who says your opponents use lasers of the same spectral class as your own? Who says all your lasers are precisely calibrated to the same wavelength, either due to a different batch of lasing material to a deliberate attempt to make this defense impossible? Not to mention that actually infrared lasers are the easiest to build and obtain high power from. Microwave "lasers" (are there such things?) would be vastly underpowered compared to IR lasers. Once again, a plasma window needs to be inside a containment field, requiring field generation devices to be on the wrong side of the shield. I am not saying those are impossible issues to solve, but something to think about when you create your laser defense/deflection system.

So, the laser deflection system *could* be possible. It still doesn't solve the cloaking aspect. Either:

1/ the EM-warping field can deflect IR, in which case you get cooked by your own heat.

2/ the EM-warping field does not deflect IR, in which case your enemies detect your IR signature.

Laser defense system: possible.
Cloaking device: not.

Anonymous said...

Babylon Freak "Laser defense system: possible.
Cloaking device: not."

Which is pretty much what I am trying to say about a cloaking field-inspired laser defense system.

As for the tunable laser frequency to the defense system, well the earlier generations of this defense system would not be completely possible or even efficiently possible. Which would mean that the system would either have a set blocking frequency or multiple modules with different frequency against certain laser types. Tunable laser defenses would more likely be a gradual and future development of such a defense system.

As for the technical part in the creation of such a laser defense system: I got nothing but I am open to any suggestions as to how this might be possible, scientifically plausible or not.

- Sabersonic
Sabersonic@hotmail.com
jrposadas@gmail.com

Rick said...

There are definitely microwave laser equivalents: - masers, which in fact were developed some time before lasers were. When lasers first appeared they were sometimes called 'optical masers.'

(Alas) I can't really see any practical, non-magical way to deflect/defocus laser beams. The closest I can come is some way to generate ball lightning, a plasmoid that would be self-sustaining, and could be maintained in the path of a hostile beam to distort it.

But a better way to get that effect might be a drone with a big Fresnel lens, or some such.

Jean Remy said...

Well, the problem with the Fresnel lens is a/ you somehow have to place the lens *exactly* between you and the guy shooting you, and b/ like a mirror, the energy of the beam will ablate the lens and eventually destroy it.

Also, if we *can* actually create self-sustaining plasmoids, wouldn't that be like a Plasma Cannon used in defensive mode? Oh noes, a plasma cannon...

I didn't say it was Plausible, merely suggested it was Possible. Practical is way over on another planet.

Jean Remy said...

Oh, and masers as we build them aren't really applicable as beam weapons as they employ resonant feedback inside a microwave cavity, and we don't actually know how to build them into radiant beam devices. The power levels of masers as they stand today are also laughably in the picowatts, when we can build large solid state lasers that can reach into the megawatts. This is due to the fact that microwaves are very low energy wavelengths.

My question as to microwave lasers as weapons was rather rhetorical since right now we don't even know what one would look like.

Rick said...

Thanks for the notes on masers - I didn't realize that they were contained entirely inside the resonant cavity. I did know that the long wavelength was (to say the least) unhelpful for energy concentration.

Keeping the Fresnel lens exactly aligned might not be such a problem (in principle!), if you're defending a specific point target - such as your own laser mirror. The lens doesn't need to be a long distance in front of the target it protects; a few hundred meters would be fine.

There's still the problem of the beam melting the lens - but the lens doesn't need to be precision optics, and even as it bubbles to extinction it will still distort the beam passing through it. :-)

Which still leaves a fair number of problems with the idea!

Jean Remy said...

My knowledge on masers is pretty recent. I was trying to figure out a way around our fragile mirrors and was starting to think about phased arrays (like the Aegis radar) to come up with something less vulnerable. To my dismay the limitations on masers shot that idea out of the water... out of space pretty quickly. I'm not sure if the optical interferometry technology used in the ESA's VLT array is applicable to laser optics, but since even those use 8m mirrors, it's not very helpful even if it was.

Back to ye olde drawing board.

Anonymous said...

If you wanted to be mean about it, couldn't you start off with say a 750kg projectile, make them burn through the armour, then just before it goes, explode it into hundreds of 1kg projectiles, which just before being disabled, again become hundreds of 1g projectiles? Etc.

Rick said...

New Anon - welcome to the discussion boards!

Fragmentation weapons is how I originally conceived of kinetics, on just the principle you suggest. But when I 'played out' the engagement between laser defense and incoming kinetics, there wasn't much advantage to fragmentation unless the individual kinetics are quite big and heavy.

But overall the best kinetics are the smallest ones that will do damage, and can be fitted with terminal guidance. And given current trends, I'd already expect guidance packages to be (relatively) small and cheap - in effect, smart bullets, rather than a shotgun blast.

Albert said...

looks like X-ray lasers are a reality...

http://www.physorg.com/news159556347.html

Are you ready for them?

-Albert

Byron said...

There are actually several different ways to make a microwave weapon. Besides the above-mentioned maser, which is unsuitable for weaponization due to power levels, there is a device called a vircator, or virtual cathode oscillator. It produces narrow-band microwaves at gigawatt power levels. It's not coherent, and it's not really useful for direct destruction, but you could use it to damage electronics. Lastly, an FEL would also work to produce microwaves.
Also, wouldn't a diffuse particle cloud be useful for defense against KE weapons, at least small ones. I imagine that the SCODs would have a hard time steering with portions of the shield vaporized, and sensor damage might result.

Rick said...

Welcome to a couple of new commenters!

I'm not entirely surprised that X ray lasers are making their debut. There are still challenges, since conventional optics don't work at all, so you can avoid them in a story setting if you don't want them. But if you do want them, this makes the case that much stronger.

Microwaves seem just not concentrated enough for most weapon roles, but I could easily be wrong.

The weakest spot of kinetics is always guidance control, because cripple, blind, or even just dazzle it and it will probably miss. Diffuse clouds might well be effective, but I suspect that point defense lasers are favored, because they direct all their energy at the actual targets, not wasting any on the space between them.

Albert said...

huh. I read somewhere in this or the other blog post on Battles of Spherical War Cows that laser optics and mirrors are highly susceptible to kinetic damage from dust or even small particles from the vaopour of zapped kinetic impactors.
I mostly agree, but I have some (rather naive) thoughts on it.

When reading Atomic Rockets, i read about that Boeing aircraft with a laser turret on the nose.
They say it never shoots directly forward, because dirt or flying insects (or even birds, for that matter) could smash on the optics damaging them.
Looks the same problem.

What if the laser mirror is placed on the side of the ship (like a cannon on a galleon in the old days) and only shoots "Zap broadsides"? (i.e. the mirror would be in some kind of sponson, not fixed to the hull to allow targeting)

This way the optics and the mirror itself are protected from spaceborne dust and the tiny pieces of kinetic impactors vapourized (a laughable threat for the ship, but supposed to be deadly for the mirror).

This layout forces the ships to carry much more armor (they must have their sides armored too if they want to shoot before getting sliced).

And also restricts the field of fire, the laser would now be unable to target things right ahead.

Oh well, it may open a can of worms or just be a crazy idea.
Galleons IN SPAAACE!!!!!
What do you think?

-Albert

Byron said...

An interesting idea, but with a rather large problem. Ships don't have to fly facing forward. In all reality, with sufficiently powerful drives (torch drives) it would actually make sense to point your engine at incoming kinetics and burn them out. Still, there is no "straight ahead," so it would make more sense to just turn the nose away.

Rick said...

This becomes more complicated if you want a big mirror, and if your laser is in the IR-visible-UV band you probably do. I suspect that these big mirrors will have to be keel mounted, though they might point either forward or to one side.

Byron said...

But what is forward? The thrust axis is the most likely answer, but "broadside" weapons are not really that different, except as being bad as pursuit weapons. Then again, it might be a good idea to build a ship with a high roll rate, heavy armor on one side, and a big mirror on the other.

Albert said...

Byron said...
" But what is forward? The thrust axis is the most likely answer,"
Yep. For "forward" I meant "thrust axis while accelerating" (and also afterwards with the nose pointed in the same general direction as the speed while coasting).

Since Rick and all of you are mostly talking of low thrust (but high Isp) drives, the ship has a pityful acceleration. This means that it must spend a lot of time accelerating with the nose pointed in the direction where dust or other particles can damage the mirror.

During a cruise this is not a problem, the mirror can be shuttered (unless it is insanely big), but during a fight this becomes a bad thing.
Or at least I think it could.

Torchships have no such problems, due to high acceleration. You can keep the mirror shutterd for the few seconds of jinking burn and then rotate the ship around like a flying pistol when shooting.

-Albert

Rick said...

I'll guess that the duration of combat is short enough (no more than hours) that you can unshutter your mirror, and natural impact damage will be a fairly minor concern. In any case, in combat you have to point it toward the enemy, whether or not that also exposes you to debris.

And yes, I'm mainly assuming Realistic [TM] deep space drives with milligee thrust, for which maneuver on the combat time scale is also pretty irrelevant. So you can put the ship in whatever attitude is needed to put the mirror on target.

If you have a torch drive, you have a different set of design constraints.

Byron said...

With a torchship, I see turrets as being practical. If your opponent can move quickly, then it makes sense to be able to track without turning the whole ship. Weapon dynamics will be driven by a lot of things, including engine technologies.
Actually, in a torchship setting, I see orbit matching and such as much more common. This is because of the prevalence of "everybody dies" combat options, which nobody wants, such as kenetic-firing passes. I would think that war is governed by a set of unwritten rules, that ensure that combat mostly occurs at low inital relative velocities. Not formal "we'll send our champion, you send yours" rules, but just that combat will be usually decided in matching high orbits.

kalyptein said...

Hello, I hope it's not bad form to comment on an old post. I've just stumbled over your blog and have been reading my way through.

I was wondering if there was a flaw in the tactic of the fragmenting kinetic bus vs laserstar. The bus breaks up after its armor is burned through, saturating an area too large for the laserstar to avoid and too numerous/heat absorbent to vaporize completely.

But the laserstar doesn't need to zap all the fragments, just vaporize all the buckshot in a hole big enough to fly through, plus some margin of error. If it has trouble spotting the shot, it can just scan its beam around in the area of concern and look for puffs of ionized vapor (or use IR sensors to spot the now heated fragments), then focus there until there's no more vaporizing and move on.

Things get more complex with multiple buses coming from different angles, since you'd have to figure out where you need the gap to be in each wave and at what time, taking in to account any maneuvering you want to do before the waves arrive.

Now if the shot itself is somewhat mobile, this gets trickier, but my understanding was that it was just a cloud of flak after the bus breaks up.

Rick said...

Welcome to the comment threads! Comments on older posts are fine. (Though there's the risk that I'll miss it - I get email notifications, but comment traffic has been getting wild lately.)

I've pretty much abandoned the idea of a cloud of debris as an effective kinetic punch, largely for the reason you hit on: the laserstar only has to target the fragments on intercept course. Which are easy to identify. Target seeking submunitions appear to be the main kinetic threat.

My guess is that simultaneous multi-axis kinetic attacks will be very hard to set up - the target may not be able to evade them outright, but can move to encounter one before the other.

The comment threads on recent posts - especially Space Warfare XIII: The Human Factor - have a LOT more discussion (and disagreement!) about laserstars versus kinetics.

kalyptein said...

Thanks, I'll shut my yap until I've gotten caught up!

Anonymous said...

Has anyone ever considered putting a layer of transparent material over the armour? This would prevent outgassing from the hole and force the laser to heat the remaining armour indirectly.

Gareth

Rick said...

Welcome to the comment threads!

Alas, I think a transparent layer would backfire - the vaporized material under it would be trapped, and build up to explosive pressures.

It might not actually be worse, but not any better either.

Anonymous said...

Pressure certainly poses a problem. Maybe a better system would be to have transparent pipes with an opaque liquid pumped through them. A relief valve can divert liquid to storage to prevent to much pressure from building up and a cooling system can remove the heat.

Gareth.

Isaac said...

As a reply to some of the comments on the best shape for a laser star, I'd like to suggest the needle.

From what I've read a powerful laser would probably be both keel-mounted, and relatively long. Stripping down on mass leaves you with an engine, generator, laser and mirror at the back of a long cone, with the shutter at its end.

Presumably the shutter would face the main enemy as much as possible; a needle minimizes the target you present, while at the same type maximizing the surface area an enemy laser would hit. The low angles of a long needle-like cone mean that the focus of a laser attacking from the front would be spread out, reducing its intensity, and hopefully deflecting some its effect. Having the ship spin could reduce the concentration of fire also.

It has been mentioned that most attacks would fall on the fore and aft of a ship. This is similar to driving in the rain - your front windscreen wipers do most of the work. Incredible speed only compounds this, making a needle the best option if you want to dodge, duck, dip, dive and dodge. Cutting a path through flak is a lot easier when your ship is thin.

Furthermore a needle, with its critical systems in the rear, puts most of its hull in between them and the enemy. Maneuverability is increased, as lateral thrusters at the end of a long ship act as a kind of lever, making pivoting on an axis much easier.

While I accept the shape poses problems if there is enfilading fire, other shapes don't do much to mitigate this. Perhaps a flattened needle, more akin to a sword, could present its point to a main enemy and an edge to the enemy support. The problem only reappears however when you have three enemy positions.

Missiles will have many of the same specifications, and problems.

On a side note, I can imagine attaching a needle ship behind an ice asteroid, with a hole cut through by and for the main laser. The asteroid would soak up fire, and could even be used as a heat sink. Sensor droids would have to be used to see round it properly though, and it may not be worth taking on the extra mass if you need to travel any distance, or at high speed.

I'd love to hear some arguments for other shapes, for missiles or ships.

Rick said...

Welcome to the comment threads!

I am *far* from being an authority, but my impression is that optimum laserstar configuration depends heavily on the type of laser, particularly wavelength.

If the wavelength is in the optical band, IR-visual-UV, you will probably be firing through what amounts to a reflecting telescope.

Other things being equal, effective zapping range is proportional to the size of the main mirror. So you want the largest practical mirror, which could result in a fairly wide forward aspect. But there is no special need for great length. So the spacecraft might be rather stubby, tucked in behind its wide main mirror.

On the other hand, X-ray lasers will require a refracting X-ray telescope, with a long focal length - so a 'needle' configuration on the lines you describe could be natural for laserstars armed with X-ray lasers.

I'm rather doubtful about armor, however, because I suspect that laser weapons aim directly at the enemy laser: an eyeball-frying contest. In this case armor won't end up providing much protection.

Isaac said...

I was imagining the main mirror being kept at the back, within the ship. Putting it out front seems to me to be leaving yourself very vulnerable - to hostile fire, or to collisions with space debris.

Having the length of the ship as a kind of barrel would also allow you to mount layers of shutters, or even a kind of spinning shutter, or both. These would be hidden from the enemy, and nearly impossible to predict. A spinning shutter would be a sphere with a hole through it, working kind of like a WW1 fighter pilots' propellor. You could time your pulses, knowing when the hole would be aligned, while the enemy would be forced to guess.

Another defence against blinding could be turning on a continuous beam as soon as any threat is made (or is even possible), not even necessarily perfectly targeted. Then, if they can see down your barrel, they are already blinded. Would it be possible to fire a low power continuous beam, and pulse fire at the same time?

Either one of these counters I think is enough to start considering developments beyond a pure blinding contest.

I should have said that the shape I described in my previous post is based upon the assumption of incredible speeds. I assume space warfare will be conducted with craft going as fast as possible, with weeks of acceleration leading up to moments of combat. I assume speed, firstly due to my belief that while sitting still makes it easier to aim, as there is no cover you are far too vulnerable, and secondly due to the advantages that pile up for kinetic weapons when they are thrown fast. Kinetics also demand that your trajectory is near-as-possible directly at them.

Putting your large, most vulnerable and expensive critical system bang on the front of something travelling very quick, seems risky in the extreme.

Isaac said...

Actually I'd like to amend what I said. It does seem unnecessary to have the mass of a really long barrel, so the ship could well be better served with a shorter, fatter cone shape. Ideally the aperture at the end of the cone/barrel would be as small as the width of your laser beam i.e. very small. For blinding attacks you'd need to hit that tiny aperture at the exact angle that would allow a path down the barrel, while incredibly far away, moving incredibly fast.

Also, I'd like to add a series of shutters rather than just one, which could be defeated with a continuous beam. These would spin at different speeds and with different patterns - and would sense if they were being burned through and then stop. If you wanted to be really certain of countering any blinding attack you'd time your pulses so that they exactly lined up with the conjunction of open shutters, meaning that if you can see down the barrel, you're blind.

On a slightly different topic, what are the limits and necessaries for heat sinks? how big for how much power? what shape? do ion engines run hot? what are the likely power sources for space? It'd be awesome to hear anyone's thoughts.

arisian said...

So, I was thinking about this again recently, and considering what happened when you scaled from one on one to fleet combat.

Let's say we have multiple laserstars, and that the distance between them is small relative to their effective range. For Spherical Cow purposes, this means that any object targetable by one laserstar can be targeted by all the laserstars in the fleet.

Since KKVs need to be launched well in advance, they're going to be locked in on a particular target long before the laserstars can begin to fire on them. The kinetistars start with a fixed size salvo (presumably, all their KKVs), and get to decide how many to task to each laserstar.

Without loss of generality, assume L laserstars, and K KKVs. By the pigeonhole principle, at least half the laserstars must by targeted by L/K or fewer KKVs.

Since the laserstars get to prioritize their defensive fire long after the KKVs have their targets locked in, the number of KKVs needed to totally wipe out a fleet is geometric in the number of laserstars. This is due to the fact that, rather than allow every laserstar to be hit, some of them can sacrifice themselves by targeting KKVs tasked to another ship. In the extreme case, the entire laserstar fleet concentrates on protecting a single ship.

If it takes N KKVs to kill a single laserstar, then the number needed to kill a ship being protected by a fleet of L laserstars is L*N. This means that in order to kill the whole fleet, you need at least L*N^2 KKVs. Again, this is due to the pigeonhole principle; if you have less than L*N^2 missiles, then at least one laserstar must be targeted by fewer than L*N missiles, and that laserstar can be saved by coordinated fleet defence.

At this point, the kinetistars would have spent their armament, and would presumably be on a trajectory that would eventually carry them into the remaining laserstar's range, at which point they could all be destroyed at the laserstar's leisure.

While this might make for a pyhrric victory, it would mean that the laserstar team would retain strategic control of the area, which could be very much worth the loss.

But the real problem is that the kinetics are a first strike weapon; anything other than total casualties among the laserstars will mean total destruction for the kinetistars. And the number of KKV's required for that scales as the square of the number of laserstars. Since the number of KKVs you can carry scales linearly with the number of kinetistars, this seems like a problem if you want to tune things for relative parity.

The upshot is that you can tune your lasers and kinetics so that, for a particular fleet size, they are balanced, but for any fleet smaller than that, kinetics will have an overwhelming advantage, and for any fleet larger, lasers will have an overwhelming advantage.

Also, a thought with respect to eyeball-frying: what if you made your mirror out of some type of nano-refractive material a la butterfly wings? It seems like it should be entirely possible to engineer something which only reflects light which is incident from a particular angle, or of a particular wavelength (the latter being easier, but constituting a less effective defence, since if your enemy manages to match that wavelength, you're screwed). At close range, it won't do anything to prevent getting burned, but at long range, it should be able to avoid focusing your enemy's attacks onto your laser optics. Thus, reducing or eliminating the "eyeball-frying contest" that everyone assumes laser combat must devolve into.

Люси Сорью said...

> Perhaps a flattened needle, more akin to a sword, could present its point to a main enemy and an edge to the enemy support.

I won't say it reminds me of a Star Destroyer. It does not.

What I'm thinking of about is a Hiigaran Battlecruiser from Homeworld 2, whose shape, incidentally, lends itself quite well to the laserstar concept.

http://postimg.org/image/pckrkswql/

(sorry if my choice of image hosting offends anybody)

Or, on a slightly more, but not at all, realistic note:

http://fc04.deviantart.net/fs71/f/2011/045/5/8/bb_taotie_by_ergrassa-d39jsad.jpg

Curiously enough, this 'flattened needle laserstar' proposal really sparked my interest.

Kurt said...

Albert,
Arguments against 'The Needle':
1. I still say that your primary propulsion method is going to be nuclear to generate massive amounts of DV by firing accel/decel from both ends of the ship. If you have huge radiation shields of carbon nanno tubes (or the titanium disulphide equivalent which the Israelis are making as lightweight tank armor) on each end of the ship, then the length-between becomes a structural vulnerability as the narrowest loaded member of needle with both ends stuck in a pin cushion.
2. I do not believe that KKVs will be practical as you will simply fly around the majority of the clouds by turning your main drive system some degree off track to create massive lateral displacements which will make a Brilliant Pebbles/LEAP approach to chemical-rocket impulse loading impractical in a SCOD. The big ship will simply put so much lateral displacement into the interceptors tracking geometry that it will not be hittable, much the way a Mach 2.8 MiG-25 could fire Mach 4 AA-6 Acrids (as -giant- AAMs) at a Mach 3.5 n SR-71 and a half G sideslip would put the Blackbird out of engagement envelope for both track and fuzing.

Kurt said...

Long post, sorry...
This -might- not apply if the SCODs were somewhat larger and could fire up Excaliber class X-Ray lasers to go for the radiation kill of the battleships' electronics and/or crew.
3. If you substitute lateral chemical thrusters for the nuclear option, you still get massively more than milligee acceleration, but you don't need to obviously turn the ship. I endorse this on the basis of keeping your sensitive systems (including large radiator panel farms) obliquely tilted away from the line of sight, behind stacked hull segments whose diameters would be unequal and would thus serve to protect the panels from nominally 'frontal' attack.
4. Finally, I do not believe that people are giving Microwaves their due. If you take two phased array apertures and cross their beams in such a way as to form a squared loop conjoined phase geometry, you can put massive amounts of power on the front end of the emitter lobe. Such 'scalar' (scaled to the number of apertures and focus area of the wavefront) weapons range may not be sufficient to act as principle weapons on ships battling at standoff ranges of multiple-thousands of kilometers but it can be used to fry electronics over tens if not hundreds of kilometers, depending on array size and operating bandwidth. Just such a capability is what they are really talking about when they mention the 'self protection jamming' capabilities of modern AESA radars on jets like the F-35 and F-22. These apertures are nominaly X-Band restricted to about 10GHz but they are considered viable for use against any emitter from C band and up. Imagine focusing dozens of megawatts of high peak power against inbound threat SCODs whose electronic architectures instantly begin propogating induced electrons in directions and power levels never intended as the scalar wave does things to their molecular and even atomic level circuit function. Gives an entirely new understanding to the meaning 'soft kill' as a KKV whose electronics went dead in the last seconds of closure would be 'as good as a hundred miles' off in it's terminal intercept with a ship that was randomly maeneuver by as little as a few dozen meters per second of shunt thrust. Most importanly, these scalar microwave emplacements can be conformally designed so that they achieve most of their lobe pointing index match through beam shift rather than aperture alignment. If you make the apertures function as plasma windows, you also get huge increases in beam pointing agility and multifrequent selective bandpass.

CONCLUSION: The combination of high agility due to front and back end propulsion, stepped fuselage segments to accomodate masked radiator arrays and elevatable endfire capped phased arrays around the primary (nuclear propulsion) blast shielding suggests a stacked toroidal shape to me with the central payload volume being both radiation and impactor protected by what amounts to a double hull and the flexibility of both component subassembly manufacture and mating (think endloaded submarine hulls) via universal adaptors as shock absorption mounts and the structural strength inherent to a discus rather than longeron based system. You can literally put more radial supports across the internal volume of the toroid to support whatever payload/habitat/propulsion systems you need than you can run longitudinally as longeron+frame station design. The ability to operate as something of a compression spring 'slinky' also allows the ship to functionally absorb the thrust differential (fore to aft load distributions) of an atomic propulsion system as shock loading without compromising the individual payload (K-star or L-star) segments whose horse-trailer slung inner modules could be treated as individual rigidity isolates as well.


KPl.

Anonymous said...

I didn't read through all 122 comments, but I did a keyword search to see if I could find anything related to my question.

A major disadvantage that both spinal and turret based lasers have to deal with, at closer distances, is aiming time. Aside from the super SF laser, the housing for these things are going to be the size of a house. So, its going to time like 2-3 seconds to lock onto each KKV on average. This means the number of KKVs that will be destroyed will drop drastically.

For super SF when light bending materials are made, stealth rockets could be launched from coilguns and activate their thrusters once within optimal range.