Wednesday, September 2, 2009

Battle of the Spherical War Cows: Purple v Green

The stately orbit of this blog was disrupted when commenter Luke, posting at SFConsim-l, provided links to two nifty laser damage simulators at his site. Of course I started playing with it, spreading out to other calculations. Severe geekitude follows. You have been warned.

Suppose that in the midfuture, 2100 or 2200, we have a nuclear electric plasma drive. The largest drive engine units put out a gigawatt of power, and have a mass of about 1000 tons including shadow shield and radiators. Spacecraft structure and propellant tankage is about 1000 tons, and total payload is 1500 tons, for a total mass, less fuel, of 3500 tons. [Note: all numbers are shamelessly rounded off, and some are SWAGs.]

These largest class fast interplanetary craft carry about 6500 tons of hydrogen propellant, so full load departure mass is 10,000 tons. Exhaust velocity is about 30 km/s, specific impulse ~3000 seconds. Acceleration at half propellant consumption is about 1 milligee, putting on roughly 1 km/s per day, and maximum mission delta v is 30 km/s.

This is a big spacecraft. The hydrogen propellant tank has a volume of 100,000 m3, equivalent to a sphere 60 meters in diameter, or a cylinder 40 meters in diameter and 80 meters long. The radiator fins are the cool end of the reactor power cycle, so they can't be too hot if the reactor is to be efficient, including not melting. At 1500 K (~2250 F) you can shed about 250 kW per square meter, half a megawatt from the two sides of the fins. You're probably dumping 2 GW of waste heat, so you need 4000 square meters of radiator fins, say a pair of 50m x 40m fins.

The drive pylon is perhaps 100 meters long, so the whole spacecraft is about 200-250 meters long and 150 meters 'wingspan.' As a transport type it might carry several hundred people, say 300-700 crew and passengers. The habitat compartment could be a drum 40 meters in diameter and 20 meters long, volume 12,000 m3. Rotating at 5 rpm the rim spins at 10 m/s, and it provides half a g. (According to notes at Atomic Rockets, this spin rate may or may not be acceptable for comfort.)


But we are here to zap stuff, not travel comfortably through space. So we remove the hab compartment and replace it with 1000 tons of armor plus a 500 ton laser installation. The power plant supplies plug power for a 250 MW laser, zapping at 400 nanometers - the extreme visible violet - through a 10 meter mirror. Spot size is 1 meter diameter at 10,000 km, and it burns through about 2 mm per second of super nano carbon [TM] armor at that range.

Regarding armor, there's no neatly tucking these huge fins away, and if you did, 2.75 GW of waste heat would require expending a ton of water flashed to steam each second to carry it off. With your huge radiator fins and bulky propellant tank, your best bet is to turn end on and put the armor into a faceplate, including the forward edges of the radiator fins. Your minimum end-on cross section will be on order of 50 meters in diameter, 2000 square meters. Thus the faceplate can have 0.5 ton per square meter, and is about 0.3 meters thick.

At 10,000 km, the laser, held steady on a 1-meter spot with the trigger held down, will burn through this armor in about 150 seconds, or 2.5 minutes of steady zapping. At 25,000 km you're burning through 0.2 mm per second, and half an hour of steady zapping will burn though 30 cm armor.

But at 100,000 km your spot size is 10 meters, equal to mirror size - producing a burn rate insignificant against armor, but when aimed at the enemy mirror it is focused right down onto their laser. So once the zapping starts, the laser battle will probably be decided very quickly, by whose laser fails first. There's little advantage to keeping shuttered, since the enemy can then zap with impunity, and zap your mirror the moment your shutters begins opening.

So it seems to me that pure laser battles, even between large conventional lasers, are decided at very long range, the winner being whoever wins the mutual eyeball frying contest.


Now, as promised, purple versus green. Imagine a 'slow' armored target seeker, closing in at 10 km/s. The defending laser burns through the armor, gradually at long range, more quickly as the range closes approaches. I did a quick and dirty Excel spreadsheet. Opening fire at 25,000 km, at range 10,000 km the laser has burned through a meter of armor. By the time a target seeker has closed to 1000 km range, 100 seconds from impact, the laser has theoretically burned through about 18 meters (!) of armor. By the time a target seeker is 200 km from target, 20 seconds from impact, the laser has ideally burned through 100 meters of armor.

This ignores the aspect ratio of the burn hole, but a single big killer bus is not effective; it cannot carry deep enough armor to get decently close.

A swarm of small, lightly armored target seekers is also not effective; if they have 10 cm faceplates the laser can burn out hundreds of them.

But 'merely big' kinetics, say with a dry mass of 5 tons and armor plug 2.5 meters deep, strike a balance. If you fire a salvo of 50, 40 of them will be burned out before they reach 200 km and 20 seconds from the target, but ten of the salvo will reach that distance before they can be engaged and fried, and one will reach 150 km, 15 seconds from the target.

These big ships, with large lightweight fuel tanks, long drive engine pylons, and huge radiator wings, cannot be kicked sideways easily. Allow it, say, 50 milligees lateral thruster acceleration, comparable to a subway train leaving a station. In 20 seconds our ship can put on 10 meters per second, and displace itself laterally by about 100 meters. Evasion cross section is thus about 30,000 square meters, 15 times the cross section of the target, so when our big seeker fragments, 1/15 of its mass or about 300 kg are on collision course with the target. With ten target seekers reaching this range, total fragment mass on collision course is 3 tons.

The laser can put out 5 GW in 20 seconds, enough to vaporize 100 kg, or shatter and disperse a ton or so of dangerous fragments. But another 2 tons will hit, delivering the equivalent of 20 tons of TNT in explosive impact energy. So sorry to say sayonara. Large fragments of 100 kg will have an impact energy equal to a 1-ton bomb, while their momentum will be comparable to a major caliber naval shell, say 12" = 30.5 cm. Even with a (massive) Whipple layer, these will be hard to stop.

So it takes 50 heavy target seekers, of mass 5 tons each and deployed at a 'slow' closing rate of 10 km/s, to saturate the laser defense and batter the armor. Say a salvo of 70 to allow ample margin.


Civil aircraft today cost about $1 million or euros per ton. (We're doing order of magnitude estimates here, so ignore exchange rates.) Military and space hardware can easily be $10 million per ton. But since this is The Future, let's use a modest cost schedule, commercial-equivalent tech, and say our laser battlestar costs $3.5 billion, while a heavy armored target seeker costs $5 million. Thus a flight of 70 target seekers - enough to scrag the target with confidence - cost $350 million, a tenth the cost of the battlestar.

If the target seekers are thrown fast, our laser has less time to fry them, and the critical range, 20 seconds of flight time, is now 600 km. The laser can only burn through 12 meters of armor, so four target seekers will be fried beyond that range, but if 10 are launched, 6 reach 200 km, about 30 tons, putting 2 tons on target, with 1 ton penetrating the close-in defense. Now we need only about 15 target seekers costing $75 million, but also an expendable delivery craft. (Expendable because it uses its full delta v for a 30 km/s closing speed.) This craft is scaled down by 10 from the big ship, and costs about $350 million by itself, so the whole high speed delivery system costs $425 million, slightly more than the 'slow' kinetic force unit.


So who wins this battle of spherical cows? I rule it a draw. On the one hand, an orbital battery of target seekers can take out a laser battlestar costing 10 times as much as they do. On the other hand, the battlestar is impervious to anything but a massive strike, or a high speed strike of similar cost.

The technical balance is such that procurement mix will be chosen due to strategy and policy, not a no-brainer technical choice. The target seekers can be moved strategically in cheap canisters, and you can play a shell game with them, but you cannot brandish them the way you can brandish a laser battlestar. To use them is to lose them, while the battlestar can engage weaker targets at practically no cost, just wear and tear on the laser.

On balance this makes the laser battlestar a weapon of the strategic offensive, capable of probing operations, while kinetics are a weapon of strategic defense, making the targets they defend risky to attack.

Opinions welcome - error corrections, too.


Related links: Laser weapons, and a two parter on kinetics.

101 comments:

Kedamono said...

Makes me wonder as to the accuracy of the targeting system. If you're using the same optics to sight the target as you use to fire your laser, wouldn't the thermal effects after a shot skew the next shot?

Would you have to have actively cooled targeting mirrors so that the post thermal shock image isn't distorted?

Also, what's the accuracy of the targeting mirror itself? From the sounds of it, at 10,000 km, it's 1 meter in resolution, so a 2 meter wide payload is basically what, 2 pixels?

If the impactor is designed to random walk laterally, it will dance within the accuracy of the targeting system, but outside the laser beam. If you add in an avoidance system that knows when the impactor is being hit, the impactor's life span doubles or triples until it gets closer to the target. But then the beam is smaller, so it does a spin along with the random walk to keep the beam from hitting the same spot twice.

Also, why not use a mirror as the primary armor, a cone shaped one to deflect the beam long enough to keep the impactor alive?

There are probably good reasons why you don't, but I'm ignorant, so I'm asking. :-)

Jean Remy said...

I did some quick and dirty calculations (by the way here's another laser calculator http://www.5596.org/cgi-bin/laser.php)

Right now the army is experimenting with modular solid-state lasers, that is a number of modules mounted in series whose power adds up to the full output of the weapon. Since we have a modular laser now we can use them as separate weapons as well.

Say rather than focusing your entire laser through the main 10m mirror you instead break it up in ten smaller laser of 25 MW each (I'm probably fudging with an addition, the truth is probably not nearly as simple as that) and fire those through smaller 2m diameter mirrors. Each 25 MW laser fired through a 2m mirror can zap through roughly half a meter of armor at 150 km (15 seconds to impact) and 1 and a half meter at 100 km (10 seconds to impact) so basically at short ranges, those ten sub lasers can actually each destroy a target, and do it again.

Say you start blasting them at long range with the 250 MW/10m setup. However once they get closer to you, and the range is now close enough for the 25 MW/2m what you lose in punching power is made up for in numbers, allowing multiple targets to be zapped simultaneously. That should even out the odds some.

Note: it's late at night so if I am missing a crucial parameter in there and this is a really dumb idea, feel free to shoot it down.

Anonymous said...

From what I am getting from the opening post, it seems that even though one weapon type has pros and cons when facing another, it would seem that the primary factor to see as to which weapon system would win over another would be situational at best.

However, this heavily depends upon the interception engagement involving no more than two combat spacecraft. One can imagine that if the Faceplate Armor arrangement is the primary way of defense for space warcraft, than the armor at directions other than forward would only be adequite to defend against micrometeorites and anything else the defense lasers can't target correctly and the craft itself can't maneuver away. It would probably give good enough reason to have constellations of two spacecrafts or more.

Even so, this post rapidly answers the (almost) age old question of Purple vs. Green with the answer of "Depends". In that it takes into account not only the strenghts and weaknesses of Directed-Energy Weaponry and Kinetic-Energy Weaponry, but also where and when the engagement occurs, who are manning the controls, who the on board commander is and how skilled they are, etc.

It certainly brings back the strategy (or is it tactics?) and drama of space battles as imagined in TV, Movies and Video Games. If only to a certain degree.

- Sabersonic

Anonymous said...

This is a conclusion similar to what I came to (but without all the quality math to back it up) based on tactical applications of these weapons. Namely that lasers can provide very focused and discreet energy delivery to very specific points. This is extremely useful for anyone that doesn't want to cause a lot of collateral damage.

Example: There's a suspicious orbital transfer vessel that you suspect is carrying contraband goods. With kinetics, you can send a seeking warhead their way, and hope the damage is limited to engines, or you can simply zap their thruster in a relatively low key way. Lasers don't leave as much debris if "law enforcement" action happens close to populated areas, they don't go bad from sitting on the shelf for too long, they can be toned down to just warm up some nose armor on a warning shot, etc. The offer a lot more levels of power with a single weapon.

Michael

Luke said...

A couple thoughts:

First, if these laser craft operated in groups of two, one could zap the unprotected sides of incoming kinetics when they were going for its partner.

Second, if it costs 10% of the price of a laser zap craft to destroy it with kinetics, it would make sense for the designers to allocate an additional 10% to the budget for kinetic defense - say an equal mass of Kirklin mine type kinetics, low delta-V munitions with maybe 10% the mass each of the expected anti-spacecraft missiles, but 10 times as many. This at least pushes you up to cost parity for blasting one of those laser cyclopes out of the sky.

Luke said...

Kedamono: Modern dielectric multilayer mirrors are 99.99% or more reflective (at a chosen wavelength and optimum angle of incidence), greatly reducing the heat load on reflective surfaces. Also, adaptive optics can be used to compensate for heat distorted optics (that's what the NIF uses).

If your laser can illuminate a 1 meter spot at 10,000 km, a 2 meter target can still be magnified to more that 2 pixels, but any features smaller than 1 meter will be smeared out into unrecognizability - you just see fuzzy boundaries and blobs on a one meter or larger scale.

The impactor cannot random walk within the accuracy of the targeting system but outside the laser beam. In the example of the 2 meter wide target and 1 meter laser spot size, the targeting system accuracy is 1 meter (at least for well designed targeting systems, the like of which are routinely used today for astronomical telescopes).

Mirrors can help if the intensity is low enough. However, mirrors lose their reflectivity if heated too much. In essence, they can delay the onset of melting, but once melting begins they become just like anything else (this threshold is a bit iffy for some materials, like diamond, that do not melt, but the principle is the same - once real damage starts occurring, the mirror does not get you much). The best mirror for something like this could be dielectric mirrors made out of layers of two highly refractory substances - say diamond and silicon carbide - but only if you know the wavelength of the incoming light and if you can be sure that you can position your mirror incident to the beam at the optimal angle. Otherwise, polished silvered (for visible), aluminized (for near UV), or gilded (for infrared) surfaces work best, but here you are getting about 90% to 99% reflectivity, not the extreme reflectivity of dielectric multilayer mirrors (http://panoptesv.com/SciFi/Mirrors.html , near the bottom).

Rick said...

Kedamono - Luke already jumped in with better answers!

And yes, as I understand it, spot size is about the same as pixel size. You can have finer pixel resolution but it will show a blurry blob. (Which is still useful for estimating the center of the blob.)


Jean - I suspect that these uber lasers would actually be a bank of lasers sharing an uber mirror. So you could have secondary mirrors.

Against a salvo all coming on similar trajectories, though, you might not need more than one mirror, because the shift from target to target is a very small angle. But optics mavens can give more informed comment on this!


Sabersonic - If weapon systems are in broad technical balance, I think which you use, or what mix, comes down to doctrinal questions.

I didn't know, going into these calculations, whether there would be broad overall balance. One or the other might turn out to be hopelessly outclassed. In fact I thought that burning through 25 meters of armor would stop anything, until I realized that if target seekers have 2.5 meter faceplates, the first 10 are stopped but #11 gets through.


But as it turned out, both weapons are viable, so you have a choice or a mix.

In fact the picture I am coming up with here fits rather neatly to a popular historical analogy - guns versus torpedoes a century ago.

I can see a 'jeune ecole' doctrine built around orbital kinetics, a sort of cross between minefields and torpedo boats. But if you want to play Alfred Thayer Mahan and rule the spacelanes, laser battlestars seem like the way to go.


Michael - Which relates to your points: What you are describing is essentially 'laser star diplomacy.' You can intimidate with kinetics, too. But lasers are more flexible along the boundary line, so to speak, between the threat of force and the use of force.


Tactical geometry gets interesting. Suppose two laser stars providing mutual defense. If they are relatively close together, their beams are nearly parallel at long range, and hitting the attackers' faceplates. But if they are widely separated to permit side shots, the side fire will remain long range and not very intense.

Both laser stars and target seekers will have to be given some side armor. But armor for mobile spacecraft is problematic. The full surface area of the laser star, excluding radiator fins, is at least 10,000 m3 and probably closer to 20,000 m3. A thousand tons of armor is nearly a third of non-propellant mass, but it won't go far when spread over so much surface, or divided between faceplate and all-round.

The fins are a huge vulnerability, but you need three attackers to force a non edge-on fire.

But I'm not sure how much armor really matters in a pure laser fight, because I don't see how laser fights become anything but eyeball frying contests between eyes of sauron.


Hmmm, this could give two medium laser stars a big advantage over one big one - and provide a reason for more than one uber mirror on a laser star. Your laser engages in an mutual eyeball fry with one of mine. Since it is more powerful it would soon win that fight.

But meanwhile your uber laser is also taking an (off center) zap from my other medium laser, which is not under attack. This zap could be worse, because it is still concentrated by your mirror, and instead of going straight into the laser cavity it is focused by your mirror onto support structure.

This argues for constellations of three or so laser stars. Or, for independent missions, a laser star with a keel mounted main mirror and steerable secondary mirror, or even a main and a pair of secondaries.

A bit of predreadnought flavor! You have two basic types of laser star:

Monitors. Robotic, fitted with a single mirror of maximum size, designed to fight in a constellation of 3 or so. Controlled in action by a command-support ship.

Armored cruisers. Manned for independent deep space missions. Fitted with a single large mirror and a pair of medium mirrors, plus crew compartment and kinetics bay.

Rick said...

Luke - Thanks for the way cool tools!

Kirklin mines raise the ante on kinetic attack. I doubt they raise it to parity, because I can deploy counter-Kirklins that also serve as decoys.

But raising the cost of kinetic attack to parity is not necessary, because it is already costly to take out a laser star, and the laser performs missions that kinetics are not suited to.

That said, I provide the 'armored cruisers' with kinetics bays, for either Kirklins or a handful of the big bruisers.

When I tested a 25 MW laser firing through a 5 meter mirror, I found that it could stop one armored target seeker, but two or three would overwhelm it. So the option of taking one out with a few armored target seekers is one more option to provide for a flexible platform for deep space military missions.

Shame on me for calling it by c. 1900 terminology. :-)

Jean Remy said...

Rick said: "The full surface area of the laser star, excluding radiator fins, is at least 10,000 m3 and probably closer to 20,000 m3."

Surface areas in cubic meters? Really? You Americans will never get the metric system (*wink wink grin*)

I've actually come up with an idea, resurrecting another warship name that has been dismissed on this very Blog, the Destroyer. Now the Destroyer's job was initially the Torpedo Boat Destroyer, it is only later it became an ASW platform.

Your big kinetics, however, have almost more in common with the torpedo boat now than a missile: it's a full blown armored, equivalent-drive-equipped, light delivery vehicle, designed to bring offensive payload within range. The fact that it is an expendable platform doesn't really change things because seriously, who wants to drive a torpedo boat against armored ships sporting 16 in guns?

Enter the "Bus Destroyer" Much smaller than the battlestar, possibly robotically controlled, basically consists of a drive and a small 25 MW laser with a 2-5m mirror. The job of the battlestar is to engage the main enemy vessel (another battlestar or the Bus Carrier?) while the folotilla of destroyers engage the incoming buses. if the constellation spreads its destroyer far apart enough to get a good parallax on the incomings, they can shoot into their flanks, bypassing the mighty 2.5m frontal shield, striking at the engines or reaction mass. At longer range they might even simply fry the buses' own targeting package.

With advantages and disadvantages seemingly equally spread, this is shaping a lot more like 19th century pre-dreadnaught fleet composition, with big ships with big guns, very small ships with big guns to take out the big ships, intermediate ships with small guns to take out the small ships. Add in coastal batteries in the form of orbital launch points for the buses and with their own big lasers (why not, they don't need to sacrifice 2/3 their mass in engine and reaction mass) and you're shaping an interesting future battlefield... er space. IN SPACE!

Jean Remy said...

A quick tack-on: I'm thinking that a light bomb-pulsed X-ray missile might be ideal for long range anti-bus defense. Maybe load your destroyer with a few of these as well, or even have two types of destroyers, one designed for long range intercept armed with a dozen of the suckers, and the laser armed destroyers for extreme close range Oh Shit defense.

Anonymous said...

I think simplification into an eyeball frying contest is a mistake. There are plenty of other factors that add wrinkles to this.

1.) If your mirrors are all tasked to covering his mirrors, they aren't doing damage to other parts of the ship. If lasers are firing at other parts of the ship, they are building up heat that the target is not, and while you're doing damage, he's building up a heat advantage for later in the battle.

2. Depending on how fast shutters can open or close, and the lag from fire order to action, there may not be enough time to zap his mirrors before he zaps yours. In this case, the default position is "shutter closed", and they are only snapped open when a valuable target presents itself. Can one make a solid-state material that changes its absorptive properties based on an electric current running through it? That would be way useful. I have no idea if it is possible.

3.) If your ship is shuttered up, with all mirrors covered by your opponent's mirrors, you launch a kinetic salvo, wait for your opponent to knock down your incoming salvo, and then open your shutters.

4.) Blow up or fold out a big reflective cover. This obscures your lasers, so you can break line of sight from his mirrors to yours. The two sides are back on even footing. If he fries your soft cover, you've got a minor, but possibly significant heat advantage.

5.) Shutters with opacities at different wavelengths. If lasers are different wavelengths, then your shutter can be made transparent to your laser, and opaque to your opponent's.

I'm not an optical expert by any means, so these ideas might be all garbage, but they might be potential complications.

Michael

Jean Remy said...

Michael

I was actually planning a rebuttal to the eyeball frying on the laser post, but since you broached it here, I have a similar take.

1/ Dialectric mirrors: dialectric mirrors are specifically designed to be 99.9% reflective only at a specific wavelength. Unless your opponent is actually using the exact same wavelength your mirror won't re concentrate their beam down into your own systems. For very paranoid empires worried about their own ships turning on them, and who have tunable lasers, you can set each ship in your fleet to a different llambda with specific mirrors that simply can't be changed on the fly.

2/ LCD type shutter: electrically activated glass windows now exist that turn from transparent to opaque (or at least merely translucent) via electric currents. If you use pulsed rather than CW lasers you could match the frequencies and have a WWI fighter-like synchronized fire system. In this case only a CW laser would get a shot in, while the lens is transparent. If for ex you have microsecond pulses with microsecond pauses you can reduce the incoming power (energy/time) of the CW beam by half.

/3 Default setting shuttered: With quick peeks with auxiliary ladar/radar pulses from expandable slots, which have far less definition but give an approximate targeting info, you could keep your main mirror shuttered until you want to seize the right opportunity, if you want to kill/kill an enemy for example (as opposed to mission kill, forcing to retreat and perhaps return later) by taking out its engines rather than its weapon.

/4 Maneuvering: keeps your optics on the move, so even if your enemy's optics are scoping out yours, you can swing it away, take a quick potshot, and shutter again. By keeping your nose swings random you can prevent your enemy from tracking your eyeball fast enough to hit it precisely when it un-shutters.

/5 Polarized lenses: since lasers by definition are phased, ie: the oscillations are parallel, you can set up a polarized lens with the slits parallel to the waves. Any incoming laser will be rotated from ideal and not penetrate.

/6 Multiple mirrors/auxiliary mirrors: in the case of multiple mirrors, you wouldn't be able to wait for the mirror to open and shoot it, because you don't know which one is going to be vulnerable next.

/7 Optically adaptive mirrors: Make the default setting (at rest) is conVEX rather than concave, thereby diffracting the incoming beam even more, while the mirror slips into concave form only long enough for the ship to fire.

I'm not sure all of these steps are possible, but at least some of them ought to be at least moderately effective. Throw in several at once and you can make "frying the eyeball" at long range unlikely, making the only sure shot is when you are close enough to vaporize the armor anyway, and it's still a case of damaging the optics without refocusing the beam inside their optics to damage the laser inside.

Rick said...

Eyeball frying.

First consider a one on one laser fight. If you come in shuttered, I can come in unshuttered with impunity, and keep up a steady zap. At long range it is too spread out to do anything but scorch paint, but I get a free shot on you while you unshutter.

Mechanical shutters will take some time. LCD glass shutters will probably be significantly heat sensitive, so even a low focus zap, kept up, will degrade them.

With a single laser you gain nothing by being shuttered, because sooner or later you have to unshutter to zap, and so long as you are shuttered the enemy can zap you with impunity.

Now, once you have more than one laser in play it gets more complicated, because an unshuttered laser can be double teamed.

Once a laser is unshuttered and zapping, though, it is both more dangerous and more vulnerable than any other target. Nothing will mission kill a laser star faster than zapping its laser. So once the shutters go open, I don't see what keeps lasers from being each other's primary targets.

But this all hinges on how vulnerable lasers and their optics really are. I just assume that they're much more vulnerable than anything behind heavy laser armor, and heavy armored shutters can't be opened very quickly. A second or so is a long time - just 0.4 seconds dumps a hundred MJ onto the partly unshuttered laser optics.

I'll take up 'destroyers' in another reply!

Anonymous said...

I think this makes it pretty clear that any laser battlestar worthy of the name will have more than one targeting mirror. All one's eggs in one basket, and all that.

Additionally, if the fighting effectiveness of a craft was heavily dependent on shutter speed, I'd bet that engineers could devise some ways to open and close the shutters pretty quickly.

One possibility, a series of light shutters that could open and close independently. You could open up the inside ones first, using the outside shutter as a mask for the state of your inside shutters. As long as the outer shutter could withstand a blast long enough to close the inside shutters, it would be as good as a single heavy shutter, but you could open the final layer much faster than a single heavy shutter.

Michael

Rick said...

I like the layered shutters idea.

But what I really don't know enough about is what happens when lasers unshutter and target each other. My intuition is that when the zapping starts the lasers will fry each other very quickly, but that is a sheer guess.

Rick said...

Jean's earlier comment on 'destroyers: Yet another Belle Epoque analogy, but it works pretty well.

In a way, though, they are less like destroyers than outworks of a fortification. (And I think they'd be robotic.) I have thought before that there is a rather 18th century flavor to space combat at this techlevel.

Not like an 18th c. naval battle, but like a battle of mobile Vauban forts. The gentle main drive acceleration and large distances means that constellation maneuvers are, shall we say, stately, laser stars and 'destroyers' taking up a geometrical formation to optimize mutual support.

Jean Remy said...

"Star Forts" are definitely appropriate!

Rick said...

Star forts, indeed!

Also - inverting current usage - I can see a mission for long range corvettes. These are essentially scaled down 'armored cruisers,' with perhaps a 10 MW laser with a fixed 3 meter mirror and a pair of movable 1 meter mirrors, a bay for light Kirklin type kinetics, and a crew compartment.

Corvettes have a very limited role in intense combat (though they can provide some off-axis supporting fire), but they do much of the regular work of the service. And they may see most of the real action.

In spite of the practical elegance of Michael's layered shutters, for cinematic purposes there is nothing like the order 'Unshutter main mirror!' ... external view, in silence, as the armored shutter slides slowly open to reveal a big laser mirror.

Rick said...

Jean - Upthread you also mentioned lasers mounted other than on than 'ships.' For very sustained zapping you need a reactor for power, but most of the heavy zapping against a kinetics wave is done in 100 seconds or so.

So an orbital defense laser can have chemical fuel, either directly for chemical lasers or powering fuel cells turbogenerators. A couple of hundred tons is enough. It should also carry some chemfuel for thrusters, but as you said it will be perhaps a third the mass and cost of a full laser star, and with comparable zapping power for a critical couple of minutes of sustained fire.

Scaled down versions of these could also be deployed in lieu of full 'destroyers' as part of a defensive screen.

Anonymous said...

This is a great post, but I have to wonder: why wouldn't BOTH ships have multiple laser-emitters and kinetics? It seems to me that you'd use the kinetics to keep the secondary lasers engaged, while trying to use your main to damage/mission kill the other guy (all while he's doing the exact same thing to you); one kinetic gets through or one laser shot gets into your main optics and its downhill after that... of course, if you throw out some inflatable, expendable mirrors into the mix, things might get interesting (is it just a .5 kg mirror or is there a penitrator rod behind it? If I zap it, will I get enough return energy to damage me before it vaporizes? Or should I expend my own kinetics to destroy them and maybe not have enough left over to threaten the enemy ship? will my expendable mirrors be effective?)

Also, the bus that the kinetics are launched from isn't going to evaporate when the primary payload is launched; it's going to continue on toward its target...so you're going to have to zap it too.

I hope this muddles things a bit.

Ferrell

Jean Remy said...

Considering a ball-turret laser mirror setup.

(http://en.wikipedia.org
/wiki/File:Airbornelaserturret.jpg)

I can see actually a geodesic dome/sphere in the nose of the ship. Each triangular panel is held by spring-loaded hinges on all three edges, the pins on the hinges themselves spring loaded and magnetically locked. At the order to unshutter, the computer determines the orientation of the mirror and decides what panels need to be opened. The appropriate hinge pins on two edges are released (the pins are pushed out of the hinge by the springs, or magnetically pulled out) Now that the triangular panel is only held by one edge, which is spring loaded, snap (you can ever hear the snap echoing through the hull) that panel folds open. Do that on enough of the panels to open a hole the appropriate size. Presumably the act of opening the panel readies an opposite spring and sets in in tension, so the open panel must be held open by another electromagnet. The hinge pins also need to have a second set of springs, or to be magnetically attracted back into place when you close it.

Maintenance on that system would be a pain because of all the springs that have to be held in tension and electromagnets need to function every time, and the precise alignment of all parts when it comes to closing the shutters again. Presumably the dome can be removed and a fresh dome put in place to reduce the Laser Star's downtime. A failsafe in case of a malfunction is to simply blow the panel.

On the other hand this is potentially a very massive and awkward, fail-prone system altogether. On the other hand, without the main mirror the Laser Star is basically a rather ineffective paperweight without its titular laser. Also since the nose dome is in, well, the nose, this could be the most heavily armored part of the ship, so why not add a few magnets and springs. (arguments and counter-arguments in the same paragraph!)

PS: now that I think of it (belatedly) memory metals and plastics may be used for some or all the system components above.

P.P.S. Why am I not posting this on the Laser discussion?

Mark said...

@Jean Remy
With a ball turret wouldn't it be easier to "shutter" the optics by turning them inward? Your idea would allow the optics to be aimed before firing, so which works better probably depends on how fast the ball can be spun and how well armored they can be.


Destroyers sound a lot like drones to me, being smaller unmanned combat ships, and since they're probably being sent forward anyway (to get lateral shots on the kinetics sooner) and if you let them keep going forward they can start shooting at the enemy. Although, considering how well lasers destroy objects that aren't both massive and numerous, most of the destroyer drones would probably be held back for defense, with a couple sent with a kinetic salvo where they might be considered low priority targets and destroy kirklin mines.

If laser fights are about shooting your enemy's optics, pitched battle will probably be decided by who has enough optics left to handle the next wave of kinetics, which certainly seems like a good argument for a bunch of small point defense turrets as well as main ship killer optics.

-Mark

Jean Remy said...

Well the ball turret itself would be vulnerable at the rotation joint. A direct hit on it might dis-align the mirrors inside, hence the geodesic armored dome.

Citizen Joe said...

I wanted to point out that eyeballs (sensors) are designed to be sensitive, that's kind of the point. That means that eyeballs will fry with significantly less power than is needed to zap armor. Which means that your eyeball frying range is likely to exceed 10 times your armor frying range and will also be a broader field (I think a bit over 3 times the diameter).

So all you really need is an occlusion flare behind/to the side of your ship to blind the enemy. Then your sensor/targeting eye can focus on spotting the enemy ship. That pretty much creates a range band where you COULD hit each other with lasers, but you couldn't guarantee it, and it would definitely be just generalized hit rather than precision strikes. An attempted strike would however guarantee power usage and waste heat on your part.

Anonymous said...

I'm thinking that sensors can have the same armored shutter mechanisms that lasers could have. At these ranges and speeds, you could probably have your sensors open 1% of the time and still have enough data about your target to engage. The practicality of this is still clearly dependent on the ability to quickly open and close your shutters. This battle could also come down to who can repair mirrors and sensors the fastest.

Michael

Glenn said...

What about a more active defense for lasers? If ship maneuver in near future terms is very hard/unlikely due to delta-v restrictions, then you have two or more closing opponents approaching along very predictable vectors (a key factor in making kinetics deadly). If that's the case, what can you throw in the path of the predictable laser paths that would either diffuse incoming beams or create a heat load problem for the other guy trying to melt the obstacle away? This might limit your own attacks unless you use mirror drones or boom extensions or some other method to shoot through your own defense(electrically powered adjustable opacity defense munition?). Could the throw away item itself be used as a kinetic impacter (a reverse defense/attack drone)? Ultimately I'd see it as a method of closing range, but the question is still what's cheap enough to resist high powered laser attacks long enough to make a difference? Or is there?

Anonymous said...

Ok, I have two things: first, Glenn, a large, inflateable defocusing lens thrown in front of the ship might be your answer.

Second: about the design of the main laser mirror; it occured to me that if there wasn't a need to 'slew' the mirror to any great degree, then why not make one that only adjusted its fine control, with the ship's manuvering thrusters providing coarse control? So, use a parabolic mirror with some hydrolic actuators behind it for fine targeting control, and ring the mirror with small emitters, themselves behind an armored ring. The parabolic mirror will reflect all incoming light from whatever angle back along a path directly away from the center of the mirror. With active cooling, the mirror should be one of the last places you'd want to shoot at. As far as the sensors go; place sterioscopic pairs of sensors on booms behind the faceplate; they pop up in a random (or psudorandom) pattern. However, a pair of secondary laser turrets or parabolic mirrors may also pop up. While the most effective sensor would be a laser run through the main mirror with sensors behind the (now moved out of the way) armored ring, but at combat ranges you would need to protect your main weapon system, so you would button up the long range sensors and use the backups, instead.

Ferrell

Jean Remy said...

There was a lot of Laser Star discussion lately, so let me swing on the other side of the equation and address a few concerns.

Rick's original post: "But 'merely big' kinetics, say with a dry mass of 5 tons and armor plug 2.5 meters deep [...]"

First of all a dry mass of five tons strikes me as far too low an estimate, even for a SWAG. Say the missile/bus is at least 1m abeam, which is no unreasonable since you're going to have to hide remass bunkerage and an engine behind, at the very least. You want the shield to be bigger than the missile itself to protect the bell thruster, and probably RCS thrusters. With a 1m diameter, 2.5m thick shield, made of carbon, you have a mass of approx 5 tons JUST in the shield, and we haven't addressed the engine yet.

Let's look at drives. You need something equivalent at least to the power of your Laserstar, so capable of milligee accelerations. In fact I would say several milligees to be sure the Laserstar won't simply move out of the way, and force the missile into a stern chase its far lesser delta-v will not allow. A VASMIR drive would allow this, but its mass would be around ten tons, not to mention it requires a power plant generating 10 MW. An ArcJet drive might be more realistic, it would still be 10-15 tons. Alternatively you could could use an external power source and say put in a laser-thermal engine. Disadvantage is you need to keep a laser beam focused onto the missile at all times, and if it has to maneuver rather abruptly at the end, it is going to find itself with no power. Or you could go that way but strap solid-fuel boosters. I'd probably strap SRB's on anyway because of their extreme acceleration capabilities.

Let's say to be generous a 10 ton engine. We are now at 15 tons dry mass.

The missile needs a body, at least lightly armored to defend against staggered destroyers or multiple Laserstars, some form of internal structure to withstand the accelerations (particularly if you use SRBs on the end run), the explosives, a mathematically precise shrapnel coating (used the missile's fragments are ok, but since they are designed for other purposes they will not be optimized to spread in an even patterns.

Even if you decide that last bit is not significant (only 1-2 tons), you still have a 15 ton dry mass missile, which is already 3 times the original estimate.

That's not really a killer for orbital defense which are limited only by how many you want to park in orbit. A Missile/Carrierstar however just saw the number of missiles it can carry for the same mission profile reduced by at least 2/3rds. Since the name of the game with kinetics is sheer numbers, now you need three times the number of Kinetistars for the same number of missiles available for the constellation.

It seems to be that kinetic buses are very much a defensive weapon, not really an offensive one, unless each one becomes a full-blown drone Star-class ship with enough delta-v to follow the Laserstars in formation the whole way (so with equivalent delta-v and endurance) which will jack up the price to nearly unacceptable levels. Even if each one is 1/5th the price of the manned Laserstar, since it takes about 50 of them to take one down, well...

It's definitely a weapon designed to defend strategically important targets around which they can stay in orbit, and they are a very effective one at that, but they are not flexible enough to belong in the Assault Constellation.

Rick said...

I played more with my spreadsheet, and discovered that I could work it down to a formula to express the laser/kinetics tradeoff.

This is before all the variations and complications discussed in comments above, to reduce things to their basic elements.

The premise is that a space laser has a basic cost based largely on its power output, and kinetic target seekers have a basic cost based largely on their total mass. How you pick these is somewhat arbitrary, but should fit your general tech assumptions.

But for any given set of assumptions, high closing speeds favor kinetics, while large optics and short wavelengths favor the laser.

A laser defeats an incoming wave of kinetics, equal to its own cost, if

200 * D / (L * V) > 1

Where

D = mirror diameter, meters
L = wavelength, nanometers
V = approach velocity, km/s

The 200 is a finagle factor based on my own assumptions, namely that a laser with power plant costs $4000 per kw of beam power or ~$1000 per kw generator power, while kinetics cost $1 million per ton of armor mass, plus $100,000 for the guidance logic.

But the finagle factor can be finagled. :-) The real point of the formula is to isolate the specific effects of mirror size, wavelength, and kinetic speed.

Example:

Suppose a 400 nm laser with a 10 meter mirror, and kinetics approaching at 5 km/s. The formula becomes

200 * 10 m / (400 nm * 5 km/s) = 0.5

This laser can zap 10 km/s kinetics equal to half its cost.

If the kinetics are coming at 5 km/s it can defeat a salvo equal to its own cost, making kinetics essentially useless against it. On the other hand, if the kinetics are coming at 30 km/s, it can only defeat a salvo equal to 1/6 its cost.

If this value is greater than 1, lasers totally dominate, and kinetics are not in use.

But if the value is less than 1, that does not mean kinetic dominance, because of the inflexibility of kinetics - when you use them you lose them. If the laser defense factor is 0.5 or even 0.25, massive kinetic strikes can defeat a laser star, but at the cost of severe attrition for the winning side. (Whereas the laser suffers no attrition if it wins.)

Against the laser specified, 5 km/s kinetics are ineffectual, and 10 km/s kinetics usable only in a single massive strike. But 30 km/s kinetics begin to tilt the advantage. The laser defense factor is 0.17, and a kinetic superbus can engage 4-5 laser stars before depleting its ordnance.

But if the laser zaps at 250 nm in the UV, and has a 25 meter mirror, its defense factor against 30 km/s kinetics is 0.67, and kinetics are again highly limited.

Anonymous said...

So it all boils down to a matter of time...if your laser doesn't have enough time to zap everything coming its way, you get slammed.

Ferrell

Jean Remy said...

Ferrell:

Battles have always been a matter of time. How long can the city hold against the siege vs how long can the besieging army stay there until defection and mutiny forces them to leave. But pretty much here, yes, of course. Zapping each missile takes time, and if you got more time than you got missiles, you're fine. If not...

Rick:

This one is definitely going in my Big Book of Science Fiction Equations! I knew there would be a correlation between closing speeds and laser killing ability, but this really highlights the importance not only of the mirror, but the wavelength as well.

However I would add a small caveat to your conclusion. You say that when the cost of the missiles becomes greater than the cost of the incoming Laserstar the missiles won't be used, or used less. However, this doesn't take into account the cost of the infrastructure you are defending. I bet the shipyards or the orbital spaceports cost a lot more even than a mere Laserstar, so who cares about the missile costs. Even if you don't have enough to kill the Laserstars, you'll at least force them to shoot them, at the minimum pushing their heat budget up in the red zone, or distracting them while your own Laserstars are working them up.

An orbital assault constellation is shaping out to be huge because, as usual, defense has the early advantage, but the late disadvantage (ie: You have walls, but your trade routes are blockaded). There had better be a very good reason to justify the attack. Of course, knowing humanity, a very good reason could be that those heathens hang red drapes in the North facing windows which is a clear offense to the Great Pasta Bowl in the Sky.

Rick said...

Ferrell - In a nutshell, yes. The faster the incoming kinetics, the less time you have. The longer range your optical system (mirror size / wavelength), the more time you have.

But I also found out that if the cost of kinetics is simply proportional to mass, the smaller the target seekers, the better. (So long as they're big enough to do damage if they hit.)

I limited this by requiring each target seeker to pay a fixed guidance cost - since big or small, it needs the same targeting data.

Anonymous said...

It sounds like a mix of kinetic weapons (different masses and velocities)might be a good option.
Two seperate laser systems might also be a better option...one high powered that supplies the main and secondary, and another (seperate) system that powers a dedicated point defense system. The main system might be electrically powered and the other chemically powered. Chemically powered lasers are open-cycle, after all, so they might be useful as a back up system.
Personally, I think that there won't be Laserstars and seperate missile carriers, but vessels that combine both functions...just as moderen navy warships have a mix of weapons so would space-going warships. Some might have a different mix, but all will have some of each...
By the way, cool equation!

Ferrell

Rick said...

Jean - Yes, the orbital defense zone is Big.

First on your earlier comment about full target seeker mass. I cheated a bit, on the basis that most of the dry mass is the shield, and it is relatively cheap compared to its mass, being just a block of Super Nano Carbon Stuff.

I ended up with quite small target seekers, shell size, with the faceplate 40 cm in diameter and 80 cm long. (16" shells!) Faceplate mass 200 kg. Say that it has a service module behind it with deflect motors, tankage, and control unit, dry mass 100 kg, and 200 kg chemfuel. Available delta v is about 1.5 km/s.

If the shield costs 'just' half a million per ton, it costs $100,000, and the service module is another $100,000, keeping overall dry cost at $1 million per ton. (But I also charge $100,000 for the guidance package.)

The Oberth effect works wonders for 'slow' kinetics. Suppose our defense platforms are on fairly long elliptical orbits, so they pass perigee at 11 km/s, just below escape velocity. A 1 km/s burn will send them out with a net departure speed of 5 km/s. And I'm firing them into the path of the approaching laser star, so encounter speed will be higher, perhaps 7 km/s.

The departure burn leaves them with just 0.5 km/s of deflect, but milligee ships take a day to change orbit by 1 km/s, so I can launch them about 12 hours before intercept. That puts the intercept in the neighborhood of 200,000 km from Earth, about half lunar distance.

And this is for 'coast defense' kinetics launched directly from planetary orbit.


Since I have deep space ships with a delta v of 30 km/s, suppose I load them aboard one, and head out into your path, putting on 10 km/s. I release the mines/torpedoes, use another 10 km/s of delta v to veer clear and decelerate, and the final 10 km/s to make a slower return to my orbital base.

This gives the kinetics an outbound speed of 10 km/s, against an incoming force still on transfer orbit, its inbound relative speed at least about 5 km/s, perhaps 10 km/s. So I can get a closing speed of 15-20 km/s without expending my booster vehicle (unless you zap it).

This could put the battle two weeks out from Earth, on order of 5 million km away - defense in depth!

And since a kinetic hitting at 15 km/s is more than twice as effective as one hitting at 7 km/s, it is well worth investing in recoverable bus vehicles, which can also be adapted into deep space missile ships.

By my formula, for what it is worth, a 400 nm laser with a 10 meter mirror brushes aside 5 km/s kinetics, and can only be taken out by a massive salvo of 10 km/s kinetics, but at 15 km/s its defense factor is down to 0.3. But if I can put a 100 nm far UV beam through a 10 meter mirror, I can swamp more than my own cost in 15 km/s kinetics.

Oh, to your point about value of the target being defended, this is true. But if kinetics capable of blasting a laser star cost more than the laser star does, why not invest in a more powerful laser star instead?

(I know there could be other reasons - if you have a good basic space industry, but not a specialized laser industry, for example.)

Citizen Joe said...

Can that formula be boiled down to an energy cost rather than a financial cost?

The Laserstar has its operating power, but that requires power production, which is mass. So you have to get all that into a ship. Then, since the Laserstar is an attack ship, not defense, it needs to have at least interplanetary capability, if not interstellar. All that adds to the mass. In the end you need a very large support system to get your Laserstar on target vs. a very small system to launch kinetics (remass, drive, navigation).

While the Laserstar might be effective in ship vs. ship combat, it would be crushed by a planetside laser since they can dump heat into the atmosphere, and have a superior dish, etc. Planetside lasers also don't need all the drive mechanisms. So what is the point of a Laserstar if, after defeating the Kinetistar, it can't beat the home planet?

In deep space, Kinetistars are kinda out of place. So, Laserstars are going to be the deep space warships. However, they are going to see each other way earlier than they can engage. So, unless they agree to a laser jousting tournament, one side or the other can just alter course to stay out of range.

Rick said...

Citizen Joe - You could do an energy cost comparison, but it is less helpful. In a spacefaring economy, propulsion energy must be cheap (or you can't have extensive space traffic going at multiple km/s). What is expensive is the capacity to produce and use energy, as a laser beam or for propulsion. Also expensive is fancy hardware, such as the service module of a target seeker.

I would indeed expect a surface based laser to be cheaper than its space-based counterpart, since it can plug into the planetary power grid and take advantage of cheap cooling.

As for lasers v kinetics in deep space, it all depends on the speed of the kinetics (to first approximation the speed of interplanetary travel) versus the kill range of the laser.

I'm still tweaking my formula; I would say that for fairly big, fancy kinetics - 1 ton of armor, costing by my formula, including guidance, $1.5 million - the finagle factor is about 300.

Notice that laser performance is defined when it is built, so it is fixed on the operational time scale. The only way to get more powerful lasers is to upgrade them. But the speed of kinetics is influenced by operational and tactical factors - the orbit they are launched from and the orbit of their target.

A laser star that can easily defeat kinetics at 10 km/s may be overwhelmed if those same kinetics are thrown at 20 km/s.


Ferrell - War craft (or at least constellations) will probably be armed with both, IF the laser defense factor is not so high as to be overwhelming, or so weak as to be pitiful.

I'm exploring mixed armament warcraft, and my thinking is that generally you use lasers for persisting combat power against weaker opponents, and kinetics for a costly but overwhelming salvo against more powerful ones.

One respect, by the way, in which World War analogies are misleading. We think of defense against torpedo craft or aircraft as a task for the secondary battery. But stopping a serious kinetic attack is the toughest assignment a laser star can face.

Imagine a relatively near future 25 MW, 1000 nanometer IR laser. Against 1-ton kinetics coming at fairly low speed, 7 km/s, it has a modest defense factor of 0.21. The laser installation costs about as much as 67 target seekers, and it will fry about 14 incomings. (But #15 will get through.) Opening fire at 1000 km this requires about 140 seconds of steady zapping.

But this same laser is capable of burning through 2 cm of armor per second at 1000 km range, so it zaps through a meter of armor in less than a minute. That is a LOT of armor for a ship to carry, so this laser has formidable offensive power even though it can be defeated by a quarter of its own cost in 'slow' kinetics.

So under heavy kinetic attack, laser stars use their main armament.

This suggests a combined arms tactic. Launch a kinetic strike strong enough to saturate the secondaries, so the enemy must engage it with their primary laser. For the duration of the attack you can zap them, while they can only zap back with secondaries, because their primary laser is busy defending against your kinetics.

Citizen Joe said...

Here's another question...

What is the operational band for the laser? If your mirrors are adjustable to focus at 10,000 km, how well can they focus at 5000? 500?

Of course the trick is to tune your frequency to adjust your focal distance. Going back to the WWII model, it is the equivalent to how many powder charges you pack into the main cannon, not the size of the cannon.

Jean Remy said...

Mixed armaments:

I very much doubt we'd see mixed weapon loadouts. For a laser you want to build as big a mirror as is technologically feasible to begin with. Probably the primary mirror will be the single most expensive component in a Laserstar, followed by the rest of the optics, like the cavity mirrors themselves, and the ones to direct the beam path into the main mirror.

At this point, since you have a big mirror, you'll want to put as much of a laser behind it as you can. If you still use chem lasers, you'll embark as much of the chemicals as you possibly can, in the case of a solid-state modular stack, ditto. FEL's might be a different issue, although I can't think bringing along a mini-cyclotron will be easy.

You'll have to cool this laser, either by dumping the chemicals (so you really really really want to fill as much of the ship as you can since now each laser shot uses up "ammo" thus removing one of the main advantages of lasers in the first place) or dumping the heat into sodium or lithium heat sinks, where you might have to dump the fluid after a while, or cycle it through a droplet system which will incur fluid losses as well, so once more: embark the maximum possible amount of heat sink fluid.

Every ton of missile you put in your ship will mean a ton of chemical or coolant you can't embark. Since kinetics are very dependent on saturation fire, to carry any significant amount would be so costly in mass to your laser system as to make that laser an afterthought, which as stated above isn't due to the investment in its mirror to begin with.

It will be a lot more efficient to build mixed fleets than mixed-loadout ships.

As far as defensive measure against kinetic attacks, I think counter-kinetics might not be a bad idea: create a cloud of shrapnel in the path of the incoming kinetics and the 5 ton SNCF (Super Nano Carbon stufF wait that copyright is already used. damn) armor doesn't matter because it gets slammed with a few Ricks. It'd be a little harder to target those incomings, but the few kinetics get passed, the fewer targets the Laserstars will have to engage.

Rick said...

Citizen Joe - First, to 'revise and extend' earlier remarks, as they say in the US Congress.

I missed your real point, which is to configure the equation to specify the firm science from the conjecture. So here is an improved version:

Suppose kinetics with faceplates of Super Nano Carbon Stuff (like graphite, but strong), 1 meter thick.

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

Where

K = kills

P = beam power (MW)
D = mirror diameter (meters)
L = wavelength (nanometers)
V = kinetic velocity (km/s)

Example. A 25 MW, 1000 nm IR laser firing through a 5 meter mirror, against kinetics closing at 10 km/s:

1750 * 25 * 5 / (1000 * 10) = 22

So this laser will zap 22 target seekers with 1-meter faceplates, coming in at 10 km/s, before getting scragged by #23.

Note that in this example a 25 MW laser succeeds in zapping 22 target seekers with 1-meter shields. In setting up examples on my spreadsheet, I found that they came out in the broad range of 1 MW needed to zap one seeker with a 1-meter faceplate.

This seems to be a rough balance point. If a megawatt of power output kills several 1-ton target seekers, lasers dominate; if it takes several MW of power output to defeat one target seeker, kinetics dominate.

Note that in this example a 25 MW laser succeeds in zapping 22 target seekers with 1-meter shields. In setting up examples on my spreadsheet, I found that they came out in the broad range of 1 MW needed to zap one seeker with a 1-meter faceplate.

This seems to be a rough balance point. If a megawatt of power output kills several 1-ton target seekers, lasers dominate; if it takes several MW of power output to defeat one target seeker, kinetics dominate.

As to your question about focusing distance, I have no idea, but I believe that it is basically like focusing a camera. Moving the mirror very slightly in or out shifts the focus point.


Jean - I tend to agree that constellations will have different spacecraft to carry different weapons.

But it isn't too hard to justify deep space craft intended for independent missions and carrying both types of armament. A laser for persisting firepower against lesser opponents, a kinetics bay for letting off a salvo against bigger ones.

Citizen Joe said...

Actually, with the range and everything based on wavelength, and lasers being very narrow in wavelength range, you could simply set your sensor on a different wavelength from your laser. So if you scan on the IR spectrum (not sure that the same mirror will spot IR and reflect Violet) then you get a wider spread, but that's ok because you don't need damaging levels of radiation, just visual discrimination. If your laser mirror is targeted, it won't fry the scanner, because the different wavelength would refocus back at the wrong point, thus missing your sensor. It would however hit your laser emitter itself. So you would be better off shuttering your laser, but maintaining the IR scan. They could try to fry your scanner with IR wavelengths, but the range on IR lasers is pathetically short compared to the Violet laser and thus not a viable option. Suddenly, you DON'T get to simply blind your opponent because he's using a frequency of EM radiation that is not suitable for long range attack but wonderfully suited for long range scanning.

That being said, your mirror and radiators are still vulnerable targets.

Rick said...

I don't think the focal length varies by wavelength, only (very slightly) by distance to the target. So if the enemy lets off a zap, the beam will be reflected onto your sensors, even though your sensors, your laser, and the enemy laser all have different wavelengths.

How reflective the mirror is DOES vary by wavelength. But whatever it doesn't reflect it absorbs, heating the mirror and degrading it if it gets hot enough.

No one seems quite sure what happens when a mirror or sensor elements get zapped, so here is my guess:

Suppose a 100 MW beam is focused onto a 1 meter spot on a mirror designed for a different wavelength. Say that 99.9 percent is reflected, but 0.1 percent, or 100 kW, is absorbed.

From Luke's sim, that is enough to heat the surface to a blackbody temperature of 1200 K, near the melting point of granite, the closest thing on his list to quartzy glassy stuff. Which is probably enough to distort the mirror surface, degrading its optical performance.

My 400 nm laser with a 10 meter mirror makes a 1 meter spot at 40,000 km. If the same beam is fully absorbed it burns through armor at about 1 mm/second.

But I'll guess that since you only need to melt the top micron or so of surface to degrade it as an optical surface, it will take about 10 milliseconds to fry the spot, and a second to fry a 10 meter mirror.

So ... an eyeball frying contest between lasers might be over in a second or so. If one laser has twice the power of the other, it will fully degrade the weaker mirror, and be about 25 percent degraded itself.

Rick said...

Or a more conservative estimate, simply that if the fully absorbed beam burns through 1 mm per second, a 0.1 percent absorbed beam will ruin the outer micron in a second, and take 100 seconds to scorch a 10 meter mirror.

Luke said...

Regarding focusing - the relevant equation is 1/i+1/o = 1/f, where i is the distance to the "image" (where the laser will be focused), o is the distance to the "object" (almost, but not quite, the location of the diverging mirror that the laser bounces off of before it reflects off the primary mirror), and f is the focal length of the mirror. For a 10 meter mirror, f may well be 10 meters. To focus at 10,000 km (10,000,000 meters) you just solve 1/10,000,000+1/o=1/10, so o=10.00001. To focus at 100,000 km (100,000,000 meters), solve 1/100,000,000+1/o=1/10, or o=10.000001. You can see that to adjust your focus from 10,000 km to 100,000 km, you move your diverging mirror toward the main mirror by 9 microns.

Z said...

I am a might too tired to be playing too much with the math, but from a tactical blue-sky perspective, eyeball zapping LaserStar fights strike me as the kind that no one shows up to, akin to a nuclear ICBM exchange. A situation where the two combatants stare unshuttered at each other until someone gets a phonecall and everyone has a 50-50 chance of dying is a battle that isn't likely to get fought, and it can only take so many years of not getting fought before it gets defunded, shrunk by treaty, or driven into obsolescence by changes in other tech or tactics.

Fitting into that same vein, I could imagine that laserstars, being massive and single purpose, are uniquely poised to be defanged by political wrangling, sabotage/first strike, etc. whereas kinetics are outgrowths of off-the-shelf drives and sensors available everywhere- again, akin to the growing realization that fancy small arms are a bigger threat to global security than nukes. By that same token, I can imagine kinetics, thanks to their dual-use, getting cheaper faster than laser forts.

In the same vein as the MAD nature of laser fights, I can imagine military planners not being too fond of laserforts thanks to their monolithic, all or nothing response to damage. A laserstar fragging kinetics will be swimming in a sea of gas and fragments of perhaps negligible threat to its armored bulk, but probably not to the optical purity of its one, sole mirror, which suddenly and catastrophically fails when it is, in effect, sneezed on. Practically speaking, the laser will have a limited duty cycle- can it keep firing long enough to vaporize the stream of paint droplets being lobbed to orbital altitude from the planetary body it would conceivably be fighting over?

A KineticStar, on the other hand, I can envision being much more durable. Really, it just needs propellant tanks, drives, radiators, and racks of missiles/lancer bays/coilguns/whatever close enough to share plumbing and wiring, with options for redundancy, interarmoring, wide spacing of components, etc, and nothing that reacts poorly to micrometroids, natural or otherwise.

I of course recognize the nature of Purple v Green, but big realistic laser ships have never seemed to have practical qualities that recommend them as weapon systems anyone would actually use.

Jean Remy said...

Z: a very good analysis if you consider Laserstars to be the equivalent of ICBMs and assume a parity in forces between opponents Cold-War style. I think it is actually a slight fallacy since a Laserstar exchange kills Laserstars, therefore military personnel but an ICBM exchange kills cities, therefore civilians. That is a HUGE difference for politicians (an public opinion in general) since military personnel generally chooses to be in harm's way and civilians, generally, tend to not.

I think the Laserstars would have more in common with Supercarriers than ICBM's. Once you launch an ICBM, that's it. Time to Tango. ICBMs are like Pringles: you can't stop with just one. Laserstars, on the other hand, could be parked off the coast... er I mean in the orbit of a nation-world (moon, planet, asteroid) as a threat, but unlike the ICBM you can fire a warning shot. Like a Supercarrier offshore can launch a quick air-strike to remove, say, a suspected chemical weapons factory or a terrorist training camp, the Laserstar can pinpoint the same type of target and remove it, without launching Armageddon in the process. I would argue then that the Laserstar can be a form of power-projection: Laserstar Diplomacy. I think Laserstars will be more politically palatable than a Kinetistar in that role. First it's not bombarding a surface with missiles. You can literally kill one tank in the middle of a crowded city square with a laser, thus reducing collateral damage. You only need one missile to go astray and public opinion can swing against you wildly. Even if you don't miss the psychological impact "back home" is all wrong. Like nuclear power, strategic missiles have a bad name. Secondly, you don't have to worry about reducing your fighting capabilities every time you fire a missile. Your laser has the same hitting power before and after a strike. The Kinetistar is down one missile.

If instead of force parity you have a hegemonic power capable of fielding and maintaining a constellation of Laserstar 10 times larger than any single other power, if this hegemon has been know to win major wars thanks to the use of Laserstars, and if its military is in love with the Laserstar concept because they are big and flashy and really impressive, then rather than being opposed to it I think politicians will be more than willing to keep up the funding.

So rather than a an ICBM MAD-like situation you have a US Supercarrier power-projection fleet fueled by an over-funded budget supported by politicians and the public, and it would create a situation where other nations try to build up their own Laserstar constellations.

Even if decades go by without a Laserstar-on-Laserstar confrontation, their uses are manifold because their power-output levels can be modulated, rather than the nothing-or-Armageddon option of an ICBM.

Mark said...

Slightly off topic, but still inspired by this post, I've been thinking. If I had a nuclear powered plasma electric engine (especially something complicated like a vasimr) I wouldn't want to clamber over the nuclear power plant to get at the engine if something fixable/replaceable failed, and since the engine isn't spewing deadly radiation in all directions (please correct me if I'm wrong about that) that the locations of the power plant and the habitat could be switched, putting the nuclear plant at the front still at the far end of a boom leading to the crew habitat right next the engine. One advantage to this arrangement is that if you hit something head on (like debris, or a kinetic weapon) it's not the hab that takes the brunt of the impact. It would take out the power plant but at least it would leave the possibility of rescue.

Now, it would probably mean no axial laser with optics a the bow, but I kind of figure that faceplate armor would all ready preclude that. I think a folding or inflatable mirror that can be deployed to one side would be a good solution, they would be much more expensive and delicate than a solid one built into the ship, but the facts that a deployable mirror can be much larger than than the diameter of the ship and it would be possible to have equally large backup mirrors seem like they would be worth it.

Z said...

Jean Remy: Decent points all, but the other half of my beef still stands- laserstars are still expensive and fragile in hard to overcome ways that don't hamper kinetics-they cost big and fail hard, which come to think of it, is the position supercarriers find themselves in today- great toys if you have them, but at billions a pop and an Exocet launch away from some quality bottom time (and the development costs of Exocet 2.0 being smaller than Carrier 2.0 and more parties possessing the purchasing power to snag the former rather than the later,) no one that doesn't own them already is interested in getting them when the missiles to sink them can be built with multi-purpose knowledge in a fraction the time and cost.

Once again, that puts us back at Purple v Green- which wasn't my point- that point being that lasers have issues that have nothing to do with wavelength, power output, or spot size. :-)

Citizen Joe said...

RE: Luke focal length and mirrors
How precisely can those mirrors be physically moved. If a micron difference (which could be caused by someone sneezing nearby) could defocus the laser from 10,000 km to 100,000 km then how practical is it as a weapon? Particularly as things are constantly moving at multiple km/s. Whether or not you can focus the laser to a 1 meter spot 10,000 km away has little bearing on the micro adjustments needed to put that spot on a particular moving target. Therein, kinetics have an advantage. Lasers can't be issued course corrections.

RE: Z Habitat vs. powerplant. There is no rescue in space, particularly if your powerplant goes down. Just a slow death as you freeze. You're better off taking the instant death, rather than endangering rescue parties that have to rush to get there in time.

Rick said...

Mark - That's an interesting question. I've seen illos of spacecraft with the reactor forward; there might be some at Atomic Rockets.

But you need robo waldos anyway to service the reactor, and the drive units themselves don't have much that onboard repair can do. They are like big electric motor. For any real work you need to take them into a cageworks and strip them down.


Z and Jean - Great discussion! Assuming that the tech balance makes both weapons potentially viable, on the strategic and symbolic level I tend to go with the super carrier analogy.

Lasers have persisting firepower, and provide rather fine tuned damage. This makes them useful instruments of dominance.

Laser stars are an excellent blockade enforcement weapon. A constellation of 3 laser stars in high orbit dominates orbital space. It can keep order with cheap, precise zaps, without resorting to expensive target seekers that smash whatever they hit. It can only be defeated by a more powerful laser constellation or a massive kinetic strike.

Laser stars 'of the constellation' may not need an onboard crew. The constellation can include a command craft / tender that controls the laser stars and carries maintenance techs to service them.

But if hair trigger situations are expected you might put a small crew aboard each laser star, basically fire control officers. This allows the constellation to spread out without concern for light lag, even if seconds are critical.

Kinetics are a weapon of deterrence and last resort. They are the weapon of choice for people who don't want to fight, but will if they have to.

Deploying kinetics does not call for much specialized military industry (really, only making armored faceplates for target seekers). The rest is essentially standard space hardware. Any EVA pod or space taxi, even a space suit backpack, can be used as a scratch target seeker, effective against undefended targets.

One schlock story line writes itself: Colonists with kinetics versus redcoat laser stars.

And yes, once the colonists have won, they too start building laser stars. :-)

Rick said...

Citizen Joe - I gather from (casual) reading / hearing about optical technology that amazingly precise movement is practical, and routine.

Imagine a big fat positioning screw, 30 cm in diameter, with 1 mm threads. Turning it by 1 mm moves it in or out by 1 micron. Add a little vernier adjust screw and you can position to a few dozen nanometers. Apparently structures are rigid enough that they don't wobble even on that scale.

Whether you can do it when adjacent to 100 megawatts of heat, let alone getting zapped, is another matter.

Citizen Joe said...

I think that the diplomatic part of the war game is to make sure that you give the opponent enough incentive that he isn't willing to sacrifice half his resources to scrag your laserstar. Just because you're not willing to accept 50% casualties, doesn't mean the enemy isn't willing.

Luke said...

Z: Laserstars are not necessarily single purpose. For example, they could be an outgrowth of laser launch technology. Or orbital debris clearing technology. When not being used to zap bad guys, they may even themselves be used to clean up orbits from debris. A 250 MW beam directed onto a 1 meter spot will evaporate nearly 12 kg of steel per second per square meter of exposed surface, at an exhaust velocity of (estimated) 623 m/s. That's faster than a rifle bullet. The force on any debris so illuminated would be over 7000 N, or about 0.7 tons, per square meter of illuminated surface. This could de-orbit debris right quick. (And this isn't counting melt ejecta, which would add to the thrust).

Anonymous said...

CJ: "...RE: Z Habitat vs. powerplant. There is no rescue in space, particularly if your powerplant goes down. Just a slow death as you freeze. You're better off taking the instant death, rather than endangering rescue parties that have to rush to get there in time."
That only applies if you're alone (i.e. no other friendly ship closer than your survival time), but most warcraft won't be operating alone (not to say it won't ever happen, but just not often) so that it may well be useful to protect the highly trained crew who would, if they survive, would eventually be the ones who actually design the later generations of Warstars.

If I was going to design a Warstar, I'd arm it with a bunch of different types of weapons to deal with various types and levels of threats...after all, even Supercarriers don't just rely on it's fighter wing exclusively...it carries guns, missiles, EW, and (soon) laser defenses. To use the 'Spacecraft Constellation as Supercarrier Battle Group' analogy, Laserstars, Kineticstars, and/or Warstars won't be venturing out by themselves...either accompanied by specialized warcraft or by other Laserstars, Kineticstars, and/or Warstars. The old adage of 'there is safty in numbers' applies even more so to space than anywhere else that I can think of.

Ferrell

Z said...

Luke: I had thought of both of those, and was actually thinking that a laser thermal system might be the only high-performance propulsion system cheap enough to put on a higher delta-v throwaway system. I am dubious of an outgrowth of laser broom technology for a couple of reasons. The first is that orbital debris is a problem that will likely need solving before people are throwing around really science-fictionally big lasers- I imagine we will start to see more satellites with electrodynamic tethers and big Mylar aerobrakes in the pretty near future- indeed, both have been tested by this point. The other is that the laser brooms under consideration for small stuff are not that potent and still capable of doing their job- the idea being more to impart enough delta-v to a paint chip to deorbit it in months rather than years. That's a job modern lasers can already fulfill.

Rick: The power projection/dominance factor is interesting, for sure, but I still suspect really big lasers are just too mired in mess to be super interesting to a military thinker. Take the eyeball frying contest you modelled of a laser and another of half the power- outcome being one fragged laser and one with 25% mirror degradation. I have a pretty strong feeling that this isn't a "shields at 50%" situation- I bet that laser will not be fired again. Those half-power lasers are bound to be less than half the cost, and the math for the big gun doesn't go well if it's getting hit from two at once. And I still wonder if the mirror will be doing well in an environment filled with dust and melt drops likely too small and numerous to be targeted.

qwert said...

Hello, interesting conversation. Have been following it without much to say.
But we are suposing that the cost lies with the laser.
What if it happens to be the other way around: suppose that in order to reduce flying time to something reasonable engines have to be hugely expensive, and that the bigger the spacecraft the more cost-efficient you get.
Suddenly kinetik killers happen to be a hugely expensive way of throwing away expensive engines.

On the other hand: if mirrors are the weak point of lasers, why not remove them completely and replace them with more maneuvering engines?
This way you target the laser by maneuvering your ship instead of using mirrors.
Maybe a 1000m long space-fighter?

Rick said...

Qwert - It might easily be the other way around. The point of my equation it to let people see the consequences of any chosen set of parameters. If powerful lasers are cheap and fast kinetics are expensive, lasers will fully dominate. If it is the other way around, kinetics will fully dominate. But there do seem to be plausible sets of tech assumptions that come out in the middle, making both potentially viable and kicking the question to policy and strategy, etc.

Mirrors, or some kind of optics, are pretty hard to do away with for lasers!


Ferrell - I can see a case for putting only a single weapon on individual warcraft, and combining them at the constellation level. The constellation is the real fighting unit; the 'ships' are components. This doesn't rule out patrol or 'cruiser' craft with a mixed armament.


Luke and Z - On the strategic level, the question of whether you can really use these weapons against peer opponents is not much different from the present day. How long will naval ships last against modern precision weapons? Not very.

Even if you ignore the whole mutual eyeball frying thing, any 'classic' slug it out battle in space is likely to use up a lot of expensive hardware very quickly.

It may or may not also use up people, but for a slug it out battle the weapon platforms could all be robotic.

Warfare as we have known it may be obsolescent, but if there are space wars they could be almost entirely strategic maneuvering, with only sporadic shooting engagements when someone misjudges enemy strength. Or is willing to take heavy losses to gain some key objective.

Jean Remy said...

Rick:

I was going to say the same thing about modern warships. I know the analogy can only be carried so far with (ahem) carriers, but in WWII, for example at Midway, a carrier that was discovered was pretty much dead. Instead of the mirror being the vulnerable spot, it was the flight deck. A single bomb in what was a very big target would rob the carrier of its assault potential. Yorktown developed a 26 degree list, which also removed its attack potential since its flight deck was useless even though it was without a scratch.

(Sidenote on degraded mirrors: a Laserstar with a 25% degraded mirror can turn back have its mirror replaced, and go back out. Even if the mirror is the single most expensive component of the ship, the sum of the rest of the ship is worth far more than a single mirror. Killing a mirror is mission-kill, not the loss of a Laserstar.)

As was said, an Exocet missile of a fraction of the cost can take out a modern Supercarrier once its CIWS is overwhelmed. So carriers are as vulnerable as Laserstars, and as costly in comparison of individual kinetics, yet they are still being built. The new class of supercarrier is being developed at a cost of 15 billion dollars with an addition 10-15 billion per unit cost. We can say what we want about the corruption inherent in the militaro-industrial complex, there has to be a real value to the supercarrier as a strategic and tactical unit. Battleships were vulnerable to torpedo boats which were a fraction of the cost, but they still built battleships. In another example, compared to one soldier a modern battle tank is very costly. Yet battlefield survivability of a tank is counted in minutes or even seconds. Yet a soldier with an anti-tank missile can detroy one for again a fraction of the cost. Like, but unlike, a Laserstar, he who gets the first shot in, wins. The examples of such force/cost disparity abound. Successful armies are balancing acts.

The fact is, war is about breaking things, and so to wage war is to accept the losses of very expensive toys. There is no doubt the Laserstar is expensive, and vulnerable, because well all weapons are expensive, and vulnerable. The fact that they are expensive and vulnerable does not invalidate the justifications that created them in the first place. The first role of an army is to look impressive enough so that the other guys thinks twice about attacking. You can say that the first job of an army is mere showmanship and appearance. Why do you think countries celebrate their national holidays with military parades? Imagine the sight of a constellation of six Laserstars in parade formation flying by a space station, and there is fully half your reason for building them in the first place. Any war you can avert by scaring the other guy into not attacking is the same as a war that you one, fully justifying the incredible cost of the Laserstar... before it has even fired a shot.

Also, someone pointed out that carriers carried more than just fighters. No, they really don't. They carry an assortment of *defensive* weapons, but when it comes to projecting power the only weapon of note is its fighter wing. Carriers do not bombard coastlines, they send F/A 18's to drop bombs on coastlines... or deep into enemy territory, hence their advantage over a battleship.

On a final note about the changing face of war. Just because the world hasn't seen a major conventional conflict in the past sixty years does NOT mean we will never see one again. I am reminded of an extremely arrogant news article talking about the fall of the USSR. It was called: "The End of History". To even think for ONE second that the temporary supremacy of one superpower indicates that there will never again be a challenger is the height of blind stupidity. History is littered with the ruins of broken Empires that believed the exact same thing.

"Look on my works, ye mighty, and despair."

Rick said...

Jean - And we veer from the hardest tech geekery to the broadest issues of strategy.

The first role of an army is to look impressive enough so that the other guys thinks twice about attacking.

Yes. The Space Race was a nominally nonmilitarized version of this. A Saturn V was of no military utility, but a very effective national display and demonstration that we could build big fast stuff to the max.

Laser stars can defeat lesser laser craft at fairly modest cost, retaining part of their zapping power. They can withstand anything less than a massive kinetic salvo. (Assuming the right tech balance.) They are visually impressive. And last but not least, they play to a cultural image older than actual space travel.

Given the right astropolitics, these are all reasons to build them, even if they will make short work of each other in any serious shootout.

Kinetics carrier vehicles can also be built big and impressive, and probably will be, even when nondescript transport types would do just as well.

I certainly don't think history is over, but I don't see future Great Power wars as inevitable or even especially likely. They may find they have more to fear from disorder than from each other - essentially what, in earlier eras, turned turbulent nobles into a cohesive oligarchy.

Anonymous said...

Jean, you're right:"Also, someone pointed out that carriers carried more than just fighters. No, they really don't. They carry an assortment of *defensive* weapons, but when it comes to projecting power the only weapon of note is its fighter wing. Carriers do not bombard coastlines, they send F/A 18's to drop bombs on coastlines... or deep into enemy territory, hence their advantage over a battleship. "
I should have said that the Carrier Battle Group doesn't rely on their air wing alone, that the carrier's escorts have a whole range of weapons and defenses. I stand corrected.

Rick: a 'Battle Constellation' may well consist of Laserstars, Kineticstars, and support/command ships...especially if the big combatants are robots. However, the smaller, mixed armament Warstars/partol cruisers (being out away from command ships) would probably need a crew...and travel in pairs. A few kinetics, a medium-heavy laser, and a bigger engine-to-mass ratio than a capital ship, (plus a habitat module), all shoehorned into a smaller overall package would make sense if you had far-flung interests that needed a lower level of on-site watching. The smaller Warstar/partol cruiser could be built for a fraction of that of a Laserstar or Kineticstar, or even a support/command ship...and since you can't be in two places at once, then having a (relatively) large number of armed high endurance spacecraft would give you flexability, both militarily and politically.

Ferrell

Jean Remy said...

To veer even further off hard geekery and into the astropolitical arena: I agree that direct Superpower confrontation is not very likely since generally a power that comes to that level of prominence tends to recognize that war on that scale will leave no winners. However, the Cold War showed us that two superpowers could fight each other indirectly. A future struggle could well happen between non-Earth colonies without spilling into an all-out confrontation back on Earth.

Schlock scenario: The Ceres Independence Movement, financed and armed by the BHG (Big Huge Republic), could force the MOD (Mean Old Dictatorship) to deploy Laserstars as a blockade. The BHG of course provides smuggled kinetic missiles. After the MOD loses a Laserstar or two and decide it wasn't worth it and withdraws, the BHG promptly forgets about Ceres and lets the insurgent leaders discuss amongst themselves who gets to be the Grand Poo-bah.

(Any resemblance with any historical fact is of course completely intentional.)

Returning to the geekery:

Mark said: "I think a folding or inflatable mirror that can be deployed to one side would be a good solution"

How likely are inflatable mirrors? I don't see them as able to survive more than a few seconds of your own shooting since they will have to be made of thin, flimsy and malleable materials. Not only that how precise is that surface going to be? It takes months to years to polish a 1m mirror to specifications of fraction of a micron errors. That folded/deflated mirror would develop creases, damage itself by friction and vibration unless you coat the surface with something. It sounds as if you'd get one shot off before you burn them yourself. Worse, if your opponent sees one being inflated/unfolding, he could well shoot at it before it is fully deploy.

However if these steps can be overcome, it sounds like a good idea as it throws the eyeball frying contest for a loop. Which is the real mirror, which is the decoy? The first guy to take a shot reveals which of his is the real one. "I am afraid you chose... poorly". Oops.

Qwert said: "On the other hand: if mirrors are the weak point of lasers, why not remove them completely and replace them with more maneuvering engines?"

Mirrors aren't there (just) for targeting, but for focusing. Even if you have a static laser mount you will need a large parabolic mirror. If you simply let the laser shoot straight out of the cavity chamber you're going to get a very divergent beam (for a laser). You're going to get diffraction anyways, but without the mirror you wouldn't be able to get enough power in one point to heat toast. The mirror is basically like the magnifying glass held to the sun to set fire to a piece of paper. Without the mirror, you get a flashlight. Granted one where are the oscillations are in step, so a nifty flashlight, but a flashlight none the less.

pspinler said...

As far as I've read through the huge and fantastic comments list, this discussion of laser v. kinetics seems predicated on the assumption of lasers burning through kinetic's armor plating.

However, that isnt the only, or perhaps even best damage mechanism. I note that any kinetics must have seeker mechanisms, which require sensors. Said sensors should be far more vulnerable to laser fire than the kinetics armor. Thus, zap the seeker(s), and jink.

This seems far simpler - so I must be missing something.

-- Pat

Anonymous said...

Pat: "This seems far simpler - so I must be missing something."
At some point, the velocity of the kinetic seeker, and the proximity to its target, means that manuver by either one isn't effective...besides, there are already sensors designed to 'Home on Jam' as well as home on lasers...they probably couldn't see anything other than a superpowerful laser...hook up a serise of thermocouples to the armor faceplate and adjust course to 'center' the heat signature, thus eliminating the need to rely on conventional sensors.

Ferrell

Jean Remy said...

Ferrell: I agree 100%, you should never deploy the Laserstar alone, unless you're pretty sure nothing will happen to it.

When I lived in Monaco (some of you might incorrectly know it as Monte-Carlo) we had US Supercarriers come to visit. I got incidentally to go on board the Nimitz as my father, an officer from the French Army Reserve, was invited with other officers by the Captain. As a twelve year old already in love with aviation, I was drooling the entire time of course. However, the carrier was not in any formation. What Carrier Battle Group it might have been with, during her stay off the port, was well beyond the horizon. So it is possible for one to find itself alone... once again, of course, in friendly territory. If you expect action, you better have all your buddies around.

I also wholeheartedly agree with your other point. The big Laserstar is the showcase. You show it around, rattle the mirror a bit, and when push comes to shove its got this big laser, see? However the "Real Work" of the navy has always been in the hands of the frigates. They're the ones escorting convoys, chasing down pirates, showing to those places that don't rate a Laserstar that yes, we're looking out for you (or AT you) However they won't stand a chance against a Laserstar: their smaller mirrors will get fried before they get close enough to heat toast. Each has its job. As I said, a successful army is a balanced army.

Anonymous said...

Jean: "Schlock scenario: The Ceres Independence Movement, financed and armed by the BHG (Big Huge Republic), could force the MOD (Mean Old Dictatorship) to deploy Laserstars as a blockade. The BHG of course provides smuggled kinetic missiles. After the MOD loses a Laserstar or two and decide it wasn't worth it and withdraws, the BHG promptly forgets about Ceres and lets the insurgent leaders discuss amongst themselves who gets to be the Grand Poo-bah."
Yes, warfare between client-states and/or secondary powers is still possible in a two superpower world, but unless someone makes a serious blunder, then Interplanetar War One probaby won't happen (although I'm sure ArchDuke Ferdinand's ghost might qubble about that)

Ferrell

Mark said...

There is a lot of of work being done on how to fit more mirror into a smaller space so they can launch satellite telescopes with bigger mirrors in current launch vehicles. the James Webb space telescope is a good example of what I was thinking with a deployable mirror. (I'll admit the stuff about inflatables was off hand, but it shouldn't be impossible)

The concern about being zapped while deploying the mirror is a good point, but the main advantage of a deployable mirror is that it can have a much larger mirror than a ship with a similar diameter and
a axial mounted mirror, so it's definitely a stand off weapon, it would probably have normal turrets for closer encounters.

qwert said...

Rick:
"Warfare as we have known it may be obsolescent, but if there are space wars they could be almost entirely strategic maneuvering, with only sporadic shooting engagements when someone misjudges enemy strength. Or is willing to take heavy losses to gain some key objective."

Yes, I have also been thinking something like this:
I also think that in space warfare tecnological superiority will probably represent a huge advantage, very similar to how it is today with air warfare, where i wouldn´t bet that a mig-29 will be able to defeat an F-22. This may be the result of the fact that there is no "terrain" in space from wich a lower tech army may take advantage, the only countering to this may be numerical superiority.

The other point is that you know from before the battle begins what the enemy "fleet" looks like. In other words: The most probable result of a battle may be known before it actually begins.

This may make strategic space warfare similar to a chess game. Moving between strategic position and wery brief battles. Like you describe.
But there may also be sacrifice - like movements were the intention is to force the enemy to comit a mistake by offering an easy prey. Combine all this and the result may be that manned "battlestars" or control ships may not exist. Otherwise their pressence will reveal which tasks-forces you expect to win and which are only sacrifices, or ther crew will know that they are being send to a defeat.

About laserstars and kinetik warheads:
Well, an important advantage for laser armed vehicles is that these will be able to control the orbit or space they have just won or conquered, while a kinetic warhead will efectively destroy itself in the attack. You could always send more kinetiks but they may have to be replaced constantly.

On the otherside, kinetik weapons of decent size may be a considerable threat to planetary targets too. Maybe a kinetiks dominated Coldwar style standoff?

wombatron said...

Would there be any advantage to having, say, an EMP warhead or a shaped nuke hiding among a wave of kinetic seekers?

Rick said...

A wealth of material to reply to!

Mark - Deployable mirrors are highly desirable if the mirror is bigger than the spacecraft. But interplanetary laser stars probably have big propellant tanks, so it isn't a problem for them unless the mirrors are really big, like 50 meter.

wombatron - There's really not much advantage to adding special warheads to the mix. Kinetic strikes on laser stars are saturation attacks by dozens or hundreds of target seekers. They nearly always either fall short or overkill the target. And most of the defensive kills are made at hundreds of km.

So it is better to spend the money on more target seekers. You're more likely to overcome the defense, and if you do you'll smash it to rubble.

For this same reason, there's not much likelyhood of laser stars limping after a couple of heavy kinetic hits. If an attack succeeds at all, they'll take a dozen or more hits.

On the strategic discussion I pretty much agree with everything being said. But I'll note that it can be hard to detect the presence of a crew at a distance. You can fit a dummy crew hab, or simply take the crew off. Comms within a constellation can be tight beam, so there's no need to generate fake chatter.

If you have an active deep space military, you'll surely have manned patrol craft, probably with a mixed armament. And they will do most of the real work. Patrol, inspection, gunboat diplomacy; craft of this type do it.

Depending on details of tech, especially propulsion, even these might be mini-constellations, though I tend to think of single spacecraft as more likely.

Anonymous said...

I want to provide a non-laser craft for this hypothetical laser star to compete with. Assuming the same spaceship technology base, we replace the laser generator and mirrors with a railgun. The ship is built around a 200m long rail. The drive is below the rail (using the office building POV), and everything else is attached to convenient locations around the (substantial) support structure for the rail.

Like the laser, we'll assume available weapon power (after inefficiencies) of 250 MW. With an acceleration track of 200m, and acceleration of about 25,000 Gs (approximately equal to the acceleration of a modern artillery shell, but for a much longer distance), we can sling a half ton projectile 10km/sec every 100 seconds.

To saturate a target 100,000 km away, we can send a series of 10 projectiles in ~1000 seconds, with velocities ranging from ~9.2 to 10 m/s. They will all reach that target at the same time, a little less than 3 hours later. The first projectile fired will deliver about 85% of the energy of the last one fired.

In these half ton missiles, lets call the 300 kg nearest the target a bundle of kinetic penetrators. We can top it off with an angled radar reflecting surface to reduce the ability of point defense radar to track it.

The other 200 kg will be used to launch and control this thing. Buried in the bundle is a reservoir of chemical propellant, attached to lateral maneuvering thrusters peaking out from the bundle along the projectile's center of mass. The back will have a receiver and modest flight control software, but no onboard target acquisition. Somewhere that is structurally convenient will be a superconducting bridge that will carry the current between the launch rails.

Once the projectile gets launched, a friendly ship can send it updates to the target's location every so often in case the target is putting on significant lateral motion. The projectile keeps the updates in its simple control computer until its receiver is completely burned out.

When it begins taking damage from defense lasers, it bursts its bundle of kinetic penetrators into 100 3 kg penetrators. The power of the burst will be varied by how close it is to the target. Each of these 3 kg penetrators (1000 in all in each 10 round salvo) delivers between 8.5 and 10x10^9 Joules, or about 2 tons of TNT.

Now, according to Rick's equations, the laser star smokes 5 tons of kinetics out of the sky without batting an eye. However, those equations take into account perfect detection of self propelled kinetics. These projectiles, however, would not ride a red-hot thermal drive to the target, they would largely coast, only using chemical rockets for last minute course corrections. Additionally, they would have a substantially smaller cross-section, making detection at long range that much more difficult, although I will admit that I don't know much about sensor/targeting technology, and these projectiles may be pitifully easy to detect and destroy at range.

More importantly, however, is the tactical flexibility this craft lends to laser armed ships. Any laserstar could call in a kinetic salvo from a rail ship that's "off the line". A rail ship a million km away could put 1000 projectiles under the control of a front line ship, arriving in about a day. All 1000 (or more, if supplies allowed) could arrive at the exact same time.

A rail ship supporting multiple laser ships could provide each one with bombardment support as they needed it from long distances away. Effectiveness varies with range, of course. Response time matters. The kicker is that if the target ship turned to use its main drive to deflect from the path of the kinetic attack, the friendly laser ship gets to attack weaker side armor. Using the main drive also precludes the use of lasers, so this pretty much leaves the targets of the kinetic attack at the mercy of close in laser ships.

I should probably stop now, as this exposition has gotten horribly long. It is late, and I hope it still makes sense.

Michael

Jean Remy said...

Michael:

I was actually thinking of a very similar system as a counter to the Laserstar, I just hadn't crunched the numbers yet.

However, let me play Devil's advocate for it just a bit, and see if this is workable.

First, there's a lot of waste heat generated by one of these railguns. I'm thinking the thermal bloom will be seen from a LONG ways away, and even at that million klick range the firing pattern is going to show on IR, and have a very specific signature, so there's no way to hide that those projectiles are inbound. Not only that, but a lot of that heat is going to sink into the projectile/bus itself. Since when it shot out the heat will transfer to the bus by conduction, but then it will only be able to leave via radiation, which is a lot less efficient, that projectile might be very warm indeed. Now you could have a lithium buffer between the walls of the bus and the individual sub-munitions, so the sub-munitions themselves might be cold and harder to track, so it depends at what range you split the bus open and let them fly. However I suspect that even cold and covered in radar absorbing materials, those sub-munitions will not be that hard to track.

The bus is going to need quite a bit of Delta-v, especially if you shoot it from a million klicks away. As I said the firing pattern will stick out like a sore thumb. That gives the enemy a day to get out of the predicted initial vector. That means those buses will have to keep up, but every time their drives light up the enemy gets a new fix. I'm not sure it's insurmountable, but it's definitely a concern.

Time on Target is obviously critical. However that means that instead of shooting everything as fast as it can go, the full salvo will be forced to move at the minimum common speed. You're sacrificing impact velocity, and maximizing the enemy's intercept window while trying to maximize the number of targets to acquire. It seems a balance will have to be struck.

The recoil of shooting half-ton projectiles at 10 km/s will have to be accounted for in the time-on-target calculations, or the kinetistar will have to make judicious use of its engines to compensate. In fact the kinetistar should be moving toward the target as fast as it can to provide that extra velocity, so while that might actually increase, and perhaps even double the approach speed, you again give the enemy plenty of data about the salvo's vector, and with all that extra velocity the buses might be less maneuverable since the projectiles would have to overcome that very momentum if they need to maneuver.

One day to time on target seems like too much time to move out of the way. Kinetistars are not artillery. Granted the efficiency of their armament does not depend on range like a laser, but since a laser is a light speed weapon the ideal balance might be struck at the exact same range as the laserstar itself is effective.

I can't think of any other argument or counter-argument right now, but this take on the kinetic bus is worth investigating.

Rick said...

Michael - I have some quibbles about the projectiles, which need a heavy armored faceplate, but the railgun idea is interesting. It certainly gets projectiles up to speed more quickly than a high ISP bus ship can. Milligee drives put on about 1 km/s per day, so they'd have to start their initial runup over a week in advance. The railgun gives a good quick boot.

You'll have to store a lot of power, though, to boot heavy projectiles. Mini target seekers fired at a round per second would be more efficient to shoot and more cost effective, but might not be heavy enough to defeat armor behind a Whipple shield.


Jean - Because of the sluggish acceleration of high ISP drives, launching a day before time on target is viable. The target can only put on about 1 km/s of deflect, and the target can easily carry enough chemfuel to match it and stay on collision course.

Jean Remy said...

Rick: Yes that is a problem with high Isp drives. How likely would it be to strap something with high thrust low Isp like a couple of SRBs or a chemical rocket? They would be emergency use only (with a big glowing red button under a transparent hood and with black-and-gold diagonal stripes around it!) They would have about 5 seconds worth of fuel, but since those engines can potentially move even a 10 kton mass at one hundredth of a g Possibly more?), for those five seconds of emergency power you can slip aside with ten times the acceleration. Even if it takes several days on conventional high Isp drives to counter the sudden boost, if you can sidestep a volley of kinetics on final approach it might be worth it.

It's 1 am. I'll crunch numbers tomorrow.

Anonymous said...

Heat is a problem, but I was under the impression that superconducting rails would mitigate that somewhat. I'm really don't know, though.

I agree that a 1 day head start could be too much lead time against any old craft out in space, but consider that using a main drive probably means no (or more limited) laser firing and side armor presented to any front line hostiles. If you're in stand-off range, you're hosed. Even if the target can keep mirrors on the front line laser star, the front line laser star might accept a burned out mirror for a chance to put a few megajoules into an unarmored reactor.

Michael

M. D. Van Norman said...

This is all great, but where are the nuclear explosions and terawatts of bomb-pumped lasers?

Seriously, though, space warfare will be about maneuver. Its highly predictable outcomes will usually mean that no one fights unless victory is assured. Of course, some will gamble when the odds appear even.

Anonymous said...

If the mini-buses are coming in on slightly diffrent vectors, then trying to get out of the way and still fight the other Laserstar might be impossible...it also might use up all your emergency fuel so you don't have any left over to dodge the next salvo from the Kineticstar later that day. If the object of the battle is to keep the enemy Laserstar and its support Kineticstar occupied with combat to keep them from targeting your troop convoy from relieving/resuppling our strategicly importaint outpost, then all theories about chess games and manuver fall by the wayside...If keeping the outpost in friendly hands out weighs the cost of a Laserstar (or a smaller Warstar), then you might break the rules for a greater payback then the potential loss of a major warship.

Ferrell

Luke said...

Michael: Rail guns require current to run down one rail, across the projectile, and back the other rail. The weak point in this system is where the electrical contact between the rails and the projectile. Since the projectile is moving at multiple km/s, you will not have direct physical contact. Instead, you need to arc across a gap to complete your circuit. The high current arc erodes the rails and projectile into plasma. In fact, modern rail gun designs propel the projectile by driving the current through a plasma arc behind the projectile, and the plasma pushes the projectile forward.

If you want superconductors to make a difference, ditch the rail gun in favor of a coil gun. No electrical contact is needed so you can levitate the projectile in the barrel (either using an inductrack design or making use of the perfect diamagnitism of the superconductors).

Luke

Anonymous said...

Luke, I'll defer to your knowledge, because I don't know the engineering of railguns, just the basic science. I was just thinking that a lot of the heat the railgun generated at firing would be due to current resistance on the rails, and that superconducting rails would help a bit. If a coil gun is better, than the rail ship ought to use a coil gun. The way the projectile is propelled is not as important as the fact that it is a projectile.

Anonymous said...

That last comment was mine.

Michael

Rick said...

Low main drive acceleration makes Realistic [TM] space combat a long slow dance, and the only way to avoid that is to break out the terawatt torch drives.

Powerful chemfuel thrusters can give a spacecraft a short fast kick to one side, but unless you carry a whole lot of chemfuel the thrusting will be brief, and a target seeker can carry just as much delta v (in a vastly smaller tank).

Much of the art of space warfare will be plotting your orbit so it get you to your objective without getting you into avoidable trouble.

If transfer speeds are high, defensive kinetics could end up striking far from the planet they are defending. You want to hit an attacking constellation before it begins its orbit matching burn, which can start a couple of weeks out for high ISP drive ships.

So you may send out your defensive delivery bus a couple of weeks earlier still, to push the kinetics up to a good speed and release them heading down the throat of the attackers. And if you have a high power railgun you can give them some extra kick.

Or alternatively the railgun can give them some side kick, allowing the delivery bus to deliver an oblique attack while staying well clear of the attackers' laser stars.

Jean Remy said...

I think if we tart throwing in torchdrive the kinetic buses will fall by the wayside. Now I'm not saying it's impossible to use kinetic in a torchdrive setting, but if starships can easily generate hundreds of km/s (or even Mm/s) you need some very hefty delta-v on your missile. The kinetics will need their own torchdrives to stay competitive, and I don't really see nuke-thermals, fusion reactors or anti-matter engines as small and cheap enough to make them viable. Skewing the purple/green fight even worse, if your trochdrive is an Inertial Containment Fusion system, the fact that it works using a powerful laser actually requires a Laserstar to *start* with, so ironically enough the weapon is determined by the engine, rather than the opposite. Not only would such a system be hard to put on anything very small, but you merely built a minilaserstar rather than a kinetic.

Rick said...

Railguns and coilguns have very different technical details, but in SF the terms are used pretty interchangeably. As I did in my last post, when I wrote 'railgun' even though I'm actually imagining a coilgun.

I think people say 'railgun' because it sends its payload at express highball speed. :-)

Anonymous said...

Correct me if I'm wrong, but I have read/heard somewhere that for a coilgun to have a range equal to that of a railgun then the coilgun's lenght would have to be about two times or more the barrel length of the railgun. However, the chief advantage of a coilgun over a railgun would be a higher Rate of Fire which is perfect for the high volume saturated fire needed to at least keep a target craft busy while it either the attacker or its buddies maneuver themselves towards that target craft's weaker sides.

However I have to ask this question: Would a self-propelled Kinetic round be a better choice over an Electromagneticly Launched Round from a dedicated coilgun either spinal or mounted upon a turret?

I ask because from what I can gather, the chief factor in the cost of the Kinetic Round would be the drive motor that accelerates the mass towards a target and be able to have a high enough DeltaV budget to not only reach the target, but to also make course adjustments to lower its chances of being zapped out of the sky and keep on track with the target craft.

But what if that round only needed enough DeltaV to make course corrections and keep on target while some other external force gave the projectile the velocity needed to cross the distance between the shooter and the target? A Coilgun-launched Kinetic Round does offer that possibility as shown by the following visual examples at 5:57 to 6:02 and 7:44 to 7:58 in the following video clip:

http://www.youtube.com/watch?gl=JP&hl=ja&v=aZ_kGr0EK3M

However I am unsure if it is a viable weapon system layout for orbital space combat, let alone deep space. Then I got this little brain fart: If diffusion of a laser decreases its damage potential of the focal point upon the target and the distance between the laser and the target having its own diffusing properties, then would it not be prudent to launch a Kinetic Round/Missile/whatever towards the enemy craft that deploys a Laser Diffusion Cloud that is closer to the lasing ship than the lased ship?

And since a majority of the combat spacecraft classes are potentially being designed with an armored face plate as evident in the previous replies, would it be too presumptuous of myself to think that a majority of the offensive weapon systems would utilize a mechanized system similar to the Disappearing Gun as this article describes:

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

And one other thing:

"In spite of the practical elegance of Michael's layered shutters, for cinematic purposes there is nothing like the order 'Unshutter main mirror!' ... external view, in silence, as the armored shutter slides slowly open to reveal a big laser mirror."

Well there's nothing really stopping one in creating that little visualization. Granted, it doesn't make mention to the inner shutters but then again, how much detail do the reader/audience really need?

- Sabersonic

Jean Remy said...

Saber: "However I have to ask this question: Would a self-propelled Kinetic round be a better choice over an Electromagneticly Launched Round from a dedicated coilgun either spinal or mounted upon a turret?"

I think one of the points we've been discussing is to actually put a self-propelled kinetic in a rail/coilgun to give it that initial kick.

Coilgun v railgun (VERY simplified)

A railgun is a Jacob's ladder on steroids. It's of a (relatively) simple construction as you basically have two conductive rails, you create a plasma arc with the projectile, and you shoot the whole thing downrange. They require a LOT of power and create a LOT of waste heat. We already know how much of a problem waste heat is in space.

A coilgun is a Maglev train, and similarly more complex in construction. The projectile is in suspension inside magnetic coils, and the polarity in the coils is changed very fast, attracting and repulsing the projectile along. They require supraconductors which either need to be cryogenically cooled, or require the invention of "warm" supraconductors. They generate less heat but as far less "brute force" approach have a lower acceleration.

Purple v Green... v Orange?

Orange Option being particle cannons. If the technology to create z-pinched near-light-speed particle cannon exists, they might have greater reach than a laser(self focusing), will not require a vulnerable mirror, will inflict kinetic damage added to thermal damage, and have a time to target close enough to a laser that the difference would be insignificant (especially compared to a kinetic bus). The disadvantages are probably the need to mount a large accelerator, they can't be turreted since deflecting the beam robs it of most of their delicious kinetic energy, requiring the entire ship to swing, and they might be deflected with magnetic shields. Their energy requirements are probably a little off the wall compared to lasers and missiles.

Anonymous said...

A minor point, but IC fusion doesn't necessarily require a laser. If the society has managed modest levels of antimatter production, you could do antimatter initiated fusion.

It seems likely that heat will by a problem with a rail gun, but does anybody know how that waste heat would compare with a similarly powered laser?

To weigh in on the particle beams issue: It seems to me that a particle cannon could have similar range and response time as a laser, but has fundamentally different doctrinal issues. Lasers seem to be the weapon to use when you need to project useful power, ie, power that you can use without causing unnecessary damage and without irking allies. Discreet, effective force projection. Particle beams, on the other hand, are the weapons you use when you want people to know that whoever stands against you will be dead, no questions asked. They get one chance to surrender, and if they don't take that chance, they die quickly from the initial damage or die slowly from a heavy radiation dose.

The United States would use lasers.
The Roman Empire would use particle beams.

Michael

Jean Remy said...
This comment has been removed by the author.
Jim Baerg said...

Jean Remy
"I think if we tart throwing in torchdrive the kinetic buses will fall by the wayside."

The NSWR ( http://en.wikipedia.org/wiki/Nuclear_salt-water_rocket ) sounds like it would scale down far enough to put in a missile that could track a target that is also using a NSWR to maneuver.

Re: rail guns vs. coil guns.

This technology: http://en.wikipedia.org/wiki/Launch_loop could be adapted to shooting 'cannonballs' at an enemy. BTW If I understand it correctly the waste heat would go into the launching loop & not into mass that is launched, so the 'cannonball' would not be enormously conspicuous in the infrared.

Luke said...

Sabersonic: In a power limited situation (such as the 1 GW reactor we have been talking about) a big (perhaps primary) advantage of the coilgun is that it can convert most of that power into kinetic power of its projectiles rather than heat power dissipated in the plasma arc. With 1 GW available, a coilgun might be able to deliver 900 to 950 MW of power in the form of the motion of the projectiles, while a railgun might only give you 200 MW.

There's also the issue that the electric arc erodes the rail, so the rail will need to be replaced frequently. In some railgun designs, the rail is part of the ammunition, and replaced after every shot.

Jean Remy: A coilgun is simply an electric motor unrolled into a line. As a linear electric motor, it no more needs superconductors than a rotary electric motor. Copper will work fine. Since the main inefficiency of an electric motor is due to electrical resistance, superconductors will increase the efficiency - but well designed electric motors already reach 90% to 95% efficiency.

I suppose, just for the sake of completeness, I will mention that there are two "flavors" of coilgun. The equivalent of a synchronous electric motor requires the projectile to be made out of ferrous metal, and the switching magnets attract the ferrous metal in the projectile. The equivalent of an asynchronous electric motor uses projectiles without ferrous metal, and pushes/pulls on the projectile by inducing eddy currents in the conductors for the magnetic field to push against.

As far as particle beams, a Z-pinch isn't really involved (you only get a Z-pinch when you have a current that is screened from its own electric charge by an ambient material). A good linear accelerator is all you need. particle beams do not self focus in space. Their main range limitation is the random thermal motion of the particles in the beam - the beam may start out a micron wide, but if the particles have an average thermal speed of 0.01 c and the beam is moving at 0.5 c, you get the beam opening in a 50:1 cone (this example is rather unrealistic for illustrative purposes - 0.01 c is not uncommon for the thermal motion in particle beams, but the speed of the particle bunches is likely to be more like 0.99 c to 0.999 c and this introduces relativistic effects into the opening angle. I can go into more details on how to calculate this if others are interested).

A particle beam does not do kinetic damage, not in the sense of a kinetic round. The momentum of a particle beam is about the same as that of a laser of the same energy, and the beam particles do not act as a continuous media to disrupt the target. Rather, each particle punches through individually, losing energy by ionizing the atoms it passes by and occasionally smacking into a nucleus and shattering it into more high speed particles. This does heat the target, but heats it deeply rather than on the surface. It also produces all the effects of ionizing radiation (which it is), such as health effects and amorphizing the crystal structure of delicate electronic components.

A particle beam can be deflected by a magnetic field. You would use a strong magnet for the turret. You would also neutralize the beam just before it left by injecting a co-propagating beam of oppositely charged particles. The primary beam will probably be protons, and it will be neutralized with electrons, giving you a beam of hydrogen plasma.

There is no intrinsic reason a particle beam needs to be inefficient. With high Q superconducting accelerating cavities, you could in principle put most of your energy into the kinetic energy of the particles. The main inefficiencies would then the the refrigeration you need to keep the superconductors cool. In principle, a free electron laser could have very nearly the same efficiency since it is essentially a particle beam that converts its particle beam energy into light energy, so it may be that particle beams and lasers have the same efficiency.

Luke

Rick said...

More in the seminar than I can comment on!

My understanding of railguns is that they are limited to a few km/s max. Any faster and you melt the rails, not good. Coilguns may be more complex, but they give higher speed and less waste heat. Without getting into SF magitech, upthread Michael outlined a coilgun about 100 m long and shooting at 10 km/s, with acceleration comparable to a rifle round.

Pretty much keel mounted, but I will argue that primary directed energy weapons will generally be keel mounted, because you can mount a longer range weapon that way. And with long range, and given limited prolonged acceleration, you generally have time to turn and fire.

Particle beams are Nasty. And they don't sound extraordinarily effective, so their use against humans might be the equivalent of gas warfare. Depending on hard it is to armor/harden electronics, they don't sound very useful against robotic ships.

At 10,000 km, not long range in space, even a beam spread of 0.01 percent means a beam diameter of 1 km and a tiny fraction of the beam energy hitting the target (unless it is humongous).

Anonymous said...

Jim, you might want to use a rail/coilgun to launch an NSWR propeled kinetic mini-bus; I, for one, wouldn't want a barely controled fission reaction going off in my face :)

Also, on a slightly different track, the minimum number and make up of a Combat Constellation would be...what? three Laserstars, a Kineticstar, and a Commandstar? or three Kineticstars, one Laserstar, and a Commandstar? Or skip the Commandstar and do three Warstars (smaller, combined arms warships)?

And, finally, what would you call a combat spacecraft the size of a Laserstar/Kineticstar but armed with rocket driven morters tipped with bomb-pumped X-ray laers and/or nuclear shaped charges?
Just some thoughts...

Ferrell

Jean Remy said...

I would rather have constellations be a main ship (Laserstar of Kineticstar) as a command ship for a small flotilla of smaller drones, themselves armed with an assortment of weapons and/or ECM. They can deploy large radar-reflective sails or overly large radiators to mask the thermal signature of your Laserstar. They jamming won't do all that much but might make it just confusing enough you have to add a few seconds for targeting computers to sort through the chaff. Use the kineticdrones to launch some projectiles in the mix to make things confusing to the other side, force them to overheat their lasers, stress their target acquisition software, and play merry hell with the enemy crew's stress levels. the laserdrones can be used as CIWS for the main vessel, or sweep the enemy ships from more angles than they can deal with.

An assault force would combine Laser constellations and Kinetic constellations, coming in from different angles. If you are the attacker and the defender has to protect a specific area, they will be faced with multi-pronged attacks. Because of the implied distances between your constellations, each main ship would be crewed to have command-level decision making in rapid comm range of the flotilla. Since none of these maneuvers can be stealthy, the enemy knows what may be happening. This is the other reason you want command-level decision-making in each constellations: if this is all posturing, there's the chance of someone on one side overreacting. If one captain jumps the gun, you don't necessarily want the whole fleet to commit.

"It was an adder!"

Rick said...

One general difference between laser and kinetic components is that there is no particular reason for big kinetics platforms (except to be big and impressive). They can just as well be deployed from multiple smaller bus vehicles, allowing some more flexibility.

But I'd expect laser stars to be big, with the largest practical power supply and weapon installation, because one maximum laser can outrange two smaller ones of equal combined power, whereas kinetics are simply additive.

On the other hand, there's reason for kinetic buses to be fast, whereas speed does not add to the direct fighting power of a laser star.

So a constellation deploying both weapons might have one big laser star, a few smaller laser craft, and a number of kinetics buses, medium sized or smaller.

Anonymous said...

I would appreciate more visual materials, to make your blog more attractive, but your writing style really compensates it. But there is always place for improvement

Byron said...

I did some caluclations on a recoverable bus, and the numbers aren't as bad as they look. If I assume the same tech as given here, and wish to throw the projectiles at 10 km/s, the ship might break down as follows:
50% kenetics
10.8% recoverable ship
28.4% launch fuel
10.8% return fuel

The actual delta-v is 30 km/s for the recoverable part, while still being able to launch 50% of the launch mass in kenetics.

Anonymous said...

I haven't finished reading through the comments but I'm left with the impression of a rock-scissors-paper type battlefield.

The best weapon to use against a laserless craft (e.g. a KEW bus) would be a single high delta V (long range) guided missile.

But a single guided missile/torpedo would be useless against a laser armed opponent.

The best weapon to use against a laser armed craft would be the KEW weapons bus (swamp the defenses).

The best weapon to use against a missile / torpedo boat would be the laser ship (if it had enough delta V to catch them).

Of course there's no reason that each of these craft can't carry a couple of auxiliary missiles or smaller weapons buses!

BUT a ship with a laser as the primary weapon will always be a warship first and everything else would be secondary.

The other weapons can simply be loaded into anything with cargo hard points (interior and exterior) and some extra delta V.

Jim

Rick said...

Yes. With a sort of meta strategic implication. Less militarized societies or communities may tend to favor kinetics as requiring less defense investment - just the actual kinetics, with a 'civil reserve' of ordinary spacecraft doing the pre-release positioning.

Turbo10k said...

In my universe, quite the opposite. Kinetics are weak to lasers unless used in massive amounts, in each shot. Since every ship capable of fighting uses a laser, with laserships just the warships with the biggest baddest lasers, Kinetic craft are expensive and rare, while lasers commonplace.

Check my scenarios in ground warfare. The pirates use a kinetic craft, while cargo ships can be refitted with lasers very quickly for combat.

Turbo10k said...

In my universe, quite the opposite. Kinetics are weak to lasers unless used in massive amounts, in each shot. Since every ship capable of fighting uses a laser, with laserships just the warships with the biggest baddest lasers, Kinetic craft are expensive and rare, while lasers commonplace.

Check my scenarios in ground warfare. The pirates use a kinetic craft, while cargo ships can be refitted with lasers very quickly for combat.

Daniel said...

>And, finally, what would you call a combat spacecraft the size of a Laserstar/Kineticstar but armed with rocket driven morters tipped with bomb-pumped X-ray laers and/or nuclear shaped charges?

Nukestars?

Speaking of which: I know the cost would go up a lot, but bomb-pumped lasers on the front would mean a lot less distance to close before being able to wreck the defending 'star, meaning less of them need to be launched. Maybe if the lasing could work with a shaped charge, then a small warhead and laser right behind the nose armor.

Couple thoughts on kinetic design:

How expensive would it be to put a small, tunable laser on the front of every bus? With a bright light being shined on the enemy's sensors, hopefully targeting would be a little more difficult. Plus, if you either find the wavelength your enemy uses or randomly go through the spectrum, then the enemies point defense optics get a little toasty.

Of course, if you use disposable, one-shot buses, might as well turn them into penetration-aids. Leave the missiles as semi-dumb hunks of metal (maybe a small warhead on the front to make a hole in any whipple shielding) while the bus tries to confuse / kill any defending sensor or laser..

Anonymous said...

I kinda skipped the other comments due to time restraints, so if any of these are repeat arguments, I apologize.

I favor kinetics for this reason:
Imagine you're walking down a dark hallway and all of a sudden someone reaches out and jabs you in the eyes. That's a laser strike.
Now imagine you're going through that hallway and someone pulls the lanyard on a cannon pointed at you. You know, one of those 19th century monstrosities that fire a solid 12-pound iron ball. At point-blank range. That's a kinetic strike.

A laser can mission-kill a target by blinding its sensors, destroying its lasers, or burning through to some critical component.

A kinetic-kill shell can mission-kill a target by obliterating the thing. And a starship (at least a "hard" SF starship) will generally be flimsy enough that it can't withstand a solid mass impacting at high velocity. Like one dropped right in front of it.

And it'll be harder for the laser to take them down if fifteen, twenty seconds out the thing fragments into 50 or so individual penetrators.

Not to mention they're harder to dodge.

-TDA

Anonymous said...

I finally re-read the other comments, and I've got a couple of other points.

If a laserstar can burn down all the kinetics coming at it, that's great. But the laser is outputting lots of heat in the process. The term "heat advantage" (or something like it) has been thrown around: at this point, the kinetic ship will definitely have that heat advantage, especially if there's a kind of "lancer" setup where most of the initial velocity comes from the velocity of the ship, not a (powered) launcher. That means the kinetic ship (or its laser-armed buddies) can outlast the enemy solely on heat absorption.

A laserstar can make more precise attacks on a ground target, but if the people you're supposed to be deterring (or blind fate) manage to damage that laser (i.e. the optics), the threat disappears. You could, however, send a command ship (which could be laser-armed) with a swarm of smaller "rocks with engines"--not literal rocks, but inert masses that have rockets, fuel, and guidance but nothing else, then set them on a decaying orbit with a command from the manned ship boosting them up every so often. Destroy that ship, no command gets sent, and you have a bunch of dumb bombs falling over the place. Not very precise, but a wonderful terror weapon. Sort of the space equivalent of a "dead-man switch."

Probably a lancer will be best for delivery of a kinetic penetrator. That will reduce the mass of fuel and engines, maybe just to s couple of solid boosters for final approach. Most of the evasive maneuvers will be handled on the part of the bus.

Again, I feel certain it will be a "combined-arms" environment, but a kinetic shell is much more damage-resistant than a laser: if all else fails, you "cross their T" and shove the thing out an airlock.

http://www.projectrho.com/rocket/spacegunconvent.php#id--Kinetic_Kill_Weapons--Equations
Go on down to the example--that's the most productive use of cat litter I've ever seen :)

-TDA

Jim Baerg said...

Hi TDA:

I don't thing your 'terror weapon' would do much.

These rocks would come in at a shallow angle like the Chelyabinsk meteor, but at 8 km/s rather than 18.6 km/s, so would have less than a quarter the kinetic energy per unit mass. The Chelyabinsk meteor had an estimated mass of 12,000–13,000 metric tonnes, but it's hard to see your 'rocks with engines' massing more than a few tonnes each. So I would expect each rock to damage a few city blocks, but come in at random & so probably land in open ocean, desert tundra etc.

To get those rocks to do some damage to the enemy you want them to come in near vertically on some target of value to the enemy. How about have a bunch of them orbiting the enemy planet at roughly lunar distance & programmed to deorbit at specific targets if they don't receive the 'no go' signal every few days?