Sunday, June 7, 2009

Space Warfare I - The Gravity Well

First in a sporadic series.

A traditional assumption in science fiction is that ships in orbit have an enormous advantage over enemies on the ground. Heinlein, evoking the Hornblower-verse, called it the gravity gauge. In general the advantages of high ground are obvious, and the image of fighting from the top of a gravity well versus fighting from the bottom is vivid. But it is also very likely wrong.

In the rocketpunk era of the 1950s there was little reason to think so. The development of bombers up to that time emphasized speed and altitude, from the B-17 and its British counterparts to the pressurized B-29, then the jet powered B-47, B-52, and V-bombers, then the supersonic B-58 and Mach 3 B-70. But the B-70 ended up getting canceled, and by the time 'Dr. Strangelove' came out in 1964 the B-52s were flying near treetop level. 'Under the radar' has now become a common metaphor.

To be sure, the B-70 fell victim not just to improvements in Soviet air defense but to competition from ICBMs that flew much higher and faster still. Even after four decades of effort and enormous expense, strategic missile defense remains uncertain at best. But this is largely a matter of short warning times, compact warheads, and most of all the conundrum that strategic nuclear defense is ineffectual unless it is perfect.

Large spacecraft arriving from deep space (such as an interplanetary armada) are quite another matter. They are much bigger targets, perhaps 100-1000 times the cross section of a warhead, and their approach track will probably be known long in advance. Once they arrive they have nowhere to hide and nothing to take cover behind. In a rock throwing contest at the gravity well, holding the high ground means no concealment, while the low ground means being able to take cover in the underbrush.

Not even the gravity well itself, as it turns out, offers much advantage. Sure, an orbiting ship can easily throw rocks at the surface, the rocks needing only a small kick to send them down from orbit. But by the standards of space tech, throwing rocks up to orbital altitude is also not very hard. Simple, single-stage boosters in the V-2 / SCUD class will do the job nicely. You'll still need a target seeker in order to hit anything, but sending it up there is not a big problem.

Nor is delivering a punch – the target's own kinetic energy will see to that. Suppose the target seeker is hanging like a popup fly, stationary relative to the Earth at the moment of impact. The target runs into it at, say, typical low orbit speed of 7.8 km/s. As Sancho Panza said in the musical play and film Man of La Mancha, 'whether the pitcher hits the rock or the rock hits the pitcher, it is going to be bad for the pitcher.' Each kilogram of impactor delivers a kinetic whack of about 30.5 megajoules, equivalent to rather more than 7 kg of TNT. (In some circles, I am honored to say, this has come to be known as 7 ricks.)

The target ship can engage the (relatively) oncoming missile, but it has only a short window, perhaps two or three minutes from launch to intercept. What really tilts the contest in favor of the side on the ground, however, is that as US Navy doctrine says, it is better to shoot the archers, not the arrows – and the archers can conceal themselves amid a planetful of ground clutter. Surface-to-space missiles can be carried by stealth aircraft or by submarines, or they can be launched from the backs of trucks. In this last case, even if the spacecraft engages and destroys the 'archer' once revealed by launch, all it has achieved is to blow up a truck. The planetary defenders' tracking system can use passive scan, hard to detect, and the command and control system is even harder to detect.

Some of these factors apply most strongly against ships in low orbit. Against ships in higher orbit, surface-to-space missiles – in contemporary usage ASATS, anti-satellite missiles – must be larger and more expensive, take longer to reach their targets, and have lower relative impact velocities. Hitting a target at an orbital altitude of one Earth radius, about 6400 km, requires an ICBM class booster, and the target will have about half an hour to engage it (or take evasive action). If the target ship is in high orbit, hitting it requires the equivalent of a deep space mission. But the ship is also farther away from any surface target it might be intending to attack.

If beam weapons are available, some of these calculations change. The ship can use lasers (or whatever) against missiles coming up from the surface. But the defender can also fire beams from the surface, and photons are untroubled by any gravity well short of a black hole. Laser cannons are less expendable than a truck launcher, but surface-based lasers are still likely to be much cheaper than similar lasers in space that need a spacecraft to carry them. Power supply and waste heat disposal are also easier to arrange on the surface than in space.

Yes, for story purposes you can handwave all this as needed. It is also true that if the attacker's objective is sheer devastation, nuclear bombardment from high orbit will do the job. (So will the ever popular asteroid toss, but this is just a Rube Goldberg way to get the same effect.) The technical possibility of overcoming enormous attrition rates by sheer overkill is a general fact of life in the nuclear age.

Nevertheless, the general upshot – so to speak – of the shortage of ground cover in space is that the presumed high-ground advantage in a gravity well fight pretty much evaporates. Instead, space forces engaging a planetary surface defense face disadvantages comparable to those historically faced by naval forces engaging coastal batteries. They are both exposed and vulnerable, far more so than the defenders. Their one strategic advantage is that they can change their mind and leave, an option not open to surface/shore defenses. Hostile space forces can also plausibly blockade a planet from high orbit, 'distant, storm-beaten ships' cutting it off from interplanetary commerce. But getting close to a hostile planet (or even one just partly hostile) places spacecraft at a severe disadvantage.

Unlike most of the issues we'll take up when we discuss deep space warfare, this has fairly immediate practical implications. Surface-to-orbit warfare disadvantages all spacefaring powers, because space access is easier denied than defended. Second and third-tier powers, with no space presence themselves, can hold space hostage by threatening orbital installations and departing or returning orbiters. The one piece of good news here is that while SCUD class boosters are already all too proliferated, this is not the case for orbital target seekers capable of zeroing in to hit a ship. Moreover, such target seekers cannot effectively be developed in secret, because they can only be reliably tested in space.


Which is why I did not start this piece with a pro forma objection to militarizing space. For anyone interested in real world(s) spacefaring, the objection is not pro forma; it is eminently (and imminently) practical. All spacefaring powers, and those that wish to become spacefaring, have a shared interest in a treaty regime that discourages development and testing of ASATS that could end up denying space to everyone. Whether this will actually happen is of course anyone's guess, but the fact that some such treaty is in the interest of all major players cannot hurt its prospects.


Related link: I shoot down space fighters here.

74 comments:

Anonymous said...

Yes, and invading a whole planet is an even bigger headache; at least a dozen individual nations can field armies of 100,000's of soldiers.
Your invading force would need to be measured in the millions. Nuclear bombardment from "on high" would probably only be used if the invading force didn't care about owning a formerly habital world. Of course, "sailing into the teeth of the enemy's guns", isn't something I'd like to do; getting shot at by hundreds (if not thousands) of missiles and beam weapons (which make for great sensor jammers, BTW), might have me so busy trying to survive that I might not have time to actually attack the planet. As any soldier will tell you, you can get just as dead by having your head bashed in by a rock, as you can by being shot by the most sophisticated weapons system. 200 British soldiers with state-of-the-art firearms vs 6000 Zulu warriors who didn't; we all know who won that battle. Of course, you still have to win all the battles to win the war, and even then you still might not really win.
Three countries have ASAT weapons; the U.S., Russia, and now China; who knows how many others have prototypes or schamatics for surface-to-orbit weapons. Although I don't have a great deal of faith in international treaties, they do serve a purpose. Your idea of a "Surface-to-Orbit Weapons Test Ban/Use Treaty" might be good to have. Maybe instead of an outright ban, how about estabilishing a 'test range' in space, in an orbit not likely to impact (pun intended), the operation of other satellites? Something to think about.
Oh, and what kind of space fighters were you talking about? Deep space space fighters, Aerospace fighters, orbital defense platforms, armed OTV's, fleet defense units, or any number of other uses for small cheap agile weapons platforms? Just like navy corvettes are nothing like jet fighters (in all their different roles), a 'space fighter' would have many roles and use tactics not normally associated with either Navy or Air Force combat units. I also suspect that the uses for these little combat spaceships (and they will be little as they evolve into more standardized forms and missions), will be a matter of trial-and-error for decades before their proper usage is found. Remember; the first 'warplanes' were observation biplanes whose pilots took up pistols and shotguns; a long way from that to today's F-22.
Ferrell

Anonymous said...

It is also true that if the attacker's objective is sheer devastation, nuclear bombardment from high orbit will do the job. (So will the ever popular asteroid toss, but this is just a Rube Goldberg way to get the same effect.)

Another objection to the crush-'em-with-rocks school of thought is that we're dealing with civilizations that toss around hundreds of kiloricks on a daily basis. I'm willing to bet that these people will have very sophisticated defence mechanisms - Magnetic and plasma field 'shields', anti-projectile lasers, rockets that drag impact-absorbing webbing, etc. And that's just for mining operations. If you see a giant rocket-propelled rock heading your way, heat it with lasers and use kinetic-kill rockets to break it up so you can redirect the mass with magnetic rams.

As for reactionless rockets as planet-killers... The only difference between a reactionless rocket and a force field is which way you point the thing.

Ferrell - Yeah, corvettes and patrol boats make a pretty good substitute for fighters. Even the spacecraft equivalent of an inflatable boat will probably have tactical uses. I do think the Hollywood image of a single- or dual-seat fighter engaging capital ships is unlikely, but a three-person anti-drone/missile craft as part of a capital ship's flank defence seems useful.

As for invading a planet, too many authors look at D-Day and the last days of the Pacific War for their model - Kill 'em all, and leave the cities in ruins. If you really want to hold a planet do it the old fashioned way: Kill off the elite, damage their armies too much to fight, and bribe the lesser aristocrats and bureaucrats to run things in your name. Leave a division to back up the new government, and make sure you don't take so much plunder that you incite rebellion.

International treaties work very well, and some have been in effect for well over a century. The ones that last deal with trade, infrastructure, and systems for dealing with national disputes (Not necessarily for 'solving' those disputes, but for giving diplomats a seat at the table and a formal set of rules for shouting at one another so that the whole thing doesn't boil over into war before the problem is solved in other ways). Direct 'problem solving' treaties never last because the specifics change too fast for the treaty writers to keep up with (Softwood lumber), but treaties that tell people how to sit down and talk work just fine.

I can see a whole series of technical treaties dealing with ASAT technology rising and falling, while behind the scenes the great powers make sure no one disrupts the multi-billion dollar communications network.

Ian_M

Rick said...

Yikes, I could fill several blog posts just answering these replies! So just a scattering of comments on comments:

Planetary invasion: WW II still looms so big that it sets misleading expectations. Unconditional surrender is the exception, and even in a setting of many colony planets I suspect full on planetary invasions would be very rare. (Of course, a minor colony somewhere might be 'invaded' by landing a couple of battalions at the shuttle port.)

Treaties: They won't stop someone fully determined to go to war, but in addition to establishing a framework for talking, they can be pretty effective in establishing norms that even ruthless power players (i.e. most of them) hesitate to flagrantly violate. You get a lot of cheating around the edges, but that itself is a useful constraint.

Slinging asteroids: Yet another problem is that it time consuming. This seems to be a case that people are so fascinated by the technical possibility that they brush off the question of utility.

Space fighters: What I had in mind was the Star Wars image of one- or two-man craft analogous in performance and missions to fighter planes, but in deep space. Aerospace fighters could be a different matter, if atmosphere fighters are not supplanted by UAVs.

Robotics will do fine to blow stuff up. If a tactical space warcraft has a human pilot/crew, it is probably a sign that the mission is not simply 'blow up X,' but 'decide whether or not to blow up X.'

Anonymous said...

"Planetary invasion: WW II still looms so big that it sets misleading expectations. Unconditional surrender is the exception, and even in a setting of many colony planets I suspect full on planetary invasions would be very rare. (Of course, a minor colony somewhere might be 'invaded' by landing a couple of battalions at the shuttle port.)"
Just off-the-top-of-my-head, I think I remember that you generally need a 3-to-1 attacker to defender ratio to successfully invade someplace; I also believe that 3% military would be a large percent of a population, with 1% or slightly less would be more common. So, a long term occupying force should be at least 0.1% to 1% of the occupied nation's (colony)to be effective. Or, so I should think.
"Treaties: They won't stop someone fully determined to go to war, but in addition to establishing a framework for talking, they can be pretty effective in establishing norms that even ruthless power players (i.e. most of them) hesitate to flagrantly violate. You get a lot of cheating around the edges, but that itself is a useful constraint."
Hmm...maybe that's the real usefulness of treaties.
"Slinging asteroids: Yet another problem is that it time consuming. This seems to be a case that people are so fascinated by the technical possibility that they brush off the question of utility."
Also, if you take all that time and energy to do something as big as launching an asteroid at a planet, you better have plenty of security because you might not get the chance to finish if someone notices you...long range lasers can ruin your whole day...

"Space fighters: What I had in mind was the Star Wars image of one- or two-man craft analogous in performance and missions to fighter planes, but in deep space. Aerospace fighters could be a different matter, if atmosphere fighters are not supplanted by UAVs."
Hollywood builds great aerospace fighters...and then uses them wrong! I know that people have this preconceived idea whenever they hear the words "Space Fighter", but like I said earlier, the diffence between real "Space Fighters" and the imagined kind would be rather more like the difference between jet fighters and navy corvettes.
"Robotics will do fine to blow stuff up. If a tactical space warcraft has a human pilot/crew, it is probably a sign that the mission is not simply 'blow up X,' but 'decide whether or not to blow up X.'"
90% of most military missions either need no thought, or a great deal of it.
Ferrell

Rick said...

Yes, 3 to 1 is the classic ratio of offense to defense. Does that apply to amphib operations as well? For occupation, the professional literature re Iraq would provide guidance.

For treaties between unfriendly powers, constraining them to cheating around the edges is indeed a major factor.

Yet one more factor with asteroid slinging - awkward to go to all that effort, only to sign a peace agreement and have to re-divert the asteroid onto a safe trajectory.

Aerospace fighters would be cool in a film, and it's a bit surprising that Hollywood has never gone that route that I know of.

I generally agree on the plausible utility of 'corvettes' in space. But they are probably so different from the conventional image of a space fighter that calling them such would be as misleading as calling atmosphere fighters 'air tanks.' :-)

Carla said...

This is rather over my head (except to say that I like the idea of the contents of the ship's cat's litter tray as a major weapons system. Though do 1000s of small fragments of kitty litter and kitty doo-doo have the same impact as a single 15 kg object?)

"As any soldier will tell you, you can get just as dead by having your head bashed in by a rock..."
Kipling would agree:
"Two thousand pounds of education
Drops to a ten-rupee jezail"

Anonymous said...

Though do 1000s of small fragments of kitty litter and kitty doo-doo have the same impact as a single 15 kg object?

No. 1000 small fragments totaling 15 kg deliver the same amount of energy as a single 15 kg chunk, but over a much larger area and probably not all at the same time. It's the difference between a blast of shotgun pellets or a single rifle bullet. Against an unarmoured target, go with the shotgun. But if you're up against an armoured craft all the shotgun will do is scratch the paint.

According to How to Make War and professional comments from some of my friends, you need 1 armed soldier per 20 civilians to hold an occupied country. That 1 armed soldier can be an infantry trooper, MP, private military contracter, or gendarme, but that's the basic ratio. That's for short term occupation of a recently defeated country. I have no idea what the ratio is to prop up a friendly government in a pacified country.

Babylon 5 touched on the idea of aerospace fighters. In one episode the base's space fighters were unable to engage aerospace fighters that kept dropping down into atmosphere. And the fighter craft in the various BSG incarnations seem to be aerospace craft.

Ian_M

Rick said...

Carla - what Ian said, regarding kitty litter versus a solid slug. On the other hand, armor is penalty mass that makes maneuver sluggish, some crucial components cannot be effectively armored - and at high enough velocities, over a few tens of km/s, even gravel is hard to stop.

Ian - re boots on the ground, for propping up friendly governments I suppose the requirement ranges all the way from nearly equivalent to direct occupation down to a nominal presence, just enough to remind everyone who is on who's side.

I seem to recall that Babylon 5 episode. Horrible confession that I've never watched the new Battlestar Galactica. But my stereotype image of Hollywood space fighters is that they tend to be semi-streamlined, but without actually looking suited to high speed atmospheric flight. (But the ones on Babylon 5 made a rare Hollywood nod to old Sir Isaac Newton.)

Sundog said...

I'd like to challenge some points here.

I don't disagree regarding low orbit. Engagement times for incoming SOMs (Surface to Orbit Missiles) are too short, and a low-orbit SOM is too small and too launcher mobile. The advantage is indeed with the ground.

Where I have the problem is control of high orbit. With a half-hour window to do something about an incoming SOM, as you point out, there's plenty that can be done to counter it. What I don't agree with is that energy weapons would take their place.

Assuming E-Weapons are in use, the energy curve is ALL on the orbital side. They can have relatively light, defensive arms to deal with SOMs once they crest the atmosphere. The ground facility needs a LOT more power - it has to punch through Kilometers of energy-scattering gas before reaching vacuum, and then still have enough cohesion to reach out to high orbit and do damage. You're talking a much larger emitter and a massively greater power source.

Now the counter argument is, of course, that since they don't have to move, the defensive facility and power source can be as large as necessary. However, this obviates the concept of "getting lost on the clutter". Besides being rather obvious visually, any such power plant is going to stand out like a flare in thermal from the waste heat. Even if you manage to pump the heat elsewhere and disguise the base, your first shot will be backtracked to your emitter site pretty much instantly.
And that heat has to go somewhere - a flare point is going to tell the orbital enemy of the existence of your base, if not it's location.

A maxim of modern warfare is "if I can hit it, I can kill it". You'll get one shot with your E-Weapon - then the Thor clusters will rain down. Simple kinetic impactors will hit with enough force to punch out any imaginable armouring. You might take out a ship - for the loss of a facility of roughly equal cost.

Finally, I think you're betting too much on the capacity to be stealthy from space. Spy satellites today have quite incredible resolution, and it's much easier to drop a tiny, hard to spot and hard to hit spy sat into low orbit than it is to find and kill said sat - especially if your major tracking stations were among the first targets destroyed. Modern spy sats can differentiate between an 18-wheeler and a bus - it's not that much of a stretch to be able to differentiate between a cargo hauler and a missile hauler.

Now, none of this invalidates your position on the near future, but I think it throws a few wrenches into the idea that the ground vs space argument is in favor of the ground.

Anonymous said...

The ground facility needs a LOT more power - it has to punch through Kilometers of energy-scattering gas before reaching vacuum, and then still have enough cohesion to reach out to high orbit and do damage.

The ground facility does not need more power to penetrate atmosphere. A ship-based weapon has to penetrate that energy-scattering gas as well. The physics work the same both ways.

A ground-based beam installation has the following advantages:

1) Way way waaaaaaaaaaaaaaay more armour than your ship. Like about a mountain's worth of rock.

2) A powerplant as big as your ship. So what if it only gets one hit? (And the idea that it will get only one hit - You're betting a lot on the idea that these guys can't hit the broad side of a barn).

3) Multiple cooling systems, all far more effective than the ones on any ship. AC, water pumps, dumping heat into a cold mountain range...

4) The base is cheaper than your ship. Powerplant, beam weapon, minimal environmental controls, all in a space carved out by ordinary mining equipment.

As for your assumption that surface-orbit missiles need a half hour to climb - Modern anti-aircraft missiles launch at hundreds of Gs, far harder than any crewed ship. I can't see launch technology getting worse in any plausible space-war scenario.

Yes, a large base will be hard to hide. But while you're targeting the large base you're also being targeted by hundreds of small SOM launchers, each firing multiple rockets.

You're also assuming that the warship will just cruise into its firing range and a proper orbit. Remember that the folks on the ground don't have to hit you, they just have to leave a few hundred kilograms of scrap metal in your flight path. Every bit of time and delta-V you spend trying to deal with that clutter is more time for the ground forces to target you. Don't forget about planetary defence craft and satellites while playing spot-the-surface-cannon.

Ian_M

Carla said...

I thought it wouldn't, but thought I had better ask in case I'd missed the point :-)

Sundog said...

The ground facility does not need more power to penetrate atmosphere...


Not in the least. The energy weapons on the ships will NEVER have to punch through atmosphere. Please read my previous post: you fire at the incoming SOMs after they crest the atmosphere. At that point they are A) much closer and B) no longer protected by the scattering effect of the gas. So the energy weapons can be much smaller and still be effective.

Spiking targets on the ground you leave to kinetic weapons. No, the physics is NOT neutral in this engagement!

1) Way way waaaaaaaaaaaaaaay more armour than...

So what? Even if you put the power source and personnel a mile down under solid rock, the delicate, easy to damage emitter assembly (or reflectors) cannot be that well armoured - simply because they MUST be exposed in order to fire. And since the enemy has the wonderful situation of lots of free energy (the gravity well) he can pound his way through ANY level of armour in short order.

2) A powerplant as big as your...

If you're building a power plant that big, and you'd need to, costs will be enormous, easily equivalent or more to the ship it kills. And it's only going to get one (maybe two, it depends on recharge times, to be fair) ecause the enemy is going to drop rocks on it as soon as it fires.

Economically, I can't help but think that actually such a facility would cost a lot MORE than one ship, given the cost of the power plant, the E-Weapon, digging the whole foundation, and armouring it all. But assuming it kills one ship, and costs one ship, such a device is still of limited utility, since the cost of defending against a fleet would equal the cost of a fleet - and a fleet would be a lot more useful for other things.

3) Multiple cooling systems, all...

So, IF a sufficiently cool location is in range to mask your emissions, you might be able to pump the heat to somewhere it wouldn't be noticed. Fair enough. You're still going to get hit as soon as you fire, but this might get you that one shot.

4) The base is cheaper than your ship...


Heh. Sorry, friend, but somehow I don't think you have a lot of experience with large scale construction projects. Moving hundreds of thousands of tons of earth and stone is BLOODY expensive. Putting all this stuff underground just means you have to dig a big hole before you start building - THEN you have to build your base. Not cheaper.

As for your assumption...

Sure. But you still have a LONG way to go to high orbit - this isn't the piddly little puddle-jumping things like the shuttle do. High Orbit is above Geosynchronus - we could easily be talking as far as 100 000 Kilometers out, using Earth as our yardstick. NO rocket is going to cover that sort of distance in short order, especially not while fighting the well all the way.

Maybe you could cut it down to twenty minutes - maybe.

Yes, a large base...

Small SOMs won't reach. They'll be eminently useful in keeping the enemy out of LOW orbit (and there are really good reasons to do that), but using any sort of reaction engine to go from surface to high orbit FAST is going to require a lot of fuel, and that means a big missile.

At the early point in the battle, I'd be a lot more worried about OOMs (Orbit-to-Orbit Missiles) and projectiles from space-based fortresses. But that's beyond the scope of this discussion.

You're also assuming...

Space is big. The chances of hitting a maneuvering ship with unguided junk is not good; guided weapons, hyper-velocity projectiles and E-Weapons are the tools of choice. Tossing a bucket of bolts into orbit is as likely to nail one of your own space-based assets as it is one of his.

I see such a battle being dual-phase - first, the fight for control of the High Orbitals, then the siege of the planet itself. It's in this second phase that the :high ground advantage" would make itself known.

Rick said...

Play nice, everyone! Don't make me come back there!

There's a LOT to cover in this last group of replies, so I will probably miss something.

As Sundog said, space based planetary defenses are outside the scope of this discussion - I'll take up orbital combat in a future post. And I agree that SOMs (a better term here than ASATs, though they refer to the same thing) lose their advantage against targets in higher orbits. Unless they have uber-drives they need big expensive boosters, and in any case the ships have plenty of time to engage them.

But while kinetics launched down from space don't need boosters, if they are launched from high orbits the surface defense also has plenty of time to engage them. And since they have to pass through the atmosphere beaucoup fast, even minor pitting will degrade their accuracy if not cause a failure.

So in a missile dominant environment, I see high orbit as a standoff, with neither side in good tactical position to reach out and touch the other.

A side note on spysats and mobile ground targets. The main problem I see is finding them. In the 1991 Gulf War, with total air superiority plus spysats, IIRC we never managed to find the mobile SCUD launchers. Admittedly that was 18 years ago, but you have to process a LOT of imagery to find a few suspicious trucks spread across thousands to millions of square km of territory.

Now, energy weapons. If effective beam range is less than orbital altitude, beams just reinforce the standoff - each side can zap ascending missiles / descending kinetics, but they cannot zap each other.

Long range beams: Now each side CAN directly zap the other, I tend to agree with Ian about the protective advantages of a surface fort versus a ship. Big construction projects are expensive, but spacecraft are REALLY expensive, even if their relative cost comes down to the equivalent level of jet planes, a minimum ~$1 million/ton.

A surface fort has simpler construction requirements (mostly concrete and dirt), simpler crew habitability, simpler waste heat disposal, no concern about mass of equipment, and certainly no drive engine. (A submarine is somewhere intermediate, but a submerged sub is mobile AND so far undetectable from space.)

Admittedly, as Sundog says, the laser main telescope mirror (or whatever emitter) has to expose itself to fire, and once it does it reveals itself. This applies to both sides. How beam weapon platforms (wherever located) fight each other is another subject for a future post, but my first guess is an eyeball-frying contest, each beam directly targeting the other, both because the emitters are vulnerable and knocking it out mission kills the target.

But on balance, I'd expect each dollar/euro/credit spent on a surface fort to buy several times the zapping power of the same money spent on a ship, so that come zapping time my eyeball gets degraded but yours gets fried. Arbitrarily, it could be something like the classic 3:1 advantage of defense over offense.

Of course the ships retain the advantage of strategic flexibility. But that is also a topic for another discussion. My strategic bias is 'maritime, implying fleets, but note that unless spaceships can easily land, the equivalent of fortified ports is difficult to arrange, Which means no 'fleets in being,' and all sorts of complications for the spacegoing equivalent of traditional naval doctrines.

Outsider said...

At least in regards to beam weapons, an advantage the space side would have over fixed ground installations would be its ability to concentrate firepower.

Ground based installations may be greatly cheaper than ship based ones, but they're effectively (and probably actually) immobile. They need to be spread around the planet to defend against attacks from any direction. Half of them will be on the wrong side of the planet entirely to shoot their beams at any attacking ships. And the closer the ships are willing/able to get to the planet, the more ground stations will be so masked*. Of the ones not masked by planet, many will have to aim low on their local horizons to bear their beams on the attacking ships, meaning those beams will be atmosphere degraded significantly more than they would were they shooting more or less straight up. The only planetary installation that gets a prime shot (minimal atmospheric degradation, ie shooting more or less straight up) will the be one that is being attacked at the moment by who knows how many ship based weapons.



*Assuming an Earth sized planet : Ships at 100 km altitude are only 'over the horizon' for ground bases within ~1200km. Which means (unless I did my math wrong) only about 1/100th of the planet's surface, and 1/100th of the ground bases, can see/shoot at them at any given time. Being able to fight a tithe of a tithe of your enemy's forces at a time would seem to be a great advantage to me.

Anonymous said...

Rick covered a lot of the topics I was looking at, but:

"Heh. Sorry, friend, but somehow I don't think you have a lot of experience with large scale construction projects."

You don't know who I am, and you know nothing about my background. Don't assume ignorance on my part and then sneer at me for your assumptions.

Outsider - The warships have the same problem. They can only engage a fraction of the ground forces at any given time. This might actually work in favour of the ground forces. They could move from their last position, forcing the warships to spend time finding them again, and they could resupply in that time.

Ian_M

Sundog said...

Ian_m, I'm sorry if you felt I was sneering at you; that was not my intention. I merely wished to convey that your mistake was mildly amusing.

However, given the same information from you, I would still doubt your acquaintance with large scale building, particularly as regards underground operations.I do not apologize for rational extrapolation.

Sundog said...

Rick, many of your points are well taken, and I'm willing to accept a higher value on spacecraft than I had been (assuming space-based infrastructure and asteroid mining, I think we can do significantly better than 1M/Tonne). However, a point that I think makes the missile game a bit less of a standoff is individual missile cost, targetability, and vulnerability.

A lifting SOM is going to be very obvious; it's thermal bloom is going to be huge, and I see no real way around that. The most obvious time for this weapon is in it's earliest boost; unless you can somehow break the enemy's target lock on after this point, he will know where the missile is from then on.

A Thor shot, on the other hand, is at it's most obvious in it's terminal phase, when it is actually punching through the atmosphere. That's not to say it's in any way invisible prior to this, but it only becomes truly obvious in the instants before impact. To me, this would indicate an innate difference in the amount of reaction speed needed to deal with these two items.

Further, a Thor shot is little more than a solid lump of metal; by the time it's entered the atmosphere, it's already either locked on target or missed outright. To stop one you need to do sufficient damage to break it up, vapourize it, or knock it off course. A SOM cresting atmosphere is still homing on it's target, carrying a reasonable quantity of volatile fuel, and likely a warhead (not to cause extra damage - a direct hit at orbital speeds would be obviously lethal - but to spread out the shrapnel and increase the damage probability). Thus, the SOM would require significantly less expenditure of energy to either destroy or to render blind, and thus harmless to a maneuvering ship.

Which brings me to point three - a ship can dodge, a base cannot. Dumb kinetic impactors can be relied upon to follow the physical laws and hit what they're shot at - but you need good (not great, just good) sensors to hit a ship, and sensors are blindable or jammable.

Anonymous said...

Yes, clearly the costs to build such a structure are prohibitive.

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

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

http://en.wikipedia.org/wiki/London_deep-level_shelters

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

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

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

If you want a more technical discussion of these issues, I'd be happy to discuss the details of the construction of the Canadian Pacific Railway. Its stretch through the Rockies seems to fit the description of majhor earth-moving project.

Ian_M

Rick said...

Everyone - There's no friction in space, and let's try to minimize it here!

Outsider - True about the general advantage of mobility, though as Ian notes this also constrains what you can shoot at. One further complication is that (absent magitech) ships can't hover, and unless they make a Really Fast hyperbolic pass, their close approach track will go halfway or more around the planet. More subtly, surface defenses will presumably be arranged to protect high value targets.

Sundog & Ian - I have no professional background in any sort of construction, but being a public transit geek I've read enough about subways to know that underground construction Is Not Cheap. (Though you're probably not building planetary-defense fortifications right under cities, and perhaps can build, then cover.) But my gut feeling is that spacecraft in the foreseeable future will be even more expensive, especially massively armored combat craft. Admittedly metrics for this are above my pay grade.

SOMs are indeed *extremely* visible in boost phase, with any foreseeable tech. Thor slugs are not, themselves, particularly visible on release, but you know where to look because they can't come out of of nowhere - they have to be released from a ship. If the defense is not tracking the attacking ships they deserve to lose. :-)

A question about Thor slugs that I have not looked into: It seems to me that they have to be fairly massive, or they'll lose excessive kinetic energy coming down through the atmosphere, which has a vertical cross section density something like 10 tons/m2. Also, how precise will an unguided one be? (For this discussion I'm assuming precision targeting of hardened installations, not area weapons.)

Sundog said...

Ian_M, I'm not saying you can't build such bunkers, nor that they're too expensive to build - but I have serious doubts regarding their cost effectiveness. If you're killing less money than you're costing, of what value are you to a war effort?

Regarding Thor slugs, all of the examples I've seen or seen considered have been slim, aerodynamic javelins of highly heat and impact resistant metal. Individually, mass may not be too great, but greatly increased by their use in swarms (which would also reduce vulnerability to interception).

Regarding accuracy, given I'd be expecting them to be encased in a plasma sheath all the way down, preventing any onboard sensors from getting data, any Thor shot would need to be lined up on it's target before atmospheric entry. This would make them less useful against "shoot and scoot" launchers and subs, unless you were willing to saturate an area, but I have my doubts regarding such being useful against targets in High Orbit, and I don't believe Low Orbit could be made safe without putting troops on the ground first. It's just too vulnerable.

Rick said...

Sundog - it seems like these projectiles should be Zeus's thunderbolts or Apollo's arrows, not Thor's hammer. :-) But we'll stick with the established name.

On reflection I think your biggest problem remains not hitting what you aim at, but knowing where to aim. If my ground defense is laser based, my mirrors are vulnerable to yours (and vice versa) in a laser engagement. But I can run them back into tunnels when your slugs are approaching, and the only vulnerable point you can clearly identify is the tunnel portal.

For that matter, if laser engagement range extends to high orbit, we've already fought a laser engagement, and either I crippled your ships or you fried my laser.

Rick said...

Addendum that if laser range does not extend to high orbit, I acknowledge that a surface defense pretty much concedes it. The advantages of SOMs are limited to low orbit.

Outsider said...

Constraints on what the mobile ships can shot at seem a lot less important than the benefit of how few of the ground bases can shoot back. After all, once a particular ground base has been destroyed, the ships just change position to engage the next. eventually all the ground bases are engaged.

And yes, the tactics of the space based side are heavily dependent on just how good their space drives are vs how powerful the weapons available are.

It also seems to favor the ground based side immensely that massive overkill has been ruled out as an option for the space based side.

Actually, given that massive overkill is not an option, why build hugely expensive bunkers at all? Just build many times as many actual weapon systems with just enough housing to keep the weather off. Staff them remotely, and only count on each one for a single shot. The ground based side isnt, after all, restricted from using massive overkill. No habitable ecosystem to ruin up in orbit.

Rick said...

Outsider - It also seems to favor the ground based side immensely that massive overkill has been ruled out as an option for the space based side.

My only reason for ruling it out, for this discussion, is that otherwise things go very quickly to GAME OVER - probably for all parties. Absent magitech such as force shields, soft targets like cities (let alone spacehabs) are so vulnerable to massive overkill that if things go a l'outrance, everyone wipes everyone out. Kinda boring!

The grand strategic implications of this will be taken up in a future post.

On the tactical level of surface defenses I'm working from an unrelated assumption, that space capable weapons are more expensive than bunkers, so that it is cheaper to conceal the weapons among multiple bunkers than to build scads of weapons. (Though for SOMs I favor mobile launchers, also relatively cheap and easy to conceal among a planet's worth of ground clutter.)

Kedamono said...

Actually, one thing ground defenses can do is to put mirrors on balloons or drones, and then send them up hight and use that mirror to redirect the beam. It's much harder to work out the angle the laser hit the balloon mirror at, and the mirror balloon is relatively cheap to deploy while the target ship is still over the horizon.

Fire a couple of times until the mirror gets shot down. Hide the ground base mirrors while the target limps overhead, probably taking hits from the other set of balloon mirrors being used by the next laser base.

Outsider said...

If space to ground/ground to space capable weapons are more expensive than building several Cheyenne Mountain sytle bunkers, and the space side won't be using massive overkill for game/story reasons, yeah, ground side gets a pretty big boost to its odds.

As to using mirrors to bounce shots over the horizon, there's a few difficulties in that.

1) Mirror Quality (1) : To reflect a shot such that it not only hits a target several thousand km away, but also maintains enough focus to damage that target requires a pretty precisely shaped mirror, I'd guess. How much would these cost, and how much would they weigh? Especially if the mirror is meant to be used more than once.

2) Mirror Quality(2) : Mirrors don't reflect all the light that hits them. Some percentage is absorbed by the mirror and turned into heat. Given that we're reflecting weapons grade lasers, even a small, small percentage of the energy will likely be enough to cause the mirror problems with distortion, if not outright destruction. Especially if the mirrors are mass minimized due to their depolyment in baloons. Less mass to spread that waste heat around in. Or you can install cooling systems for the mirrors. But again, thats probably mass intensive.

3) Atmosphere(1) : Baloons will need to be in it, and will therefore be subject to the it. Hitting a only somewhat predictably moving baloon at 50km wont be a huge problem, but bouncing a shot off of it to hit a spaceship 1000km farther on would be, I am thinking.

4) Atmosphere(2) : The baloons will be in the atmosphere. Any shots relaying around the curve of the planet by bouncing off of them will also be in atmosphere, almost all the way to the target. That's a lot of atmosphere to degrade the beam.



It'd be a lot better to use orbital mirrors to bounce shots around the planet, since their motions are far more predictable than anything in atmosphere, and they'd be bouncing the beams around above the atmosphere. But then, any space based attacker should clean everything out of orbit from long range (a rain of kitty litter, as someone said) before getting anywhere near a planet.

Anonymous said...

Hi, again. I've got a few things:
1. It seems that everyone has ignored the possibility that the ground-based laser bases only have the one emitter; they they don't seem to have any kind of secondary or point-defense weapons, or that they operate in a vacuum (pun intended), without support from any other military units.
2. The ground-based defenders aren't meant to move, but the attacking spacecraft are, and they have a finite amount of fuel for their manuvering engines; they can't jink all day.
3. Why haven't there been more discussion about EW? A surface base should be able to have much more Electronic Warfare capabilities than a spacecraft. Or so I would think.
4. Why do you think that SOMs or even higher-orbit capable missiles, couldn't be fired at the ships except for when they're nearly underneath them? When launching a weapon, why not use the mass of the planet to sheild the boost phase of the missiles? Or even launch massive amounts of them from multiple points/trajectories? That's what I'd do.
5. Sundog: your Thor "rocks-from-space" weapons system is way cool and mightily destructive- but it's not 100% effective; that much concentrated metal will show up on radar, high-contrast optical systems can track them (especially since the people on the ground will know where to look), and there are counter-measures to impacting rocks; railguns, lasers, high-tech flak guns, Fuel-air blasts in their path, and (I'm sure)many other counter-measures of varing effectiveness. Plus, unlike the spacecraft, the ground bases can use all of them.
So, just some thoughts; I'd like to know yours on the pros/cons of mine.
Ferrell

Anonymous said...

"4) Atmosphere(2) : The baloons will be in the atmosphere. Any shots relaying around the curve of the planet by bouncing off of them will also be in atmosphere, almost all the way to the target. That's a lot of atmosphere to degrade the beam."
Oh, this just occured to me: we ALREADY have adaptive optics; they compensate for atmospheric degradation of beam-focus. as for ballons, there are multiple technologies (both old and new) for tracking/verifying the location of objects. Also, even huge, heavy-payload ballons aren't very observable.
Ferrell

Jim Baerg said...

Outsider
Re: Mirror Quality
If you have a really good mirror that reflects the vast majority of the beam energy, then you also have excellent shielding material against the beam weapon.

One reason to bullets & missiles to remain much more important than laser beams as weapons.

Rick said...

Kedamono - The balloon idea is interesting. The mirror would be an easy target in space, but a space observer looking down has to separate it from the clutter of the planet. OTOH, once it bankshots a zap it reveals itself, and will soon be history. So the big question is what cost fraction of the whole laser weapon it embodies. Possibly quite a bit, since we're talking observatory grade and scale mirrors.


Outsider - My comment on multiple bunkers was for much less fancy ones than Cheyenne Mountain. (A general problem here is talking qualitatively about things that have a big quantitative component.) But broadly, my bias is toward concealment as a larger component of surface defense than armor, though both come into play.

Space based mirrors could play a part, till they get scragged. Planetary surface defense probably would end up being one component of a layered defense - and not the least reason for wanting one is so that your own space forces aren't tied down to orbital defense.


Ferrell - The lateral range of SOMs depends on their performance range. The cheap ones have SCUD-like performance and limited lateral range. For higher performance you need an SOM more comparable to an ICBM, more expensive but capable of going half way around a planet to bag a target in low orbit.

Good point that a planetary defense will probably include a range of weapons, including point defense. Part of what motivated this post is that planetary surface defense is under-discussed compared to open space combat.

Which sort of applies to EW as well. My impression is that most EW plays off the limitations of radar operating near ground and atmospheric clutter. In opens space passive scan detectors play a much bigger role.


Jim - One constraint on mirrors as a protection. A laser mirror has extremely low absorption at one wavelength, but if the enemy laser has a different wavelength, a lot more will be absorbed. Plus it takes a LOT less zap energy to degrade a mirror than to burn through refractory armor.

That said, my own usual bias is in favor of missiles as offensive weapon, with lasers mainly as point defense. This thread has been more laser oriented because long range lasers create a more complicated planetary defense picture.

Sundog said...

Ferrell - Your note on point defense against Thor shots is well taken. I'm not certain conventional munitions would have the speed to generate an intercept, but lasers and/or magnetic accelerators certainly could.

I think I'd go with the railguns. A laser strike on a Thor shot would be of limited effectiveness, due to the relative simplicity of the impactor and the possibility of increased degradation on energy weapons. Once just one Thor shot got through, the dust thrown up would inhibit a laser, perhaps fatally - railguns would have no such difficulty.

As to the difficulties with the system: A Thor shot will be a very difficult target. Spotting it will be easy - even if it were made of something radar absorptive (which is highly unlikely) the plasma sheath generated by it's descent through atmosphere is almost a perfect radar reflector. The difficulty would lie in striking a long, thin target going very, very fast. Nevertheless, I have no real doubt of the possibility, especially if using multiple PD weapons.

You'd also have to strike with sufficient force to either knock the shot off course or break it up into harmless fragments (given it's speed, to qualify for "harmless" they'd have to be very small indeed). Here the speed of the Thor shot works with you AND against you - deviating it's course would be hard, smashing it to pieces relatively easy. A high-velocity railgun shouldn't have much trouble.

The question that would have to be asked: can what can clearly be done to a single shot be done to an entire cluster coming down? If the answer is yes, then your bunker is now holding all the aces - it is invulnerable to the enemy's primary ground attack weapon. If the answer is no, then the enemy will eventually do enough damage to either take out the PD System or render the primary weapon system ineffective.

Personally, I don't think it'll be so cut and dried. ANY PD system can be overwhelmed; the question is, how do the economic costs match up? You may have just made the bunkers economical again.

Rick said...

Sundog - An off the wall thought, but how about a barrage balloon? Hitting a bullet with a bullet is hard, but I know the path the Thors must follow to hit the target, and if they are coming from a high orbit I have time to position my balloon across their path, a few km up.

Of course a Thor will go right through the balloon, but I just want to nick its nose. At Mach 25+ the aerodynamic loads from passage through the lower atmosphere are ginormous, and the Thor depends on a clean swan dive. If airflow is disrupted above some critical point, the Thor will tumble and deceleration will drastically increase. At minimum its impact speed will be reduced and its surface impact geometry spoiled, robbing it of penetrating power.

Anonymous said...

Part of the problem with this sort of conversation is dueling tech assumptions. Are we talking about edge-of-tomorrow space conflict or 23rd+ Century societies at war?

If we're talking about edge-of-tomorrow conflict (Thor projectiles and massive surface-to-orbit missiles) why are we talking about large warships battering the planet? It's probably their home.

If this is a system with two or more inhabited planets (Earth, Mars, maybe a few other settlements), and the political situation is far gone enough that polities are building warships, then someone has thought of defences to the weapon systems Jerry Pournelle dreamed up in the 1970s. Someone else has designed countermeasures for those defences, and someone else has designed counter-countermeasures...

To put it another way - Define launch technologies, space-drive technologies, weapons and defences, and what kind of polities we have in the conflict. Then we can talk logistics and strategy.

Ian_M

Rick said...

Ian - Yeah, dueling tech assumptions are a challenge! And I didn't exactly go out of my way to define a framework. But as it happens, 'edge of tomorrow' and '23rd+ century' more or less brackets the tech era I have in mind, which I tend to call the midfuture or (a bit recklessly) the foreseeable future.

It starts perhaps around midcentury, a design generation beyond where we are now, and extends to perhaps 2200 or thereabouts - with great haziness about the far end, obviously.

If there is a Singularity, all bets are off. Flip side, we could be heading into a period when a lot of techs mature and see only incremental improvements, like sailing ships around 1550-1850, after the full-rig revolution and before steam.

Compare to airliners, which after changing radically by the decade from their inception to midcentury, have stabilized into the broad performance envelope of the 707 in spite of enormous subtler improvements.

One thing that strikes me about the biggest tech revolution of my adult life, computers and the Internet, is how totally different it is from what was anticipated. AI in the HAL 9000 sense isn't even in the picture. This blog is basically just a combination of word processing and quasi-spam email, which (tarted up with graphics) describes most of the Internet. It requires enormous crunching power, but who'd of thunk such simple stuff would have so much impact?

Which doesn't exactly answer your points, but supplies another item on my list of Things To Post About!

Sundog said...

The Barrage Balloon idea has merit, but I can see a major difficulty. The balloon would have to be constructed of something strong enough to disrupt plasma sheath around the incoming javelin, but also light enough to be made made into a rigid-skin airship (imagining a substance that is ALSO flexible enough to form an inflatable is a little much). An Aluminium alloy, perhaps? Or maybe a Titanide (though then you're really stretching the idea of it being economically viable).

Rick said...

How about a wire mesh, or even an array of beads? It needn't be integrated with the balloons; you could have an array of balloons with a net suspended from them. I don't know the minimum diameter of an effective Thor, but the defense designers will, and can use an mesh size such that the Thor will be sure to hit a wire or nodule.

Chainmail to stop a Thor - it seems rather appropriate. :-)

Sundog said...

I have serious reservations that a net would have the tensile strength to do enough damage - I'm afraid it's at this point my lack of a high-level maths background stumps me. I'll talk to some people I know and get back to you on this.

Anonymous said...

Balloons as cheap point-defence platforms could work. A few thousand stratelites could carry radar/ladar-targeted rapid-fire ultravelocity cannons. Incoming projectiles would have to fly through clouds of explosive shells. A mix of stratelites, drone aircraft, and interceptor jets carrying point-defence weapons would be a good 'armour' for a larger base or mobile platform.

Throw in a mix of launch technologies for anti-orbital weapons (Everything from cheap British Black Arrows to small laser-launch facilities and vehicle-based launchers) and you've got a range of defences that could be built with current technologies.

Ian_M

Rick said...

Sundog - I think that tensile strength might not be critical - at these enormous speeds, a dense wire or nodule won't have time to break up before it smacks the nose of the Thor. But all this is way above my math pay grade! Hitting a 'big enough' obstruction will certainly cause the Thor to fail, but the viability of this defense all depends on what is 'big enough.'


Ian - In the particular role I'm thinking of, the balloon doesn't need a gun. (You can also have guns deployed, of course.) The key to the 'barrage balloon' defense is that the Thor is launched from a long ways off, fairly high orbit, at a small target. So you have time to position the balloon/net across the trajectory of the incoming Thors.

Anonymous said...

Here's an option for the barrage balloons, if the material isn't strong enough to deal with projectiles: Impact explosives. Shockwave hits balloon, micro-payloads across its surface go boom.

Another question about Thor systems: How hard would it be to set the projectile tumbling, and what would happen to what is essentially just a steel girder? Would it deform? Break up? Be blown apart by its own plasma sheath?

Ceramic or quartz spheres might turn out to be a better choice. You can deflect them or destroy them, but it doesn't matter if they tumble (Or maybe it does. Curveballs from space?).

Rick - I thought of point-defence stratelites because we could build them now, without worrying about the tensile strength of the balloon or any mesh it might carry. But it really does depend on what it would take to seriously impact (Deflect or destroy) incoming projectiles. The ideas aren't mutually exclusive either. Cheap expendable barrage balloons and reloadable point-defence stratelites could work together.

Ian_M

Rick said...

Ian - last point first, agree that these defensive systems are not mutually exclusive!

Impact explosives could be a nice options, though they actually won't add much more energy than the impact itself, which releases several times the energy per unit mass of TNT.

Tumbling the Thor is exactly my objective. Sophisticated calculations are way above my skill level, but here is my basic take, from pretty much high school physics:

Thors, except for jumbo ones (in the tons), have to be long and slender to minimize their cross section so that they don't shed their speed = kinetic energy by punching through the atmosphere.

A column of air 10 cm in diameter extending up through the atmosphere has a mass of about 80 kg, and a Thor with a diameter of 10 cm has to push this air aside, so to speak. To first approximation, the air is slapped aside at roughly the speed that the Thor hits it - so if the Thor also weighs 80 kg it will transfer much of its energy to the air, and by the time it hits the ground it will be a 'spent bullet,' with a much lower impact speed and thus much less kinetic energy and penetrating power. A sphere 10 cm in diameter, even of dense stuff, would only weigh about 10 kg.

A long slender rod with a sharp nose means more mass per cm of cross section AND the air does not get pushed aside as fast, so less energy is lost. (This is a REALLY crude model, but you get the idea.)

But at supersonic and especially hypersonic speeds most of the decelerating force acts near the nose, so the Thor is doing a dynamic balancing act; if knocked slightly off true it will tend to tumble. And if it tumbles, its cross section is larger, and the decerating forces are greater.

This is what did it for the shuttle Columbia. I believe it was killed not directly by heat getting inside, but by unbalanced aerodynamic forces. So long as the tumbling forces were small enough to be counterbalanced by the attitude jets its reentry remained controlled, but once the attitude jets were overpowered it tumbled and almost immediately broke up.

A solid Thor is vastly stronger, but the lower atmosphere is 4000 (!) times denser than at 60 km where the Columbia broke up. Also a fair amount of the energy lost to deceleration is converted into heat. So if a Thor tumbles it is subjected to enormous stresses and heating.

The devils are in the details, AKA the specific numbers and dynamics, but I suspect that a Thor that tumbles will break up and explode in the air. At minimum it will hit a lot slower, and with a lot less penetrating power due to greater impact cross section as well as lower speed. The key question is how much disruption of air flow is needed to tumble it. Which this crude modeling doesn't answer at all.

Anonymous said...

Et All- as far as I can tell, if a relitively small force is applied asymetically (i.e. hits it off-center), it will disrupt the Thor and cause it to tumble and explode; however, this asysmetircal force is differnt at different altitudes and entry speeds as well as the mass of the weapon. So, a hand grenade-sized explosive going off slightly to one side might be enough to cause the distruction of the Thor projectile, it greatly depends on where in the reentry track the weapon is.

Because ground based instillations have greater redundency than a spacecraft, the builders of the spacecraft must either choose the absolute best weapon for a very narrowly defined mission, or the best-all-around-weapon for a much more broadly defined mission or range of missions. The Thor, I think, falls into the latter. The real question comes down to: will the percentage of individual weapons that get through the defenses do enough damage to accomplsh the mission? Unfortunately, that question probably can only be answered by actual combat and probably will, sometime in the future.
Ferrell

Rick said...

Both of these points sound valid, though for destabilizing a Thor it may not be necessary to tumble it directly, just create an asymmetrical airflow. (In which case the higher you do it, the more time for it to tumble.)

Another question for Thors is the nature of the targets. If the defense is mobile missiles, or 'guns' of whatever sort that are light enough to be mobile, there may not be many tactical targets to shoot at except by lasers that have no delay.

mark said...

Decoys might be useful in an orbital "blockade" (keeping with the nautical terminology) you won't fool anyone into thinking they are spacecraft, but if you flood LEO with cheap inflatable decoys it will probably create enough clutter to hide a constellation of spy satellites (especially if they are also inflatable), and if they shoot down the decoys then every SOM they use isn't killing something important, and if they use lasers that's wear and tear for every shot (and each decoy would require a shot instead of putting shrapnel in LEO to scrape it clean like you could with a SOM)
-Mark

Sundog said...

Okay, I think we can reasonably state that, with assistance from point defence systems and mobile launchers, a system of well-emplaced planetary defence centers (PDCs) can stop an invasion force from taking low orbit and fight for a considerable time against high orbit opponents.

However, I think the final word is going to be with the orbitals. Thor shots can be stopped, one way or another, but can you stop the orbitals from upscaling?

After a relatively short period of the siege, they're going to get a pretty good idea of where the PDCs are. At this point they pull out Thor's big brother - in keeping with the theme, let's call it Odin.

Odin is just Thor writ large. Where Thor shots might come in at a quarter tonne, Odin shots weigh in at 20 Tonnes. And Odin is not a slim, precise rod of metal - it's just a solid ball. Drop half a dozen of these on each PDC - remember, all you need to do is kill that big E-Weapon and the PDC is just another bunker for your ground troops to worry about.

The sad thing is, the orbital side can keep on "raising the stakes" like this as long as they like, up to the point where they are doing significant climatological damage (or even after - if they're careful, the climate damage can inconvenience and demoralize the planet owners, but still clear up in a few decades). Big Bunkers are just big targets.

Rick said...

Mark - Very good point about orbital decoys. The standard rap on decoys (at least in the haunts of SFConsim-l) is that they can't maneuver without giving themselves away. But forces in orbit don't necessarily HAVE to maneuver, and until/unless they do they are not so easily distinguished from decoys (or general clutter).

Which somewhat anticipates an upcoming post!


Sundog - On one level this is one of the most basic military realities: If you come to the party with enough toys, I can break a lot of them and you'll still take my cake.

But there are two different cases to consider. If really long range ground based zappers are available, they will scrag ships even in high orbit. If they are not available, I'll concede high orbit, and defend low orbit with mobile based SOMs. Which are hard for kinetics launched from high orbit to take out, since they can move during the kinetics' flight time. (And in the case of truck launched SOMs, the trucks are low value targets once they've launched their shots.)

All of this is dealing with tactical combat. You have the option of falling back on strategic targeting of my supply chain. Here a completely different dynamic comes into play. My gut feeling is that soft area targets are extremely vulnerable to attack from space, to the point that MAD rules apply. This requires that I have a space based deterrent, but it does not have to have much tactical fighting power.

Anonymous said...

Ok,first: I'm amazed that this is post is still getting replies. Second, let me see if I've understood correctly what we're talking about: We have a planet that's being assaulted by an enemy spacefleet; the planet has many defensive bases capable of orbital defense as well as many moble units of various types also capable of defense of LEO and upper atmosphere. The spacefleet has point-defense weapons(lasers) and Thor type ground attack weapons.

Now, how does the spacefleet replenish it's stock of Thors? Does it mine asteroids, do supply ships shuttle back and forth beteween their base and the fleet, or do the attacking spacecraft periodically withdraw to resupply? Because, let's face it; the planet defense bases can each have many times the spares/supplies/weapons/ammo than the entire enemy fleet combined.

Another question would be; what kind of orbital-based defenses do they have and how quickly/easily can the planet replace them?

If the attacking spacefleet can't defete the space defenses of the planet pretty quickly, then they will be forced to withdraw, simply so they can refit.
Ferrell

Rick said...

This thread is pretty outrageous! It's the most replies I've had on this blog, and heavyweight replies to boot, stuff that makes my brain explode.

Your summary of the scenario is correct, but Thors are potentially cheap, just big spikes. A couple of transports could carry a lot of them. Probably they're not quite so cheap in practice, since they need some kind of precision guidance to hit point targets.

I ignored orbital defenses for this discussion; though part of a planetary defense their tactical role falls under 'space battles.' And you might want your costly space forces taking the war to the enemy, not in defensive orbits!

The general argument of this post is not that 'planets are invulnerable' - they aren't - but that surface-based defenses are more formidable than commonly imagined, and pose space forces with challenges not unlike those naval forces have historically faced against coast defenses.

Jim Baerg said...

Coming in late to this discussion, but I though I should mention the space battles in _Antares Dawn_ by Michael McCollum. He seems to have though of most of these points when he wrote the book in the 1980s.

The situation involves aliens who think that there is room for only one intelligent species in the universe & immediately start trying to exterminate humanity one contact is made. FTL in this ficton is similar to the Alderson drive in _The Mote in Gods Eye_.

The battle involves an attacking force getting some ships through the jump point defences & the defenders using lancer tactics to destroy some of the incoming fleet so planet based defences can take out the rest.

The planet based defences use oceans & ice caps as heat sinks for their massively energetic weapons.

Rick said...

The situation involves aliens who think that there is room for only one intelligent species in the universe

There's some harrowing commentary on this at the Atomic Rockets site that I'm gonna have to take up at some point.

As for using the oceans and icecaps as heat sinks, those must be whomping powerful weapons! And a scenario where global warming is distinctly the lesser of evils ....

Z said...

I hate to keep resurrecting ancient threads, Rick, but this stuff is just so much fun, and I kind of came to the party late.

I think the case for Rods from God is not nearly as open and shut as lots of people are thinking. Sandia actually did quite a bit of examination on the topic- granted, for the modern era, and not for whatever shiny fusion powered future we are conjecturing about, but all the same, their analysis was not terribly rosy.

First (not a notion raised by Sandia, but I thought of it) most of the references to kinetic impactors speak of releasing them, when in truth, you need to deorbit them, or in the classical Pournelle scheme, cancel all orbital motion so they simply fall- a maneuver that takes a rather substantial burn that can be observed.

Second (and this point is raised by Sandia) the super high energy impactors will take forever to get there. A fall from a sufficient height to deliver one rick of damage is 460km, with a fall time of 12 minutes- insufficient warning to move out of the way of a nuclear blast, but if all you have to dodge is a conventional equivalent bomb, its fine. A fall from geosync altitude delivers ten ricks, but also takes six hours- with the deorbit/orbit cancelling manuever making a big observable exhaust, and six hours to look, I doubt any asset that could conceivable be moved would be in the same county.

The last issue is penetration. Sandia did penetration tests with long rods of all different materials (the stronger the better) and their conclusion was that maximum penetration occurs at 1km/s. Beyond that, you simply can't make a penetrator strong enough to not functionally liquify at impact and thus dump all its energy into the uppermost layers of the target. Of course, at 1km/s, the altitude it can be dropped from is much lower and the warning time and booster exhaust plume associated with deorbit are much smaller-but at that speed the projectile deal 1/9th of a rick in damage-not so thrilling, and probably in need of a real warhead.

So, in conclusion:

TNT-equivalent impactors have a long enough warning time to conceivably scoot something mobile. Conceivably being the operative word- it's the the same sort of destructive energies, detection possibilites and response times we associate with strike aircraft, which sometimes make the mark and sometimes don't.

Two, geosync level rods provide nice intermediate levels of destructive force between nukes and bombs-but with their cripplingly long response time and low penetration, they can really only threaten fixed surface targets- certainly a big category, but most things that shoot, also move. It just changes the nature of the battlespace.

Third, kinetic rods are in no way a panacea against deeply buried targets- far from it. If you want to take out bunkers, you are dropping the rods from very low, and they are packed with explosives.

Rick said...

I like seeing old posts show life! After all, the space fighters post is still going strong after two years.

Kinetic bombardment of planets strikes me as one of those generally overrated things, where conceptual coolness trumps practicality. The Sandia people have (shock!) a good point that uber-fast impacts turn any impactor into a fluid, and its kinetic energy gets transferred quickly.

Note that 1 km/s is near the muzzle velocity of conventional artillery.

Damien Sullivan said...

Submarines got mentioned a bit but I suspect are underrated. More expensive and smaller than bunkers, but both mobile and somewhat stealthy. Can pop up to fire missiles -- or a laser!, with ocean as nice heat sink compared to a spaceship -- then submerge and move away from orbital response. And have meters or hundreds of meters of water as shielding against a fast response.

Concentration of force got mentioned; it was rebutted by noting orbital can't actually orbit well, except in geosync or Molniya (high elliptical) orbits, but space forces can still share orbit and rain down fire in a pass. Bunkers can't move, but submarines could congregate, if there's a reason.

Then there might be submersible 'bunkers', much larger, that don't move fast laterally but can pop up for heavy fire then submerge again.

Rick said...

Welcome to the discussion boards!

Submarines definitely have potential as a planetary defense weapon, for the reasons you give. A full circle of sorts, since early naval submarines were regarded as largely a coast defense weapon.

Byron said...

What about using kenetic weapons launched by coil/railguns. I know that the atmosphere has usually been seen as the problem with that, but I did some rough calculations and to launch something up 100 km, not counting air resistance, would only take Mach 4 from sea level. That would run into air resistance, but if you launched from either a mountain or some sort of balloon it could work without the thermal flare of a missile launch.
Also, why does a laser only have to have one mirror? I know that there is a discussion on atomic rocket of a ship with one generator and multiple mirrors, so why not do the same with ground defenses?

Turbo10k said...

W00t Thread revival FTW!

I'm new here, and after doing quite a bit of reading (Whole Atomic Rocket site, the Space fighter threads (whole two years of them) and this...), I think I can join in.

My thing to say;

Byron: I believe the Railgun/Coilgun launch concept works only in two situations. First would be deccelerating a Thor rod from orbit without a long, highly visible flare. Angled, it can even give quite a kickstart to the rod, reducing the altitude it has to be launched from.
Advantages: -Lower altitude launch
-No visible flares, except after heat sink is cooled down (quite a delay in my opinion for laser-equipped warships)
-Only uses a fraction of *limitless* power supply a nuclear generator makes

Disadvantages: -Uses up heat sink, not good if has to be saved for laser point-defence.
-Low penetration. After launch, speeds only increase until the lower atmosphere. Might prove problematic with rods melting due to friction before hitting the ground.

The second situation would be planetary defences trying to hit low-orbit ships VERY quickly. Especially combined with air-launch or mountain-top defences.
Advantages: -You could get a projectile 'up there' much faster than a rocket.
-Launches would be hard to detect, and projectiles cannot be stopped by point defence.
-Does not have to worry about power loss as lasers do (given enough initial speed that is)

Disadvantages:-Just like lasers, is only useable until the gun is found, unlike for mobile missile launchers.
-Slower than lasers.
-Cannot be course-corrected.

I hope I haven't made any gross inconsistencies yet :P

Rick: Subs are great, yep. However, depth pressure constraints have reduced submarines mostly to the size we find them today ie cylindrical, length/radius ratio not too large or small, ballast tanks proportionate to density....
All the above creates a situation where supermassive submarines would be very slow , turn even slower, and surface/dive with difficulty. In other words, I don't think submarines with weaponry to rival that of ground installations feastable.

<>

Except that they don't pop up, steel ain't THAT strong a material. Furthermore, a ship in orbit can always parachute a torpedo down to the surface, and hunt the sub in its own element.

Hope my first post is up to standard!

P.S. 1: I think the latest metrological satellites can detect underwater mountains and elevations by measuring how the surface rises relative o the rest of the area. A 'congregation' of submarines in calm weather could be detected by this method by superfine sensors...

P.S. 2: I think of my lasers as very large, very expensive and very heavy things. More 'jet engines with a mirror at the end' than clinical 'zap, your dead as many times as I want' view of them. Otherwise my second argument (use by planetary defence vs LO ships) for railgun/coilguns is void.

Turbo10k said...

Part 1

W00t Thread revival FTW!

I'm new here, and after doing quite a bit of reading (Whole Atomic Rocket site, the Space fighter threads (whole two years of them) and this...), I think I can join in.

My thing to say;

Byron: I believe the Railgun/Coilgun launch concept works only in two situations. First would be deccelerating a Thor rod from orbit without a long, highly visible flare. Angled, it can even give quite a kickstart to the rod, reducing the altitude it has to be launched from.
Advantages: -Lower altitude launch
-No visible flares, except after heat sink is cooled down (quite a delay in my opinion for laser-equipped warships)
-Only uses a fraction of *limitless* power supply a nuclear generator makes

Disadvantages: -Uses up heat sink, not good if has to be saved for laser point-defence.
-Low penetration. After launch, speeds only increase until the lower atmosphere. Might prove problematic with rods melting due to friction before hitting the ground.

The second situation would be planetary defences trying to hit low-orbit ships VERY quickly. Especially combined with air-launch or mountain-top defences.
Advantages: -You could get a projectile 'up there' much faster than a rocket.
-Launches would be hard to detect, and projectiles cannot be stopped by point defence.
-Does not have to worry about power loss as lasers do (given enough initial speed that is)

Disadvantages:-Just like lasers, is only useable until the gun is found, unlike for mobile missile launchers.
-Slower than lasers.
-Cannot be course-corrected.

I hope I haven't made any gross inconsistencies yet :P

Turbo10k said...

Part 2

Rick: Subs are great, yep. However, depth pressure constraints have reduced submarines mostly to the size we find them today ie cylindrical, length/radius ratio not too large or small, ballast tanks proportionate to density....
All the above creates a situation where supermassive submarines would be very slow , turn even slower, and surface/dive with difficulty. In other words, I don't think submarines with weaponry to rival that of ground installations feastable.

<>

Except that they don't pop up, steel ain't THAT strong a material. Furthermore, a ship in orbit can always parachute a torpedo down to the surface, and hunt the sub in its own element.

Hope my first post is up to standard!

P.S. 1: I think the latest metrological satellites can detect underwater mountains and elevations by measuring how the surface rises relative o the rest of the area. A 'congregation' of submarines in calm weather could be detected by this method by superfine sensors...

P.S. 2: I think of my lasers as very large, very expensive and very heavy things. More 'jet engines with a mirror at the end' than clinical 'zap, your dead as many times as I want' view of them. Otherwise my second argument (use by planetary defence vs LO ships) for railgun/coilguns is void.

turbo10k said...

Part 3

Enough replying to the others. My own voice now;

What if...it wasn't the whole planet the attacking fleet is fighting? Several nations on the surface, some friendly, others hostile? Not so much a 'balkanised earth' setting than today's map, or even simpler, US vs USSR or somethink like than.

If you keep that in mind, then you can forget half of the defender's options. Can't run away indefinitely, can't build launchers and guns over the planet, can't always have access to mountain-tops or favourable ground, and now you got an ally that negates ground/air supremacy of the defender in ways Space Marines (R) and Aerospatial fighters can never do.

It alse makes things more complicated. Attackers would have to avoid commercial/allied orbits, and can't send down raining hell for fear of hitting friendlies. Defenders would have to identify targets before ingaging in 'Fast responce' maneouvers. Even worse, it now has to deal with fighters, armies and navies from neighbouring countries. Mix in ambiguity about who's targeting who with nuclear missiles and nations switching sides and you'll get strategic headaches to no end.

Food for thought!
:))

Daniel said...

Yay for thread necrothurgy!

Railguns: how many shots would they get? Everything I've read about current attempts says that barrels are only good for a couple of shots. That doesn't sound like something that could be put aboard something autonomous.

Anyway, attacking a planet from orbit. Everybody seems to be concentrating on hitting bunkers and the comparable costs. Why not just hit the economy? Hit the stockpiles of ready-made materials, factories that make the material, road and rail leading to both bunkers and said places, and earth mover concentrations; in other words, the strategic bombing of world war 2 writ large. Reflecting the differences in economy, I'd also drop something big into bodies of water with oil rigs.

To minimize casualties, the fleet can separate into an autonomous ammunition dispenser part and a manned C&C in higher orbit. Given that the autonomous part doesn't need to remain alive after the initial salvo, it doesn't have to be that much more expensive than the ammunition it carries. All it would need to do would be spread a system of spy, kinetic launcher, and decoy satellites around the planet.

If I sends a fleet that takes out your ability to reconstruct for the same cost as the bunkers the you used to kill it, I still have shipyards to make another fleet. I just cost you not only the cost to replace everything just destroyed, but also the wealth that could have been made by the targets during the period when they don't have a replacement.

For less collateral, I think something can be done with fighters. Not Hollywood's image of semi-streamlined airplanes, but jets with a disposable heat shield. They probably wouldn't need to be manned. Just some basic AI for navigation and collision/munitions avoidance, with a pilot in high orbit for the trigger. That way we get to bring in point-blank toys like bunker-busters and HARMs under the radar. To be reusable, drop a tanker with a large booster either with them or right before they need to leave.

We all here 'ships' and think maritime models. Maybe we should head back to the Air Force model.

Daniel said...

Sorry to double post, but just found an interesting concept in terms of defeating armor. (obligatory Atomic Rockets link): http://www.projectrho.com/rocket/spacegunconvent.php#Nukes_In_Space~Nuclear_Shaped_Charges
With these, nuclear weaponry would probably be wider used, as smaller warheads could be used with less fallout. I also suspect that tandem charges would show up at some point.

Anonymous said...

i no this thread i dead but:

like Daniel said it seems much more sensible to take out enemy infrastructure and production facilities and other soft targets with tactical nukes and Thors and Odins. the ability to penetrate bunkers is not an issue as hey would all be soft targets.
it could then be possible just to wait it out. the planets defenses would collapse through lack of supply, the break down of order among the general population ad even possibly the collapse of the planets government. Pre-infiltrated commandos could possibly add to the chaos.

Martin said...

Considering that according to whatever the name of that rule, that a PC will be 13 trillion times smarter than a human in 2100, and that space wars will not be reality until we live both on Earth and on Mars.

Will it not be possible to boost some thousands jet fighter sized smart drones across the solar system, let them survey the planet from high orbit, and enter into the atmosphere, find their targets, and take em out, with no loss of human life on the attackers side? No need of a starship, just a big or several small boosters for the drones.

Rick said...

Welcome to the comment threads! (A belated welcome for a couple of you!)

The underlying problem with tactical nukes is that once you cross the nuclear threshold you invite retaliation in kind, and it is by no means a sure thing that even interplanetary distances rule out 'strategic' retaliatory strikes.

Martin - by 'the rule' you mean Moore's Law? It will probably not scale indefinitely. That said, we'll probably see growing use of drones in warfare. See Space Warfare XIII: The Human Factor for a discussion with extended comments!

Falkon1313 said...

Excellent topic. Very thought provoking. I'd just like to add to Turbo10k's submarine comments:

>I don't think submarines with weaponry to rival that of ground installations feasable.

Cold War era boomers could lurk underwater for 4 months or more (more would be less comfortable for the crew, but potentially feasable in wartime). They could throw enough SLBMs to deliver 200 to 300 warheads each.

Yeah, you could build a bigger, more vulnerable ground installation, but just the two top classes, the Ohios and Typhoons alone, held enough power to throw around 6000 warheads before they needed to reload. And they had stealth and the ability to put a couple hundred meters of ocean between them and an incoming strike. They largely eclipsed the ICBM silos by being potent, mobile, and stealthy.

>Furthermore, a ship in orbit can always parachute a torpedo down to the surface, and hunt the sub in its own element.

Modern torpedos have a fairly short range and aren't that much faster than modern subs (for example, the difference between 40 knots vs 32). ASW helicopters need to get pretty much right over a sub to have a chance of hitting it with a torpedo. You'd have to have incredibly good targeting info and would probably need an insider on the sub feeding you their course and speed in order to threaten subs with torps from space.

Randy Campbell said...

Necro-Threading I know but I happened across this post and noted a "missing" element for the planetary defender against "high" ground spaceships:

Reverse "Thor" aka the "Nuclear-Verne-Gun" KK-vehicle launcher :)

http://nextbigfuture.com/2010/03/150-kiloton-nuclear-verne-gun.html

Bit hard to "dodge" a dumb-projectile coming at you at speeds in excess of 15km/s...

"Worse" is said "projectile" blows apart into hundreds of "rods-to-the-Gods" just after it leaves the atmosphere...

All of a sudden it seems an "invading" fleet might want to find a convinently larg mass to hid behind most of the time. Say like a handy Moon of some such... Of course a "savy" defender might have placed a couple of dozen "NVGs" on THAT too...

Thoughts?

Randy

Byron said...

I've been thinking about submarines quite a bit lately, and come to the conclusion that they're near-useless. We assume that detecting them from space is very difficult, if not impossible. However, blue-green lidar systems are under development that should allow fairly easy detection of submarines from orbit. One Swedish test model has worked at depths of up to 200 m. Admittedly, that was from an aircraft, but given reasonable development, it would render the oceans a lot more transparent. 200 meters is deeper then any submarine I know of is capable of launching missiles, and even communicating with submarines at that depth is a decidedly nontrivial task.
Actually killing the submarine might be harder then detecting it. Nuclear depth charges and homing torpedoes are both options, but a fast-moving submarine might be able to evade them.
My opinion as to the best option: make your missile trucks look like regular semis.
Also, another thought. How do phased arrays show up from the target's point of view? Could one of those be used to hide the transmitter?

Byron said...

One more thought on railgun-type defenses. It's been done. Project HARP was doing exactly the same thing back in the 1960s. Or similar enough that I'm convinced that it could be done, at any rate.

FBH said...

This is an interesting post, but I think you're kind of underestimating the advantage being able to up and leave gives the attacker.

Really they never need enter the envelope of the defender at all. They can come in, drop off a bunch of weapons, letting them run down the gravity well and leave again without coming anywhere near low orbit.

This doesn't even have to be some kind of nuclear annihilation strike. Assuming even marginal increases in accuracy it could easily (case in point. modern Russian tactical missiles have CEP of under one meter. Modern Chinese and Iranian ballistic missiles can potentially strike a moving ship) allow the equivalent of smart bomb strikes against enemy ground infrastructure.

So no, I don't think that an attacker is going to be all that vulnerable to a defender. A much bigger problem is that a bombing campaign like this, without nuclear weapons isn't likely to do all that much. It would be the future equivalent of say, the NATO bombing of Serbia. Effective enough at beating up the Serbians infrastructure, but not likely to bring the government to heel without additional forces.

Rick said...

Belatedly, interesting point!

On the other hand, vulnerability to mostly ineffectual attacks is not a very critical vulnerability.

Anonymous said...

On the topic of torpedoes: modern supercavitating torpedoes are airdroppable and archieve speeds well in excess of 200 knots with ranges over 10 kilometres. Question is, couldn't you just shoot it out of the air? And modern subs can launch AA missiles while submerged.

Another thing that caught my attention: The attackers fleet is in orbit. If i'm not wrong that would mean that, unless geosynchronous, they either would have to constantly expend delta-v, or have only limited time to engage each sector of ground defences, before allowing them a day to resupply. Is GEO low enough to make that a serious tactical limitation?

Finally: Strategically, the proposed method of wrecking the economy from afar reminds me a bit of medieval sieges: The defenders have fortified positions that the attackers can't easily overrun, but have to rely on a limited stockpile of supplies. To win they have to outlast the attacker's ability to continue the siege, which can be undermined by limited supply, a relief force, or by diplomatic means (for example through influencing the global opinion of the conflict, so that the attackers have to lift the siege to avoid seriously harming their image). Assuming, of course, that there's somebody else out there.

One last point (really, this time): If attacker and defender are on the same planet, then it would be impropabel that space would be part of the war, for the same reason that the US doesn't deploy their "Rods from the Gods" right now: Anything you can accomplish from space, you can accomplish vastly more cost-effective from the planet. You could drop Thors on the defenders economy, or carpet-bomb it to hell with a couple of strategical bombers for a fraction of the cost. And if you're already superior enough to be able to afford that, it's kind of overkill. Also, having people of your own on the planet should be a serious deterrent from emploaying WMDs for fear of going MAD.

Anonymous said...

Of course, another thing to bear in mind is that actually downing one of these ships is a double edged sword for the planet, depending on the size and umber of the ships, having debris raining down on the surface could be devastating, though the debris that remains in orbit would form a nice impromptu minefield for the other ships as well.

Rick said...

True! Though note that unless the ships are humongous, random impacts at anything close to orbital speed are not all that devastating. If the planet has an atmosphere, larger wreckage won't burn up entirely, but it will be decelerated, and hit at speeds comparable to an airplane crash.

Having said that, if a 100,000 ton ship impacts on a city, the city could be left in pretty bad shape.

Anonymous said...

I feel that everybody forgot important point: ground defence should be anywhere on planet to counter spaceship fleet, therefore as fleet can concentrate his firepower. It could supress defences on one side of the planet and use marines to dismantle defences on the other side.