thoughts on space battles

I had a discussion recently with friends about the various depictions of space combat in science fiction movies, TV shows, and books. We have the fighter-plane engagements of Star Wars, the subdued, two-dimensional naval combat in Star Trek, the Newtonian planes of Battlestar Galactica, the staggeringly furious energy exchanges of the combat wasps in Peter Hamilton’s books, and the use of antimatter rocket engines themselves as weapons in other sci-fi. But suppose we get out there, go terraform Mars, and the Martian colonists actually revolt. Or suppose we encounter hostile aliens. How would space combat actually go?

First, let me point out something that Ender’s Game got right and something it got wrong. What it got right is the essentially three-dimensional nature of space combat, and how that would be fundamentally different from land, sea, and air combat. In principle, yes, your enemy could come at you from any direction at all. In practice, though, the Buggers are going to do no such thing. At least, not until someone invents an FTL drive, and we can actually pop our battle fleets into existence anywhere near our enemies. The marauding space fleets are going to be governed by orbit dynamics – not just of their own ships in orbit around planets and suns, but those planets’ orbits. For the same reason that we have Space Shuttle launch delays, we’ll be able to tell exactly what trajectories our enemies could take between planets: the launch window. At any given point in time, there are only so many routes from here to Mars that will leave our imperialist forces enough fuel and energy to put down the colonists’ revolt. So, it would actually make sense to build space defense platforms in certain orbits, to point high-power radar-reflection surveillance satellites at certain empty reaches of space, or even to mine parts of the void. It also means that strategy is not as hopeless when we finally get to the Bugger homeworld: the enemy ships will be concentrated into certain orbits, leaving some avenues of attack guarded and some open. (Of course, once our ships maneuver towards those unguarded orbits, they will be easily observed – and potentially countered.)

Now, let’s talk technology.

First, pending a major development in propulsion technology, combat spacecraft would likely get around the same way the Apollo spacecraft went to the Moon and back: with orbit changes effected by discrete main-engine burns. The only other major option is a propulsion system like ion engines or solar sails, which produce a very low amount of thrust over a very long time. However, the greater speed from burning a chemical, nuclear, or antimatter rocket in a single maneuver is likely a better tactical option. One implication of rocket propulsion is that there will be relatively long periods during which Newtonian physics govern the motions of dogfighting spacecraft, punctuated by relatively short periods of maneuvering. Another is that combat in orbit would be very different from combat in “deep space,” which is what you probably think of as how space combat should be – where a spacecraft thrusts one way, and then keeps going that way forever. No, around a planet, the tactical advantage in a battle would be determined by orbit dynamics: which ship is in a lower (and faster) orbit than which; who has a circular orbit and who has gone for an ellipse; relative rendezvous trajectories that look like winding spirals rather than straight lines.

Second, there are only a few ways to maneuver the attitude of a spacecraft around – to point it in a new direction. The fast ways to do that are to fire an off-center thruster or to tilt a gyroscope around to generate a torque. Attitude maneuvers would be critical to point the main engine of a space fighter to set up for a burn, or to point the weapons systems at an enemy. Either way, concealing the attitude maneuvers of the space fighter would be important to gain a tactical advantage. So I think gyroscopes (“CMGs,” in the spacecraft lingo) would be a better way to go – they could invisibly live entirely within the space fighter hull, and wouldn’t need to be mounted on any long booms (which would increase the radar, visible, and physical cross-section of the fighter) to get the most torque on the craft. With some big CMGs, a spacecraft could flip end-for-end in a matter of seconds or less. If you come upon a starfighter with some big, spherical bulbs near the midsection, they are probably whopping big CMGs and the thing will be able to point its guns at you wherever you go. To mitigate some of the directionality of things like weapons fire and thruster burns, space fighters would probably have weapons and engines mounted at various points around their hull; but a culture interested in efficiently mass-producing space warships would probably be concerned about manufacturing so many precision parts for a relatively fragile vessel, and the craft would likely only have one main engine rather than, say, four equal tetrahedral engines.

How about weapons? Well, we have to consider just how you might damage a spacecraft to put it out of action.

Explosions are basically a waste of energy in space. On the ground, these are devastating because of the shock wave that goes along with them. But in the vacuum of space, an explosion just creates some tenuous, expanding gases that would be easily dissipated by a hull. No, to damage spacecraft systems, you can’t hit them with gas unless it’s really, really concentrated and energetic. So unless you want to just wait till your enemy is close enough that you can point your engines at him, the best bets for ranged weapons are kinetic impactors and radiation.

A kinetic impactor is basically just a slug that goes really fast and hits the enemy fighter, tearing through the hull, damaging delicate systems with vibrations, throwing gyroscopes out of alignment so that they spin into their enclosures and explode into shards, puncturing tanks of fuel and other consumables, or directly killing the pilot and crew. You know…bullets. But it sounds much more technical and science-fictiony to say “mass driver” or “kinetic lance” or something of the sort. Of course, the simplest way to implement this sort of weapon in space is just as some kind of machine gun or cannon. Those will work in space (ask the Soviets, they tested a cannon on their first Salyut space station), and the shells will do plenty of damage if they hit anything. However, space is filled mostly with empty space, and hitting the enemy ships might be a challenge. Furthermore, if the impactors are too large, the enemy could counter them by firing their own point-defense slugs and knocking the shells out of line. Therefore, I contend that the most effective kinetic space weapons would be either flak shells or actively thrusting, guided missiles. The flak shells would explode into a hail of fragmented shards, able to tear through un-armored systems of many craft at once without the shell directly hitting its target, or able to strike a target even after it tries to evade with a last-minute engine burn. The missiles would be a bit different from the missiles we are used to on Earth, which must continuously thrust to sustain flight. In space, such a weapon would rapidly exhaust its fuel and simply become a dummy shell. No, a space missile would either be fired as an unguided projectile and power up its engine after drifting most of the way to its target, or it would fire its engine in sporadic, short bursts. A definite downside to kinetic weapons on a starfighter is that they would impart momentum to the fighter or change its mass properties. Very large cannons or missiles might therefore be impractical, unless the fighter can quickly compensate for what is essentially a large rocket firing. Even that compensation might give the enemy just the window he needs…

Radiation-based weapons that burn out the electronics of a spacecraft sound exotic, but are still potentially achievable. This would be the attraction of nuclear weapons in space: not the explosion, which would affect just about nothing, but the burst of energetic particles and the ensuing electromagnetic storm. Still, such a burst would have to be either pretty close to the target vessel to scramble its systems, or it would have to be made directional in some way, to focus the gamma-ray and zinging-proton blast. But while we’re talking about focused energy weapons, lets just go with a tool that we already use to cut sheet metal on Earth: lasers. In space, laser light will travel almost forever without dissipating from diffraction. Given a large enough power supply, lasers could be used at range to slice up enemy warships. The key phrase there, though, is “given a large enough power supply.” Power is hard to come by in the space business. So, expect space laser weapons to take one of three forms: small lasers designed not to destroy, but to blind and confuse enemy sensors; medium-sized lasers that would be fired infrequently and aimed to melt specific vulnerable points on enemy space fighters, like antennae, gimbals, and maneuvering thrusters; and large lasers pumped by the discharge from a large capacitor or similar energy storage device to cut a physical slice into the enemy craft wherever they hit. Such a large weapon would likely only be fired at the very beginning of a battle, because the commander of a ship with such a weapon would not want to keep his capacitor charged when it might unexpectedly blow its energy all at once once he’s in the thick of things.

Deflector shields like those in fiction are not possible at present, but it would still make sense to armor combat spacecraft to a limited extent. The spaceframes of the fighters would likely be designed solely for the space environment; the actual ships would be launched within the payload fairings of a rocket or assembled in space. If launched from the ground, armor must be minimized to reduce the launch weight of the spacecraft. But if built and launched in space, it would make sense to plate over vital systems of the vehicle. Thick armor would prevent flak or small lasers from piercing delicate components, and might mitigate a direct strike from a kinetic impactor or heavy cutting laser. However, the more heavily armored and massive a space fighter is, the more thrust it will take to maneuver in orbit and the more energy it will take to spin in place. (Here’s where computer games get space combat all wrong: the mass of a huge space cruiser would not place an upper limit on the speed of a vehicle, but it would reduce the acceleration a given engine could produce compared to the same engine on a less massive vehicle.)

I’m assuming that we’d have some intrepid members of the United Earth Space Force crewing these combat vessels. Or, at least, crewing some of them – robotic drone fighters would be a tremendous boon to space soldiers, but the communication lag between planets and vessels in orbit would make the split-second judgments of humans necessary at times. (Until we perfect AIs… but if we’re giving them the space fighters from the beginning, we deserve the robot uprising we’ll get.) The crews will hardly be sitting around nice conference-room command bridges with no seat belts; nor will they be standing upright in slate-gray console pits with glowing glass displays all over. It’s not even a good idea for them to have windows, which would be vulnerable to flak and could give the crew an intense sense of disorientation as the spacecraft maneuvers, and could give them tremendous trouble adapting to rapid changes in light levels as the ship rotates near a planet or star. No, they should be strapped into secure couches and centrally located in the most protected part of the spacecraft. They should also be in full pressure suits, and the interior cabin of the spacecraft should already be evacuated – to prevent fires, or any secondary damage if all the atmosphere rushes out a hull breach. This also reduces the need for escape pods. Camera views from the exterior of the ship and graphical representations of the tactical situation would then be projected directly onto helmet faceplates.

Now, for the final word, let’s say the United Earth Space Force defeats the Martian rebels in orbit. What do we do to hit them on the ground? Well, strategic weapons from space are easy: kinetic impactors again. You chuck big ol’ spears, aerodynamically shaped so they stay on target and don’t burn up in the atmosphere, onto ground targets and watch gravitational potential energy turn into kinetic energy and excavate you a brand-new crater. At some point, though, the imperialist Earthlings probably want to take over the existing infrastructure on Mars. Time to get out the Space Marines!

It’s not terribly expensive or difficult, comparatively speaking, to get people from orbit down to a planet surface. You fall. This is the purpose of a space capsule. What’s really, really, prohibitively difficult is getting them back up again. So, the victorious orbital forces would have to bring in a transport ship chock full of Space Marines and drop them all at once in little capsules (little because they can only be so big for the atmosphere to effectively brake them, and because you don’t want all your Marines perishing in some unfortunate incident). Some orbital forces would remain in place to threaten the ground with bombardment and give the Marines a bit more muscle, but really, the ground-pounders are going to have to be pretty self-sufficient. If they ever want to come back up, they would have to build and/or fuel their own ascent vehicle. (This is the problem facing any NASA Mars efforts, too: getting back up through the Martian atmosphere is much harder than any of the lunar ascents were.)

[ADDENDUM, 14 Dec 09: What would combat spacecraft end up looking like?

Well, there are good arguments to have both large and small spacecraft in the Earth forces. A big spacecraft could have a lot more armor to keep its systems and crew safe, more room for large fuel tanks and electrical power supplies, and larger mass to resist impulses from cannon recoil. However, a smaller craft would be less visible to radar, more maneuverable, and could achieve higher accelerations for constant engine thrust. As with just about any military force, the role of the craft would be tailored to the tactical operations required, so the Space Force would probably include several sizes of craft.

Enemies could come at your ship from any direction in space, which means that you would want to react, strike, and counterattack in any direction. So, you would either have to mount weaponry all around your starfighter, put the weapons on gimbals so that they could rapidly point in any direction, or make the fighter maneuverable enough that it could rapidly point in any direction. Gimbals would be a bad option, because they would introduce points of increased vulnerability, unless they could be very well-armored. I conclude that the big ships would have many weapons, pointed in many directions; the small ships would have a few weapons, with the main weapon systems pointed in one direction.

Maneuverability (angular acceleration) you could achieve with gyroscopes, or by mounting engines or thrusters away from your fighter’s center of mass. For the highest levels of maneuverability, the spacecraft should be close to spherical and these engines should be as off-center as possible, which might mean putting thrusters on long booms or struts. The problem with this kind of Firefly-like engine layout is that it becomes very vulnerable. If a fighter can achieve high maneuverability with gyros, those are probably the best option.

So, I think the small fighter craft would be nearly spherical, with a single main engine and a few guns or missiles facing generally forward. They would have gyroscopes and fuel tanks in their shielded centers. It would make sense to build their outer hulls in a faceted manner, to reduce their radar cross-section. Basically, picture a bigger, armored version of the lunar module. The larger warships would also probably be nearly spherical, with a small cluster of main engines facing generally backward and a few smaller engines facing forward or sideways for maneuvering. Cannons, lasers, and missile ports would face outward in many directions. On a large enough space cruiser, it would even be a good idea to put docking ports for the small fighters, so that the fighters don’t have to carry as many consumables on board.

I think it’s time to sketch some pictures and write some stories!]

I certainly hope we don’t get into any space wars. Human nature being what it is, though, and given how scarce a lot of resources really are on the scale of a solar system or a galaxy, I don’t think it’s out of the question. I would like to think that when we start colonizing other worlds, we will be sufficiently enlightened to do so from on board the Ship of the Imagination, and not as futuristic conquistadores. Still, the part of me that loves science fiction has fun with these thought experiments.

93 thoughts on “thoughts on space battles”

  1. “No, a space missile would either be fired as an unguided projectile and power up its engine after drifting most of the way to its target, or it would fire its engine in sporadic, short bursts.”

    probably a bunch of them could be placed in some cleverly calculated orbit around the earth (or later sun), and deployed on notice/in emergancy just by correcting their course while keeping kinetic momentum

  2. The equivalent of nuclear mines with small maneuvering thrusters is probably a great way to conduct space warfare. Simply release them with some momentum in the direction of the invading forces. Inertia on both sides will keep things on target, and the relatively light mass of the mine with the thrusters can get them close enough. The mines get close enough to the invading ships, spin until they are able to point their focused detonation (xray laser style) point at the invading ship and then explode.

    More than likely you’d see one or two large ships coming at you instead of a swarm of smaller ones. That’s just the economy of scale.

  3. Chad: I think it might be even more effective to have the nuclear blast directed *away* from the target ship. That way, instead of the explosion dissipating into the intervening space, it would propel the mine structure towards the target at staggering velocity, right after blinding the enemy sensors.

  4. Wow, I’ve seen this discussion like a dozen times already. A couple things to note:
    1) You’re going to be spotted in space, but not via radar, rather your IR signature. Against the backdrop of space, even a small ship with basic life support is going to be visible at planetary ranges. So going small isn’t going to help you in deep space. Now, in lower orbit where a planet occludes your IR signature, smaller ships would benefit.
    2) Lasers require focal arrays (usually mirrors) in order to convert relatively low power (non ship melting) over a broad area down to high power on a small spot. If you can damage a ship at X distance, you can blind it at 100 X using the same laser. One of the first targets is the opponent’s focal array. This tends to lead to both sides firing up their lasers for blinding purposes at several months prior to contact. Eventually, one side or the other will pick up too much heat gain on their focal array and ruin the mirror, which is a mission kill.
    3) Basic survival in space requires radiation shielding and electronics hardening such that the radiation from a nuke would be insignificant compared to a coronal mass ejection.
    4) Your top speed is going to be limited by your sensors not your thrusters. Space is MOSTLY empty, it is not entirely empty. The faster you go, the better your sensors need to be in order to avoid incoming space debris. If you can see a pebble at a few kelvin at five seconds out, then you can see a warship (billions of times larger signature) at months away.

  5. It would be interesting to see how the economy of tactics would work out in an engagement around a planet. As you point out, the lower, faster orbits would be prized, but, depending on the planetary body in question, there is a limit to how low fighters could go before they have to contend with increased atmospheric drag. I wonder if the advantages might be great enough, though, that we could see a special class of fighter designed to be able to enter and fight from the upper atmosphere.

  6. Oho, an upwards-weaponized U2, as it were? Interesting idea. You could always launch Pegasus missiles at low orbits.

    Citizen Joe:

    Hmm, interesting points. While I agree that IR detectors would be important, I don’t think they’re necessarily going to be more important than radar. That’s because, first, we’re pretty good at cryocooling and IR shielding (a fact that both my research and all the IR space telescopes rely on!) and, second, we have the capability now to image planets (e.g. Mercury, from Earth) in radar but not IR. I’m talking about an active radar scan, looking for reflections of a signal from your ship.

    Yes, you could use a killing laser to blind at a much longer range, but that’s not guaranteed to be effective, because the other ship could have shielding over its critical systems. The “focal array,” as you put it, is probably a lens at the laser aperture if these space lasers will be anything like current ground lasers. The laser cavity, power source, and lens would be buried in the bowels of the ship; a beam path of mirrors or optical fibers could carry the laser energy to a turret on the hull to prevent enemy lasers from doing exactly what you refer to.

    Yes, you’d have to shield against CMEs, but those shields might not encompass the entire ship. You’re right, though, that the radiation from a nuke going off is probably less of a concern than laser hits – or even natural sources.

    Finally, while space is “only” mostly empty, as you point out, that doesn’t really put a damper on your speed unless you get relativistic. Even if you fly through the Asteroid Belt at 1% lightspeed, you are extremely likely to have no incidents.

  7. Interesting article. Have you read any of Jack Campbell’s “The Lost Fleet” series? While rather more futuristic than much of what you’re positing, it does still rely on kinetic impactors as the primary weapon, and emphasizes the importance of orbits and trajectories, and the effectiveness of orbital bombardment.

  8. Cryocooling doesn’t help (it may actually aggravate the problem). The heat doesn’t just magically go away, you have to get rid of it somehow. In space, that means radiating it out. That means visible IR signature. You can cool part of your ship (down to 3 K?) at the expense of radiating about 4 times as much heat in some specific direction. Another option, which I find more valid, is to push an ice asteroid ahead of you and dump your waste heat into it. You’re still very visible from the other side of the asteroid, but the idea is to bring your own occlusion.

    If you’re using robotic ships, you can just take your chances and accept the rare losses. When you put people on those ships “acceptable losses” is political suicide. The speeds at which a pebble could be mission kill are in the planetary orbital speeds (30 km/s). The mess we have in orbit of Earth is a big problem. Various armors (including the Whipple shield) can be effective against these micro meteoroids, but as you start traversing the distance between planets. As a matter of reference, our fastest manned vehicle has managed about 11 km/s while our fastest unmanned vehicle has managed about 70 km/s. 1% of C is 3000 km/s. The ISS orbits Earth at about 7.7 km/s while the Earth orbits the Sun at about 30 km/s. The worst case scenario would be an Earth crossing asteroid perpendicular to the plane of the ecliptic. Both the Earth and the asteroid are moving at 30 km/s but 90 degrees to each other. End result of about a 40 km/s impact give or take another 7 for the orbital speed around Earth. Kinetics start doing damage equivalent of TNT at about 30 km/s and Nuke equivalent damage around 190 km/s. Fortunately, most things are orbiting in lock step with each other (or they would have already impacted). However, when you start moving around in a ship, you’re interfering with the natural order of things.

  9. House: I haven’t read “The Lost Fleet,” but I’ve seen other Campbell stuff, so I’ll put it on my list!

    “You can cool part of your ship (down to 3 K?) at the expense of radiating about 4 times as much heat in some specific direction.”

    Precisely. You can dump your heat out in the direction opposite to your enemy, and you’re invisible.

    As for evading orbital debris, I think you’re getting your issues confused. While it is true that orbital velocities are very fast (by the way, New Horizons is the fastest manmade object, with a peak heliocentric velocity of around 27 km/s), you would actually be much safer in interplanetary space than in orbit around the Earth. Even the density of material in the middle of the main Asteroid Belt is tiny, compared to the debris situation around Earth, thanks to the recent Chinese satellite destruction test and the Iridium-Cosmos collision. So, yes, the potential damage from a collision is large, but the likelihood of such a collision is very small – probably a smaller risk than being on a ship that sinks in a hurricane.

  10. The space fights in Walter Jon Williams’ “dread empire’s fall” series are quite interesting; he assumes a technology that produces large amounts of antimatter, which is used to accelerate ships and missiles to nearly arbitrary degrees, only limited by human endurance. Lightspeed information delays are an important factor in his stories.

  11. Also interesting would be the “Antares Trilogy” by Michael McCollum. He is a graduate of Arizona State University with a degree in Aerospace Engineering. The Books are not very new, but the Spacefights sound very “realistic”.
    Its pure military SciFi (wich i did not like till that point), but because of the very realistic description of the maneuvers it was a pleasure to read. And besides the realism its really bombatstic. =)

  12. This guy and anyone else interested in this should try out, as massive multiplayer online game set in a solar cluster a billion astronomical units from earth. You play as one of many capsuleers, defined as a person who pilots his or her space vessel inside a pod filled with advanced sensors and neuro-embryonic fluid. You can find out more by watching the video Incarna on you tube. Almost all of eve is scientifically correct, while being allowed to remain “fun”. Email me in the game my player name is dever rulk. Have fun, and happy criticism!!!

  13. You forgot the nuclear Orion drive from “Footfall”. Earth can quickly throw a battleship (or a spaceship of similarly large mass) around the solar system, with nuclear explosions. Irritating small ships get cooked with X-ray lasers which are powered by the main drive’s flash.

    Earth might avoid ground combat by dropping asteroids on Mars. However, Martians would be first in the asteroids so Earth might have the greater worry from falling rocks.

    Earth would have the advantage at present because Earth already has nuclear bombs and manufacturing facilities. But Mars has more fissionables available in the long run, because Mars has easier access to the asteroid belt. If there is a long period before the war, Mars may have the nuclear advantage… whether they use it for their battleships or to drop rocks on our nest.

  14. Read about this on Gizmodo. I really enjoy all of the points you bring up, and I like your attention to detail when referring to the movies and shows we have all come to know and love. I really would wish that you could/would draw or photoshop what that “perfect” starfighter might look like, just to see how wrong everyone is. Definitely going to bookmark your site, keep up the good work, man.

  15. Thank you for a very interesting read. I’m constantly dreaming about the possibility of exploring space in big ships, but I’m thinking the reality will be much less romantic. I’m far from an expert, but don’t you think something like swarms of self-replicating Nano-bots would come around the corner way before we have the ability to move huge mass loaded with people very far? By combining something as small as nano-bots together with information via laser or radio waves we could explore much more in many directions at the same time. Nano being small we also need to use much less energy and hopefully we might be able to go beyond the speed of light (I read somewhere that the speed of light might have been different in the past, leading to the idea that we might be able to change it) although it’s constant in the Universe today.

    We could send the bots in search of building blocks at locations sustainable for some kind of Human 3.0, build and then move on(since they are self-replicating only a few needs to stop on a target, the rest could just move on). Even with the speed of light this would take around 100 000 years though.

    Thanks again and please do post sketches of ships. I have been thinking myself and have an idea for a “soft” version being launched from the ground and placed in some kind of hard shell in orbit.


  16. An idea about defenses versus low powered energy weapons:

    I’ve heard of sand casters in popular science fiction ( physical contraptions that fire canisters of sand or some other material to disperse the energy of a laser ) so that got me to thinking about a reactive armor that does the same thing.

    You take some kind of highly reflective particulate with a relatively high melting point and pack it into a foam interlaced with explosive beads that burst when heated. The beats burst in the armor foam coating, creating a cloud of dust that expands immediately from the spot impacted by the laser.

    With the exception of accelerating away from ones own cloud, would this actually be a good idea?

  17. The Orion propulsion system makes a pretty cool appearance in “Anathem,” as well. It’s always struck me as a tad…impractical…though I guess not much more so than any other ideas being thrown around here. You certainly wouldn’t want to use such a drive until you got into interplanetary space, to avoid slinging radiation all around the planets you’re interested in.

    Mike: some of the other grad students in my research group have been looking at that very option. We would print spacecraft with extremely simple processors, instruments, and communications on silicon chips, run them off in batches of thousands or millions, and daisy-chain them together in a communications net. The radiation pressure from the Sun would be enough to push them away from the Earth and towards other planets or even stars. It’ll take some serious advances in technology to get them to do anything on planet or asteroid surfaces, however, such as building other spacecraft. It’s still quite a challenge, right now all our group is looking at is sending up a chip-sized verison of Sputnik that goes beep-beep-beep!

    Chad: Probably a good idea. I recall something similar in the background story material for the game Homeworld; that the ships’ armor had an outer ablative layer that puffed out into gas which would absorb or disperse laser beams. If you knew the wavelength of the enemy lasers, you could also put mirrored surfaces on your craft
    (since it’s the *absorption* of laser light that would heat hings up), but then your ship would be more visible in those wavelengths.

  18. @Joseph, the problem with the Orion propulsion system is that it is best at lifting huge payloads from the planet’s surface into orbit. Which is exactly the last place you’d want to be spreading fallout. Especially if the planet is Earth.

    Once your spacecraft is in orbit, there are lots of propulsion systems with superior specific impulse to Orion. So there is a good reason not to use Orion for liftoff, and no good reason to use Orion in space.

    I’ve seen some papers that claim that the fallout from an Orion liftoff is minimal if the launch pad is covered in sheet iron, but none of the authors have offered to live down wind of the launch site.

  19. I’ve written a pen and paper boardgame on this topic, and it covers most of the issues raised. It’s currently in development for a second edition, due out next Spring.

    Joe is correct on nukes – anything currently envisioned that will keep humans alive in the radiation environment of interplanetary space will make enhanced radiation from nuclear devices a non-issue. By the time you’re close enough that the neutron flux from a blast will penetrate radiation shielding with 1/r^2 fall off, you’re close enough that the X-rays will brehmstrallung and cause the armor to evaporate. As near as I could figure from unclassified sources, a nuke had to get to about 3 km, minimum, to be effective.

    On lasers and sensor blinding – this looks to be an arms race; I’d expect that it would stabilize in a dynamic equilibrium over time.

    The problem with IR signatures is MUCH more challenging than “directing the heat away”.

    Two things make this unpleasant. The first is that radiators are more efficient by a 4th power law when running at high temperature. Doubling the temperature of your radiator for a given surface area increases its efficiency by a factor of 16. That also makes it brighter, and can reveal important information about your onboard power supply, because the optimum temperature of your cold side of a heat engine cycle is about 0.75x the temperature of your hot side. So, if someone has a radiator at 1600K, that means that their reactor runs (normally) at 2000K.

    The second problem is just how much heat is generated; for every W of useful power you generate in a space environment, you’re going to have dissipate 4W of waste heat. You’re also going to need lower temperature radiators for the crew compartment and that all adds up into mass limits, and big vulnerable surfaces to be shot at. (Higher temperature radiators can, for the given emissions budget, be smaller – and somewhat more durable).

    Likely types of radiators are liquid metal droplet sprays – take lithium or sodium (both of which have high specific heat), liquify them, put a very faint charge on them, and spray them as droplets towards a catcher on the back of your ship, which has a charge to catch them. You may or may not want to make these retractable. If you’re worried about them getting shot, you put them into diamondoid composites.

    So – the total surface area of your radiators is going to be huge, compared to the surface area of your ship, they’re going to be very hot, and while you may be able to run with them off for a few hours, tops, you’re going to be doing your approach (assuming a low thrust burn) of about 280 days from Earth to Mars.

    If you’re doing a faster transit with higher thrusts (a brachistone orbit), you can do Earth to Mars in about 40 days…but that rocket you’re using will be a NAKED EYE VISIBLE star of a magnitude ranging from -1 to -4, that visibly moves across the sky by a few degrees per hour…

    With a spectrum that is unlikely anything else in the solar system.

    You’ll also be able to observe the emissions spectrum of the rocket, get a good idea of how fuel efficient it is, and how much mass is being thrown overboard; correlating that with the observed motion of the payload, and you’re sitting on a pretty solid estimate of the mass of the ship.

  20. Correction to the above:

    Your optimum temperature for the cold end of a heat engine cycle when you can only dissipate heat by radiation is about 0.75x the temperature of the hot end of the heat engine cycle.

  21. Great stuff, Joseph. Thanks for sharing your thoughts, ran into this on Giz as well.

    There’s been a good number of links and works mentioned. I’d like to throw one other out that I used to work on as I had time – . Some work on superintelligence (IE, beyond human) and highly plausible to vaguely plausible future weapon systems such intellects might come to bring to play.

    As previously mentioned, heat (IR) is the sensor channel of choice outside atmosphere. Even relatively low power systems will need to vent heat, something that’ll be useful in determining just what kind of mares’ nest waits for you. The next may be some form of gravitic sensor (see for modern day capabilities) if you can wait long enough – can’t hide moving mass, and all mass moves if you pick an appropriate set of frames of reference. It’ll just take a while for the sensor to pass far enough. (“C. It’s the law”)

    Orbital mechanics in gravity wells are going to be useful, but don’t forget that your orbital mechanics have no firm ‘roof’ – someone on newtonian courses that graze your gravity well won’t necessarily behave as per an orbit. As such, any non-trivial defense of a stationary target (read, star & system) will require a *LOT* of highly visible energy expenditure across broad swathes of space, barring some form of FTL and/or unobservable/unobtanium drive. Yes, once things are in a nice orbital pattern, there’ll possibly be some savings, but you’re still going to have processing going on -which requires power, and thus generates heat.

    Another major difference may well be the lack of self-preservation in non-sentient (but ‘brilliant’ or all-but-sentient) systems designed as such. The mass wave tactics used when commanders didn’t care all that much about their troops (or had no other effective measure) may make a comeback, especially if other technologies like some future version of RepRap or other desktop manufactory come into reality.

  22. One of the plausible futures for space combat is that humans won’t be doing it; our near AI autonomous drones will be. Modeling space maneuver outside of a low-Earth orbit context is something that any computer made in the last decade can probably do passably.

    It tends to result in very boring movies and games.

  23. I agree with Ken Burnside’s comment about drones. Traditional spacefighters like in Star Wars won’t exist, especially when fighters in aviation today are on the way out. Everything will be drones, missiles (the difference from drones being that missiles are not remotely-piloted) and directed-energy weapons.

  24. There’s a potential issue with the use of gyroscopes for maneuvering that you don’t really address. Using a gyro system for maneuvering your ship may be more damage-resistant, a gyro big enough to spin the ship rapidly enough to be useful would also add a great deal of mass to the ship and while I’m no NASA scientist, I know enough about orbital mechanics to know that thrust-to-mass is a Really Big Deal. Something like a Babylon-5 Starfury might be more fragile, but it would also have a lot less mass to push around and thus, at least theoretically, would be able to pile on a lot more delta-V, make itself a more difficult target, and have a larger potential radius of action.

  25. I see that Ken and Winchell already found this place so no use to link thier respected sites again but I recomand them to anyone who is intrested in space combat.

    @Ken, mate what are the chances to be able to get the 2nd ed in PDF format?

  26. John: I forgot about thermal issues in my post; you’re right that IR sensors would be desirable. I think they ought to be part of a suite of sensors, which probably also includes radar because we are very good at radar technology. Gravity sensors capable of the resolution necessary to find individual spacecraft might be a little sensitive for combat vessels… I don’t understand your point about orbits. A Newtonian course passing by a gravity well can, after all, be considered a hyperbolic orbit. I’m also not sure what strategic point comes of that, except that the relative positions of planets in a star system will dictate the most energy-efficient and faster approaches from one planet to another.

    James: yeah, I agree that drones would be incredibly important. However, it still makes sense to me to have a couple manned command and control ships for the strategic input they would provide, and to cut down on communication time with planets. That, and it makes for slightly fewer dramatic opportunities for fiction, in my opinion. But the real situation would likely involve a lot more remote drone engagements than anything else, just as the USAF is now shifting to more drone-based operations.

    Samuel: CMGs could be massive, or they could have a high spin rate to achieve some desired angular momentum. Reaction wheels on spacecraft are pretty common today, and there are actually some very good reasons why you would want some thrusters anyway if your primary maneuvering system is based on CMGs or reaction wheels. The major downside to having thrusters as your maneuvering system is that they require propellant, and when you run out of fuel, you lose the capability to maneuver, which is bad for not only staying in the fight, but for engine burns and thermal management as well. Now, a Starfury-like or Firefly-like arrangement (where your engines are mounted on long booms) would potentially give you the ability to put a lot of torque on your craft, but it would also add a lot to the inertia. I decided to advocate a nearly spherical inertia for better maneuvering properties. If there are ever starfighter engineers in the future, they will have to figure out what design represents the best trade.

    There was a comment here that I’ve moderated out, not because I disagree with the point it makes (that thinking about space *combat* should not be the first thought of those interested in space and may be due in part to the fact that I’m American), but for language and tone. If you posted that and want to clean it up, go right ahead. In response, I would say that this is not the first speculative blog about space I’ve made, but it is the first to involve combat. I’m not just interested in supporting peaceful space exploration, but in fiction, which is where I hope combat like this will forever live. And after all, if we’re not coming up with such fictions, how can we anticipate how to prevent wars from breaking out?

  27. If you have never seen it, you should check out the game Attack Vector: Tactical by Ad Astra Games ( The game takes pretty much all of this article into account. Only license on reality the game takes is on assumption of a workable fusion torch drive technology. This game has a lot of tactical depth, with players having to manage manuevering, fuel supply, power, heat, different weapon systems, etc. Gives a good feel on what space combat might really be like someday in the not too distant future.

  28. What about more exotic forms of attack. For example, get a drone to attach to an attacking ship, infiltrate their control network, and then, for example, fire all the manoeuvring engines simultaneously. It might not destroy the ship before fail-safes cut in, but should put it out of action for a while.

    This presumes that we understand the technology of the attacking fleet and have a Jeff Goldblum available to hack it 🙂

  29. Clearly, that will result in a Jeff Goldblum arms race!

    Getting spacecraft to dock autonomously is actually quite difficult compared with getting a drone to just ram into the other ship, so you probably wouldn’t see such limpet-like attacks. You have touched on another aspect that I didn’t address, though: the information warfare part of space combat. I would imagine that since each side would depend a great deal on their communications, sensor, and computer systems, that efforts to infiltrate those systems would be a big part of space engagements.

  30. Why bother with a complicated drone so? Use one of the flak shells you mentioned to let off some of limpet mines close by. The advantage to this being that there will be lots more pretty shards for the ships crew to worry about, and they mightn’t spot the limpets attaching.

    If drones become a popular way of attacking, methods of disrupting or taking them over are going to suddenly prove very popular. Just have a look at what’s already happening with UAVs!

  31. I still have a really hard time seeing armor as a valid option for spacecraft. Throughout history, it has always been easier to build more powerful, more accurate weaponry than it has to create more effective armor. With as critical an issue as mass is to making any sort of spacecraft do anything, it just doesn’t seem like a good way to go.

    If a spacecraft is going to have defensive systems at all, it seems to me that active defenses will always be a better option, either through point-defense weaponry to shoot down incoming projectiles and drones, or through electromagnetic shields of some kind that can provide a strong enough barrier without adding unwanted mass to your ship. Naval ship design gave up on armor by the 1950s, and even modern armored vehicles are starting to move in this direction, since it’s far too easy to use a cheap RPG to penetrate the armor of a multi-million dollar Bradley or Striker. Better to use a device that can detect the RPG round incoming and swat it down, and there are a number of devices coming into service now that do just that.

    Honestly, I’ve always envisioned space combat to wind up being very similar to submarine warfare. You have a fully 3-dimensional environment to operate in, and the pace of combat is driven almost completely by stealth. Modern submarines operate in a hostile, fully 3-d environment, and have almost no use whatsoever for armor, since the weapons being deployed against them are powerful enough that any amount of armor that would be useful, would also make the vessel too slow to do its job. Instead, they rely on stealth to remain undetected, and do their fighting primarily though the use of smart-weapons.

    I’ve always envisioned space combat operating according to the same rules. Your manned capital ships rely as much as possible on stealth and emissions control to remain undetected, and battle by proxy using smart-weapons and drones. Without the necessity to care for the physical requirements of a human passenger, an unmanned, computer-controlled drone doesn’t have to devote mass to life-support systems, and can accelerate at rates that would be fatal for a human occupant. A capital ship can deploy these things in large numbers and at great distance, and if real-time control is necessary, you can deploy stealthy manned control-fighters acting as forward observers that dive in along with a swarm of unmanned combat vehicles and control the battle from close-in while not giving away their position.

  32. Awsome topic and discussion… I wish I could add more, but I am not a scientist, but I have been looking for this discussion by experts for a while.

  33. A key question to ask about combat maneuverability: how exactly is this supposed to be useful to you? Outside of quite esoteric technological assumptions, beam weapons are likely to have effective ranges of less than 0.1 light-seconds, and in the 0.2 second lag between what the sensor sees and when the shot arrives, a 1G ship can move by all of 20 centimeters, which won’t dodge much. The situation is worse for evading missiles — the optimal impact solution for a missile in space is very simple (compare the target’s motion against the starfield. If it’s zero, you’re on target, otherwise thrust in the direction of its apparent motion), and basically means that missiles can’t be evaded unless you can out-accelerate or outrun them. As missiles don’t have much to do other than be a rocket carrying a payload, out-accelerating is unlikely, and outrun will use up huge amounts of fuel. In terms of turning to face threats, lasers will have already hit you by the time you’re aware of them, and other attacks will generally offer minutes, hours, or even days of warning, thus not requiring a lot of angular forces.

    Also, the primary likely weapons for spacecraft (missiles and lasers) can fire just fine from a fixed location. For a missile, just kick it out the tube, it then turns and accelerates towards the target. For lasers, the laser itself doesn’t have to move, you just need to use optics to route the beam to where it’s needed.

  34. I suspect that combat maneuverability will only be useful for very small manned vessels, at ranges where the 8-10gs of acceleration they can apply can move them out of the targeting solution of direct-fire weapons; or for equally small unmanned weapons systems who can apply a lot more delta-V. If the state of the art in terms of weaponry is primarily smart-weapons, then they’ll have to be agile enough to dodge point-defense fire to hit their target, or stealthy enough that they can’t be detected until they’re close enough to do their damage. Even though the chances of any given single smart-missile getting past a radar-guided point-defense gun aren’t so hot, especially if it’s an energy weapon, if you can throw more missiles at a target than they have guns to shoot them down with, your chances are pretty good at getting something through. This is the reality of modern ship-to-ship combat, and moving things into a three-dimensional space doesn’t necessarily change things that much.

    Larger capital craft will also need to able to apply lots of Delta-V, although in their case it’s likely to be less for the purposes of dodging fire, and more for the purpose of being able to get from where they are to where they need to be in order to get their job done. Just being able to match orbital trajectories with an enemy craft to the point where you can shoot at them effectively is likely to be a tricky business, and a vehicle with a lot of armor mass is going to have a really hard time bringing the fight to an enemy. I can see orbital stations being pretty well armored, but not anything that needs to go somewhere to do its fighting.

  35. re: Joseph, 18 December 2009 at 10:40

    Thanks for the reply.

    Re: Radar – it’s a double-edged sword. Yes, we’ve gotten good at it, but it’s also a decent self-illumination that will be suitably rewarded. I’m thinking along the lines of ‘wild weasel’ air-to-air and air-to-ground missions…

    Perhaps a radar drone that is little more than an emitter, with the receivers/processing on the main vessel? That’d be reasonably cheap and potentially survivable against some of the threats mentioned here. (There would be some interesting angularity issues for the receivers to handle, especially if the emitter is moving with respect to the receiver)

    re: LIGO et al – agreed in hot combat time, but think of them more as determining enemy order of battle/capabilties prior to active ‘hot’ conflict. Intel!

    I agree that Newtonian hyperbolic orbits are well within the range of options – my point is that most people think more along the lines of elliptical paths with a mass at one focus when they hear ‘orbit’. At least, that’s been my experience. Thus bringing up the option was, I hope, somewhat useful.

    I agree with some of the other comments – gyroscopic attitude adjustment comes at either a low angular rate of change and/or high percentage of net mass. Commo/sensor duels (EM, ECM, ECCM…) will be an extremely non-trivial portion of the conflict.

    Finally, while nukes aren’t going to likely be very useful as offensive weapons as per the main body, I would suggest that they’ll remain very useful in defensive roles along the lines of flares, chaff, and dazzler devices/techniques.

  36. John-

    I don’t think radar will be quite as bad as you imagine. Yes, it will announce your presence to the enemy – but they can at best only extract directional information from the radar ping, since they have no way of knowing how long it took to travel before it hit them. Even getting that directional information requires a directional antenna, and localizing the signal down to a precise angular position would be best done by a dish-like receiver, which only covers a narrow angle of sky. So such devices could be used to pinpoint e target ship after its general direction has been established.

    I also don’t think IR is as good as everyone seems to think it would be. The argument that IR would be the best sensor choice basically goes as follows: Ambient space is ~2.7 K. A spacecraft has engines that generate a lot of thermal radiation when fired, and is otherwise full of humans who like temperatures of ~290 K. A 290 K object will throw a lot of radiation into a 2.7 K environment, and the enemy will be able to see that radiative power. However, while I could make arguments about radiative shielding (such as MLI) or absorbing the thermal energy temporarily in a phase change (see how they cooled the Apollo LRV batteries, for example), the problem with IR detection is actually the detector. You don’t just get to immediately “see” any radiation thrown your way. For a good signal-to-noise ratio for detection, you have to avoid the IR telescope optics throwing any thermal radiation onto the CCD – which means you must cryocool the optics. Modern space telescopes can do this passively (e.g. Sptizer), but that is because they don’t have thermal sources like humans or big engines. So, basically, my point is that if you want to detect a spacecraft in IR, you’re going to face a similar set of challenges to hiding a spacecraft from IR!

    Orbit dynamics enter into my research, so I am quite familiar with the different types of orbits available. If you want some weirder options to look at, check out non-Keplerian three-body orbits! Using some of those techniques, aliens could hide an armada in a halo orbit behind our Moon, entirely without us knowing!

    Anthony, Samuel-

    Maneuverability would be important both to aim and fixed weapon systems like cannons or lasers without coarse-adjustment optics, and to aim the spacecraft engines to quickly perform orbit maneuvers. It’s also possible to use maneuverability to mitigate laser damage – spin your spacecraft so that the beam doesn’t spend enough time on any one part of the spacecraft surface to heat it beyond tolerance.

    For missiles, in particular, keep in mind that those missiles also must carry propellants and must rapidly exhaust their propellant supply in carrying out any maneuvers. They couldn’t just thrust constantly the whole time from launch to impact. More likely, there would be a major burn right after launch to get them going, followed by either a series of small mid-course corrections or a period of inert flight before the missile exhausts all its propellant in a final, guided dash toward impact. So out-running or out-maneuvering a missile is a distinct possibility with relatively small maneuvers, as long as your ship can “out-propellant” the missile! Even if such out-maneuvering is not practical, given the situation, maneuvering capability could be an important defense element against missiles as it would let your ship bring the right countermeasures (e.g. lasers, flak guns) to bear and then move out of the way of the missile debris.


    Yeah, several other people on Gizmodo, and Winchell himself here, have pointed that out to me. I like the site, it’s pretty comprehensive….The downside seems to be that it sticks to the tropes of Golden Age sci-fi (e.g. poo-pooing staged rockets? disregarding information warfare? disregarding ion, electric, or VASIMR propulsion?) and it’s willing to take SF stories as primary sources.

    I have to admit that I didn’t do any “research” into my initial post, other than my own experience with physics and spacecraft engineering research. That’s because I was just musing about these ideas, and didn’t have any particular goals in mind. Little did I know the attention I would receive!

    Finally, every treatment of sci-fi space combat, mine included, is missing two things: practical implementation, and a live opponent. Between getting these technologies to work, and trying to counter our opponents’ technologies, we would likely uncover tactics and technologies currently unknown. In my initial post, I tried to restrict myself to technologies that would work now, and counters to the most obvious interplay. But I obviously didn’t take this out into the realm of “research,” and I’m probably not going to.

  37. The radar issue is a bit more complicated than has been addressed here. Even without any stealth technologies at all, active sensors can always be detected from further away than they can detect things themselves. This has been a fact of naval warfare ever since the invention of radar and sonar, and is unlikely to change in space. Using active radar or sonar is like walking around in the dark with a flashlight. It gives you very precise sensory data, but the flashlight can be seen much further away than they light it casts can generate a visible return. Using active sensors to locate targets is therefore only a good option if you’re certain the enemy already knows where you are, and is within detection range.

    This is where radar drones would come in, devices that can do your searching for you without revealing your own location, and provide you with a firing solution without giving your opponent one on your own vessel.

    Honestly, I think the way you’ve described missiles being used is likely to be the way spacecraft engage in combat as well; Using their engines to put themselves into an orbital trajectory towards where they expect the engagement to occur, and then running with full emissions control to remain hidden until they’re sure they’ve detected something to shoot at. Sensor and weapons drones will duel with each other, with each side focusing on trying to locate the opposing capital ships without revealing their own location until it’s too late.

  38. You know, you really have me wondering. I am not a scientist, but I wrote a story once, wherin, as ridiculous as it is, present day (ish) astronauts had to attack a space station, and the only thing they could gerrymander on short notice as a weapon was a large gun – held by a shooter in a space suit and sort of bazooka like so that equal force could prevent the hooter from rocketing off into space. Is that sorta feasible, would you say ?

    And if the Russians actually test fired a machine gun – would not the gun have been propelled backwards?

  39. In some ways it might resemble warfare under sail, with orbital dynamics taking the place of wind and weather. Combat might break out anywhere, just as it can at sea, but the tactics would be dominated by getting and keeping an advantageous orbit. And although the whole of space reachable without FTL would be potential battle-space, strategy would be dominated by things like the “interplanetary transport network” of low-energy paths, and of course, the location of stuff one side cares about. Similarly, sea battles could happen almost anywhere, but tended to happen at strategically important choke points on the major trade routes. And a major problem would be finding the enemy in the vast spaces, as it still is at sea.

    In other ways it wouldn’t be at all like that; three dimensions, probably one hit to kill for all practical purposes, and IR signatures visible at very long ranges. In fact, very long range would characterise a whole lot of things. Perhaps a little like modern submarines, but with the constrained tactical mobility of sailing ships.

  40. Thanks for the great article. It really put things into a different perspective than all the sci-fi shows/movies/books. Walter Jon Williams also has some interesting ideas in his novel Implied Spaces about ship design and ranged space weapons (attacking orbital AI arrays with particle weapons and the necessary countermeasures).

  41. Pingback: Episode 83
  42. We definetly have enough wars on earth! We like movies and stories of star wars, but lets hope we never need to fight in space … enough is enough!

  43. Hey I’m just woundering how we haven’t been flying in outer space we have all the stuff we need to push forward on it, so why not start on it, and we have a new power of energy to our use but yet we still use oil and gas to keep moving why its goin to kill our planet if we don’t

    so yea does everyone on this earth want to die from us using up the earth resources that is needs, cuz if we don’t stop the earth is dead, and so are we, and obama he shouldn’t have shut down the space rocket center, and we need them if we had space crafts and was able to get to the other planets around us, we can use the resources on that planet to our use but not so much to where it will kill the planet but to keep us going.

    oh yea by the way this war is whats stopping us from doing it, we all should be together and have a big nation together to control our solar system, so people stop being stupid and get smarter and better in life ok its not hard all you got to do is think ok just think with that head of yours

    My name is richard byram thanks for reading and listing to what I had to say in this message.

  44. i was recently sent this article from a friend via e-mail and regarding the addendum What would combat spacecraft end up looking like? what about the Starfury design from the Babylon 5 series?

  45. I think the Starfury design looks about right: concentrated inertia in the middle, powerful engines in line with the cockpit pod, and weapons and thrusters out on appendages. However, I don’t think they’re really big enough – they need someplace to store all their propellant!

    1. there’s also the Thunderbolt which is larger and also equipped for atmospherical battles

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