Projecting Space Battle Physics

When I wrote my original article on the physics of space battles, and the accompanying short story, I made the creative decision to speculate on how space battle technologies and tactics would play out if we built from the present day – or, at least, the very near future. The obvious thing to look at next is what a more distant future might hold – so, I’ll embrace my status as That Space Battle Physics Guy!

A possible near-future space fighter radiating excess heat between battles

I think that extrapolating or projecting space battle technologies forward in time is a difficult thing to do, even for the cleverest science fiction geeks. I say this for two reasons: first, aside from some general trends, it’s hard to predict exactly where technology will go in the next ten or twenty or fifty years; second, nobody gets to play this game against a live opponent – and that’s really how combat tactics and technology develop. Still, given the trends, it’s fun to speculate! Physics won’t change radically for quite some time, so we have some direction in which to proceed.

I’m going to proceed from the assumption that “spacecraft” are different from launch and reentry vehicles. Let’s take some possible combat spacecraft systems, think about the related problems that spacecraft engineers try to solve, and see what might (!) happen if the aliens wait till we have some operational space colonies before they invade…

(By no means, of course, is this an exhaustive list, nor have I projected out as far as is possible. That would take about a think tank more than one sci-fi geek spacecraft engineer physicist blogger!)


This is the captain. We have a…little problem with our engine sequence, so we may experience some slight turbulence, and then…explode.

-Captain Malcolm “Mal” Reynolds

One of the challenges in propulsion technology today is that engineers typically face a choice: we can give our spacecraft powerful engines or energy-efficient engines, but not engines that are both at the same time. The powerful engines are things like chemical rockets, which are great for high-thrust things like boosting out of planetary gravity wells or for rapid maneuvers. The efficient engines are ion engines. These engines aren’t good for strong thrusting or rapid maneuvers, but they’re wonderful for speeding up long trajectories like going between planets. So, until the discovery of some new physics, combat spacecraft would probably have both: interplanetary cruise engines and combat maneuvering thrusters. The cruise engines would be of the highly efficient variety, used to break or enter planetary orbits and accelerate the spacecraft along transfer trajectories. The combat thrusters would be high-thrust engines designed to handle rapid maneuvering.

Right now, there’s a lot of research into the propulsion technologies that could be used as interplanetary cruise engines. This research includes solar sails, ion engines, and the VASIMR engine. (VASIMR will soon be flying up to the Space Station for tests and is the engine NASA Administrator Charlie Bolden was talking about when he mentioned proposed NASA tech research programs taking us to Mars in a few months instead of years.) There are also orbital maneuvers a spacecraft can do if it can interact with planets electromagnetically or gravitationally. Those techniques, however, are better at making interplanetary trajectories more energy-efficient than they are at making rapid course corrections or accelerating a spacecraft in a short period of time.

A possible next step could be nuclear rockets, but one of the most transformative propulsion technologies on the horizon would be a matter-antimatter annihilation engine – using the most efficient way possible to convert mass into energy. Physicists – including me, in an undergrad physics lab – have been creating and using antimatter on a particle-by-particle basis for decades. (This is easy: some radioactive decay processes produce positrons.) But if we learn to produce and store large quantities of antimatter, we will have at our disposal the most powerful rocket propellant in the known universe. Antimatter-fueled engines would allow truly relativistic spacecraft. While the stars would still be years away (to planetbound observers), making any interstellar trips substantial endeavors, our Solar System might be only weeks across. In addition, spacecraft with such powerful engines could execute extremely high-thrust maneuvers. Such propulsion systems would also provide plenty of surplus power with which to run other systems and charge batteries. And antimatter rockets would give space fighters an extremely powerful weapon: their own exhaust! This sort of engine, and its weaponization, appears fairly regularly in fiction. For example, the climax of Poul Anderson’s novel Harvest of Stars describes two antimatter-fueled spacecraft dueling – playing chicken with each others’ exhaust tails.

What about technologies even farther afield? Well, I have no idea what the practical applications of a lot of current theoretical physics might be. Maybe, someday, we can find some way to manipulate gravity or spacetime. Some thoughts on how to do this are already out there, and NASA has in the past studied such concepts. As an example of the kind of thing I’m talking about, we know that the reason why light can’t escape from within the event horizon of a black hole is that within the horizon, space itself is getting sucked in towards the singularity faster than light – at least, as measured by an external observer – carrying the light with it. Maybe there’s a way to push space along so that it carries our ships with it in a similar way. (“Warping” spacetime in this way is the usual handwaving explanation for how the USS Enterprise can exceed the speed of light with its – hey, hey! – warp drive.) Of course, this sort of technology is well into the realm of what Sir Arthur C. Clarke called “indistinguishable from magic,” so I hesitate to make claims about its capabilities. And these methods, if they are even possible, would require phenomenal amounts of energy. So now we run into the size problem!

Even for the most exotic propulsion systems, a spacecraft can only store a finite amount of energy and propellant. (The author of one spacecraft engineering textbook used at Cornell even calculated that every time Captain Kirk orders “all stop – full reverse!” at any speed greater than a fraction of Warp 1, the Starship Enterprise must use antimatter reserves with at least as much mass as the entire rest of the ship!) So, even the most farfetched engines cannot be on all the time and the spacecraft must follow the physics of orbits. When not directly engaged in maneuvers, the spacecraft would drift around or between planets and moons according to the laws described by Kepler, Newton, and Einstein. Space combat near planets and moons will involve ships jockeying for the most tactically advantageous orbit.

But fear not, space battle fans! Having to obey orbit mechanics doesn’t mean that you can’t attack your foes from any possible direction. You just come in at an orbit with a different eccentricity or inclination, and you’ll approach your quarry from “above,” “below,” or “sideways.” But orbit mechanics will mean that certain interplanetary trajectories make more sense than others, so you can try to predict your opponent’s moves and sabotage their plans by anticipating those paths. More on tactics later!


This is a Viper Mark II. It’s as maneuverable as a jackrabbit and can flip end for end in point three five seconds. You have never flown anything remotely like it, so don’t think that you have. Today we will be doing basic launch, approach and landing maneuvers. Anyone not paying attention is liable to end up as a puddle of something to be hosed out of the cockpit by the chief of the deck.

-Lt. Kara “Starbuck” Thrace

Even when limited to Keplerian orbits, an enemy starfighter could attack your own ship from any direction relative to whichever way your ship and its guns are facing. It would be critically important to respond to attacks as quickly as possible – by bringing your own weaponry to bear, bringing defensive lasers and heavily armored areas into line, or perhaps by simply positioning your main engines for a good thrust out of the line of fire. So, your space fighters need agility – the ability to spin in place quickly.

Modern spacecraft typically use off-center thrusters, wheels with variable speed, gyroscopes, or some combination of these to change orientation in space. Of these, gyroscopes are the most efficient at turning stored energy into rotation. One way to think of a gyroscope is as a device that stores angular momentum. Gyroscopes store more momentum when they have more inertia or spin more rapidly. So I would expect the most maneuverable starfighters to have some massive rotors whirling around somewhere within their bodies.

The physics of momentum and inertia are very unlikely to change in the future. For a given amount of momentum, an object with smaller inertia will spin faster. This means that if we want a space fighter that can spin around quickly, we need to give it a small inertia, and the smallest possible inertia for a fixed mass and density is a solid sphere. So the most maneuverable fighters should be as sphere-shaped as possible – or, at least, have their most massive components clustered as close to their center of mass as possible. As with everything written here, this is an engineering tradeoff. Which is more important: having a fighter shaped like a perfect sphere for agility, or having gun turrets protruding out from its surface? Having the sphere, or giving the fighter beefy engines? Spherical shape, or preferentially armoring certain sensitive areas? I suspect that the most maneuverable fighters of any space fleet will be the most sphere-like, but they will not actually be solid spheres.

One possible alternative to building spherical space fighters that can spin rapidly in place would be space fighters that can spin rapidly about certain axes of rotation but not others. Perhaps some craft can exploit the physics and stability of rotations to achieve certain kinds of maneuverability at the expense of others. Or, we could design spacecraft with segmented, articulated arms. Those vehicles could gyrate like gymnasts: while one part of the spacecraft twists out of the line of incoming fire, another part could be swinging in to return shots with its own guns.

The drawback: any mechanisms, including gyroscopes, on a spacecraft are a weak point. Modern spacecraft typically don’t have many mechanisms, because the vibration of launch could shimmy mechanical components just enough out of alignment that they jam when they’re needed. Such issues have been responsible, for example, for the deployment failure of Galileo‘s high-gain antenna. (Engineers figured out another way to have the spacecraft send its amazing data back.) The more mechanisms there are on a spacecraft the more chances there are for something like that to go wrong. Of course, part of the problem nowadays is that we have to pack our spacecraft into cramped launch vehicle fairings to get them into space. If we could build them in orbit in the first place, and had people or robots on hand to fix the glitches…

Spacecraft Structures

Correct! 6,000 hulls.

-Professor Hubert Farnsworth

Right now, our spacecraft are severely limited by both the mass and volume our launch vehicles are capable of lofting into orbit. Even when we build modular structures in space, they have to be very low-mass. On a combat spacecraft, that means small fuel tanks, few weapons, and skimpy armor. Unless something fantastically new comes along to make it cheap and easy to put a lot of mass into space – not impossible, if unlikely in the next decade or so – we won’t be able to build a lot of capability into our space fighters. So the thing that would let us build hefty combat spacecraft structures is the ability to use resources that are already in space.

This is called in-situ resource utilization, and I am thinking specifically of nickel-iron asteroids. These asteroids are made of metals that could, potentially, be processed by robotic factories. The foundry robots could easily push processed materials, or even finished components, out of the asteroids’ shallow gravity wells. It seems funny to think of spacecraft made out of iron or steel, but if the raw material is already up there, then mass becomes less of a concern except as something that reduces the ship’s maximum acceleration. Mass would no longer be prohibitive in assembling and launching spacecraft.

Asteroid bases in our future?
Asteroid foundries and shipyards?

Now you can start to imagine hulking space battlecruisers with thick armor plating; their shapes governed by zero-gravity maneuvering and propulsion requirements rather than by aerodynamics. With asteroid-processing capabilities, there wouldn’t be any reason not to armor combat vessels, particularly if there are humans on board. The standard tradeoff applies: if you’re willing to lose maneuverability and acceleration, you can go ahead and cover your star destroyers with layers of metal plating. (What an image: space ironclads!) In fact, I’d go ahead and build the biggest battle stations by burrowing into the metal asteroids themselves.

Almost every spacecraft we have ever built, from capsules to the Space Shuttle, has some direction that qualifies as “down.” There’s a very simple reason for this trend in design: we built those spacecraft on Earth. But if we build the spacecraft directly in space, then we can build them specifically for zero gravity. There would be no need for a “deck” structure on spacecraft, so you won’t see things with mostly flat shapes. (Includes the USS Enterprise, Star Destroyers, Terran Battlecruisers, the Battlestar Galactica and the like.) I’ll give it to on-screen depictions of space vessels: it’s hard to film in zero-g, so everyone invents artificial gravity. But, even in movies, the outer spacecraft structure need not look like an oceangoing ship – and, in far-future real life, it won’t. If there is any orientation to the interior structure, it would be with “down” pointing toward the engines so that the crew can have a tiny bit of gravity while the ship is under thrust.


Okie-dokie, okie-dokie… Let’s fire blue particle cannons, full; red particle cannons, full… Gannet magnets, fire them left and right and let ’em run, all chutes… While you’re at it, why dontcha toss that at ’em, killer. That should take care of old lobster-head, shouldn’t it?

-Jason Nesmith

You might be surprised just how much space weapons experience we have from the Cold War – even including Soviet manned space stations with guns on board. Much of that experience is with, in science fiction parlance, kinetic energy weapons.

Even the tiniest bits of matter flying around in orbit are enough to damage and destroy spacecraft. Space debris, or space junk, is a growing problem. (This is one reason why it’s such a big deal that the Chinese sometimes blow up satellites in orbit.) So if we want to destroy an enemy vessel, we should just throw a bunch of junk and shrapnel at it at high speed. Debris clouds would, in addition, make excellent space mines. I’m not the first to think this: A Soviet experiment even went so far as to test a flak-like warhead.

hypervelocity impact
No, not a laser - a hypervelocity projectile simulating a debris impact

I think missiles are unlikely as space weapons until antimatter engines are available. A chemical rocket would start at a disadvantage after a large initial burn to pick up speed, and then would rapidly run through its propellant if it constantly thrusts towards the target. If it’s only making course correction maneuvers, the name of the game would be evading the projectile until it expends all its propellant and can no longer adjust to your ship’s course corrections. With a matter-antimatter engine, though, the missile could easily achieve relativistic velocity (making evading it much, much harder) and it would be able to use its propellant efficiently to match any maneuvers its target makes.

If guns and missiles aren’t science-fictiony enough for you, how about some energy weapons? Lasers could travel for hundreds of kilometers to melt and destroy things. The US Air Force’s megawatt-class Airborne Laser Testbed does exactly that from a Boeing 747. A similar space-based laser might have an even longer range. Such weapons would be devastating to spacecraft. They would easily mangle delicate instruments; even the tiniest hole in the wrong place could be catastrophic. However, these things would take a lot of power to fire, which might be a disadvantage. They also won’t travel forever before the beam disperses or defocuses, so although a laser strike travels at light speed, it won’t expand the theater of space combat beyond a local orbit. (Kinetic weapons, on the other hand, would actually have a near-infinite range, though they would be easier to dodge because fighters could see them coming!) Weaker lasers might still find uses on the smaller starfighters, though, as weapons to blind enemy instruments or destroy incoming ordnance – exactly what the Air Force’s ALTB is intended for.

A more exotic idea might be some other kind of energy burst. We know that solar flares can disrupt satellite operations, and high-energy bursts from all the way across the universe can blind our instruments. Computers and electronics are the guts of spacecraft. Suddenly hitting a spacecraft with an intense electromagnetic field could erase hard drives, scramble data, lock up transistors, and overload sensitive components. This might be the use for nuclear weapons in space – though it would be better to find a way to generate an EMP more efficiently, without all the waste heat and dangerous residual radiation of a nuclear blast.

All this reliance on computers and instrumentation opens up another avenue for attack in space: electronic warfare and information warfare. Decoy drones could broadcast radio and infrared radiation to confuse adversaries. Positioning systems, radar, or other instruments relying on received transmissions could be spoofed, fooling them into giving their operators false data. Space fighters might even try to hack into enemy systems and plant viruses, take control of enemy starfighters, or just scramble enemy computers on a ship-by-ship basis to take them out of the fight. As we’ve learned throughout the history of space travel, even a single misplaced or mis-entered command can disable a spacecraft.

None of these are the most exotic future space weapons I can think of (though they are certainly ones that I might expect to appear in space wars). Remember back when I wrote about propulsion systems, and speculated that at some point we might develop propulsion systems based on direct manipulation of gravity or spacetime? Future space warriors could employ little drones with those propulsion systems, designed to travel faster than light and then ram into enemy spacecraft. They would be impossible to detect before their devastating impact. It gets worse, though: just imagine weapons that operate by stretching or squeezing spacetime in some nefarious way around your foes’ starships. (Perhaps these are the “wormhole weapons” Scorpius was always going on about.) I shudder to think of an advanced enough, evil enough people to deploy spaghettification as a weapon.

Similarly terrible are the weapons that might be deployed from space to planet surfaces. Devastating weapons would be terrifyingly easy to set up.

Sensors and Stealth

They can’t have disappeared. No ship that small has a cloaking device.

-Captain Needa

There are two ways to detect objects in space: we can either detect the radiation that the object emits, or we can bounce some of our own radiation off it and look for the return.

Spacecraft will certainly emit radiation. Heaters that maintain components at working temperature, or crew cabins in comfort, emit thermal radiation. Electrical systems emit low-level radio signals. And spacecraft near planets and stars will reflect light. Managing thermal radiation is a challenge even now, for spacecraft that aren’t trying to hide from detection. For combat spacecraft, the problem becomes one of minimizing the amount of radiation emitted towards the enemy and detecting the emissions from an opposing vessel.

Against the background of a star, planet, or moon, detecting radiation emission and discriminating it from the background – quickly – could be quite difficult. There are even challenges when looking against the background of space: detectors must be kept cooled to cryogenic temperatures so that thermal radiation from the detector optics doesn’t overpower the emissions from the target. (The cryocoolers will also make parts of your space fighter hotter and, therefore, easier to detect.) These technologies may improve in the future – we’re reaping those rewards now, with better and better space telescopes peeling back the layers of the universe. The more reliable way to detect an enemy starfighter is the second option. Technologies like radar and laser rangefinding will find application in locating spacecraft for quite some time to come. Radar would also be the device of choice for identifying and tracking incoming weapons fire. If the alien space imperium has flak-cannon-equipped battlecruisers, then radar would immediately allow your own fleets to track and evade the incoming shrapnel.

How about hiding from enemy sensors? Well, we’ve pretty much got radar-stealthed aircraft figured out. Faceted, uneven surfaces reflect radar pings away in a pattern that leaves little signal power headed back to the receiver. The same principle would apply to stealthing spacecraft from radar detection. Even more exotic devices, however, are on the horizon: cloaking devices made out of metamaterials. These already work in radar wavelengths. One possible sci-fi application works like this: take a space fighter and cover the exterior surfaces with tiny nanostructures that redirect radiation around the craft. Voila! Invisible spacecraft. Another interesting idea: these metamaterials could also channel the thermal radiation signature of your fighter away from the enemy, to keep their best thermal sensors from detecting your ship.


Not equipped with shields…then buckle up!

-Terran Battlecruiser Commander

Engines, mechanisms, and sensors would all be weak points on a combat spacecraft. In the face of all these flak bursts and energy discharges, how could a space cruiser defend itself? Well, heavy armor would be one way to handle impacts. But that requires either that the ships be built in space, since launching heavy things gets very expensive very quickly; or developing armors that are extremely low-mass for the protection they offer. The latter possibility is not out of the question, if we can come up with some type of exotic composite or extreme non-Newtonian fluids. Those armors are too thin to protect electronics from energy bursts, however.

Another possibility: Scientists and engineers on Earth today are looking into magnetic deflector shields to protect humans from radiation on a journey to Mars or beyond. These shields work just like the Earth’s magnetosphere, protecting a spacecraft from charged particles and plasma. Such devices could help defend spacecraft against radiation-based weapons. Strong enough electromagnetic fields might even help deflect shrapnel clouds, though that would take more effort to design and implement.

My thought is that starfighter defenses will be largely the same as starfighter weapons: guns and lasers. Those weapons could shoot down missiles or knock bullets off course if your ship can track incoming weapons fire accurately enough and swivel its point-defense guns around precisely enough. That’s another reason why I think missiles would have limited application in space battles, and why flak would be a terribly effective weapon – your enemy is not likely to be able to deflect every piece of shrapnel. Nor are you, for that matter!

Communications and Control

What matters is we built the ansible. The official name is Philotic Parallax Instantaneous Communicator, but somebody dredged the name ansible out of an old book somewhere and it caught on.

-Colonel Graff

Communications will likely be by lightspeed means for a long, long time to come – radio and laser devices. The thought of developing something like Orson Scott Card’s “ansible,” from the Ender’s Game universe, has kept many science fiction fans intrigued (myself included). Often, the ideas of quantum teleportation or quantum entanglement get called upon to explain those devices. Unfortunately, though you could use quantum entanglement to embed a message, part of the communicating device must operate by other means – limited by the speed of light. It seems like instantaneous communication may have to wait until we figure out how to use wormholes and can send couriers or light beams through those.

In my first article, I assumed a near-current level of technology and concluded that communication lag would make on-site humans necessary to coordinate our defense against the alien invaders. But perhaps the first aspect of technology to advance beyond the level I described earlier will be robotics and computer control. Even now, we’re making advances in autonomous rendezvous and docking between spacecraft. And on the ground, we have robots and computers capable of driving themselves, flying themselves, coordinating their actions…all sorts of autonomous operations!

With the right advances, we could go right ahead and build squadrons of autonomous drone fighters. Human operators would control overall strategy, but not the maneuvers of each drone. With powerful enough engines, the drones could even execute maneuvers much faster than a human could react, making direct human-in-the-loop control of the drones (like the US Air Force does today with UAV’s) impossible. (Readers of Haldeman’s The Forever War and Hamilton’s Night’s Dawn Trilogy will be familiar with this concept. In fact, I quite like Hamilton’s description of the “combat wasps,” where overall strategy is dictated by a human being but the drones go out on their own to execute 50-gee thrusts, laser and antimatter barrages, and virus transmissions. Too bad the books’ deus ex machina ending was terrible.)

I can’t see us trusting everything to the machines, though, which means we need a place to put the brave human starfighter pilots and battle station crews. Since humans are squishy, the best place to put the crew cabin of a fighter or the command bridge of a space destroyer would be in the very center, where the rest of the spacecraft protects the humans within from harm. So we won’t be getting any giant glass windows on our bridge or bubble cockpits on our fighters – but a projection of the view outside. In fact, the virtual and augmented reality technologies appearing on Earth today would be perfect inside the cabins of space fighters.


He’s intelligent, but not experienced. His pattern indicates…two-dimensional thinking.


What might the disposition of forces in a typical admiral’s space fleet look like? Well, I think it likely that, with the advent of in-space construction, that fleet could include a wide variety of ships. Since interstellar and interplanetary distances are so vast, the heart of the fleet would no doubt be some very large craft to act as staging areas, transports, repair yards, and supply ships for the smaller vessels. I can also imagine several classes of smaller warships, from gunships to one-man fighters to robot drones.

The largest battlecruisers, which would already have huge masses and inertias, could take a wide variety of shapes – all heavily armored. As I wrote above, perhaps the easiest way to build such ships would be to hollow out asteroids. During combat, they would hang back and coordinate fleet actions while the smaller, more maneuverable ships jockey for position with the enemy. Those ships would be more agile, tending towards the spherical shapes I referred to before. Given that resources are limited, it makes sense for there to be only two main engines per craft (cruise and combat engines), only one or two forward-facing weapon systems on the smallest fighters, and a few turrets on the mid-size vessels. The gyrating ships would be more exotic, and probably would be either of the robotic or mid-sized variety.

Having a mothership/smaller ship architecture to interplanetary battle fleets makes sense for a number of reasons. The smaller fighters and gunships could dock to the mothership while in transit, allowing the mothership to charge their batteries, replenish their consumables, and give their systems a chance to power down for maintenance and to avoid fatigue. The hulking asteroid dreadnoughts will need to include vast life-support systems (CO2-to-O2 converting algae tanks, perhaps?); huge solar panels, nuclear reactors, or other generators or energy stores; supplies for combat, maintenance, repair, and perhaps even planetary occupations after the battle is done; all the landing pods and troops needed to secure a planet; plus the tremendously powerful cruise engines necessary to move all this stuff. All that might leave little space for guns and hefty enough maneuvering systems, so the smaller ships would do most of the fighting.

I’ve stressed, in my first article and again, now, how even the most advanced combat spacecraft will have to obey the physics of orbits for most of their combat flight time. This isn’t necessarily a limiting condition! All this fact means is that orbital dynamics will be the “terrain” on which spacecraft maneuver. Whether a more tactically advantageous orbit is at higher or lower altitude, greater or lesser eccentricity, or at a different inclination than the target spaceship’s orbit will dictate the tactical decisions a commander makes. It’s all about relative motion: lower orbits go around planets faster; inclined or eccentric orbits seem to oscillate around a circular orbit of the same radius. Different points in an orbit around a planet are better or worse for firing engines to escape; likewise, when coming in towards a planet on a transfer trajectory, some timings are better or worse for firing the orbital injection burn that makes a craft stay around the target planet. This slow dance would be choreographed by strategists and computers trying to estimate and predict enemy motions, but it would be punctuated by brief instances of faster-than-the-eye-can-see action. As technology advances more and more, the information warfare aspect will become more important during the slow periods and the fast encounters will happen more and more rapidly.

Doesn't this suggest orbit trajectories to you?

Moreover, the planets and moons are in orbits around their central bodies. So, depending on the relative configuration of all the planets and the technological capabilities of each side (any ion engines? antimatter engines? pokey solar sails?), one faction could try to predict the trajectories an invading force would take. Fleet admirals would have their choice of higher- or lower-risk launch windows: some might be easier for the adversary to predict, while others would leave their fleet with more fuel remaining for maneuvers once they have reached the destination. Commanders might elect to send decoy forces out along some trajectories, or just put piles of junk in orbit to screw with the enemy’s sensors and navigation.

As one fleet comes in towards their quarry’s homeworld, or as opposing fleets close in interplanetary space, the first thing any veteran interstellar patrol admiral would do is to depressurize his or her entire fleet, ordering the crews into spacesuits, to keep this from happening. While closing, each side might throw huge clouds of debris, shrapnel, and flak at each other. This would confuse sensors and be a huge hazard for the approaching ships. Each side would have to start up active radar scans to identify and evade the shrapnel clouds; perhaps tracking the radar pings that filter through the flak would allow the opposing forces to track each other, as well. The energy weapons would come into play next: because these weapons would require a huge energy discharge, they will need large batteries and capacitors to operate. Carrying a fully charged capacitor into battle would be a liability, so ship captains would fire their energy blasts as soon as possible – and probably leave the weapons unused after that. Perhaps the largest, most heavily armored ships could risk holding off on energy fire, or even recharging those weapons over and over again during battle. Finally, at the closest ranges, the guns and missiles would fire. It would certainly be spectacular to see – even without the fiery, gasoline-fueled explosions Hollywood transplants into outer space – and the wreckage afterwards would be a colossal problem to deal with. Hopefully, though, we will have shown the alien invaders who’s boss. If they do come all this way just to get into a fight, they aren’t going to pull any punches.

It’s How You Use It

Make no mistake: a space war would be a terrible thing. Even with all the humans ensconced in their spacecraft, it would be a bloody experience, ravaging lives, infrastructure, and planets. (After all, if you’re out there just to kill your enemies, you can drop asteroids on their planet.) It also wouldn’t bode well for any future contacts with alien species.

The good news, though, is that most of the technologies I’ve written about have civilian applications. These are the technologies that will help us colonize the Solar System, advance scientific knowledge, and defend ourselves against the forces of nature.

In-situ resource utilization will help us build not space warships but space colonies and transports to other worlds. High-powered lasers can give scientists better instrumentation, manufacturers precise machining, the populace better communications, and fusion reactions ignition. We must understand the physics of orbital debris in order to make space safe to travel. Radiation-armored crew cabins are going to be necessary to send humans into space for long periods. Agile spacecraft could observe astronomical phenomena that change on a rapid timescale, like imaging volcanoes on Io, tracking near-Earth objects, or responding to short-lived supernovae. Hypervelocity impacts are important to understand to advance our knowledge of impact cratering on planets. The cloaking devices that shunt thermal radiation around might be used to manage heat loads on a spacecraft to keep sensitive detectors and other components cold. Antimatter – perhaps the most inherently destructive material in the universe – would serve as the best interstellar spaceship fuel, and I certainly want to see interstellar exploration happen. Even the most destructive, overtly weaponized ideas I’ve written about may have applications to deflecting asteroids or other threats away from the Earth. (Some serious ideas include continuously blasting asteroids with intense light to ablate material and planting a factory that turns the asteroid into bullets that get hurled out of a mass driver; both impart a thrust on the asteroid to knock it away from Earth.)

I think that space combat physics packs a good double impact for young minds: with exciting stories, cool effects, and wild ideas, we can engage their interest; then as these ideas transfer over into technology development, we can develop the capabilities to expand human civilization out into the wider Solar System.

13 thoughts on “Projecting Space Battle Physics”

  1. Cool articles about space battles.
    I love hard Sci-Fi and I was always wondering how real space battles may look like.

  2. I know I’m a little late here but, Great article. I’ll definitely be incorporating these ideas in the table top RPGs I play.

    Three comments that have probably been thought of but I want to put them put there nonetheless.

    1: While implied it was never explicitly mentioned that combat ships should have built in redundancy in all vital systems including vital crew members. This not only allows a damaged ship to stay in the fight but if a space battle drags out over days (as many probably will) people can catch much needed rest by swapping out with the next shift. To conserve space, ships could practice “hot bunking”, where different crew shifts take turns using the same bunks. Extra systems will add significantly to the cost and mass of the craft so space navies will only use this on large “capital ships”. Redundant systems would be wasted on fighters and drones that would have a slim chance of surviving a strike anyway, so it’s best to leave them as small and agile as possible.

    2: I don’t see how the capacitors for large lasers would pose any more of a threat to a vessel in the space navy than the highly explosive ordnance packed into magazines do to the vessels of the world’s blue water navies. A fact infamously demonstrated by the HMS Hood. Actually capacitors could be made less dangerous to their own craft by using a set of distributed capacitors spread around the hull in place of one large component. This way any one exploding capacitor is unlikely to cause significant damage and, while it will weaken the energy output, will not take a vital big gun out of the fight.

    3: This one is pretty far fetched, but if some type of “mind uploading” or brain transfer technology is ever developed then it would be possible to field a space navy without any of the hassles of hauling delicate humans around the galaxy. A spaceman’s mind / brain could be placed into a body that was manufactured or genetically engineered to be without many of the vulnerabilities that keep mankind out of deep space today while avoiding the problem of handing your fleet over to potentially rebellious AI. In fact different body types may be specifically tailored for different shipboard positions. At the completion of his service, depending on how the tech works, our spaceman would be placed back in his original human body or possibly even grown a new one.

    1. Some of your ideas already form the basis of exciting science fiction stories! Keep thinking, and I’m sure your RPGs will get all the more fun.

  3. 1) Laser ablative propulsion. Good specific impulse, good thrust, and you get to leave the mass of the reactor at home or on the mothership.

    2) It should be noted that there’s not really a sharp divide between flak and missiles. Flak and warheads (kinetic or nuclear) would be delivered via the same mechanism– missiles. Flak is just a kinetic impactor that’s more easily stopped by armor (like atmosphere) but that’s harder to shoot down with hard kill countermeasures. Note that flak is, in itself, a hard kill countermeasure. The only difference between shooting down a ship and shooting down a missile is that the missile is smaller and has faster acceleration.

    3) Missiles don’t have to worry about saving enough delta-V to recover to a decent orbit and they don’t have to carry anything except for reaction mass and payload. Meanwhile, delta-V on a gunship is a precious, precious commodity, and the gunship is probably at least a thousand times more massive than the missile. If you can force a gunship to spend 10 tons of reaction mass outrunning a missile’s 10kg of reaction mass, it’s a win even if you miss.

    4) Even if you do need ultimate human responsiblity, that responsibility can come at a high level. If you’re 30 light minutes away from command, command merely has to authorize or not authorize engagement with undocumented signals. Your admiral in the field isn’t going to have good enough information to make that decision anyways.

    1. Great thoughts! I’ll just make a couple comments:

      First, I wouldn’t characterize laser ablation propulsion as high thrust. It also might be tactically dubious, if your enemy can throw junk in the way of the laser beam, or take out the last installation…

      Second, the big difference between flak and a missile is that flak is a whole cloud of impactors, and therefore much harder to avoid. You don’t even need to pack the flak into a guided missile, you could simply fire it out if a gun and rely on the natural dispersion of the cloud to cover a wide area. Then, when your ship is out of missiles because I blasted them all with flak bursts, I’ll still have shells left for you… 😉

      1. The thrust of laser ablative propulsion is proportional to the strength of the laser. If you’re already positing laser weapons capable of cutting through the metal hull of a rotating craft, that’s not a problem. You actually get more usable energy out of your lasers this way than by using them to burn through hulls, because it’s a bonus when you heat the plasma cloud instead of the stuff beneath it. Meanwhile, the mass requiring thrust is reduced by not having to carry the energy to accelerate its exhaust. Flak isn’t a problem for more than microseconds– after all, it is entering the path of a powerful laser designed to ablate metal. A few flakes of flak will instantly turn into superheated plasma and disperse. (Never mind the fact, why is the flak in between you and your command? At reasonable engagement ranges, that shouldn’t happen.)

        I don’t think guns make a lot of sense in space. Muzzle velocity is just too low for any conceivable barrel length. Let’s say you can manage 40k g over a barrel length of 100m (about 3 times the length of any gun ever built ever) without somehow tearing the barrel apart. Forget the awful moment of inertia that means for your ship. All that nets you is 9 km/s muzzle velocity. You’re not even going to hit Voyager with that, much less some futuristic spaceship that can outmaneuver missiles. And you’ve invested a huge amount of your mass into a single gun barrel that will probably need replacing after a handful of shots.

        Flak isn’t any easier to carry than missiles are. When my ship is out of warheads, your ship is out of flak.

        The ideal warhead, to my mind, is nuclear. If you think about it, nuclear warheads are just flak taken to the ridiculous extreme, with very dense flak the size of elementary particles. If you can use the same warhead for hard kill point defense that you use to destroy ships, that’s a bonus. Usually, hard kill point defense is considered a losing proposition only appropriate to the Goliath in asymmetrical engagements, because it’s always going to be cheaper to shoot more bullets at the person holding the gun than it will be to shoot down their bullets. However, that can always change at long enough range– eventually, it becomes easier to hit the bullets than to hit the guy shooting them. The relative effectiveness of point defense is probably going to determine engagement ranges.

        1. a very good taktick would be to spray out a huge amount of bolts (any hard small object works fine, even pencels would do) in front of an orbiting or fast moving enemy ship and it would be ript apart.

      2. or punt the flak in a carbord box filt with some gas and shoot that box (with a few springs) in front of the enemy ship. The box wil be ript apart and all the flak would be shot out into a big cloud. Try to avoid that

  4. the best thing that could hapen to aviation and airplanes was WW1 during that period the power and capebilety of airplanes incresed tenfold. A space war coud be the best thing to happen for space crafts and space exploration!

  5. Great, thought-provoking post. One correction, though. Credit for the word ansible should go to Ursula K. LeGuin, not Orson Scott Card. When Col. Graff says they “dredged the name ansible out of an old book somewhere” that’s OSC’s way of paying tribute to UKL’s The Left Hand of Darkness. She chose the word because it sounded like a contracted version of answerable and was later delighted when a fan pointed out that it was also an anagram for lesbian.

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