Innokenti asks

Weapons in space. I imagine Sci-Fi shows lie to us lots about the sort of stuff that might be effective in a space-battle. For example as I understand nukes would only be of minimal use out there in space.

What are the most efficient weapons for space-battles though? (Assuming largely human technology of near-future imagination rather than magic alien energy shields and stuff.)

Yes. Yes they do lie to you, in the same way that spaceships don’t actually handle like jet fighters in a vacuum what with having no atmosphere to react against. Space combat, if it ever happened, would likely be ridiculously crude and nasty thanks to the Newtonian nature of space. Things are whizzing around very quickly making them hard to target, but at the same time you can accelerate a projectile up to unheard-of velocities thanks to not having to worry about any of that pesky atmospheric drag. Most current theories about space weapons involve adaptations of current Earth-based weapons systems, but they all carry certain advantages and disadvantages inherent in their design.

Real examples of weapons in space.

There is one! Back when the Cold War was in full swing the Soviets decided it would be a good idea to mount a 23mm anti-aircraft cannon on Salyut-3 (a space station) to defend against “US space-based interceptors”, with integrated rocket boosters to cancel out the recoil thrust that might have resulted in de-orbiting the space station. It wasn’t the most elegant of space weapons since it could not track a target independently, instead requiring the entire space station to be oriented towards the target. There are conflicting reports on whether it was ever used; it was certainly never used while there were cosmonauts on board due to the inherent risk of firing high-explosive cannon shells via an untested system in a vacuum, but it may have been test-fired after the cosmonauts left. Barring any of the top-secret weapons programs so enamoured of Hollywood, this remains (to my knowledge) the only actual example of the weaponization of space.

Anyway, you wanted to know about current or near-future weapons systems that might be adapted for space use. This means we’re talking bullets, missiles or (mirroring current developments in the way high-technology nations fight wars) drones of some kind. However, thanks to the ranges at which a space engagement would be fought and the speeds at which spaceships travel, there are some quirks involved with each one.

1) Conventional high explosives are now pretty much useless.

High explosives are “high” because they have what is called a high brisance; essentially the rate of expansion of the explosive gas. If this is very high it’ll compress the atmosphere around it and force it outwards in a highly destructive shockwave that does most of the damage – it’s like being hit by a solid wall of air moving at the speed of sound, which is easily enough to knock down buildings and rip limbs from their sockets. But in space, of course, there is no atmosphere; no medium through which the explosive can transmit its destructive force. All it’ll have left will be the force of the explosive gas itself which, while considerable, will diminish considerably over distance thanks to the inverse square law. This means that most conventional explosives – including nukes – are much less effective in space. There are two ways you could adapt an explosive to make it more useful:

Use it as the explosive force for some kind of flak or fragmentation shell. This at least alleviates the problem of having your destructive force dispersing uniformly into an expanding sphere by transferring it to discrete fragments or projectiles which concentrate the kinetic energy of the explosion. Unfortunately I doubt you’d get a whole lot of velocity out of a high explosive burst, so the fragments themselves still wouldn’t pack that much of a punch. Much like real-world flak this would be useful for area denial and little else.

Shape the explosion so that it is focused in one direction. Shaped charges are all the rage these days, and if you got your shaped charge in contact with an enemy spaceship there’s no reason why it wouldn’t do just as much damage to it as a High Explosive Anti-Tank (HEAT) shell would to an Iraqi T-55. This too has a drawback, though, and it’s that if you have to score a near-hit with a shaped charge to do any damage, you may as well take out the explosive and make your shell a solid lump of metal instead. This brings us to…

2) Bullets are now absurdly deadly.

Or at least, their lethal potential is now drastically increased. A regular gun you could buy in a shop in the US would work just fine in the vacuum of space – the primer and cordite explosive used to accelerate the bullet come with their own oxidiser, so lack of oxygen would not be a problem. The bullet would also leave the barrel slightly faster too what with it not having to force its way through any atmospheric gas. However, a regular gun is not going to be significantly more lethal in space than on Earth. If whatever you’re shooting at is armoured in any way then the bullets will still bounce off. Bullets do most of their damage via kinetic energy, or

Which is about the zillionth time I’ve used this equation. There’s a maximum velocity achieveable by gunpowder weapons (details of why are in my post on light gas guns), and so there’s a hard ceiling on the potential kinetic energy of a normal bullet. We’re not too concerned about this on Earth because honestly the guns we have kill people pretty good, but if you took even the anti-aircraft cannon they mounted on Salyut and tried to kill a spaceship with it you’d run into a big problem: namely that spaceships move really fast. We’re talking relative velocities of at least several kilometres per second. Unless it’s coming towards you, the spaceship will be able to simply outrun your bullets, and even if they were they would be an incredible pain in the ass to target. Consider that Goalkeeper/Phalanx CIWS systems have trouble shooting down incoming anti-ship missiles — which are moving a lot slower than our hypothetical spaceship — and you have some idea of the scale of the problem.

The “good” news is that even future spaceships will likely not mount a huge amount of armour plating without some kind of revolutionary new engine system that renders all that extra mass irrelevant. If you scored a hit with even a simple kinetic slug you’d do an awful lot of damage; micrometeoroid impacts are a big problem for orbiting satellites, and those are just tiny chunks of rock a few millimetres in diameter. The trick, both to ensure a hit and to ensure that hit scores a kill, is to make your projectile go as fast as possible. This is something that gunpowder weapons simply aren’t capable of so you’d need to chuck out that system and replace it with a functioning railgun system or something, but it’s certainly theoretically possible. Even then, though, at the engagement ranges spaceship battles are likely to take place at (thousands of kilometres at the very least) it would be trivial for your target to take evasive action if they saw you coming. So you either have to blanket space with a lot of projectiles, or else make your projectiles guided in some way.

3) Missiles are a middle-of-the-road approach.

When I talk about space missiles, I’m not talking about what you’d normally conceive of as a missile, with the rocket booster that constantly burns to provide thrust. This would be redundant and silly on a space missile, since if you had the tech to accelerate a kinetic projectile up to several km/s as in 2) it’d be far easier to launch the missile that way rather than relying on chemical fuel rockets. No, a space missile would consist of a very sparse maneuvering system for making course corrections along with a guidance package to make sure it hits the target. It’d have more in common with the ubiquitous idea of the “killsat” – a satellite designed to take out other satellites by colliding with them – than it would a conventional missile. The advantage of this design would be that your chances of hitting the target increase exponentially once you make the projectile guided. The disadvantages would be exactly the same as those of regular missiles: they would need some sort of active sensor system in order to track their target that the target would see coming several thousand kilometres away.

4) Manned space fighters are not going to happen.

Sorry, but there aren’t going to be any Starbucks or Apollos flying around in the space battles of the future. While it might seem like a neat idea to get in an X-Wing and go gallivanting around the galaxy, if you actually put a human in a military space vehicle all you would be doing is introducing a massive weak point and drain on the resources of the spacecraft. Humans need food, water, oxygen, heat, and all those other little amenities we take for granted here on Earth, and any manoeuvring the spacecraft did would be limited by the requirement to not kill the people inside through excessive G-forces. All this, and a human wouldn’t actually add very much to the spacecraft. Like jet airliners modern spacecraft are all flown by computers these days anyway (yes, even the Space Shuttle) so there’s no real need to have humans on board.

5) Drone fighters almost certainly are.

That thing in the picture? That’s a Predator drone, one of many which can be found flying over Afghanistan and Iraq looking for “terrorists”. At first Predators were simple reconnaissance craft that were supposed to guide vehicles driven/piloted by actual live humans to their targets, but eventually some bright spark came up with the idea of arming Predator drones with Hellfire missiles. Now the Predators hunt all on their own, with the only human intervention coming in the form of a control signal from a trailer park near Las Vegas, Nevada.

That, if anything, is the sort of weapon that is going to be fighting a space war; an autonomous computer-controlled spacecraft capable of deploying subsidiary weapons systems on its own say-so¹. Solving the problem of true autonomy is a significant hurdle, but if an AI can be developed which is capable of running a spacecraft on its own with very little intervention from Earth beyond broad strategic directions then drone spacecraft would be by far the best option for fighting in space. They can move faster, react quicker and are actually capable of targeting other spacecraft moving at several km/s with a fair chance of scoring a hit. A drone fighter wouldn’t look like a Predator; instead, it’d resemble a militarised version of a space probe since aerodynamics and armour would be completely irrelevant in space. At its most basic level the drone would simply attempt to collide with an enemy spacecraft, much like the guided “missile” concept above. There’s more potential in it than that, though; you’d need to launch the drone from somewhere and that somewhere would probably be a larger drone mothership which would be the actual military asset, the smaller drones fulfilling a role similar to cruise missiles on Earth.

Wars in space would therefore take place with a minimum of human intervention. You would need the long-term strategic planning capacity of the human brain, but past that everything would be in the hands of the machines. It would be a war fought by remote control, where the combatants and casualties have no first and last names but merely a make and model. We’re moving in this direction in our enthusiastic pursuit of atmospheric combat at the bottom of a gravity well, so I see no reason why we wouldn’t apply the same technology and the same concepts to space.

Of course, this assumes that the human race would ever get around to fighting a space war. Right now we can’t even be bothered to go to the Moon; interplanetary war seems at least a couple of centuries beyond us. By then technology will have likely changed beyond all recognition, so all of what I just wrote was complete bollocks. I just hope it was entertaining bollocks, is all.

1. Predator drones don’t quite have this level of autonomy because it makes people a bit nervous, but they could if the US military didn’t have a problem with a machine making a wrong call and incinerating a bunch of civilians with an erroneously-targeted Hellfire missile. Oddly enough it’s A-OK when human pilots do this, as if having your bloody violent death dispensed by an actual person is somehow a more palatable idea for Western civilization to swallow.

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