Space Carriers

Two space-fighter games recently came out in quick succession. Both are free, downloadable fan-made takes on popular franchises, and both show very high production values. The first is Wing Commander: Saga, based on the 1990s-era Wing Commander space simulator games.* The second is Diaspora: Shattered Armistice which lets you hop in the cockpit of your favorite fighter from Battlestar Galactica, accelerate out a launch tube, shoot up some Cylon raiders while flying sideways, and then burn in for a combat landing.** There’s also a recent article on the Foreign Policy web site about carriers in space. So now I’m thinking about that favorite military sci-fi trope: the space carrier!

Whether it makes sense, from a military, technical, or economic point of view, to build a carrier vessel to launch smaller fighting craft is a complex argument. (The FP article discusses more of this than I will here.) The major reasons to do so would be the same reasons why we build naval aircraft carriers now: the ship provides a base of operations for the aircraft, and allows them to participate missions that they could not perform on their own. That’s the sort of argument that even a far-flung space military would go for – if backed up with plenty of supporting evidence – but whether their space carriers launch single-seat fighters, small-crew attack ships, or robotic drones is up for grabs. I think that we can’t completelyanswer that question without knowing more about the reasons for this space military’s existence and the socioeconomic conditions during the Space War!

Let’s just suppose that it makes sense to have some kind of mother ship carrying some kind of smaller craft in a space military. I’m going to take a couple examples of carriers from military science fiction and grade them on what they do well and what they don’t. My examples are going to illustrate some common types of space carriers in media: space carriers from Star Wars, space carriers from the 2004-2010 TV series Battlestar Galactica, and space carriers from from the “Wing Commander” games.

First of all, I’ve got to get one thing off my chest. There’s one thing all these space carrier depictions do terribly: show proper behavior of gravity. All three have decks laid out like an oceangoing ship. In fact, all three move mostly in two dimensions, only occasionally dipping into the third spatial dimension. This phenomenon has more to do with making Hollywood production easier than anything else. In reality, everything in the carrier would have to be constructed to withstand the force of thrust – so it’s far more likely to have decks stacked “up” from the engines. I don’t think a carrier would spin for centrifugal artificial gravity, because that huge momentum would affect maneuvering; the spin would also affect how fighters get launched or recovered. (Even if we do find some other way to make artificial gravity, gravity is an attractive force so I think we’d see more spheres with grav-generators in the center or cylinders with grav-generators running down the axis than we would decks with grav-generators spread all around as flat plates.)

The battlestar Galactica and all the “Wing Commander” carriers all have hangar bays that run the full length of the ship, just as an oceangoing aircraft carrier has a runway along its length. This may seem like a good idea, but there is actually a major design flaw here! It has to do with a concept called “plume impingement.” In space, there’s no air to damp out or guide the motion of all the reaction mass expelled by a rocket engine. Rocket exhaust will just spray out of the nozzle, not in a nice flame-shaped jet going backwards, but in a cone that sweeps out to the sides as well. That exhaust is moving at high velocity and could pit or scrape up any surfaces it encounters, including fighter cockpits, gun ports, and sensor apertures. On top of that, if we’re talking about ion engines (and from the pale blue glows of most sci-fi space carrier engines, they seem to be using ion propulsion!) then the exhaust consists of charged particles. If a fighter runs into that stream of ions, then not only will all its surfaces get corroded, but the fighter is going to start picking up a charge – too much charge, and electricity will eventually arc from one surface to another, potentially damaging the fighter craft!

The upshot of all this is that there should be a big huge keep-out zone for fighters anywhere aft of a space carriers beefy engines. (I assume that one reason to have the space carrier in the first place is to let fighter craft hitch a ride on something with dedicated gargantuan rockets!) Here’s my crappy rendition of the Galactica and the TCS Victory, and where fighters should stay away:

Keep out!

The battlestar’s keep-out zone is slightly more favorable than the other carrier’s. Still, if you can see the carrier’s engines, chances are lots of ions are hitting your cockpit canopy. The best thing to do would be to approach the battlestar sideways, just behind the flight pod, and turn in at the last second – or approach from the front.

Tyrol will not be happy with me.

The Star Wars carriers, on the other hand, never seem to incorporate this flaw. From Home One to Devastator, hangar bays seem to point out radially from the ship’s central axis. So, fighters coming in for landings aren’t going anywhere near the spray of particles ejected from the rear of the carrier spacecraft! (This seems like just about the only instance when the Empire could have included a design flaw but did not…)

Key point: flight paths into/out of hangars are perpendicular to engines

The battlestar design is superior to the Star Wars carriers in at least one respect: just as the carrier engines will muck up the fighters, so will the fighter engines muck up the carrier! TIE fighters streaming out of that Imperial hangar bay are likely to cause all sorts of problems on the deck. When a battlestar launches its Viper complement, though, it accelerates the fighter craft with a catapult-like device; only after exiting the launch tube does the Viper appear to really light its engines.

In the design of a space carrier, engineers would have to keep in mind exactly what the purpose of the carrier is. Is it to carry common supplies for the fighter craft? Serve as a mobile refuel and repair station? Shield fighters from a first strike attack and only disperse them in close to the enemy?

I think that for long journery it might very well make sense to build a big propulsion, supply, and support ship that carries smaller fighter vehicles along with it. I’m not sure that one-man fighters make sense, but spreading an attack force out to cover multiple approaches would certainly be an advantage. I picture a large cylindrical center stage with fighter craft docked along its length: when it’s time for launch, the fighters can be ejected with some catapult mechanism. They would be recovered using the reverse process, just like a docking maneuver.

* In Wing Commander, you fly a dogfighting space plane off of a hollow carrier and blast lasers at catlike versions of Klingons, just like the games from way back. It’s got a lot going for it, especially for such a big project done entirely in hobbyists’ off hours – lots of the game design is clearly an homage to the original games. As long as you don’t mind that your first briefing officer  sounds like Strong Bad’s parody of anime.

** I have to say, “Diaspora” really nailed the whole feel of Battlestar Galatica. Everything from the frenetic combat, the harried atmosphere, and even the little sounds the Viper makes. The game sometimes crashes out, but it’s a tremendous achievement and a tremendous amount of fun. If you like Battlestar Galactica at all, you own a computer, and you like games, there is no reason at all not to download this.

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