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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7 Responses to Space Carriers

  1. Lubos says:

    Hi,

    here is my thought about how the carrier might work and be useful in space combat:

    As a massive ship controlling thousands of drones.

    The ship will be one massive container full of people in charge of the battle (navigators-guiding the drones, technicians-fitting the drones, commanders, etc.) each with specific task to do. The hull should be massive to protect them from missiles/projectiles/shrapnels. For me it would make sense to have them hidden behind steel/asteroid and truly protect them, while they control the drones that fight the actual battle.

    I would use many specific drones (as we currently do with air warfare for example). Few of them would be hidden relays (to transfer signal, with minimal heat signature), squads of fighters/bombers, electronic and heat defence (creating false images for the enemy, or blinding his sensors), kamikazes, and many more designs we deem useful. The possibility of few basic drone hull designs should make us to be able to retool them between battles, or surprise enemy with new tactic. I would leverage the AI or automatics as much as possible, so the navigators should only input the strategy, and the execution will be done by drones (even with some randomness added).

    But we should not put all our eggs (people) into one basket (ship). So ideally there would be few 4-3 similar carriers, with each carrier being able to get control of all friendly drones in area.

    This has its downsides. The carriers are huge target, and you would need protection drones to repel the incoming projectiles, as the carrier might be the only target of the enemy. But you could add drone-only carriers to the fleet to give you more firepower/drones, and to act as a bait for enemy fire.

    How you see this? Would it work?

    Luboš

  2. Joseph says:

    Yeah, I definitely agree! Some kind of drone carrier would be a good idea. It might even out-perform any carrier with human-crewed or human-controlled fighters. For a drone carrier, the “mothership” would simply serve as a big delivery vehicle – something that can spend its own reaction mass getting to the fight, so that the drones can engage in whatever combat maneuvering they need to do. Smaller craft are also easier to accelerate and maneuver, so the drones would stand a better chance of evading enemy fire and getting into advantageous positions than a fighter built to support humans would.

  3. Christopher Phoenix says:

    Interesting post!! SF writers should be more careful with using naval metaphors to build a space fleet. Additionally, they rarely explore logistics- the old bromide is that “amateurs study tactics, professionals study logistics”. Interestingly, several “space carriers” from SF shows- namely, the Imperial Star Destroyers and Omega-class destroyers from Babylon 5- resemble the Soviet Kiev class heavy aviation cruisers more than, say, the USS Enterprise (the carrier, not the Star Trek ship!). Star Destroyers and the Omega class combine the heavy firepower of a cruiser with the air wing of a carrier, much like the Kiev class.

    “Motherships” that carry smaller combat spaceships into action make sense. The mothership has the big propulsion engines, supplies, support facilities, docking positions for the smaller craft, and the long-range endurance needed for long cruises, while the smaller craft can be solely designed for short-range operations. Such a mothership probably won’t look anything like an aircraft carrier, as you don’t need a flight deck in space- just a hatch or a point to dock on the hull. The “daughter craft” could be small assault craft or even medium-sized short-range combat ship. Space fighters are considered unlikely by hard SF fans, although you can argue that a compact craft will substantially outperform a larger ship. This line of reasoning will probably result in a “space torpedo boat” rather than a space fighter, though…

    A recent example of “space carriers” which don’t resemble aircraft carriers are the Nazi “space zeppelins” from the recent film Iron Sky. These ships carry hordes of heavily armed flying saucers and drag large meteoroids behind them to use as giant kinetic impactors. I guess they are spoofing the “motherships” of UFO fame. :-)

    The rocket exhaust “no-fly-zone” is interesting- I guess those little fighters wouldn’t want to fly anywhere near the big engines!! This would be an even bigger problem in a space carrier with thruster engines pointing in every direction, like the ARMD carriers from Robotech– the Lancer II space fighters are flying out of launch bays dangerously close to very large maneuvering thrusters (which aren’t firing at the time). I’ve heard that ion engines neutralize the ionic exhaust to avoid building up exactly the sort of charge you are describing, so are you sure that a space fighter would pick up a charge?

    Atomic Rockets describes a sample “space carrier” here. Going by the artwork in the margins, it seems that space carriers waaay predate Lucas and Co., going back to stories from the 1930s!! It should be noted these space carriers are large motherships that launch hordes of assault ships, not the pseudo-aircraft carriers of Wing Commander. This sort of ship could be quite practical for planetary invasions- the smaller ships could ferry troops and attack ground installations while the carrier acts as a base of operations and launching point for weapons…

    • Joseph says:

      You’re right, many types of ion engines contain some sort of built-in device to neutralize the ions – however, no such device is going to be 100% efficient. I can tell you that we in the real (not just SF) spacecraft industry worry about this; google “ion thruster plume impingement” and you’ll turn up all sorts of scholarly articles, NASA models, and so on.

  4. Christopher Phoenix says:

    You’re right- charge neutralizers prevent an ion drive spacecraft from building up a charge itself, but the plume still contains energetic ions in addition to neutral gas and sputtered thruster material. An ion thruster plume erodes spacecraft surfaces, causes components to build up charge, and contaminates surfaces with sputtered thruster material. This is already a problem for satellites and NASA probes. The plume impingement problem will be even worse with the far more powerful ion and plasma engines used by fictional space carriers.

    It is pretty amazing that the technical challenges of ion propulsion (a term most people first encounter in SF) is involved with keeping the satellites that provide us with our TV signals on track! Most people never think about how important space has become to their everyday lives, but every time they turn on a TV set, see a weather forecast, or use certain communications systems, they are directly relying on a geosynchronous satellites that use ion thrusters to avoid being pulled off course by the Sun’s gravity. I thought of ion engines as the propulsion thrusters for NASA missions and far future spaceships, not something important many aspects of everyday life- but they are.

    Thanks- now I’ve learned something about fictional spacecraft and real spacecraft design!

  5. Wessmaniac says:

    Nice article! Thanks! I worked on the X-Wing series of Star Wars space combat simulator games. I don’t recall exactly when, but we did introduce “engine wash” causing damage at some point (maybe TIE Fighter.) This was partly because it seemed more realistic that way, but also to address an exploit in the game where players would fly up to a Star Destroyer’s engines and fire away with impunity.

  6. AlexT says:

    With current tech, space carriers make sense because engines can have high Delta-V OR high thrust BUT not both. Hence a setup where combat ships have high thrust and are carried by efficient, slow motherships which could also serve as supply base and hotel for the crews.

    In defense of Galactica, I don’t think they actually made their deck layout visible. So it’s possible that their decks are actually stacked such that thrust is up. On the other hand, ships in this universe don’t really need to thrust much, they do most of their traveling via FTL.

    So no, the Galactica would realistically not need ion drives or any kind of efficient electrical propulsion. Actually the enemy Basestars have no reactive propulsion at all.

    The rocket nozzles are always glowing, though. That’s probably due to the art director saying “Rocket engines need to glow!” while banging his shoe against the table repeatedly.

    As for plume impingement, the battlestar would probably turn off its engines if Flight Control has fighters approaching from the rear. Which is something to avoid, but combat landings in the heat of battle are inherently chaotic. This is not a deal breaker, because a battlestar doesn’t rely on dodging ordnance. It’s built strong enough to survive whatever the Vipers don’t intercept and ballistics don’t shoot out of the sky.

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