Something seemed to me a little bit bizarre when watching some movies or series that take place in space.

When someone wants to leave a ship (either alone or with a smaller vehicle), there must be air going with him.

In real life spaceships, such things are avoided as much as possible by depressurization, but in movies, it's not.

You will tell me: "yes, it loses a bit of air, but that's ok because they'll refill the ship with it next time they land on a planet with oxygen", which would be a wise answer, but what about Battlestar Galactica? They don't land on planets (or if they do it was not something they could count on) and, more than any other serie or movie, their airlocks are enormous rooms in which one can still breath before the opening (no spoilers there, but sometimes you see people evacuated from a room where my whole house could fit).

Obviously, they don't plan to keep their air for further breathing. So my question is: is the air kept with some kind of "air-only magnetic field"? do they produce air out of the void of space? Something else?

  • 3
    Is the gist of what you are asking: "How do ships in the BSG fleet that open airlocks without depressurization replenish their air reserves?"
    – HNL
    Feb 4, 2012 at 11:16

4 Answers 4


I'm assuming you are referring to the newer series and that you're referring to when Callie and Galen were in the airlock, and when ships launch from and land in one of the flight pods on the Galactica. We also see executions, usually using a launch tube. In any case, I'll cover those instances and a couple of others.

In summary, most of the time they can control if more than a little air is lost.

First, when Callie and Galen are in the airlock, the only way to handle it is to blow the outer door and let the air vent. That means air is lost.

Second, for an execution, there are two ways it could be done. The first is to just depressurize the airlock and let the condemned die. The second is to open the outer door, which may lead to the body being pushed out into space. (Which means no clean-up afterwards.) The first means no air is lost. The second does involve losing air.

Third, in the case of regular entrance and exit, the airlock is depressurized before the outer door is open. Little or no air is lost.

Fourth, in the case of a Viper taking off, it is in a launch tube. Launch tubes are separated from the hangars by airtight doors. Vipers are placed in the launch tubes, and then the tube is sealed off and the Viper is launched. This can be done without loss of air by pumping the air out of the tube before launch, but it's not specified in the wiki if this is always done, or even done sometimes.

Fifth, when a ship lands, it does so on the landing deck on one of the flight pods. The landing deck is provided with artificial gravity, but is exposed to space. When a Viper or Raptor lands on the landing deck, it can be lowered into the hangar below with an elevator. Then, after the hatch separating the landing deck and the hangar is closed, that chamber can be pressurized. Other ships that land on the deck are not lowered down to the hangar, but can dock with a docking collar so that those onboard can enter the Galactica without needing pressure suits.

(It is not specified that the lowering of a Viper from the landing deck to the hangar is done in an unpressurized setting, followed by the the chamber being pressurized. The loss of air over the length of such an operation would not only be significant, however, it would also result in injuries to the crew in the hangar deck and loss of light equipment that gets pushed out by the air.)

(Much of this is discussed in the Battlestar Galactica wiki. I've filled in some of the details, but they provide enough that I'm not guessing.)


Yes, they lose air. If there was a Star Trek-style field that kept the air in while letting the other items out of the airlock, then when people are spaced, they wouldn't be sucked out. The air rushing out into space provides the propulsion for the person to be hurled out into space.

However, the amount of air this wastes is pretty tiny, in the grand scheme of things. We're dealing with a single room losing all the air inside. Assuming their atmosphere is 20% oxygen like Earth, then you'll have to multiply the volume of the airlock by 20% to find how much important air is lost. This is one room on a huge Battlestar. They lose far more air when a fire breaks out, or when the hull is breached.

For replacing the lost air, or maintaining reserves, they have numerous options. The ship Cloud Nine has a park, with plants. This would provide a natural source of oxygen that can be ferried between ships in the fleet. I'm sure with the fleet's advanced technology, they could also process carbon dioxide and pop off the carbon atoms, resulting in shiny, new oxygen. There are also many ships that we do see enter planets; Raptors specifically are shown as scouting planets several times. It's feasible that these ships have air compressors on board that could suck up a bunch of the atmosphere of a habitable planet, and store it. Then when they return to the Battlestar, they then add this to their reserves.

As mentioned in the comments, they could also obtain oxygen from mining. Fortunately, they have some mining ships in the fleet. I don't recall this being explicitly stated in the show, but it's possible.

  • The series bible (which can be found online) states that there are very few habitable planets in the Galactica universe. Do you have a source for this?
    – Tango
    Feb 4, 2012 at 8:35
  • The fleet has mining capability. And carbon and oxygen is one of the most abundant elements in the universe.
    – HNL
    Feb 4, 2012 at 11:11
  • @TangoOversway Is my edit clearer?
    – user1027
    Feb 5, 2012 at 2:17
  • Actually, @HNL's comment does a good job of explaining it -- mining for the gas would work.
    – Tango
    Feb 5, 2012 at 3:59
  • +1 for the Cloud 9 plants. I was pretty sure there were a few others, but I could be wrong.
    – Chris Lutz
    Feb 5, 2012 at 22:19

As it sounds like you do want to know about other series, I'll address the two I know.

In Star Wars, the big ships that launch fighters have a force field over the opening that keeps air in but lets fighters out. In Star Trek, they depressurize the launch bay before launching shuttlecraft. In both, if they're going through an airlock, they depressurize it before opening the outside.


As an aerospace engineer, you'd be pretty dumb to build an airlock on a BSG-type ship and not have the normal procedure be to pump down the room before opening the external door. That would limit your losses to what couldn't be pumped out. You've already plumbed the room to fill it with air; shouldn't be too hard to make sure it can pump down too.

Now if you're making someone walk the metaphorical plank, then pumping down the airlock with unsuited people inside could make a big mess (see comments). In that case, the cost of the lost air seems reasonable. Hopefully the ship isn't executing enough people to run out of air that way.

  • Either that, or you could spread Saran Wrap over the floor before executions!
    – Tango
    Feb 4, 2012 at 18:14
  • "...pumping down the airlock with unsuited people inside makes a big mess." Ah, no, that's a fallacy -- people don't explode in vacuum. They'd die. Then you have to get rid of the body, but it's not especially messy. Feb 5, 2012 at 4:41
  • @KateEbneter Good point. I wasn't very clear about what I meant. People don't explode, but they might bleed, and I would think you'd want to clean up any blood. They also might struggle or otherwise cause damage that would be more trouble to recover from than just dumping a small room full of air.
    – Adam Wuerl
    Feb 5, 2012 at 19:58

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