I saw Gravity the other day and while visually and emotionally compelling, and besides the liberties taken with orbits, something else struck me as unrealistic, but I'm not sure if it is or isn't: the apparently lack of physical security on spacecraft. As for its counterpart, I have a vague notion there is ferocious information security so someone with a transmitter can't deorbit a satellite.

While getting into orbit is something of an obstacle, are there no locks on airlocks? Is space like Canada?

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    $\begingroup$ This is one more great opportunity to bring up the fact that we currently have 500 kg of weapons-grade highly enriched Uranium orbiting the Earth. The IAEA spends enormous resources hunting down grams of this stuff. space4peace.org/ianus/npsm3.htm $\endgroup$
    – AlanSE
    Commented Oct 11, 2013 at 22:11
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    $\begingroup$ "Do you have the key?" "What? I thought you brought the key!" "Oh, crap." $\endgroup$
    – Mark Adler
    Commented Oct 11, 2013 at 23:31
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    $\begingroup$ @Scott We have that covered already. Can I borrow a lunar rover? $\endgroup$
    – user
    Commented Mar 20, 2016 at 22:10
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    $\begingroup$ @MarkAdler "I thought I left it under the doormat ..." $\endgroup$ Commented Apr 6, 2016 at 16:07
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    $\begingroup$ And now the movie The Martian is relevant to this question as well. $\endgroup$ Commented Apr 6, 2016 at 20:11

3 Answers 3


First, I have to mention I haven't seen the movie yet. I've resisted temptation after seeing so many technical inaccuracies mentioned on Twitter by the International Space Station (ISS) astronauts that I follow. No, not the astrophysicist Neil DeGrasse Tyson, even though he was mentioned most frequently in the mass media for taking it a personal quest of his to debunk all the inaccuracies that were apparently littered throughout the movie, about its physics, technical details, even visuals. I mean people that were actually there, and most of them actually enjoyed the movie (I've read many of their reviews of the movie so this is my impression), albeit mostly for other reasons than its accuracy.

I could give you detailed technical specification of all the airlocks, hatches and whatnot that has access to and from the ISS (yes, there are several, although I suspect the movie tried to present the Quest joint airlock?), So I think this is best left to be explained by those that were both there, and have seen the movie. For example, Leroy Chiao (@AstroDude on Twitter), a former NASA astronaut and commander of the International Space Station (ISS) said in his review of the movie for Space.com:

... existing spacecraft are depicted with hatches and other controls that are in the wrong places.


... there is no way to enter an airlock from the outside, unless it had already been prepared for such an entry. The inner hatch would have to already be sealed.

Astronaut Leroy Chiao in a Russian Sokol spacesuit.

Astronaut Leroy Chiao in a Russian Sokol spacesuit (Source: Space.com).

Additionally, again from my experience on Twitter, I've seen it mentioned that the repressurisation process in the movie took perhaps 3 seconds. That is again highly inaccurate and the repressurisation of the crew lock takes roughly 45 minutes, but can be somewhat hurried in case of an emergency. It would most certainly not be 3 seconds from 0 psi (0 kPa) to 14.7 psi (101 kPa) that is the ISS internal atmospheric pressure on astronauts' return from their EVA (Extravehicular Activity).

For example, when Luca Parmitano's helmet started filling with water from his PLSS (Portable Life Support Unit) and he rushed back to the airlock, it took many agonizing minutes to repressurize it, as he wrote in one of his blog posts. If it took 3 seconds, or thereabouts, that would literally feel like being inside an explosion. This repressurisation process can be somewhat appreciated by looking at the reverse, the depressurisation process for the Quest joint airlock:

The usual pressure inside the ISS is 1 bar, though in the Quest airlock this is 0.7 bar during depressurisation in connection with nitrogen purging. When the astronauts are in the crewlock ready to start their EVA this pressure is reduced first to 0.35 bar when a leak check is performed on the suits. If this is ok the crewlock is reduced in pressure down to 0.2 bar. The final depressurisation to vacuum occurs through venting through a valve in the EVA hatch. The hatch can now be opened and the EVA can begin.

The hatch remains open for the duration of the EVA for several reasons, among which also for astronauts to be able to return in an emergency, and also to conserve the volumes of the nitrogen and oxygen in the external tanks that are used for nitrogen purge, repressurisation and also to recharge the EMUs (Extravehicular Mobility Unit, of which there are two types onboard the ISS).

And no, none of the ISS external airlocks or berthing hatches open from the outside, so no keys there. Not the Russian docking ports on Poisk, Pirs, Rassvet or Zvezda service module, not on Leonardo cargo bay, Tranquility, Harmony, the JAXA's Kibō that has an airlock with a key release of the CYCLOPS (Kinetic Launcher for Orbital Payload Systems) small satellite launch system but from within the ISS, and not on the Quest joint airlock. The only hatches that have a sliding opening door that opens from the outside are on the resupply vehicles (there's many, so I'll spare you with the list), that are mostly tightened in place with a set of bolts that need to be removed with a torque wrench.

Anyway, I didn't see the movie yet, but I guess its script likely wouldn't work, if they tried to make it 100% accurate. The preparations for EVA take roughly one day with all kinds of, in terms of motion pictures, rather boring procedures that I don't expect anyone would be too interested in. Not in an action movie at least. Maybe in a documentary, but even there it likely wouldn't take longer than perhaps 10 minutes to go through it? So my advice would be that if you've forked out for the tickets, then make the best of it and enjoy the ride. ;)

P.S.: Oh, and about information security in space that you also mention in your question, here's a nice relevant thread from Information Security Stack Exchange on What would one need to do in order to hijack a satellite?

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    $\begingroup$ Good, complete answer. I would still going and watch the movie if I were you though. All performance art requires some form of suspension of disbelief. $\endgroup$
    – Diederik
    Commented Nov 1, 2013 at 20:08
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    $\begingroup$ I think that when you are professionally involved in something you get more picky about the little details no one else notices. I cringe when I see an enlisted or junior officer casually address a senior officer in TV shows... that sort of thing just doesn't happen beyond your first week of basic. I loved the series JAG but some episodes it was really hard to watch. $\endgroup$
    – Chad
    Commented Dec 30, 2013 at 22:35

Locks aren't needed, because it is physically impossible to open the hatch from outside unless the airlock is depressurized.

All airlock hatches are inward opening (the STS Orbiter side hatch was not an airlock hatch) and the air pressure inside amounts to tons of force keeping the hatch closed.

For example, check out this picture of the ISS US airlock. That white thing flipped up is just a thermal cover. You can see the actual outer hatch hinges behind Cassidy and the hatch is down behind his backpack.

enter image description here

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    $\begingroup$ ... it is physically impossible to open the hatch from outside... well, a large can opener like they'd use in Spaceballs had they any need for it would have done the trick :) $\endgroup$
    – TildalWave
    Commented Jul 27, 2015 at 16:47
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    $\begingroup$ Does this still apply if you're willing to break stuff (and have tools to do so)? $\endgroup$
    – ikrase
    Commented Oct 14, 2020 at 20:05
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    $\begingroup$ @ikrase if you're willing to kill everybody inside you could drill or blast a hole and let the pressure drop until you could open the hatch. $\endgroup$ Commented Oct 14, 2020 at 20:06
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    $\begingroup$ I was thinking of a somewhat less aggressive level of "break stuff". Seems like under some circumstances, drilling a hole and then patching it with tape could make an airlock cycle. $\endgroup$
    – ikrase
    Commented Oct 14, 2020 at 20:08
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    $\begingroup$ @ikrase The inner hatch is kept open (space.stackexchange.com/a/19284/6944) so not sure how to do it from outside without depressurizing the whole ISS. $\endgroup$ Commented Oct 14, 2020 at 20:10

There are three major arguments against physical security on manned spacecraft:

  1. A lock is a point of failure. Given the dire consequences of an astronaut being locked out after a spacewalk, you need to make really sure people can get in in an emergency. So adding a lock would make the hatch design a lot more complicated, for no added value (see point 2).
  2. Hijacking a manned spacecraft is really unlikely. There are only 3 nations on Earth capable of launching a manned mission. If one of them decides to hijack another nation's mission, they'd have an international crisis on their hand, if not a war. So the hijacker pays a huge price, for no benefit (see point 3).
  3. Why bother? Manned missions are largely peaceful scientific missions. If you want to take part, pay a few dozen million and you can send an astronaut up to the ISS. No need to kick in the door. Also, there's no point in hijacking a manned mission. Say you've taken over a spacecraft: what are you going to do with it? There's no benefit to hijacking.

For unmanned satellites the situation can be more complicated, esp. in the case of military satellites. It's likely those have countermeasures against remote tampering (hacking) on board.

Physical security? Again, unlikely. Launching a space mission isn't covert: anyone can track your spaceship, so if you launched a mission to hijack an enemy's satellite, they'd know it's you. Their response would be to bomb your launch site, so you'd get to do this no more than once. Again high cost, little benefit. The only problem military satellites face is getting blown up by an antisatellite missile, and those are difficult to defend against. A ballistic missile defence system is huge and expensive, to add that to a satellite would add several tons of weight and cost a fortune.

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    $\begingroup$ 4 nations can send mens to space ? I count only 3: US, Russia, China (with Russian gear) $\endgroup$
    – Antzi
    Commented May 30, 2015 at 16:30
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    $\begingroup$ you're right, of course. $\endgroup$
    – Hobbes
    Commented May 30, 2015 at 16:34
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    $\begingroup$ For the moment more like 2: Russia and China (I guess communism lost the space sprint but won the marathon :P). $\endgroup$
    – Nick T
    Commented Jun 1, 2015 at 16:27
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    $\begingroup$ Point 3 sounds a lot like cutting Lex Luthor a check. (Warning: TV Tropes link!) $\endgroup$ Commented Jun 18, 2021 at 13:24

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