I just finished watching the Sci-Fi movie Stowaway where the crew of the spacecraft MTS-42 heading to Mars, gets in all kind of troubles after the failure of the single life support system. My question is whether the life support system is in reality completely redundant on the ISS or in previous manned spacecraft (or future ones for which the design has been finalized)? If not, what procedures are in place for dealing with the event of a life support system failure?


3 Answers 3


Partial answer to

whether life support system is in reality completely redundant on ISS or in previous manned spacecraft

(emphasis mine)

For shuttle, a previous manned spacecraft, the life support system was at least one-fault-tolerant for everything except structural failure of the pressure hull i.e. cabin leaks and fires. You can get an idea of the fault tolerance by looking at the go-no go criteria for Life Support.

life support go/no-go criteria part 1 life support go/no-go criteria part 2

(INVOKE MDF means cut the flight short, ENTER NEXT PLS means land at the next opportunity to KSC or Edwards)

If not, what procedures are in place in the event of a life support system failure in order to keep crew alive?

Procedures were in place even for the redundant systems. Here are the procedures included in the ECLSS section of the shuttle Orbit Pocket Checklist (which listed failures requiring quick responses)


Without going through them in detail, you can see there were procedures for the cabin losing pressure, problems with the supply and potable water systems, problems with the cooling systems, and fires.

The "long form" Malfunction Procedures document contains a lengthy section dealing with life support system problems that did not require immediate attention. For further information, browse Section 6 of this nearly 1000 page pdf!


  • 1
    $\begingroup$ but I do not believe it is posted online Maybe submit an FOIA? $\endgroup$
    – forest
    Commented May 3, 2021 at 23:07
  • 2
    $\begingroup$ @forest thanks for the impetus for me to actually look for it! JSC actually posted the document, although it is not linked on their main Flight Data File page. $\endgroup$ Commented May 4, 2021 at 0:35
  • $\begingroup$ What criteria would trigger an emergency landing to one of the emergency landing locations (mostly friendly miltary airfields) scattered around the world? Simultaneous failure of a primary and backup system? $\endgroup$ Commented May 4, 2021 at 5:02
  • $\begingroup$ @DanIsFiddlingByFirelight pretty much. Impending loss of cabin atmosphere, all cooling, all electrical power, etc could have forced a "contingency deorbit". If they were lucky enough to have a reachable airstrip, they'd go there, otherwise bail out. nasa.gov/centers/johnson/pdf/359894main_C-DO_G_L_8_P%26I.pdf See page 27 for table of contents. $\endgroup$ Commented May 4, 2021 at 12:55
  • $\begingroup$ FYI, this is a downstream product of a Failure Modes, Effects, and Criticality Analysis (FMECA), which is where the actual effects of each failure would be identified. $\endgroup$
    – fectin
    Commented May 4, 2021 at 18:13

Painting in broad strokes:

In addition to the above answer, you could look at the ISS as almost two separate space stations - the US orbital segment and Russian orbital segment. If the above covers similar ground to the US OS by way of similar technology and coming from the same agency, the other side is the Russian OS which also has its own life support system.

FGB (first module launched) and Zvezda are autonomous vehicles, that is, unlike the US modules, are (or were) able to be launched and operate under their own power and contain their own life support systems.

With life support, the ROS can simply close doors and keep its life support separate from the rest of the station, and the US orbital segment can do the same. You could view that as a back-up of sorts.

Each segment has its own way of recycling moisture and generating oxygen.

Power-wise, with the two OS linked, the ROS shares a bit of the power coming from the main array on the USOS; indeed in the early days of construction, the ROS was powering the USOS before the solar arrays arrived.


Yes and no.

Orbital spacecraft are generally "single-fault tolerant": that is, there's no single failure that can cause an unsurvivable situation. This doesn't mean full redundancy, though: instead, there's often an alternate option that will acheive the end goal of keeping the astronauts alive. Some examples:

  • The Apollo EVA life-support systems dealt with the failure of either the oxygen or cooling systems with an open-circuit air-supply mode. Instead of cycling cooling water through a radiator and using lithium hydroxide to remove carbon dioxide from the air, oxygen from a dedicated tank would flow through the suit once, then be vented into space, giving 30 minutes to get back inside the LM.
  • Vostok 1 was intended to be launched into an orbit that would decay in only a few days, in case the reentry burn failed. (The actual periapsis was slightly too high, and would have resulted in reentry after 20 days).
  • The ISS has chemical oxygen generators that can be used in case the primary oxygen supply system fails.

Partial redundancy is also common. For example, the Space Shuttle had three fuel cells, any two of which could provide sufficient power, and the Crew Dragon space capsule can land safely as long as three of the four main parachutes deploy.

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    $\begingroup$ The advantage of orbital spacecraft though, is that it's relatively easy to break orbit and go home, so your backup doesn't need to last forever. When you go off into deep space, things change. Apollo had a number of single-points-of-failure. Apollo 13 isn't a perfect example, but they patched around several there, managing to use equipment in a way it was very much not designed to work. $\endgroup$
    – AI0867
    Commented May 4, 2021 at 13:58
  • $\begingroup$ @AI0867 "relatively easy" is subjective point of view. Not the same parameters to land with or without cargo. And "dumping" cargo in case of urgency still requires time. Space shuttle total mission time was close to 1323 days for 135 missions, close to 10 days per mission. Average person inhales 11000 liters of air and reduces concentration from 20% to 15%. Minimum allowable concentration of oxygen is 19.5%. Crew of shuttle can be up to 8 people. This means at least 293333.3 liters of breathable air just for one day. $\endgroup$
    – WOW 6EQUJ5
    Commented May 4, 2021 at 17:56
  • $\begingroup$ Capsules have it easy. They're designed to easily separate from any cargo and in theory they can land every orbit, though landing near recovery crews may delay that some. The shuttle was a lot more finicky, what with the internal payload bay and need for a runway. Apollo had it a lot harder. If you're 400 megameters away from earth, you're not coming home today. On an interplanetary journey, you'll probably have to complete the trip, or you're not going anywhere, so your backups needs to be essentially just as capable as the primary. $\endgroup$
    – AI0867
    Commented May 5, 2021 at 9:09

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