How long does it take to get from a spacewalk to being inside the ISS and out of your suit in an emergency?

Question

I just saw a show that featured an incident in which an astronaut on a spacewalk to install the Canada 2 arm on the ISS was temporarily blinded by contaminated water inside his helmet. His colleague said something like "I was getting ready to help him get inside and out of his suit in a relative hurry so he could get help".

I would imagine that it takes at least 20 minutes to get into the airlock and close the door, and about as long to get out of the suit. Am I in the right ballpark? How long would it take in an emergency?

Answer 1

Although not the incident you are referring to, an incident outside the ISS in 2013 during EVA 23 is a good reference point for your question -- where Italian astronaut Luca Parmitano had water leaking into his helmet. My answer is based primarily on information in the official NASA report regarding the incident. There is also a good summary on this site.

During this emergency, it seems there was some debate about whether or not to repressurize the airlock faster but in the end it was decided to repressurize at a normal rate -- with the two options for ending an EVA prematurely being "terminate" and "abort", they chose to "terminate", making sure to tie up any loose ends before returning. It took 31 minutes from the time they decided to return until the time they opened up the inner hatch. Parmitano took 6 minutes to get inside the outer hatch, his EVA partner Chris Cassidy took another 9 minutes, and then it took another 5 minutes until they closed the outer hatch. Repressurization began 3 minutes later and lasted 8 minutes. After that, they performed an "expedited suit doffing" (faster-than-normal removal of a spacesuit), but I cannot track down how long that is supposed to take.

It took quite a while because nobody was really sure exactly how bad the situation was becoming. Let's say they chose to abort instead of terminate, in which case I imagine both astronauts would have returned immediately to the airlock (that gets rid of 9 minutes). The 8 minutes between the time they were both in the airlock and when repressurization began was most likely spent going through checklists of protocols -- let's say we can cut that down to 1 minute in an emergency. Repressurization took 8 minutes at the nominal rate, but according to recommendations in the linked report, this could be achieved in just over 1 minute (in fact, the system is capable of doing it even faster but it would likely cause adverse health effects on the astronauts). So that reduces the 31 minutes to only 8 or 9 minutes, followed by the unknown time to doff the suit.

I suppose in certain situations just getting inside the pressurized station is good enough, in others you might only need to get the helmet off (as in the case of EVA 23), then in more dire situations you'd need to remove the entire suit or at least expose the chest.

Answer 2

If there is a true emergency, a spacewalk will be "aborted". An EVA Abort procedure seems to be pretty simple:

1. Both astronauts go in crew lock (yes, only one can go if desired)
2. Close and lock outer hatch
3. Turn inner hatch pressure equalization valve to emergency setting
4. Open manual pressure equalization valve from inside the station
5. Ensure manual pressure equalization valve on outer hatch is closed
6. Turn water off in the suit control system
7. Open inner door (require maximum 0.5 psi pressure differential)
8. Open space suit purge valve
9. Turn off suit oxygen
10. Turn off suit fan
11. Check that relative pressure in suit is less than 0.4 (psi I assume)
12. Remove gloves
13. Remove helmet

There are a couple of checklist items, but those are placed so that they can be done while waiting for something else to complete. The things that require waiting are airlock pressurization (at emergency speed) and space suit pressure equalization (purge valve open).

The emergency speed airlock pressurization to a normal atmosphere is said (in the report) is said to be +0.34 psi/sec, which makes it last around 45 seconds. The high flow rate setting on the suit oxygen purge valve is rated as 7.75 lb/hr (of pure oxygen vented to space from 4.3 psia), which through numerous quick approximations would mean that it would take around a minute to get from 4.3 psia to 14.7 psia.

So, to summarize: there are two waiting periods of around one minute, that cannot be sped up, before you can remove the helmet, but otherwise it is pretty much limited to as fast as you can move.

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Also of note is that Parmitano mentions that during airlock repressurization he is able to open the helmet if necessary. If this is true, then in an extreme emergency I would guess that an astronaut can open the helmet immediately after the outer hatch on the airlock is closed, probably losing consciousness but surviving.