I have searched and searched and cant seem to find any media whatsoever that explains or outlines exactly how the airlock is operated. What exactly is the process you go through to open it, do you have to do a complicated procedure to depressurize or do you just flip a switch, is there a lock? I don't know! Can anyone explain the procedure, or direct me to a source that can?

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    $\begingroup$ IIRC there are no locks but all the hatches open inwards and are thus held firmly shut when pressurized. Also IIRC, the ISS airlock hatches cannot be opened from outside without assistance from inside the station. I'll see if I can track down sources for this. $\endgroup$ Commented Dec 28, 2018 at 22:57

1 Answer 1


The airlock opening procedure is on the Crewlock Depress/Repress Cue Card, found in the EVA checklist on the JSC FDF page.

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Here is a brief decoding of the steps.

1&2 - ensure the suit communications system is properly configured

3&4 - start the depressurization pump and open the valve in its plumbing. This pump scavenges ~10 psi of the air in the airlock by pumping it back into the main body of the ISS. The starred block checks to make sure it's working.

5,6,7,8 - Once the crew lock is at 5.5 - 6 psia, close the valve, and do a leak check on the suit. The starred block handles the case of a failed leak check.

9&10 - reopen the valve, and then open the Manual Pressure Equalization Valve in the hatch, to dump the remaining air overboard. The scavenge pump runs during this time to get what additional air it can.

11&12 - at 2 psi, turn off the pump and close the valve.

13 - attach safety tethers.

14&15 - open the hatch, close the MPEV

The post-depress steps configure the suit and airlock for egress.

Enjoy your EVA!


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