In the L-474 Logbook I have talked a bit about the Prep & Post class, in which I had the chance to perform the suit IV tasks for crewmate Butch and JAXA astronaut Norishige Kanai. As I mentioned then, the Prep & Post class is about all that happens in an EVA day, minus the time spent outside.
Airlock configuration is something we would take care of in earlier days, but sure enough the first procedures of the “day of” guide us through a final check to make sure that all equipment is in the proper configuration and all switches in the expected position.
Then we start the pre-breath protocol, whose goal is to purge nitrogen from the body to mitigate the risk of decompression sickness when exposed to the low pressure in the suit (about a third of atmospheric pressure): the EV crewmembers don their oxygen masks and the pre-breath clock starts.
We all work together to power up the suits and check their configuration and then it’s time to take the suits apart, so that the EV crewmembers can don the lower component (legs, up to waist). Before they can come off the masks to don the upper part of the suit, we close the hatch to Node1 so that we are isolated from the rest of Station. We then reduce pressure in the airlock by about a third and wait for the oxygen concentration to stabilize at a higher percentage than normal to comply with the requirements of the pre-breath protocol.
Then it’s time for me to help them don the suit. They need to “slide” the upper body into the suit torso and then it’s my job to build the suit around them: connect the legs to the torso, attach the gloves, help then don the com cap, put the helmet on. It’s hard work, especially in 1G! Luckily I had help and guidance from a suit technician.
After more verification steps on the suit and a leak check, we initiate a purge procedure to create a pure oxygen environment inside the suits and I reopen the hatch to Node1. At this point, I help the EV crewmembers work through the In-Suit-Light-Exercise protocol: for about 50 minutes they need to perform cycles of light exercise, mainly moving their legs, to bring up their metabolic rate and accelerate the purge of nitrogen.
Once that is complete, I’ll help them move in the smaller section of the airlock (the one that is depressurized to vacuum), close the hatch behind them and get ready to assist in running the depressurization procedure once they reach a minimum of 100 min of in-suit pre-breath time.
As you can see, it’s a long day before an EVA can even start!
PS: thanks to Josh Matthew for the pic!
EMU check. Credits: Josh Matthew
18/08/2013