L-390: Rehearsing pre- and post-EVA

As mentioned in yesterday’s logbook, Terry and I spent the day in the airlock mockup to rehearse pre- and post-EVA procedures.

The most important topic of the day was the pre-breath protocol. Before depressing the airlock to vacuum and opening the hatch to go on a spacewalk, we need to pre-breath pure oxygen to purge nitrogen from our bloodstream and prevent decompression sickness symptoms while out on an EVA. Yes, it’s the same problem that divers might have when they resurface: going from a higher pressure to a lower one. The suit, in fact, is only pressurized to about a third of atmospheric pressure: otherwise it would be too rigid and it would be impossible to do complex work in it.

There are different pre-breath protocols. The one that is commonly used now is the In-Suit Light Exercise. After breathing pure-oxygen through a mask for about an hour while performing initial preparatory work, EVA crewmembers don the suits, purge them for a few minutes to get a pure oxygen atmosphere inside and then do little movements with arms and legs for about 50 minutes. That increases the metabolic rate slightly and speeds up the nitrogen purging.

One of the goals of yesterday’s Prep & Post class was for Terry and me to understand how intense (or actually little intense) that in-suit exercise has to be to hit the target metabolic rate. Medical personnel gave us feedback real-time based on our CO2 production so that we could adjust the intensity of the work and, hopefully, develop some memory for the ideal level of exertion that is required.