Tuesday, May 24, 2011

Spacewalk Prep: "Slow-Motion Hokey-Pokey"

Two Endeavour spacewalkers are stepping through a new exercise protocol aimed at avoiding decompression sickness while obviating the need to isolate astronauts in the U.S. Quest airlock prior to an excursion outside the International Space Station.

Mission specialists Drew Feustel and Mike Fincke first breathed pure oxygen through gas masks to start ridding their bloodstreams of nitrogen gas bubbles that could cause painful or even deadly bouts with what SCUBA divers call "the bends." Pressure within the U.S. Quest airlock is being reduced from 14.7 psia -- the same pressure encountered at sea level -- to 10.2 psia as part of a standard procedure.

The new twist will take place after Feustel and Fincke climb into the bulky white spacesuits. The astronauts will spend 50 minutes doing light exercise -- slowly moving their legs back and forth -- to raise their metabollic rates. Doing so will more quickly purge nitrogen from their bloodstreams.

"This is what we call the slow-motion hokey-pokey," NASA lead spacewalk officer Allison Bolinger said.

The new procedure is being used for the first time in orbit. It obviates the need to "camp out" overnight in the Quest airlock and also saves limited supplies of oxygen on the International Space Station. Additionally, it reduces the amount of time astronauts need to breathe pure oxygen before exiting into a vacuum environment in a low-pressure spacesuit.

Given an option, NASA flight controllers would prefer not to isolate spacewalkers in the Quest airlock overnight -- currently, the standard operationg procedure. The one drawback to the new protocol: astronauts have to get started about 30 minutes earlier in their spacewalk preps.

The new protocol passed a peer review by the NASA Engineering and Safety Center before it was approved for trial on the Endeavour mission. Here is the NESC Assessment. Lengthy appendices are HERE

If all goes well, the procedure might be used prior to the shuttle crew's fourth and final spacewalk on Friday.

Endeavour's third spacewalk remains scheduled to start at 1:46 a.m. Wednesday.

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