The Fitness Fixer
The Fitness Fixer

Space Walks

The space shuttle Endeavour landed yesterday at Kennedy Space Center in Florida.

Endeavour's two-week assignment to the International Space Station was shortened for safety arrangements concerning Hurricane Dean.

The Endeavour name uses British spelling because it was named for the HMB Endeavour, a sailing ship commanded by 18th century explorer James Cook. Before launching the space shuttle Endeavour, NASA hung a humorous, quickly replaced "GO Endeavor" banner. The formal name is STS - Space Transportation System. This mission was STS-118.

During STS-118, crewmembers went outside the vehicle for assorted tasks. Going out is called extravehicular activity (EVA). Space doesn't support human life. Crew going on EVA wear pressurized suits to protect against radiation, space debris, temperature extremes, and low air pressure. The suits aren't just called suits, they are Extravehicular Mobility Units (EMUs). EVAs get interesting because EMUs are pressurized higher than the near vacuum of space, but aren't pressurized as much as inside the shuttle. Because of the lower air pressure inside EMUs, risk increases for problems like gas embolism, but chiefly, decompression sickness, also called the bends.

Air pressure around us keeps nitrogen gas dissolved all over in our body all the time. When you go up a mountain, in a high airflight, or on an EVA, there is less surrounding pressure. Nitrogen becomes undissolved. If you reduce pressure slowly enough, nitrogen comes out peaceably and you can breathe it out. If you come up from a scuba dive or jump out for your EVA too fast, nitrogen offgases too fast, making bubbles, which are believed to be the basis of decompression sickness. Beside the role of exercise in countermeasures for space health and after returning, exercise is one of several factors affecting risk of decompression sickness. The post Exercise and Fitness in Decompression Sickness Risk explains.

If you could start an EVA with less nitrogen in your body, you could reduce your risk of decompression sickness. Crew preparing for an EVA do lengthy de-nitrogenation procedures. They breathe oxygen instead of air, and do physical exercise to "wash-out" nitrogen in several stages taking many hours. One goal of aviation scientists is to develop faster protocols for denitrogenation without increasing risk of decompression sickness during EVA.

American and Russian space programs use different denitrogenation protocols and different EVA suits. Russians use EMUs with higher suit pressure. The American suit design uses lower pressure, making it more flexible and maneuverable. The lower pressure suit is considered riskier for decompression sickness, and needs longer prebreathing and denitrogenation exercise. The Russian suit, higher pressure inside, is stiffer, needing more muscle to move. My Russian scientist friends say it is like the AK-47 - tough but good. My American scientist colleagues state that the Russian egress suit is a bull, lacking dexterity. My Russians reply they don't need it, as their vehicles, suits (and cosmonauts) are built strong and austerely, not needing fussy fine-tuning. Da.

My crew surgeon friends from both agencies are all submerged in triplicate paper forms for permissions to send me mission stories and photos to post for you. Nice that everyone can feel universally understood.



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Endeavour STS-118 on Pad39A photo by jurvetson
Endeavour STS-118 blastoff by jurvetson
STS-116 Spacewalk over Cook Strait New Zealand photo by elroySF
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About the Author


Dr. Bookspan is an award-winning scientist whose goal is to make exercise easier and healthier.