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Shuttle Extravechicular Moblity Unit The shuttle EMU provides necessities for life support, such as oxygen, carbon dioxide removal, a pressurized enclosure, temperature control and micrometeoroid protection, so astronauts can leave the orbiter and work effectively in space. The life-support subsystem contains seven hours of expendables (oxygen, battery for power, water for cooling and lithium hydroxide for carbon dioxide removal) and 30 minutes of emergency life-support oxygen. The EMU can be donned in about 20 minutes, is pressurized to 4.3 pounds per square inch differential (psid) and can be recharged from orbiter supplies during a mission. It weighs about 250 pounds on Earth and is designed for a 15-year life with cleaning and drying between flights.
The shuttle EMU uses a microprocessor to monitor vital functions and automatically alerts the wearer if something is wrong or if expendables are running low.
The space suit assembly comes in various sizes so that, prior to launch, spacewalking astronauts have their suits custom-assembled. Modules are reusable and are designed to fit men and women from the 5th to 95th percentiles of body size.
The EMU donning procedure is simple. The astronaut first puts on the liquid cooling and ventilation garment and then the lower-torso assembly, with attached boots. The hard upper torso and attached life-support backpack are mounted on a special fixture in the orbiter airlock. The astronaut squats under this assembly and slides up into it. Next, he or she connects the two halves with a waist ring. Gloves and helmet are then put on and the entire EMU is disconnected from the mounting fixture.
Prior to extravehicular activity, astronauts use a time-efficient sequence to remove nitrogen from their body tissues. They prebreathe 100 percent oxygen for one hour at 14.7 pounds per square inch absolute (psia). Then the Space Shuttle's cabin pressure is lowered from 14.7 psia to 10.2 psia. After 12 to 24 hours, they don their space suits and, during the EMU checkout, spend an additional 40 minutes breathing pure oxygen prior to depressurizing the airlock.
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