Spacesuits prepped for upcoming spacewalks

NASA astronauts have been busy getting their spacesuits ready to go in preparation for a suite of 10 spacewalks outside the International Space Station. The first of five spacewalks to replace nickel-hydrogen batteries on the space station's truss with newer, more powerful lithium-ion batteries is set to begin Sunday, Oct. 6, with four more following before the end of the month.

Another five spacewalks to repair the Alpha Magnetic Spectrometer-a cosmic ray catcher searching for evidence of "dark matter" in the universe and mounted on the exterior of the station-will follow in coming weeks.

The spacesuit worn during these excursions is the Extravehicular Mobility Unit, or EMU. This suit is essentially a personal spaceship that keeps astronauts safe and ensures they are able to perform complex, difficult work in the vacuum of space and the microgravity environment of low-Earth orbit. The spacesuit provides life support including breathing air and thermal controls, critical in space where temperatures range between plus or minus 250 degrees Fahrenheit, battery power, communication systems, and protection from radiation and tiny space debris-all of which are necessary for spacewalker safety and productivity.

Once outside the safe haven of the orbital laboratory, astronauts typically spend about 6.5 hours spacewalking, not including the time it takes to prepare to float out of the hatch. Spacewalking is one of the most dangerous tasks performed during an astronaut's mission, and to ensure top performance, safety and range of motion during the intense process that is a spacewalk, a properly fitting spacesuit is key.

Before ever launching to space, astronauts train for spacewalks at NASA's Neutral Buoyancy Lab (NBL) located at the Johnson Space Center in Houston. This underwater laboratory simulates the microgravity environment of space by using foam and weights to make astronauts neutrally buoyant-they neither float to the top nor sink to the bottom of the pool.

Here, crewmembers are sized and fitted for each component of the spacesuit. EMU's are made up of a collection of parts put together to fit a particular astronaut. The parts include the hard upper torso (HUT) that encloses the upper torso of the body, legs, lower arms, waists, boots, sizing rings and gloves. Each of these spacesuit components is interchangeable. There are three HUT sizes (medium, large and extra-large), four leg sizes, seven lower arm sizes, two waist sizes and two boot sizes. Due to the nature of spacewalks being hand intensive, and to ensure best fit for crewmembers, the glove fit is much more complicated and occasionally custom gloves are built for specific astronauts.

During ground training, astronauts evaluate suits of multiple sizes to improve planning flexibility on orbit. Some crewmembers fit only one size HUT, while others are able to fit between two sizes and could perform a spacewalk in multiple sizes, if necessary. While training at the NBL, astronauts can choose a prime and an alternative suit size based upon performance, fit, safety and a number of other factors.

Though suit sizes are determined on the ground, once on orbit, size adjustments can be made to take into account how astronauts' bodies change during spaceflight. These changes require anywhere from 15 minutes of crew time for a minor adjustment, to up to 12 hours for a complete HUT removal and replacement task. If a complete HUT replacement is required in space, water inside the suit must be cleaned and checked for contamination; hardware must be physically changed out; and the various suit systems must be verified with the ground crews to confirm the suit is safe and ready to wear.

Aboard the International Space Station, NASA keeps enough components on hand to make four complete spacewalking suits, of which two HUTs of the same size can be available at any given time. The spacewalking suit sizes that are ready to go are based on the needs and preferences of the astronauts expected to wear them.

Due to a number of factors, ranging from safety to fit and performance, a crewmember may decide in orbit that their size preferences have changed. This is not uncommon, as astronauts' bodies change on orbit and ground-based training can be different than performing spacewalks in the microgravity environment outside the space station. When that occurs, the teams on the ground determine what course of action will best accommodate both the astronauts' preferences and the demands of the space station's schedule.

For the upcoming series of 10 spacewalks, all of the spacewalkers prefer to use a medium HUT, so two medium sizes have been readied for duty. Each crew member will be able to perfect their suit's sizing using the many adjustments available in the various components that make up their suit.

Live NASA Television coverage of the first spacewalk in the series will begin at 6:30 a.m. EDT Sunday, Oct, 6.

Related Links
International Space Station
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