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An extravehicular activity is most commonly referred to as an EVA. It refers to any activity done outside of a spacecraft by a human. EVA’s can be performed for any number of reasons, including deploy/retrieve experiments, repair satellites, or place new satellites into orbit. The first extravehicular activity was performed by Alexey Leonov in 1965 during the Voskhod 2 mission. Here are the answers to several common questions that many people have about EVA’s.
EVA’s are performed in a space suit for obvious reasons. The space suit is called an Extravehicular Mobility Unit(EMU). While in the EMU, astronauts breath 100 percent oxygen. The EMU is pressurized to about 1/3 of atmospheric pressure. The amount of oxygen contained in air at this pressure is not adequate, so pure oxygen is used. Each EMU has two oxygen tanks that are a lot like scuba diving tanks. These tanks work with a carbon dioxide removal system that allows an astronaut to walk in space for up to 8.5 hours.
Since an EVA can last up to 8.5 hours, some people wonder if an astronaut can eat or drink while on a spacewalk. Yes, they can. Each EMU has a drink bag which attached to the front interior of the suit. The bag comes in two different sizes 21 oz and 32 oz and it is crew choice as to which bag they fly. The bag has a drink tube with a valve which prevents free flow of water into the suit. The valve is opened when the crew sucks on the tube for water. Snacks are a fruit bar wrapped in an edible rice paper. The fruit bar is in a sleeve attached to the neck area of the EMU. All a crew member has to do is bend their neck down and take a bite of the bar and slide it up. This system is inconvenient, so most astronauts scheduled for an EVA simply eat prior to suiting up.
Another question is about the suit itself…why is it so bulky? The bulk is as much a result of the suits function as anything else. The primary function of a spacesuit is to provide a pressurized volume for its crew member. The existing design is reliable and proven. It also accommodates a wide range of sizes of crew members. There have been lots of new designs investigated, but all of them are equally bulky. Making the suits more flexible and less bulky is too cost prohibitive to be practical. Improvements such as better gloves, thermal comfort enhancements, and better helmet lights continue to be implemented as they are developed and made available.
Now that you understand the suit, some have wondered how the airlock is vented so that the EVA can begin. The airlock is vented directly into space. The atmosphere could be saved and reused, but the equipment to do so would increase the weight of the spacecraft, requiring more fuel for liftoff, thus costing more than is justifiable. The exception is any mission from the ISS. The nitrogen and oxygen onboard the ISS must be conserved, so very little can be vented safely., thus pumps are in place to conserve those gasses.
The early extravehicular activities were quite dangerous. The suit swelled on Leonov and he barely made it back into the spacecraft. Ed White(first American to perform an EVA) had difficulty opening the hatch. The time spent working on the hatch nearly cost him and his crewmate their lives. Today, an EVA is a nearly routine, thanks mainly to those early pioneers.
We’ve also recorded an episode of Astronomy Cast about the space shuttle. Listen here, Episode 127: The US Space Shuttle.