TheExtravehicular Mobility Unit (EMU) is an independentspacesuit that provides environmental protection, mobility, life support, and communications for astronauts performingextravehicular activity (EVA) inEarth orbit. Introduced in 1982, it is a two-piece semi-rigid suit, and is one of two types of EVA spacesuits used by crew members on theInternational Space Station (ISS), the other being the RussianOrlan space suit. It was used byNASA'sSpace Shuttle astronauts prior to theend of the Shuttle program in2011.
The EMU, like theApollo/Skylab A7L spacesuit, was the result of 21 years of research and development.[Note 1] It consists of a Space Suit Assembly (SSA) assembly which includes theHard Upper Torso (HUT), arm sections, gloves, an Apollo-style "bubble" helmet, the Extravehicular Visor Assembly (EVVA), and a soft Lower Torso Assembly (LTA), incorporating the Body Seal Closure (BSC), waist bearing, brief, legs, and boots, and a Life Support System (LSS) which incorporates thePrimary Life Support System (PLSS), electrical systems, and a Secondary Oxygen Pack (SOP).[1] Prior to donning the pressure garment, the crew member puts on aMaximum Absorbency Garment (MAG) (basically a modifiedincontinence diaper – Urine Collection Devices (UCDs) are no longer used), and possibly a Thermal Control Undergarment (long johns). The final item donned before putting on the pressure suit is theLiquid Cooling and Ventilation Garment (LCVG), which incorporates clear plastic tubing through which chilled liquidwater flows for body temperature control, as well as ventilation tubes for waste gas removal.
After donning the LCVG, the astronaut then puts on the LTA, before entering the airlock. The astronaut then dons the HUT, connects the LCVG umbilical to the umbilical in the HUT, and then locks the two parts of the suit together using the Body Seal Closure. Once the suit is turned on and checked out, the astronaut dons a "Snoopy cap", a brown and white fabric communications cap dating back to theApollo days, which incorporates a pair of earphones and microphones, allowing the EVA astronaut to communicate with both the crew members in theorbiter and ground controllers inHouston. After donning the "Snoopy cap", the gloves and helmet are then locked on, pressurizing the suit. The suit's regulator and fans activate when the servicing umbilicals are removed and the suit reaches an internal pressure of 4.3 psi (30 kPa). A typical EMU can support an astronaut for 8.5 hours, including 30 minutes of reserves in the case of primary life support failure. To perform an EVA from the shuttle, the cabin pressure was reduced from 14.7 to 10.2 psi (101 to 70 kPa) for 24 hours, after which an astronaut had topre-breathe for 45 minutes.[2] For EVAs on board the ISS, the astronaut must pre-breathe for about four hours,[2] although since 2006 most ISS EVAs have instead employed a "camp out" procedure where the spacewalk team sleeps in theQuest airlock module while the atmosphere is adjusted.[3]
The EMU hardware and accessories (PLSS, helmet, communications cap, and locking rings for the helmet and gloves), is manufactured byHamilton Standard (later theHamilton Sundstrand division ofCollins Aerospace) inWindsor Locks, Connecticut, while the suit's soft components (the arms of the HUT and the entire LTU) are produced byILC Dover (a former division ofPlaytex) inFrederica, Delaware. The two companies, who were rivals during the early days of Apollo for the contract to build the "Block II" (moonwalking) space suit, teamed up in 1974 against theDavid Clark Company andGarrett AiResearch for the EMU development and construction. During Apollo, the ILC Dover-produced A7L used thelife support backpack, helmet, and locking rings supplied by Hamilton Standard, but originally, ILC Dover was to just supply the arms and legs of the suit, a similar process that still occurs.
In total 18 EMU suits with PLSS were manufactured; 5 were lost during missions, 1 was lost in ground test, and, as of 2017, 11 remain complete and functional.[4]
Upon receiving the contract to build the EMU in 1974, Hamilton Standard and ILC Dover delivered the first EMU units to NASA in 1982. During the research and development phase (1975–1980), a suit being tested caught fire, injuring a technician and forcing a redesign on the regulator and circulation fan. OnSTS-4 in July 1982, the astronauts practiced donning and doffing the suit in the Shuttle's airlock. The first Shuttle EVA was to occur onSTS-5, but an electrical failure on the circulation fan forced the EVA to be cancelled. The first EVA of the new EMU finally occurred onSTS-6 whenStory Musgrave andDonald Peterson went out in the payload bay of theSpace ShuttleChallenger and tested techniques to lower the launch cradle of a solid-fuel upper stage used to boost aTracking and Data Relay Satellite (TDRS-A) into a geostationary orbit.
Other EVAs followed on the Shuttle, notably those onSTS-41-B (the firstManned Maneuvering Unit flight),STS-41-C (theSolar Max repair mission),STS-41-G (the first AmericanEVA involving a woman), andSTS-51-A (where two stranded satellites were retrieved and returned to Earth), but the majority of EMU uses occurred on the servicing missions of theHubble Space Telescope. For those flights, two sets of EVA astronauts would venture out of the orbiter, thus requiring NASA to fly four sets of suits (along with repair parts). 41 EVAs using EMUs had been conducted out of the Space Shuttle airlock prior to the start of ISS assembly in November 1998.[5]
With the building of the ISS, Hamilton Sundstrand and ILC Dover refined the Shuttle EMU by making the suit modular. This allowed an EMU to be left on the ISS for up to two years and resized on-orbit to fit different crew members. The ISS EMUs also have increased battery capacity, theSimplified Aid For EVA Rescue (SAFER), improved cameras and radios, and a new caution and warning system. Another feature is an additional battery to power heaters built into the glove, allowing astronauts to keep their hands warm during nighttime passages on each 95-minute orbit.
The ISS EMUs and the Russian Orlan suits are used by crews of all nationalities on the International Space Station. The two EMUs are stored within theQuest Joint Airlock.
As of 2019[update], NASA plans to use Exploration Extravehicular Mobility Unit (xEMU) system duringArtemis program, derived from the spacesuit technologies used in the past.[6]
On June 1, 2022, NASA announced it had selectedAxiom Space andCollins Aerospace to develop and provide astronauts with next generation spacesuit and spacewalk systems to work outside the International Space Station, explore the lunar surface on Artemis missions, and prepare for human missions to Mars.[7]
Kenneth S. Thomas; Harold J. McMann (2006).US Spacesuits. Chichester, UK: Praxis Publishing Ltd.ISBN 0-387-27919-9.
