Extravehicular Mobility Unit

Extravehicular Mobility Unit

The Space Shuttle/International Space Station Extravehicular Mobility Unit (EMU) is an independent anthropomorphic system that provides environmental protection, mobility, life support, and communications for a Shuttle or ISS crew member to perform extra-vehicular activity (EVA) in earth orbit. It is currently one of two space suits used by crew members on the ISS, the other being the Russian Orlan space suit.

uit components

The EMU, like the Apollo/Skylab A7L spacesuit, was a result of years of research and development. It consists of a Hard Upper Torso (HUT) assembly, a Primary Life Support System (PLSS) which incorporates the life support and electrical systems, arms, gloves, Apollo-style "bubble" helmet/Extravehicular Visor Assembly (EVVA), and a soft Lower Torso Assembly (LTA), incorporating the Body Seal Closure (BSC), waist bearing, brief, legs, and boots. Prior to donning the pressure garment, the crew member puts on a Maximum Absorbency Garment (MAG) [basically a modified "Depends" incontinence diaper] (Urine Collection Devices or UCDs are no longer used), possibly a Thermal Control Undergarment (long johns), and then the "Liquid Cooling and Ventilation Garment" (LCVG), that incorporates clear plastic tubing through which chilled liquid water flows for body temperature control, as well as ventilation tubes for waste gas removal.

Once the astronaut dons the LCVG, the astronaut then puts on the LTA, similar in nature to a firefighter putting on the pants and boots of a fire protection suit. The astronaut then floats into the airlock, dons the HUT, connects the LCVG umbilical to the umbilical in the HUT, and then the two parts of the suit are locked together using the Body Seal Closure. Once the suit is turned on and checked out, the astronaut then dons a "Snoopy cap," a brown and white fabric communications cap dating back to the Apollo days that incorporates a pair of earphones and microphones, allowing the EVA astronaut to communicate with both the crew members in the Orbiter and ground controllers in Houston. 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 8½ hours, with 30 minutes of reserves in the case of primary life support failure.

Comparison between Apollo A7L/A7L-B, Shuttle EMU, and Shuttle ACES suits

Although the EMU is in many ways identical in appearance to the Apollo A7L space suits, and functions in the same manner as that of the Shuttle ACES suit, there are major differences in appearance and function.


The EMU hardware and accessories (PLSS, helmet, communications cap, and locking rings for the helmet and gloves), is manufactured by the Hamilton Sundstrand division of United Technologies out of Windsor Locks, Connecticut, while the suit's soft components (the arms of the HUT and the entire LTU) are produced by ILC Dover out of Frederica, 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 the David Clark Company and AiResearch for the EMU development and construction. During Apollo, the ILC Dover-produced A7L used the life support backpack, helmet, and locking rings supplied by Hamilton United, but originally, ILC Dover was to just supply the arms and legs of the suit, a similar process that is still going on today.


Upon receiving the contract to build the EMU in 1974, Hamilton United 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. The first EMU flew on STS-4 in July, 1982, during which the astronauts practiced donning and doffing the suit in the Shuttle's airlock. The first Shuttle EVA was to occur on STS-5, but an electrical failure on the circulation fan forced the EVA to be cancelled. The first EVA of the new EMU finally occurred on STS-6 when Story Musgrave and Donald Peterson went out in the payload bay of the Space Shuttle Challenger and tested techniques to lower the launch cradle of a solid-fuel upper stage used to boost a Tracking and Data Relay Satellite (TDRS-A) into a geo-stationary orbit.

Other EVAs followed on the Shuttle, especially that on STS-41-B (the first Manned Maneuvering Unit flight), STS-41-C (the Solar Max repair mission), and STS-51-A (where two stranded satellites were retrieved and returned to Earth), but the majority of the EMU's use occurred on the servicing missions of the Hubble 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).

With the building of the ISS, Hamilton Sundstrand and ILC Dover refined the existing Shuttle EMU by making the suit modular. This allowed the EMU to be left on the ISS for up to 2 years and resized on-orbit to fit various crew members. They also made provisions for an increased capacity battery, the Simplified Aid for EVA Rescue (SAFER), improved cameras, radios and a new caution and warning system. Another feature incorporated into the new ISS suits are 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. Currently, the ISS EMU and the Russian ORLAN are used by crews of all nationalities on the International Space Station.

Future Use

NASA will continue to use the EMU once the ISS is completed and the Space Shuttle is retired from active service in 2010. With the upcoming Constellation Program to the ISS, Moon, and Mars to commence in 2015, NASA has decided to replace the EMU and the ACES pressure suit with the new Constellation Space Suit system, which is derived from the ACES suit and the ILC Dover-developed and tested Mark III and I-Suit space suit systems.

The new suit, which is capable, depending upon the configration, of protecting the astronaut during launch, in-flight emergencies, reentry and landing, and both microgravity and lunar EVAs, will feature common hardware and the modular features used in the ACES and EMU suits. On June 11, 2008, NASA awarded a contract for Oceaneering International for the development and manufacturing of the new suits, with the David Clark Company and United Space Alliance being two of seven contractors in the new endeavor. Oceaneering International, based out of Houston, Texas and made famous in 2000 with the raising of the "C.S.S. Hunley", the first submarine credited with a "kill" in modern naval warfare, beat out the Hamilton Sundstrand/ILC Dover partnership in the manufacturing of the new space suit.

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