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.

Suit 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.

A7L & A7L-B Suit Shuttle EMU Suit Shuttle ACES Suit
Manufacturer ILC Dover (suit), Hamilton Sundstrand (backpack) Hamilton Sundstrand (HUT and hardware, including PLSS), ILC Dover (Arm assemblies, gloves, LCVG, and LTA), Airlock (Helmet, EVVA, bearings, BSC, disconnects, etc.) David Clark Company
Main Functions Protection from cabin fire and sudden depressurization when in Apollo CSM or LM and as an EVA space or moonwalking suit Protection from near-vacuum conditions during EVA Sudden depressurization during launch and entry while in Orbiter; bailout protection in controlled gliding flight below 50,000 ft.; water immersion for 24 hrs.
First Used 1968 Apollo 7 1984 STS-6 1981 STS-1 – a modified U.S. Air Force high-altitude pressure suit was used for the first four flight. 1995 – replacement for partial-pressure "Launch-Entry Suit" used since STS-26 in 1988.
Last Flight 1975 Apollo-Soyuz Test Project Still in Service 1984 STS-4 – reintroduced after Challenger Disaster as partial pressure "Launch-Entry Suit" (LES), replaced fleetwide with current ACES model in 1998.
Features One piece five-layer "torso-limb" suit augmented with a 3-layer "cover layer" made from Teflon-coated fiberglass thread for IVA (non-spacewalking) suits or a 17-layer "cover layer" for EVA (spacewalking) suits (A7L-B lunar suits had additional layers due to the longer surface EVAs, while A7L-B Skylab suits had fewer layers due to the near-Earth environment). First suits to use "bubble helmets" (eliminating the need for a visor seal), and communication ("Snoopy") caps and connectors allowing the suits to be hooked up to both the spacecraft and the life-support backpack at the same time. Two-piece 17-layer suit incorporating both the life-support and micrometeoroid protection. HUT has life support backpack and controls integrated in system. Uses same bubble helmet and communications cap from Apollo, although helmet is augmented with a EVA visor assembly incorporating lights and TV cameras. One piece five-layer "torso-limb" suit with a two-layer NOMEX cover layer colored international orange for easy spotting in the case of an emergency Orbiter bailout in controlled gliding flight. First post-Apollo suit to incorporate a full-pressure helmet with a faceplate that can open and close, and augmented with a sunshade visor for glare protection from the sun. Inflatable bladders in legs act as "g-pants" for astronauts during reentry phase as a precaution against fainting.
Weight (fully loaded) 245 lb (111 kg) (A7L-B lunar suit) 195 lb (88 kg) (current Shuttle/ISS version) 80 lb (36 kg) (current model)
Advantages and Disadvantages Suits were custom-made for each astronaut, with each prime crew having three suits and each backup crew having two. Suits were worn only once for each mission, especially those in the last three Apollo flights when the fine powdery dust ground into the cover layers of the suits, turning the white suits in a deep gray color. Also, astronauts had to assist each other when donning the suits, especially with the A7L when the zipper ran vertically up and down the back of the suit (the A7L-B suit's zipper ran from the left hip, across and diagonally across the back to the right shoulder, allowing the astronaut to somewhat don the suit himself) Only the gloves have to be custom-made, costing over $40,000 USD for each pair – the suits can be reused up to 25 times with regular maintenance and are assembled from components based on the astronauts height, weight, and body structure. Suits are custom-made for each astronaut, but, with proper maintenance, can be reused like their Air Force counterparts (used on both the U-2 and SR-71 spyplanes). Suit cannot function in near-vacuum (above 50,000 feet), due to the anti-suffocation valve located on the helmet, thus a cabin leak during launch would require the crew to perform a risky "Return to Launch Site" (RTLS) abort to Kennedy Space Center.


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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