Extravehicular Mobility Unit
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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 suits used by American crew members on the ISS, the other being the Russian Orlan space suit.
Suit Components
The EMU, a result, like the Apollo/Skylab A7L spacesuit, of years of research and development, consists of a "hard upper torso" (HUT), which incorporates the life support and electrical systems, arms, gloves, and EVA helmet assembly, and a soft lower suit, incorporating the waist seal, legs, and boots. Prior to donning the suit, the astronaut puts on a urine containment device (UCD), over which a special union suit, called the "liquid cooling and ventilation garment" (LCVG), that incorporate clear plastic tubing for body temperature control (via chilled liquid water) and ventilation tubes for waste gas removal, is worn.Once the astronaut dons the LCVG, the astronaut then puts on the soft lower suit, similar in nature to a firefighter putting on the pants and boots of his or her fire protection suit on Earth (or a pair of chest waders for fly fishing in high stream waters). The astronaut then floats into the airlock where the LCVG umbilical is connected to the umbilical in the HUT, after which the two parts of the suit are locked together using the waist seal. Once the suit is turned on and checked out, the astronaut then dons a "Snoopy cap," a brown fabric communications cap dating back to the Apollo days that incorporates a pair of earphones and microphones, allowing the EVA astronaut to communicate with the crew members in both 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. A typical EMU can support an astronaut for 8 1/2 hours, with 30 minutes of reserves in the case of primary life support failure.
Comparison between EMU and Apollo A7-L Suit
Although the EMU is in many ways identical in appearance to the Apollo A7-L space suits, There are major differences in appearance and function.
- The Apollo A7-L suit was designed for wear inside the spacecraft for launch, in-space activities, and landing, along with all in-space and lunar EVAs. The EMU, from the start, was designed solely for wear in a space vacuum, while another suit, the ACES full-pressure suit, is worn for launch, landing, and emergency bailout from the Orbiter.
- The Apollo A7-L had six life support connectors, allowing for the astronaut to wear a life-support backpack or umbilical. The EMU has the life-support backpack directly attached to the HUT, eliminating the need for a life-support umbilical or life-support connectors.
- Each Apollo suit had to be customized for each astronaut, costing over $100,000 in 1969 USD, and could only be used once per flight (especially evident in the last three Apollo flights, when the lunar regolith, which has a high concentration of pulverized glass, caused problems with the protective outer layer cover and life-support connectors), while the EMU can be sized (from X-Small to X-Large) from different components, and is certified for 25 EVA with routine maintenance in between flights. Only the EMU gloves are custom-made, and costs approximately $25,000 USD (1983) for a pair.
- The Apollo suit had a total of 21 layers--a five-layer torso-limb suit, and a 17-layer protective micrometeoroid cover that had materials that had to be fire resistant (beta cloth) to the pure-oxygen atmosphere in the Apollo spacecraft. The EMU has 15 layers, incorporating the pressure assembly and micrometeoroid protection, with the suit being made mostly of Gore-Tex and Kevlar. The Apollo suit for the last three Apollo flights weight 235 lb., while the EMU weights only 185 lb.
Manufacturer
The EMU hardware and accessories (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 lower soft unit) 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.History
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 construction phase (1975-1980), a suit being tested caught fire, injuring a technician and forcing a redesign on the 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 a regulator failure 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), of which some suits would be exposed to the complete vacuum of space for up to four days. For all of those flights, astronauts either used the Manned Maneuvering Unit or the SAFER emergency pack.
With the building of the ISS, Hamilton United and ILC Dover refined the existing Shuttle EMU by incorporating the SAFER rocket pack into the life-support back pack, along with enough oxygen, electricity, and water for EVAs totaling up to 9 hours (plus a 45 minute reserve), bringing the EMU up to the same specifications of the Russian Orlan spacesuit. Another feature incorporated into the new ISS suits are heaters built into the glove, allowing astronauts to keep their hands warm during nighttime passages on each 95-minute orbit. Currently, the ISS EMU is used by American, European, and Japanese astronauts while its Russian Orlan counterpart is used by Russian, European, and American crews.
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