View source for Extravehicular Mobility Unit

{{Short description|Series of semi-rigid two-piece United States space suit models since 1982}}
[[File:STS-118 EVA EMU Suit.jpg|thumb|200px|The Enhanced EMU Suit. The suits are white to reflect heat and to stand out against the blackness of space; the red stripes serve to differentiate astronauts.]]

The '''Extravehicular Mobility Unit''' ('''EMU''') is an independent [[spacesuit]] that provides environmental protection, mobility, life support, and communications for astronauts performing [[extravehicular activity]] (EVA) in [[Geocentric orbit|Earth 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 the [[International Space Station]] (ISS), the other being the Russian [[Orlan space suit]]. It was used by [[NASA]]'s [[Space Shuttle]] astronauts prior to the [[Retirement of the Space Shuttle|end]] of the [[Space Shuttle program| Shuttle program]] in [[2011 in spaceflight|2011]].

==Suit components==
[[File:Emu spacesuit control module.jpg|right|thumb|200px| The E.M.U Display and Control Module (DCM).]]
The EMU, like the [[Apollo/Skylab A7L]] spacesuit, was the result of 21 years of research and development.<ref group=Note name=Note01/> It consists of a Space Suit Assembly (SSA) assembly which includes the [[Hard 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 the [[Primary Life Support System]] (PLSS), electrical systems, and a Secondary Oxygen Pack (SOP).<ref>{{cite web | title = EMU Data Book | url = https://www.lpi.usra.edu/lunar/artemis/NASA-EMU-Data-Book-JSC-E-DAA-TN55224.pdf}}</ref>  Prior to donning the pressure garment, the crew member puts on a [[Maximum Absorbency Garment]] (MAG) (basically a modified [[urinary incontinence|incontinence]] diaper – Urine Collection Devices (UCDs) are no longer used), and possibly a Thermal Control Undergarment ([[long underwear|long johns]]). The final item donned before putting on the pressure suit is the [[Liquid Cooling and Ventilation Garment]] (LCVG), which incorporates clear plastic tubing through which chilled liquid [[water]] 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 the [[Project Apollo|Apollo]] days, which incorporates a pair of earphones and microphones, allowing the EVA astronaut to communicate with both the crew members in the [[Space Shuttle orbiter|orbiter]] and ground controllers in [[Johnson Space Center|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 {{convert|4.3|psi|kPa|abbr=on}}. 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 {{convert|14.7|to|10.2|psi|kPa|abbr=on}} for 24 hours, after which an astronaut had to [[Decompression sickness#Exposure to altitude|pre-breathe]] for 45 minutes.<ref name=Foot01/> For EVAs on board the ISS, the astronaut must pre-breathe for about four hours,<ref name=Foot01/> although since 2006 most ISS EVAs have instead employed a "camp out" procedure where the spacewalk team sleeps in the [[Quest Joint Airlock|Quest airlock module]] while the atmosphere is adjusted.<ref>{{cite web | title = International Space Station Status Report #06-7 | url = http://spaceflight.nasa.gov/spacenews/reports/issreports/2006/iss06-7.html | archive-url = https://web.archive.org/web/20060615191754/http://spaceflight.nasa.gov/spacenews/reports/issreports/2006/iss06-7.html | url-status = dead | archive-date = 2006-06-15 | publisher = NASA|author=NASA|access-date=2006-02-17}}</ref>

[[File:Space suit patch.jpg|thumb|NASA's Extravehicular Mobility Unit ''[[Vitruvian Man|Vitruvian]] Spaceman'' patch ([[Space Shuttle]] version, with three stars representing NASA's [[human spaceflight programs]])]]

==Specifications==

===Baseline EMU===
*'''Manufacturer:''' [[ILC Dover]] (suit) and [[Collins Aerospace]] (primary life support systems)<ref name=Foot01/>
*'''Missions:''' [[STS-4]] (1982) to [[STS-110]] (2002)<ref name=Foot01/>
*'''Function:''' [[orbit]]al extra-vehicular activity<ref name=Foot01/>
*'''Operating pressure:''' 4.3 psi (29.6 kPa)<ref name=Foot01/>
*'''EVA suit weight:''' 109&nbsp;lb (49.4&nbsp;kg)<ref name=Foot01/>
*'''Total shuttle EVA suit weight:''' 254&nbsp;lb (115&nbsp;kg)<ref name=Foot01/>
*'''Primary life support:''' 8 hours (480 minutes)<ref name=Foot01/>
*'''Backup life support:''' 30 minutes<ref name=Foot01/>

===Enhanced EMU===
*'''Manufacturer:''' ILC Dover (suit), Collins Aerospace (primary life support systems) and NASA ([[Simplified Aid For EVA Rescue|SAFER]])<ref name=Foot01/>
*'''Missions:''' since 1998<ref name=Foot01/>
*'''Function:''' orbital extra-vehicular activity<ref name=Foot01/>
*'''Operating pressure:''' 4.3 psi (29.6 kPa)<ref name=Foot01/>
*'''EVA suit weight:''' 122&nbsp;lb (55.3&nbsp;kg)<ref name=Foot01/>
*'''Total shuttle EVA suit weight:''' 275&nbsp;lb (124.7&nbsp;kg)<ref name=Foot01/>
*'''Total ISS EVA suit weight:''' 319&nbsp;lb (145&nbsp;kg)<ref name=Foot01/>
*'''Primary life support:''' 8 hours (480 minutes)<ref name=Foot01/>
*'''Backup life support:''' 30 minutes<ref name=Foot01/>

==Manufacturer==
The EMU hardware and accessories (PLSS, helmet, communications cap, and locking rings for the helmet and gloves), is manufactured by [[Hamilton Standard]] (later the [[Hamilton Sundstrand]] division of [[Collins Aerospace]]) in [[Windsor Locks, Connecticut]], while the suit's soft components (the arms of the HUT and the entire LTU) are produced by [[ILC Dover]] (a former division of [[Playtex]]) in [[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 [[Garrett AiResearch]] for the EMU development and construction. During Apollo, the ILC Dover-produced A7L used the [[Primary Life Support System|life 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.<ref name=Foot04/>

==History==
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. On [[STS-4]] in July 1982, 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 H. Peterson|Donald Peterson]] went out in the payload bay of the [[Space Shuttle Challenger|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 geostationary orbit.

Other EVAs followed on the Shuttle, notably those on [[STS-41-B]] (the first [[Manned Maneuvering Unit]] flight), [[STS-41-C]] (the [[Solar Maximum Mission|Solar Max]] repair mission), [[STS-41-G]] (the first American [[Extra-vehicular activity|EVA]] involving a woman), and [[STS-51-A]] (where two stranded satellites were retrieved and returned to Earth), but the majority of EMU uses 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). 41 EVAs using EMUs had been conducted out of the Space Shuttle airlock prior to the start of ISS assembly in November 1998.<ref name=Foot02/>

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, the [[Simplified 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 the [[Quest Joint Airlock]].

==Future use and replacement==
{{asof|2019}}, NASA plans to use Exploration Extravehicular Mobility Unit (xEMU) system during [[Artemis program]], derived from the spacesuit technologies used in the past.<ref name=Foot03/>

On June 1, 2022, NASA announced it had selected [[Axiom Space]] and [[Collins 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.<ref>{{cite web |url=https://www.nasa.gov/press-release/nasa-partners-with-industry-for-new-spacewalking-moonwalking-services|date=June 1, 2021 |title=NASA Partners with Industry for New Spacewalking, Moonwalking Services |work=NASA |access-date=June 5, 2021}}</ref>

==Gallery==

<gallery mode=packed heights=220>
Image:NASA EMU without visor.jpg |{{center|EMU without Extravehicular Visor Assembly}}
Image:STS51 EVA cropped.jpg |{{center|EMU without television camera and SAFER}}
</gallery>

==Notes==
{{reflist|group=Note|refs=
<ref name=Note01>This length of time is derived from the opening of the contract to develop the [[Apollo/Skylab space suit|Apollo A7L space suit]], to the first EVA conducted with the Space Shuttle EMU on STS-6 in 1983.</ref>
}}

==References==
{{reflist|refs=
<ref name=Foot01>{{cite book |title= US Spacesuits |author1=Kenneth S. Thomas |author2=Harold J. McMann |year= 2006 |publisher= Praxis Publishing Ltd. |location= Chichester, UK |isbn= 0-387-27919-9 | url= https://books.google.com/books?id=cdO2-4szcdgC}}</ref>
<ref name=Foot02>{{cite web |url=https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20100024222_2010025676.pdf |title=EVA 2010: Preparing for International Space Station EVA Operations Post-Space Shuttle Retirement |author1=W. West |author2=V. Witt |author3=C. Chullen |publisher=American Institute of Aeronautics and Astronautics|year=2010|access-date=June 16, 2013}}</ref>
<ref name=Foot03>{{Cite web|url=http://www.nasa.gov/feature/a-next-generation-spacesuit-for-the-artemis-generation-of-astronauts|title=A Next Generation Spacesuit for the Artemis Generation of Astronauts|last=Mahoney|first=Erin|date=2019-10-04|website=NASA|access-date=2019-10-11|archive-date=2019-10-19|archive-url=https://web.archive.org/web/20191019231635/https://www.nasa.gov/feature/a-next-generation-spacesuit-for-the-artemis-generation-of-astronauts/|url-status=dead}}</ref>
<ref name=Foot04>{{cite web|url=https://oig.nasa.gov/docs/IG-17-018.pdf  |title=NASA's Management and Development of Spacesuits  |date=2017-04-26  |agency=National Aeronautics and Space Administration  |department=Office of Inspector General  |access-date=2019-01-29 }}</ref>
}}
{{cite book |title= US Spacesuits |author1=Kenneth S. Thomas |author2=Harold J. McMann |year= 2006 |publisher= Praxis Publishing Ltd. |location= Chichester, UK |isbn= 0-387-27919-9 |url= https://books.google.com/books?id=cdO2-4szcdgC}}

==External links==
{{commons and category|Extravehicular Mobility Unit|Extravehicular Mobility Unit}}
*[http://www.nasa.gov/audience/foreducators/spacesuits/home/clickable_suit_nf.html Learn About Spacesuits NASA]
* [https://history.nasa.gov/alsj/ILC-SpaceSuits-RevA.pdf ILC Spacesuits & Related Products]
* [https://web.archive.org/web/20100606193135/http://quest.nasa.gov/space/teachers/suited/index.html Suited for Spacewalking Teacher's Guide]
* [http://www.nasa.gov/pdf/188963main_Extravehicular_Mobility_Unit.pdf NASA EMU PDF]
* [https://web.archive.org/web/19991012124805/http://spaceflight.nasa.gov/gallery/images/shuttle/index.html Shuttle Mission Images]
* [https://web.archive.org/web/20100925140253/http://www.asc-csa.gc.ca/eng/educators/resources/spacesuit-donning.asp Donning a Spacesuit]
* [https://www.pbs.org/kcet/wiredscience/video/326-nasa_space_suit_emu.html EMU Video]

{{Space suit}}
{{Space Shuttle}}

{{Use American English|date=January 2014}}

[[Category:American spacesuits]]
[[Category:Extravehicular activity]]