Editing Auxiliary power unit (section)

==Spacecraft==
The [[Space Shuttle]] APUs provided [[Hydraulic machinery|hydraulic]] pressure. The Space Shuttle had three [[redundancy (engineering)|redundant]] APUs, powered by [[hydrazine]] fuel. They were only powered up for ascent, [[re-entry]], and landing. During ascent, the APUs provided hydraulic power for [[gimbal]]ling of the Shuttle's three [[rocket engine|engines]] and control of their large valves, and for movement of the [[flight control surface|control surfaces]]. During landing, they moved the control surfaces, lowered the wheels, and powered the [[brake]]s and nose-wheel steering. Landing could be accomplished with only one APU working.<ref>{{cite web
 | url = http://spaceflight.nasa.gov/shuttle/reference/shutref/orbiter/hyd
 | archive-url = https://web.archive.org/web/20010602114515/http://spaceflight.nasa.gov/shuttle/reference/shutref/orbiter/hyd/
 | archive-date = 2 June 2001
 | title = Hydraulic System
 | website = spaceflight.nasa.gov
 | publisher = NASA
 | access-date = 8 February 2016
}}</ref> In the early years of the Shuttle there were problems with APU reliability, with malfunctions on three of the first nine Shuttle missions.{{refn|group=Note|Early Shuttle APU malfunctions:
*STS-2 (November 1981): During a launchpad hold, high oil pressures were discovered in two of the three APUs. The gear boxes needed to be flushed and filters replaced, forcing the launch to be rescheduled.<ref>{{cite web
 | url = http://www.nasa.gov/mission_pages/shuttle/shuttlemissions/archives/sts-2.html
 | title = Space Shuttle Mission Archives STS-2
 | website =  www.nasa.gov
 | publisher = NASA
 | access-date = 18 February 2016
}}</ref>
*STS-3 (March 1982): One APU overheated during ascent and had to be shut down, although it later functioned properly during re-entry and landing.<ref>{{cite web
 | url = http://www.nasa.gov/mission_pages/shuttle/shuttlemissions/archives/sts-3.html
 | title = Space Shuttle Mission Archives STS-3
 | website =  www.nasa.gov
 | publisher = NASA
 | access-date = 18 February 2016
}}</ref><ref>{{cite interview
 | title = Jack R. Lousma Edited Oral History Transcript
 | url=http://www.jsc.nasa.gov/history/oral_histories/LousmaJR/LousmaJR_3-15-10.htm
 | date=15 March 2010
 | access-date=18 February 2016
 | last=Lousma | first=Jack R.
 | subject-link=Jack R. Lousma
 | interviewer=Ross-Nazzal, Jennifer
 | work=NASA Johnson Space Center Oral History Project
}}</ref>
*STS-9 (November–December 1983): During landing, two of the three APUs caught fire.<ref>{{cite web
 | url = http://www.nasa.gov/mission_pages/shuttle/shuttlemissions/archives/sts-9.html
 | title = Space Shuttle Mission Archives STS-9
 | website =  www.nasa.gov
 | publisher = NASA
 | access-date = 18 February 2016
}}</ref>}}