View source for Astronomy:Orbital replacement unit (HST)

An '''orbital replacement unit''' or '''orbital replaceable unit''' is a [[Engineering:Line-replaceable unit|modular component]] of spacecraft that can be replaced upon failure either by robot or by [[Astronomy:Extravehicular activity|extravehicular activity]]. The [[Astronomy:Hubble Space Telescope|Hubble Space Telescope]] (HST) was designed with 70 such parts,<ref name=HST-ORU>{{cite web |url=http://setas-www.larc.nasa.gov/HUBBLE/HARDWARE/hubble_ORU.html |title=Returned Hardware: Orbital Replacement Units |work=Hubble Space Telescope Archive System |publisher=NASA{{\}}Langley Research Center |first=William H. |last=Kinard |accessdate=27 March 2013 |url-status=dead |archiveurl=https://web.archive.org/web/20130219022932/http://setas-www.larc.nasa.gov/HUBBLE/HARDWARE/hubble_ORU.html |archivedate=19 February 2013 }}</ref> including scientific instruments and limited-life items such as batteries.<ref name=HST-ORU/>

On HST some parts were designed from the start as ORUs and all used captive bolts with a standard 7/16" double-height hex head;<ref name=SM3A-MG>{{cite web |url=https://asd.gsfc.nasa.gov/archive/hubble/a_pdf/news/SM3A-MediaGuide.pdf |format=PDF |title=Hubble Space Telescope Servicing Mission 3A Media Reference Guide |publisher=[[Organization:NASA|NASA]] |agency=Lockheed Martin Missiles and Space |accessdate=21 September 2010}} Section 2.2.</ref> later when it was decided to avoid returning HST to Earth for repair, more systems and modules were designated as ORUs (but used a wider variety of fasteners).<ref name=SM3A-MG/> HST servicing mission 3A (SM3A) replaced (or added) 15 ORUs,<ref name=SM3A-MG/>{{rp|fig 2-1}} e.g. it replaced the [[Astronomy:DF-224|DF-224]] computer with the ''Advanced Computer''.

The [[Engineering:Electrical system of the International Space Station|electrical system of the International Space Station]] also has such subsystems that provide power generation, power distribution and energy storage.<ref>{{cite web |url=http://spaceflightsystems.grc.nasa.gov/print/eps_prt.htm |title=Glenn Leads Sustaining Engineering of Power System Hardware |publisher=NASA{{\}}Glenn Research Center |date=14 February 2008 |accessdate=27 March 2013 |url-status=dead |archiveurl=https://web.archive.org/web/20120222024245/http://spaceflightsystems.grc.nasa.gov/print/eps_prt.htm |archivedate=22 February 2012 }}</ref>

== See also ==
* {{section link|Hubble Space Telescope|Servicing missions and new instruments}}
* [[Engineering:Orbital replacement unit|Orbital replacement unit]], about the ISS ORUs

== References ==
{{Reflist}}

[[Category:Hubble Space Telescope]]
[[Category:Spacecraft components]]



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