Orbital replacement unit (HST) explained

An orbital replacement unit or orbital replaceable unit is a modular component of spacecraft that can be replaced upon failure either by robot or by extravehicular activity. The Hubble Space Telescope (HST) was designed with 70 such parts,^[1] including scientific instruments and limited-life items such as batteries.^[1]

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;^[2] 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).^[2] HST servicing mission 3A (SM3A) replaced (or added) 15 ORUs,^[2] e.g. it replaced the DF-224 computer with the Advanced Computer.

The electrical system of the International Space Station also has such subsystems that provide power generation, power distribution and energy storage.^[3]

See also

• • Orbital replacement unit, about the ISS ORUs

Notes and References

1. Web site: Returned Hardware: Orbital Replacement Units . Hubble Space Telescope Archive System . NASALangley Research Center . William H. . Kinard . 27 March 2013 . dead . https://web.archive.org/web/20130219022932/http://setas-www.larc.nasa.gov/HUBBLE/HARDWARE/hubble_ORU.html . 19 February 2013 .
2. Web site: Hubble Space Telescope Servicing Mission 3A Media Reference Guide . PDF . . Lockheed Martin Missiles and Space . 21 September 2010. Section 2.2.
3. Web site: Glenn Leads Sustaining Engineering of Power System Hardware . NASAGlenn Research Center . 14 February 2008 . 27 March 2013 . dead . https://web.archive.org/web/20120222024245/http://spaceflightsystems.grc.nasa.gov/print/eps_prt.htm . 22 February 2012 .