Orbital replacement unit (HST)

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]

This article is about orbital replacement units of the Hubble Space Telescope. For orbital replacement units of the ISS, see orbital replacement unit.

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]:fig 2–1 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

References
  1. Kinard, William H. "Returned Hardware: Orbital Replacement Units". Hubble Space Telescope Archive System. NASA / Langley Research Center. Archived from the original on 19 February 2013. Retrieved 27 March 2013.
  2. "Hubble Space Telescope Servicing Mission 3A Media Reference Guide" (PDF). NASA. Lockheed Martin Missiles and Space. Retrieved 21 September 2010. Section 2.2.
  3. "Glenn Leads Sustaining Engineering of Power System Hardware". NASA / Glenn Research Center. 14 February 2008. Archived from the original on 22 February 2012. Retrieved 27 March 2013.


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