Orbital replacement unit (HST)

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An Orbital Replaceable Unit/Orbital replacement unit is a modular component of spacecraft that can be replaced upon failure by a robot or by an Extra-Vehicular Activity.

The Hubble Space Telescope (HST) was designed with 70 such parts.[1] They include the 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 these use 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[edit]


  1. ^ a b "HST Orbital Replacement Units". Setas-www.larc.nasa.gov. Archived from the original on 2013-02-19. Retrieved 2013-03-27. 
  2. ^ a b c Lockheed Martin Missiles and Space. "Hubble Space Telescope Servicing Mission 3A Media Reference Guide" (PDF). NASA. Retrieved 2010-09-21.  Section 2.2.
  3. ^ "Glenn Leads Sustaining Engineering of Power System Hardware". Spaceflightsystems.grc.nasa.gov. 2008-02-14. Archived from the original on 2012-02-22. Retrieved 2013-03-27.