Search as I might, I couldn't find them labeled on any schematic or mentioned in any fact sheet.

My guess is Shuttle bay interface/attachment, but I also could not corroborate it by searching engineering journals from the 80s and 90s.

It may also have been discolored after a while, or painted yellow (not necessarily actual paint; they could also have been replaced) during one of the service missions (again could not find anything). My understanding is that yellow is used for the parts the astronauts can grab onto.

Photos below (click to expand) show the structures, and the original color(?) in the Shuttle bay before launch.

circled features HST in bay
Image sources: NASA, Public domain, via Wikimedia Commons; NASA, Public domain, via Wikimedia Commons

  • $\begingroup$ I think the payloads are secured in the bay with trunnion pins, though maybe that's what the aft structure is? are the fore and aft circled features the same? $\endgroup$
    – Erin Anne
    Commented Dec 30, 2023 at 12:12
  • $\begingroup$ @ErinAnne: With the aid of OM's answer, I think the scuff plates (fore and aft) look identical. $\endgroup$
    – ymb1
    Commented Dec 30, 2023 at 13:26

1 Answer 1


They are indeed the trunnion pins used to hold the scope in the Shuttle's payload bay during launch.

enter image description here

Labeled in this paper about re-entry analysis of the scope: https://www.hou.usra.edu/meetings/orbitaldebris2019/orbital2019paper/pdf/6125.pdf (LIDS stands for Low Impact Docking System.)

They were held in the payload bay by Payload Retention Latch Assemblies, electrically operated latches.

enter image description here

PRLA reference: https://space1.com/Artifacts/Space_Shuttle_Artifacts/Other_Parts/Payload_Ret__Latch/payload_ret__latch.html

Images showing a pin and the fore and aft scuff plates:

-V2 view of the Hubble Space Telescope's (HST) aft shroud showing yellow hand rails.  Photo taken during the STS-125 mission.

-V2 view of the Hubble Space Telescope's (HST) forward shell showing a scuff plate and the High Gain antennas.  Photo taken during the STS-125 mission.

  • 4
    $\begingroup$ Using the technical term you mentioned, PRLAs, I arrived at the name and closeup images of the "scuff plates" (image example). So I take it the scuff plates envelope the PRLAs? Many, many thanks OM! $\endgroup$
    – ymb1
    Commented Dec 30, 2023 at 13:01
  • 4
    $\begingroup$ @ymb1 The scuff plates helped guide the pins into the trunnions when a payload was being berthed, mainly. At one point it was planned for the scope to be retrieved and returned to Earth. $\endgroup$ Commented Dec 30, 2023 at 13:04
  • 2
    $\begingroup$ trunnion (from Old French trognon 'trunk') is a cylindrical protrusion used as a mounting or pivoting point. First associated with cannons $\endgroup$
    – Woody
    Commented Dec 31, 2023 at 0:10
  • $\begingroup$ Yeah, I should have said trunnions into the PRLAs. Realized it too late to edit. $\endgroup$ Commented Dec 31, 2023 at 0:29

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