NASA lists hubbles masses:

  • At launch: 11,110 kg
  • After the last service mission: 12,247kg.

That's a 1137 kg increase, about 10%!

Which parts are responsible for this increase ? And is there a detail list of each weight gain/loss ?

  • $\begingroup$ @uhoh I sourced both informations, as well as the dates for each ones of them (ok, I listed events instead of dates, but that's more or less the same). Hubble doesn't use any cryogenic material that would boil off, nor propellant. I hope I made the question clearer tho. $\endgroup$
    – Antzi
    Apr 23, 2018 at 9:12
  • $\begingroup$ The answer to this would be a long list. I expect the press kits for the servicing missions will contain these lists. $\endgroup$
    – Hobbes
    Apr 23, 2018 at 9:13
  • 1
    $\begingroup$ @Hobbes: I think we don't need every last gram like "used 0.3% thicker screws" or "replaced bearings with new, heavier by lubricant" - I'm sure a couple of items from top of the list, contributing majority of the extra mass would suffice. $\endgroup$
    – SF.
    Apr 23, 2018 at 9:38

1 Answer 1


For the first servicing mission, there's a nice weight breakdown in the spress kit. For later missions, that table isn't included. I've added weights of the major replacement units where possible, but the list remains incomplete.

First servicing mission was STS-61. This is the list of items carried up/down by that mission. Not all of this was installed on Hubble.

enter image description here

Installed on Hubble:

  • 2x solar array and drive unit
  • 2 Rate sensor units
  • Wide Field/Planetary Camera 2, 619 lb (281 kg) replaces WF/PC1 (610 lb/227 kg)
  • COSTAR replaces the High Speed Photometer (HSP) (487 lb/221 kg)
  • at least 1 Magnetic sensing system

total 2300 lbs added, 2135 lbs removed in this mission. (changeout complement total)

Servicing Mission 2: STS-82.

  • Goddard High Resolution Spectrograph (GHRS) is replaced by the Space Telescope Imaging Spectrograph (STIS), 825 lb (374 kg).
  • Faint Object Spectrograph (FOS) is replaced by Near Infrared Camera and Multi-Object Spectrometer (NICMOS), 861 lb (390 kg). NICMOS included a cooling system with 104 kg of solid N2

Other components swapped:

  • Reaction Wheel Assembly (RWA)
  • Fine Guidance Sensor (FGS)
  • Data Interface Unit (DIU)
  • Solar Array Drive Electronics (SADE)
  • Engineering/ Science Tape Recorder (E/ STR)
  • Solid State Recorder (SSR)
  • Magnetic Sensing System (MSS) covers
  • Optical Control Electronics Enhancement Kit (OCE-EK). (most of these are swapped with identical units. The SSR replaces a tape recorder, so there's a small weight reduction there)

Servicing Mission 3A:

  • replace 3 Rate Sensor Units
  • replace the DF-224 and its co-processor with the Advanced Computer
  • replace 1 Fine Guidance Sensor
  • replace a tape recorder with a new Solid State Recorder (SSR)
  • install a new S-band Single-Access Transmitter (SSAT),
  • install Voltage/ Temperature Improvement Kits (VIK) for the Telescope’s nickel-hydrogen batteries

Servicing Mission 3B:

  • Advanced Camera for Surveys (ACS), 875 lb (397 kg), replaces the Faint Object Camera, 700 lb (318 kg)
  • Aft Shroud Cooling System (ASCS) for the other axial science instruments.
  • new cryogenic cooler for the Near-Infrared Camera and Multi-Object Spectrometer (NICMOS).
  • replace the HST flexible Solar Arrays (339 lb each) with new high-performance rigid arrays (640 lb each)
  • Replace the Power Control Unit (PCU).
  • Replace a Reaction Wheel Assembly (RWA).
  • Install New Outer Blanket Layer (NOBL) insulation panels.

During SM4, two new scientific instruments were installed:

  • the Cosmic Origins Spectrograph (COS) replaces COSTAR.
  • Wide Field Camera 3 (WFC3) replaces WFC2.


  • the Space Telescope Imaging Spectrograph (STIS)
  • Advanced Camera for Surveys (ACS)
  • batteries
  • gyroscopes
  • science computer
  • fine guidance sensor
  • insulation on three electronics bays
  • $\begingroup$ This will be quite and effort, kudos to you! $\endgroup$
    – uhoh
    Apr 23, 2018 at 10:22
  • 2
    $\begingroup$ Don't forget the 100 kg block of solid nitrogen for NICMOS which "disappeared" en.wikipedia.org/wiki/… $\endgroup$
    – uhoh
    Apr 23, 2018 at 10:22

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