STS-61 was NASA's first Hubble Space Telescope servicing mission, and the fifth flight of the Space Shuttle Endeavour. The mission launched on December 2, 1993, from Kennedy Space Center (KSC) in Florida. The mission restored the spaceborne observatory's vision (marred by spherical aberration in its mirror) with the installation of a new main camera and a corrective optics package (COSTAR). This correction occurred more than three and a half years after the Hubble was launched aboard STS-31 in April 1990. The flight also brought instrument upgrades and new solar arrays to the telescope. With its very heavy workload, the STS-61 mission was one of the most complex in the Shuttle's history.

STS-61 lasted almost 11 days, and crew members made five spacewalks (extravehicular activities (EVAs)), an all-time record; even the re-positioning of Intelsat VI on STS-49 in May 1992 required only four. The flight plan allowed for two additional EVAs, which could have raised the total number to seven; the final two contingency EVAs were not made. In order to complete the mission without too much fatigue, the five EVAs were shared between two pairs of different astronauts alternating their shifts. During the flight, mission specialist Jeffrey A. Hoffman also spun a dreidel for the holiday of Hanukkah to a live audience watching via satellite.

Crew

Backup crew

Spacewalks

  • Musgrave and Hoffman – EVA 1
  • EVA 1 Start: December 5, 1993 – 03:44 UTC
  • EVA 1 End: December 5, 1993 – 11:38 UTC
  • Duration: 7 hours, 54 minutes
  • Thornton and Akers – EVA 2
  • EVA 2 Start: December 6, 1993 – 03:29 UTC
  • EVA 2 End: December 6, 1993 – 10:05 UTC
  • Duration: 6 hours, 36 minutes
  • Musgrave and Hoffman – EVA 3
  • EVA 3 Start: December 7, 1993 – 03:35 UTC
  • EVA 3 End: December 7, 1993 – 10:22 UTC
  • Duration: 6 hours, 47 minutes
  • Thornton and Akers – EVA 4
  • EVA 4 Start: December 8, 1993 – 03:13 UTC
  • EVA 4 End: December 8, 1993 – 10:03 UTC
  • Duration: 6 hours, 50 minutes
  • Musgrave and Hoffman – EVA 5
  • EVA 5 Start: December 9, 1993 – 03:30 UTC
  • EVA 5 End: December 9, 1993 – 10:51 UTC
  • Duration: 7 hours, 21 minutes

Crew seat assignments

{| class="wikitable" style="text-align:center"

! Seat

! Launch

! Landing

|rowspan=8| 150px<br />Seats 1–4 are on the flight deck.<br />Seats 5–7 are on the mid-deck.

|-

! 1

|colspan=2| Covey

|-

! 2

|colspan=2| Bowersox

|-

! 3

| Thornton

| Hoffman

|-

! 4

|colspan=2| Nicollier

|-

! 5

| Hoffman

| Thornton

|-

! 6

|colspan=2| Musgrave

|-

! 7

|colspan=2| Akers

|}

Mission highlights

Launch

thumb|upright=1.0|right|Launch of the first servicing mission

Endeavour was switched from Pad 39A to Pad 39B due to contamination of the Payload Changeout Room after a windstorm on October 30, 1993. The internal HST payload package was not affected because it was tightly sealed, and the contamination appeared to have been caused by sandblasting grit from recent Pad A modifications. On November 18, 1993, Endeavour experienced a failure of a transducer on the elevon hydraulic actuator. To replace the actuator would have required a rollback to the Orbiter Processing Facility (OPF) because access to the actuator was only through the Main Landing Gear wheel well. Since there were 4 delta-P transducers and the Launch commit criteria (LCC) required only 3 of 4, the transducer was depinned and would not be consulted during flight. The flight crew arrived at the KSC Shuttle Landing Facility (SLF) on November 27, 1993, and the payload bay doors were closed at 20:20 UTC on November 28, 1993. The first launch attempt on December 1, 1993, was scrubbed due to weather constraint violations at the Shuttle Landing Facility. Just before the scrub the range was also in a no-go situation due to an long ship in the restricted sea zone. A 24‑hour scrub turnaround was put into effect with a launch window extending from 09:26 to 10:38 UTC on December 2, 1993. Launch mass was . Payload mass was . The multi-axis RCS terminal initiation (TI) burn, which placed Endeavour on an intercept course with HST and set up commander Dick Covey's manual control of the final stages of the rendezvous, occurred at 05:35 UTC. Covey maneuvered Endeavour within of the free-flying HST before mission specialist Claude Nicollier used Endeavours robot arm to grapple the telescope at 08:48 UTC, when the orbiter was several hundred kilometers east of Australia over the south Pacific Ocean. Nicollier berthed the telescope in the shuttle's cargo bay at 09:26 UTC. Everything was on schedule for the first planned spacewalk scheduled for 04:52 UTC. After capture, additional visual inspections were performed using the camera mounted on the -long shuttle remote manipulator arm (Canadarm).

Earlier in the day, controllers at the Goddard Space Flight Center (GSFC's) Space Telescope Operations Control Center uplinked commands to stow HST's two high-gain antennas. Controllers received indications that both antennas had nested properly against the body of the telescope, but microswitches on two latches of one antenna and one latch on the other did not send the "ready to latch" signal to the ground. Controllers decided not to attempt to close the latches, as the antennas were in a stable configuration. The situation was not expected to affect plans for rendezvous, grapple and servicing of the telescope.

Spacewalk #1 (Flight Day 4)

Story Musgrave and Jeffrey A. Hoffman started the first EVA about an hour earlier than scheduled by stepping into the cargo bay at 03:46 UTC. They began by unpacking tools, safety tethers and work platforms. Hoffman then installed a foot restraint platform onto the end of the shuttle's remote manipulator arm (Canadarm), which he then snapped into his feet. Nicollier drove the arm from within the shuttle and moved Hoffman around the telescope. Meanwhile, Musgrave installed protective covers on Hubble's aft low gain antenna and on exposed voltage bearing connector covers. The astronauts then opened the HST equipment bay doors and installed another foot restraint inside the telescope. Musgrave assisted Hoffman into the restraint and Hoffman proceeded to replace two sets of Rate Sensing Units (RSUs). These units contain gyroscopes that help keep Hubble pointed in the right direction. By 17:24 UTC, Hoffman had finished replacing RSU-2 (containing Gyros 2–3 and 2–4) and then replaced RSU-3 (containing Gyros 3–5 and 3–6). The astronauts then spent about 50 minutes preparing equipment for use during the second space walk and then replaced a pair of electrical control units (ECUs) (ECU-3 and ECU-1) that control RSU-3 and RSU-1.