STS-61


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 in Florida. The mission restored the spaceborne observatory's vision with the installation of a new main camera and a corrective optics package. 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, 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

Mission highlights

Launch

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 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 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 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. After launch, the astronauts carried out a series of checks on the vehicle and went to sleep seven and a half hours after liftoff.

Flight Day 2

Endeavour performed a series of burns that allowed the shuttle to close in on the Hubble Space Telescope at a rate of per 95-minute orbit. The crew made a detailed inspection of the payload and checked out both the robot arm and the spacesuits. All of Endeavours systems functioned well as the crew got a full day's sleep in preparation for the evening's rendezvous. At the end of Flight Day 2, Endeavour was behind HST and closing.

Flight Day 3

HST was sighted by astronaut Jeffrey A. Hoffman using binoculars, whereupon he noted that the right-hand solar array was bent at a 90° angle. These solar arrays, provided by the European Space Agency, were scheduled to be replaced during the second spacewalk because they wobbled 16 times a day, thus disturbing Hubble's ability to maintain precise pointing.
The closing speed remained the same until the next reaction control system firing, at 02:34 UTC, December 4, 1993. This height-adjusting burn changed the shuttle's velocity by, modified the high point of Endeavours orbit, and fine-tuned its course toward a point behind HST. The next burn, an orbital maneuvering system firing designated NC3, was scheduled for 03:22 UTC and changed Endeavours velocity by. Endeavours catch-up rate was adjusted to about per orbit and put it behind HST two orbits later. A third burn of just, called NPC and designed to fine-tune the spacecraft's ground track, was executed at 15:58 UTC. The multi-axis RCS terminal initiation 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.
Earlier in the day, controllers at the Goddard Space Flight Center 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, 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. These units contain gyroscopes that help keep Hubble pointed in the right direction. By 17:24 UTC, Hoffman had finished replacing RSU-2 and then replaced RSU-3. 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 that control RSU-3 and RSU-1. The astronauts also changed eight fuse plugs that protect the telescope's electrical circuits. Hubble now had a full set of six healthy gyroscopes.
The astronauts struggled with the latches on the gyro door when two of four gyro door bolts did not reset after the astronauts installed two new gyro packages. Engineers who evaluated the situation speculated that when the doors were unlatched and opened, a temperature change might have caused them to expand or contract enough to keep the bolts from being reset. With the efforts of determined astronauts in Endeavours payload bay and persistent engineers on the ground, all four bolts finally latched and locked after the two spacewalkers worked simultaneously at the top and bottom of the doors. Musgrave anchored himself at the bottom of the doors with a payload retention device which enabled him to use some body force against the doors. Hoffman, who was attached to the robot arm, worked at the top of the doors. The duo successfully latched the doors when they simultaneously latched the top and bottom latches.
The spacewalkers also set up the payload bay for mission specialists Tom Akers and Kathy Thornton who would replace the telescope's two solar arrays during the second spacewalk. In anticipation of that spacewalk, Musgrave and Hoffman prepared the solar array carrier which is located in the forward portion of the cargo bay, and attached a foot restraint on the telescope to assist in the solar array replacement.
Musgrave and Hoffman's spacewalk became the second longest spacewalk in NASA history, lasting 7 hours 50 minutes. The longest spacewalk occurred on STS-49 in May 1992 during Endeavours maiden flight. Spacewalking crew members during that flight were Thomas D. Akers, Richard J. Hieb and Pierre J. Thuot. A number of spacewalks have since surpassed these.
In spite of the kink in array, after a review by HST program managers, flight controllers decided to continue with the pre-flight plan and attempt to roll up and retract the solar arrays at the end of the first EVA. The stowage of the solar arrays is a two step process with the initial step involving the rolling up of the solar arrays and the second step involving the actual folding up of the arrays against the telescope. Each array stands on a four-foot mast that supports a retractable wing of solar panels long and wide. They supply the telescope with 4.5 kW of power.