STS-61

Mission Insignia
Mission Statistics
Mission:	STS-61
Shuttle:	Endeavour
Launch Pad:	39-B
Launch:	2 December 1993 4:26 am
Landing:	KSC 13 December 1993 at 12:26.25 am EST Runway 33.
Duration:	10 d 19 h 58 min 37 s
Orbit Altitude:	321 nautical miles (594 km)
Orbit Inclination:	28.45 degrees
Distance Traveled:	4,433,772 miles (7,135,464 km)
Crew photo
Missing image STS061(S)002.jpg

Contents

1 Crew 2 Mission Parameters 2.1 Space walks 3 Mission highlights 4 Trivia 5 Related articles 6 External link

Crew

• Commander: Richard O. Covey (4)
• Pilot: Kenneth D. Bowersox (2)
• Payload Commander: F. Story Musgrave (5)
• Mission Specialist 1: Kathryn C. Thornton (3)
• Mission Specialist 2: Claude Nicollier (2) - ESA Switzerland
• Mission Specialist 3: Jeffrey A. Hoffman (4)
• Mission Specialist 5: Thomas D. Akers (3)

Mission Parameters

• Mass:
  • Orbiter landing with payload:94,976 kg
  • Payload: 10,949 kg
• Perigee: 291 km
• Apogee: 576 km
• Inclination: 28.5°
• Period: 93.3 min

Space walks

• Musgrave and Hoffman - EVA 1
• EVA 1 Start: December 5, 1993 - 03:44 UTC
• EVA 1 End: December 5, - 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, - 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, - 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, - 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, - 10:51 UTC
• Duration: 7 hours, 21 minutes

Mission highlights

With its very heavy workload, the STS-61 mission was one of the most sophisticated in the Shuttle's history. It lasted almost 11 days, and crew members made five EVA sorties, an all-time record. Even the spectacular Intelsat IV retrieval of STS-49 in May 1992 required only four. To be on the safe side, the flight plan allowed for two additional sorties which could have raised the total number to seven EVA's but the final two contingency EVA's turned out not to be necessary. In order to bring off this exploit without too much fatigue, the five extravehicular working sessions were shared between two alternating shifts of two astronauts.

After launch on 2 December 1993, the astronauts carried out a series of checks on the vehicle and went to sleep seven and a half hours after liftoff.

On Flight day Two (2 December 1993) Endeavour performed a series of burns that allowed the shuttle to close in on Hubble Space Telescope (HST) at a rate of 60 nautical miles (111 km) per every 95 minute orbit. The crew made a detailed inspection of the payload and checked out both the robot arm and the spacesuits. Cabin pressure was also dropped 45% in preparation for the spacewalks on Flight Day Three. All of Endeavour's 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 190 nautical miles (352 km) behind HST and closing.

On Flight Day Three, HST was sighted by astronaut Jeffrey A. Hoffman using a pair of binoculars and he noted that the right-hand solar array was bent in a 90 degree angle. These 12 m (40 ft) solar arrays, built by the European Space Agency (ESA), are planned to be replaced during the second spacewalk because they wobble 16 times a day each time the telescope heats up and cools off as it passes from the dark side of the Earth to its light side and vice versa.

The closing speed remained the same until the next reaction control system firing, at 8:34 p.m. CST (MET 1/17:07). The NH burn changed the shuttle's velocity by 4.6 ft/s (1.4 m/s), adjusting the high point of Endeavour's orbit and fine-tuning its course toward a point 40 miles (64 km) behind HST. The next burn, an orbital maneuvering system firing designated NC3, was scheduled for 9:22 p.m. (MET 1/17:55) and changed Endeavour's velocity by 12.4 ft/s (3.8 m/s). Endeavour's catch-up rate was adjusted to about 16 nautical miles (30 km) per orbit and put it 8 nautical miles (15 km) behind HST two orbits later. A third burn of just 1.8 ft/s (549 mm/s), called NPC and designed to fine tune two spacecrafts' ground tracks, at for 9:58 p.m. CST (MET 1/18:31). The multiaxis RCS terminal initiation or "TI" burn, which places 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 12:35 am (MET 1/21:08).Commander Richard O. Covey maneuvered Endeavour within 30 ft (10 m) of the free-flying HST before Mission Specialist Claude Nicollier used Endeavour's robot arm to grapple the telescope at 3:48 am EST when the orbiter was several hundred km east of Australia over the South Pacific. Nicollier berthed the telescope in the shuttle's cargo bay at 4:26 am EST.

Earlier in the day, controllers at the Space Telescope Operations Control Center at the Goddard Space Flight Center uplinked commands to stow HST's two high-gain antennae. Controllers received indications that both antennae 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 antennae are in a stable configuration. The situation is not expected to affect plans for rendezvous, grapple and servicing of the telescope.

HST was captured by Swiss astronaut Claude Nicollier shortly before 5 am EST on 4 December 1993 and everything has gone on schedule for the first planned spacewalk scheduled for 11:52 pm EST on 4 December 1993. After capture additional visual inspections were performed using the camera mounted on the 50 ft (15 m) long shuttle remote manipulator arm.

F. Story Musgrave and Jeffrey A. Hoffman started the first EVA about an hour earlier than scheduled by stepping into the cargo bay at 10:46 pm EST. 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 Remote Sensing Units. These units contain gyroscopes that help keep Hubble pointed in the right direction. By 12:24 EST Hoffman had finished swapping out RSU-2 (containing Gryo's 2-3 & 2-4) and then swapped out RSU-3 (containing Gryo's 3-5 & 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 (ECU3 and ECU1) that control RSU's 3 and 1. The astronauts also changed out eight fuse plugs that protect the telescope's electrical circuits. Hubble now has 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 Endeavour's 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 replaced the telescope's two solar arrays during the second spacewalk which began at 10:35 pm EST today. The solar arrays provide power to the telescope. 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 h 50 min. The longest spacewalk occurred on STS-49 in May 1992 during Endeavour's maiden flight. Spacewalking crew members during that flight were Thomas D. Akers, Richard J. Hieb and Pierre J. Thuot.

In spite of the kink in array (about a panel and a half from the end), 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 12 m long and 2.5 m wide. They supply the telescope with 4.5kW of power.

Flight Day 5 began on Sunday night (5 December 19933) at 10:35 EST. Astronauts Thomas D. Akers and Kathryn C. Thornton replaced HST's solar arrays during the second planned EVA (Thornton has red dashed stripes on her spacesuit while Tom Akers has diagonal red dashed stripes which helps flight controllers tell the two spacewalkers apart.) At the start of the EVA, the pressure in Thornton's vent garment was 0.2 lbf/in² (1.4 kPa) instead of the normal pressure of 4 to 6 lbf/in² (28 to 41 kPa). This was due to a possible ice plug in the suits plumbing which shortly melted. Thornton then topped off her suit. There were also other problems with Thornton's EVA suit. Her communications receiver malfunctioned in a way that allowed her to communicate to Akers but not to Mission Control. The crew decided to use a technique of relaying all commands for Thornton via Akers instead of switching to the backup comm channel. The backup channel is used for suit biomedical telemetry and would have limited Mission Control's ability to monitor that telemetry.

Akers started the EVA by installing a foot restraint on the RMA for Thornton and proceeded to begin disconnecting 3 electrical connectors and a clamp assembly on the solar array. He had a slight problem with the clamp assembly but had the connectors demated by 11:17 pm EST. Thornton held the array in place so that it would not drift freely after being detached. The solar arrays weigh 160 kg (352 lb) and are 5 m long when folded. The astronauts dismounted the damaged array at 11:40 pm EST above the Saraha Desert (during a nighttime pass to minimize electrical activity) and Thornton held the array until the next daylight pass (approximately 12 min) before throwing it overboard at 11:52 pm EST over Somalia. The jettison during daylight allowed the astronauts and flight controllers to accurately track its position and relative velocity. The release by Thornton imparted a 1 ft/s (305 mm/s) velocity to the arrays and then the orbiter did a small burn with the RCS that imparted an additional 4 ft/s (1.2 m/s). The array, moving away from Endeavour at 5 ft/s (1.5 m/s), will separate about 11 to 12 miles (18 to 19 km) each orbit. The crew then installed a new array, (finishing around 1:40 EST) and rotated the telescope 180 degrees. They then replaced the second solar array which was stowed away for return to ESA. After the 6.5 hour EVA, successful functional tests were performed by the Space Telescope Operations Control Center (STOCC) on four of HST's 6 Gryos. Gryos 1&2 were not able to be tested due to the orientation of the telescope and were tested during the crew sleep period Monday afternoon (6 December 1993).

Flight Day 6 EVA # 3 began Monday night (6 December 1993) AT 10:34 pm EST while Endeavour was over Australia. Hoffman installed guide studs on the Wide Field Planetary Camera (WFPC) and prepared the WFPC for removal while Musgrave setup a work platform and worked on opening an access door to allow observation of WFPC status lights. Hoffman attached the support handle to the WFPC and, with assistance by Claude Nicollier on the arm and a free floating F. Story Musgrave, removed the WFPC during the night pass starting at 11:41 pm EST. The WFPC was clear of the telescope by 11:48 pm EST and moved back into its storage container. A protective hood was then removed on the new WFPC (protecting its fragile external mirror) and the new 620 lb (280 kg) WFPC was then installed at 1:05 am EST. Ground controllers then ran an Aliveness Test and 35 minutes later reported that the new camera successfully performed its series of initial tests. The new Wide Field and Planetary Camera has a higher rating than the previous model, especially in the ultraviolet range, and includes its own spherical aberration correction system.

Following the WFPC installation, Hoffman changed out two magnetometers on board HST. The magnetometers, which are located at the top of the telescope, are the satellite's "compass". They enabling HST to find its orientation with respect to the Earth's magnetic field. Both original units were suffering from problems of background noise. During installation, 2 pieces pealed off the magnetometers and flight controllers are accessing any possible impacts. The EVA lasted 6 hours and 47 min.

Flight Day 7 EVA # 4 began Tuesday night (7 December 1993) while Endeavour was flying over Egypt at 10:13 pm EST with Thornton and Akers. The primary task of the EVA was to replace HST's High Speed Photometer (HSP) with a device called COSTAR. This acronym stands for the Corrective Optics Space Telescope Axial Replacement system and the unit corrects HST's spherical aberration of the main mirror for all instruments except the WFPC-II camera, which has its own built in corrective optics. Akers received a go for the opening of HST's -V2 aft shroud doors at 10:45 pm EST. The doors were scheduled to be opened during a night pass to minimize thermal changes and reduce the possibility of out-gassing of components that could contaminate the optics. The High Speed Photometer (HSP) was powered down at 10:54 pm EST and the door opening started at 10:57 EST. Shortly after partially opening the door, the astronauts practiced reclosing the door. The door exhibited the same reluctance upon closing that was experience on different doors during previous EVA's. The doors were fully opened by 11:00 pm EST and 4 power and data connectors plus 1 ground strap were disconnected from the HSP. The HSP was removed at 11:27 pm EST and then reinserted to practice for the COSTAR installation. HSP was then parked on the side of the payload bay while COSTAR was removed from stowage and successfully installed in the HST by about 12:35 am EST. The astronauts closed out the HST equipment bay doors and stowed the HSP. At 2:25am EST they started upgrading HST's onboard computer by bolting on an electronics package containing additional computer memory and a co-processor. The computer system was then reactivated and passed its aliveness and functional tests at 4:41 am EST. The EVA was 100% successful and lasted for 6 h 50 min. It will be 6-9 weeks before optical alignments can confirm that HST is completely repaired.

Pilot Kenneth D. Bowersox, using Endeavour's RCS system, performed two orbital manueuvers and boosted HST from a 321 by 317 nautical mile (594 by 587 km) orbit to a 321.7 by 320.9 nautical mile (596 by 594 km) circular orbit at 9:14 pm EST. COSTAR functional tests were also completed. There was some concern about the health of the onboard HST DF-224 computer and recently installed memory and co-processor when a memory dump failed. After much analysis by a team at the GSFC, it was determined that the dump failure was due to noise on the communications link between the spacecraft and the ground.

Flight Day 8 EVA #5 began on Wednesday night (8 December 1993) at 10:14 pm with a go for airlock depress over the Indian Ocean with Musgrave and Hoffman performing the EVA. Story Musgrave's EVA suit failed its initial leak check and Story performed steps on the 5 lbf/in² (34 kPa) contingency checklist. He rotated the EVA suits lower arm joints and the suit passed 2 subsequent leak checks. The EVA started at 10:30 EST and lasted 7 h 21 min.

Musgrave's and Hoffman's first task was to replace the solar array drive electronics and they began the SADE operation while ground controllers initiated the first step in solar array deployment by commanding the Primary Drive Mechanism (PDM). Endeavour was placed in free drift to disable any RCS firings that could disrupt the solar arrays and the PDM motors were engaged at 10:48 pm. The latches were unlocked but the arrays failed to rotate to the deploy position. No motion was detected and the STOCC sent commands to drive a single array with two motors with no success. Finally, the astronauts cranked the deployment mechanism by hand and deploy was successful. After the SADE was swapped out, the crew fitted an electrical connection box on the Goddard High Resolution Spectrograph at 3:30 am EST and it passed its aliveness test. The crew then installed some covers on the magnetometers, fabricated onboard by Claude Nicollier and Kenneth D. Bowersox. These covers will contain any debris caused by the older magnetometers that show some signs of UV decay. The EVA ended at 5:51 am EST bringing the total EVA time for this mission to 35 h 28 min. The HST High Gain Antenna (HGA) was deployed at 6:49 am EST and completed by 6:56 am EST. Release time for HST was set for 2:08 am EST.

Flight Day 9 began on Thursday night (9 December 1993) but concerns about one of HST's four onboard Data Interface Units (DIU's) delayed release. The DIU's are 35 lb (16 kg) electronic units that transfer data between HST's main computer, solar arrays and other critical systems. A failure on Side A of DIU # 2 experienced erratic current fluctuations and some data dropouts. Controllers at the STOCC and mission control came up with a troubleshooting procedure to determine the extent of the problem. HST was transferred to internal power and disconnected from its power umbilical at 11:43 pm EST. Controllers then switched channels on the DIU from the A side to the B side and then back to the A side. They determined HST should be deployed. The drum brakes on the new Solar Array were applied to prevent them from vibrating during future observations. Claude Nicollier then took hold of the satellite with the robot arm. Hubble was switched back to internal power mode and the umbilical cord linking it to the Shuttle was disconnected. The satellite was then lifted and moved away from Endeavour. The telescope's aperture door was then reopened (a 33 min procedure) and then released at 5:26 am EST. Commander Dick Covey and pilot Kenneth D. Bowersox fired Endeavour's small maneuvering jets and moved the shuttle slowly away from HST. The next servicing visit to HST is scheduled for 1997. Landing occurred on Runway 33 at 12:26 am on 13 December 1993.

Trivia

This mission was the first to use a computer-controlled space tool, the Power Ratchet Tool (PRT).

Related articles

• Space science
• Space shuttle
• List of space shuttle missions
• List of human spaceflights chronologically

External link

• NASA mission summary (http://science.ksc.nasa.gov/shuttle/missions/sts-61/mission-sts-61.html)