With all scheduled telescope work completed, two astronauts will go into the payload bay of Discovery one more time tonight to install extra protection over some aging insulation on the Hubble Space Telescope.
Mission specialists Mark Lee and Steve Smith are expected to spend about four hours working to add several thermal insulation blan kets to the three areas along the top of the Support Systems Module section of Hubble housing key data processing, electronics and scientific instrument telemetry packages. Specifically, the work will be done on bay 7, which holds electronics and mechanis ms for the solar arrays; bay 8, which contains pointing electronics and a Retrieval Mode Gyro Assembly; and bay 10, which houses the Science Instrument Control and Data Handling Subsystems.
Mission managers added the fifth space walk to the flight plan on Saturday because of Hubble managers' concerns about several separations in the external insulation on the observatory. Hubble managers were concerned that the separated areas could trap light and cause localized heating, damaging Hubble's sensitive systems.
Because of the additional extravehicular activity, the final firing of the steering jets to reboost Hubble to its deployment altitude (333 by 320 nautical miles) will occur at the end of tonight's spacewalk. Deployment of Hubble is now set for 12:41 a.m. CST Wednesday morning.
All the instruments installed by the STS-82 crew during the first four spacewalks have been checked by the HST controllers and all verification tests look good. The final check outs will take place once Hubble is again flying on its own.
Following the completion of a 6 hour, 34 minute spacewalk by astronauts Greg Harbaugh and Joe Tanner early this morning, the replacement and installation of all the science and engineering components for the Hubble Space Telescope have been completed.
Harbaugh and Tanner began their second spacewalk and the fourth of the mission by emerging from Discovery's airlock at 9:45 p.m. Central time Sunday night. Their first task was the replacement of a Solar Array Drive Electronics (SADE) package which is used to control the positioning of Hubble's solar arrays. Harbaugh and Tanner next ventured to the top of the telescope where they replaced covers over Hubble's magnetometers, which are used to sense the telescope's position in relation to the Earth through data acquired from the Earth's magnetic field. The spacewalking astronauts then placed thermal blankets of multi-layer materi al over two areas of degraded insulation around the light shield portion of the telescope just below the top of the astronomical observatory. The astronauts had trained for the repair work before the flight in the event such repairs would be needed.
While Harbaugh and Tanner were finishing up their work in the payload bay, Pilot Scott Horowitz and Payload Commander Mark Lee were busy on Discovery's middeck fabricating additional thermal insulation blankets that will be installed on the telescope during a fifth spacewalk planned for late tonight. The additional spacewalk by Lee and s pacewalking teammate Steve Smith was incorporated into the mission timeline to shore up weathered insulation covering three equipment bays along the top of the Support Systems Module section of Hubble housing key data processing, electronics and scientifi c instrument telemetry packages. The fifth spacewalk is expected to last around four hours.
Harbaugh and Tanner returned to Discovery's airlock at 4:19 a.m. this morning, bringing the total spacewalking time for the mission to 27 hours and 54 minutes over the past four days.
Because of the additional spacewalk, the final firing of the steering jets to reboost Hubble to its deployment altitude will occur at the end of the final spacewalk tomorrow morning with the deployment of Hubble now set for 12:41 A.M. Central time Wedn esday morning. Discovery's landing at the Kennedy Space Center is scheduled for the predawn hours Friday morning.
The STS-82 astronauts will be adding some insulation repair work to their plans for tonight and tomorrow following a decision earlier today to conduct a fifth spacewalk during the Hubble Space Telescope servicing mission.
Since HST has been in the Discovery's payload bay, several separations in the external insulation on the observatory have been noted. HST managers are concerned that the separated areas could trap light and cause localized heating, damaging Hubble's se nsitive systems. Consequently, mission managers decided to add a fifth spacewalk Monday night to give astronauts time to repair the insulation.
Before the repair work begins tonight, astronauts Greg Harbaugh and Joe Tanner will complete the scheduled work on the telescope. Harbaugh and Tanner will first replace a Solar Array Drive Electronics package. Then the HST flight control team will com mand the telescope to redeploy the booms carrying its high gain antennas. The telescope will then be turned and tilted slightly to give the spacewalkers access to the top portions of the telescope where Harbaugh and Tanner will replace covers over severa l magnetometers. While at the top of the telescope, they also will place patches made of insulation material over the tears in the telescope's light shield. The entire spacewalk is expected to take about six hours and will begin between 9 and 10 p.m. Cent ral time tonight.
On Monday night, astronauts Mark Lee and Steve Smith will go into Discovery's payload bay again to repair thermal insulation which has degraded on three key equipment bays near the middle of the telescope.
Because of the additional spacewalk, the final firing of the steering jets to raise Hubble's altitude has been moved from the end of tonight's EVA to the end of tomorrow's EVA, and Hubble's redeployment has been shifted one day from Tuesday to Wednesd ay. Discovery's landing at the Kennedy Space Center still remains on track for early Friday morning.
Mission managers decided this morning to add a fifth spacewalk to Discovery's flight to refurbish the Hubble Space Telescope to allow flight controllers and the astronauts time to repair the tattered thermal insulation on the12-ton observatory. The dec ision came after astronauts Mark Lee and Steve Smith completed a 7 hour 11 minute spacewalk to replace various components on the telescope.
The revised plan calls for Greg Harbaugh and Joe Tanner to conduct the fourth spacewalk of the flight tonight to replace a Solar Array Drive Electronics package and to replace covers on Hubble's magnetometers near the top of the telescope. They will al so repair ripped thermal insulation on the light shield of Hubble below the areas where the magnetometers are located. On Monday night, Lee and Smith will venture into Discovery's cargo bay again to repair additional thermal insulation which has degraded on three key equipment bays near the middle of the telescope.
Hubble's redeployment will be shifted one day from Tuesday to Wednesday with Discovery's landing at the Kennedy Space Center still planned for early Friday morning before dawn.
The third spacewalk began at 8:53 p.m. Central time Saturday evening. Lee and Smith removed and replaced a Data Interface Unit (DIU) which provides command and data interfaces between Hubble's data management system and other subsystems. They also replaced an old reel-to-reel style Engineering and Science Tape Recorder with a new digital Solid State Recorder (SSR) that will a llow simultaneous recording and playback of data
The final task for Lee and Smith was the changeout of one of four Reaction Wheel Assembly units that use spin momentum to move the telescope toward a target and maintain it in a stable position. All of the new components are reported to be in excellen t condition.
Discovery's small maneuvering jets were then fired for about 20 minutes to gently raise Hubble's altitude. The reboost maneuver by Commander Ken Bowersox and Pilot Scott Horowitz was the third in the past two days. Lee and Smith returned to Discovery's airlock at 4:04 A.M., with 21 hours 20 minutes of spacewalk servicing time having been logged during the first three excursions in the Shuttle's cargo bay.
Updates will continue to be posted if any more EVA's are scheduled for this day. If needed, Day 9 could also be used to add extra EVA's.