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Astronauts complete fourth spacewalk
In this story:
February 17, 1997
- Fixing the solar panels
- "Using up absolutely everything"
- Second time for five spacewalks
- More permanent repairs later
- Related stories and sites
Web posted at: 7:00 a.m. EST (1200 GMT)SPACE CENTER, Houston (CNN) -- A record-tying fifth spacewalk is ahead for Discovery's astronauts after the fourth spacewalk Sunday to patch insulation on the Hubble Space Telescope.
Working six stories over the cargo bay of space shuttle Discovery, with the cloud-covered blue Earth as a backdrop, Gregory Harbaugh and Joe Tanner fitted insulation blankets over two rips in the protective Teflon cover.
There was not enough time to do all the repairs, so NASA ordered the crew to conduct an extra spacewalk Monday night to finish covering the torn insulation.
The insulation repair is not considered urgent, but scientists do not want to wait until the next servicing mission in late 1999. Additional sun damage to the insulation could allow Hubble's electronics to overheat and could unbalance its mirrors.
"We've got a $2 billion investment here," said Ed Weiler, NASA's chief Hubble scientist. "Why take a chance?"
The spacewalk lasted 6 hours, 34 minutes, bringing the total for Discovery's mission to 27 hours, 54 minutes. The total for the 5 spacewalks in the 1993 mission was 35 hours, 26 minutes.
Images from the spacewalk
Fixing the solar panels
During Sunday night's spacewalk, the astronauts also equipped Hubble with new drive electronics for its solar panels and sturdier caps for two magnetometers. The caps fit over gold-colored Baggies, fastened with plastic tie-wraps, installed by two other astronauts in 1993 -- another on-the-spot, unplanned repair."Using up absolutely everything"
Before the insulation repairs could begin, Horowitz was cautioned not to start the work until engineers on the ground were sure they had thought of everything as there were limited supplies aboard the shuttle.
"We are using up absolutely everything we have and if we get something cut the wrong length then we will have done a bad thing," astronaut Jeff Hoffman warned from mission control.
Ground controllers faxed the crew five pages of instructions and 14 diagrams to show them how to build sunshields from spare insulating foil, electrical wire, ropes, cords, alligator clips and wrap ties, using scissors, wire cutter, crimp tools and sticky tape.
"We expect the middeck to look as neat as your garage," Hoffman joked.
The bulk of insulation repairs will be completed during the newly scheduled spacewalk No. 5 on Monday night by Mark Lee and Steven Smith, who installed three Hubble parts Saturday night. The crew was originally supposed to spend Monday night relaxing and gazing at Earth.
Second time for five spacewalks
Americans have conducted five spacewalks on a single mission just once before -- during the 1993 mission to correct Hubble's blurred vision.
Discovery's astronauts found the ruined insulation late last week. The worst damage was on the side of the telescope exposed to the sun's heat and intense ultraviolet radiation during the seven years since its launch.
Hubble's exterior is subjected to extreme temperature changes each time the telescope's orbit carries it in and out of sunlight.
Only the outermost layer of Teflon insulation has peeled away and only in six places on the telescope, which is 43 feet long and 15 feet in diameter. The 16 remaining layers of tissue-thin, reflective insulation do not appear to be damaged; neither do any of the telescope components.
The peeling insulation does not seem to be brittle, easing scientists' initial fears that flakes could drift toward the telescope's open aperture and contaminate Hubble's sensitive optics.
More permanent repairs later
Astronauts on the 1993 repair mission noticed spidery cracks in the insulation but no peeling. This crew is equipped with more powerful cameras, however, and has had more time to survey the telescope.
More permanent repairs will be made during the 1999 tune-up.
The extra work will push Hubble's release from the shuttle from Monday night to early Wednesday. Discovery still is scheduled to land at Kennedy Space Center early Friday following a 10-day mission.
Correspondent John Holliman and the Associated Press contributed to this report.
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Related stories:
- Three down, two to go - February 16, 1997
- Astronauts dodge space junk for third spacewalk - February 16, 1997
- Astronaut savors first walk in space - February 15, 1997
- Spacewalkers get to work on Hubble tuneup - February 14, 1997
- 'It's a beautiful sight' - February 13, 1997
- Shuttle Discovery blasts off on Hubble service mission - February 11, 1997
Related sites:
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- Hubble Space Telescope Science
- Johnson Space Center Shuttle Countdown STS-82
- Space Station Mir Info Page
- Tracking the mission
- Meet the Crew
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