Astronauts ventured out for the fourth spacewalk in as many nights Sunday to patch insulation on the Hubble Space Telescope that’s peeling off like worn wallpaper.
Gregory Harbaugh and Joe Tanner took along swatches of material from emergency kits aboard space shuttle Discovery to cover the damaged thermal insulation, and copper wire for fastening the pieces to the telescope.
There was not enough time to do all the repairs, so NASA ordered the crew to conduct an extra spacewalk tonight, to finish covering the torn insulation.
The repair was not considered urgent, but scientists did 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?”
Sunday night’s spacewalk was supposed to be for equipping Hubble with new drive electronics for its solar panels, a tricky job that the astronauts accomplished in 2-1/2 hours, and sturdier caps for two magnetometers, part of the guidance system. Mission Control added some of the mending to the spacewalk.
The bulk of insulation repairs will be conducted during the newly scheduled spacewalk No. 5 tonight by Mark Lee and Steven Smith, who installed three Hubble parts Saturday night. The crew was supposed to spend tonight relaxing and gazing at Earth.
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’ fears that flakes could drift toward the telescope’s open aperture and contaminate Hubble’s optics.
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.