NASA Plans 5th Spacewalk to Fix Hubble

NASA on Sunday ordered the space shuttle Discovery’s crew to conduct an extra spacewalk to patch insulation on the Hubble Space Telescope that’s peeling off like worn wallpaper.

The astronauts will cover the damaged thermal insulation with swatches of spare material carried on the shuttle.

Although the repair is not considered urgent, scientists do not want to wait until the next servicing mission in late 1999. More sun damage to the tissue-thin reflective insulation could allow the telescope’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?”

Mission Control added a little of the mending to Sunday night’s spacewalk--the fourth of the mission--on which the astronauts were to equip the telescope with new drive electronics for its solar panels and sturdier caps for its two magnetometers, instruments that are part of its guidance system.

The bulk of insulation repairs will be conducted during a newly scheduled spacewalk tonight by Mark Lee and Steven Smith, who installed three Hubble parts Saturday night. The crew was supposed to have tonight off.

Americans have conducted five spacewalks on a single mission just once before, during the 1993 mission to fix Hubble’s blurred vision.

Discovery’s astronauts found the ruined insulation late last week. The worst damage was on the side of the telescope most often exposed to the sun.

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Only the outermost of 17 layers 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 extra work will push Hubble’s release from the shuttle from tonight to early Wednesday. Discovery is scheduled to land at Florida’s Kennedy Space Center early Friday.