Astronauts take third spacewalk

CAPE CANAVERAL, Fla., March 6 (UPI) -- Shuttle astronauts overcame a late start due to a leaking spacesuit Wednesday and flew through what was expected to be the most challenging task of an 11-day mission to service the Hubble Space Telescope.

"It was just spectacular," said Hubble program manager Preston Burch.

Two hours later than planned, astronauts John Grunsfeld and Richard Linnehan floated through Columbia's airlock and got to work replacing Hubble's primary power control system -- a tedious job that was expected to take at least 7 1/2 hours.

Not only were the astronauts under pressure to finish within the nine hours the spacesuits safely can operate, but Hubble itself, which had to be completely powered down during the change, could survive the cold of space for only about 10 hours.

The start of the spacewalk was delayed when Grunsfeld's cooling system began to leak about a half-hour before he and Linnenhan were to leave the shuttle. Grunsfeld changed into another spacesuit and then had to repeat a procedure to purge nitrogen from his body by breathing pure oxygen.

"Anyone who doesn't believe in Murphy's Law certainly wasn't watching today," Burch said.

Once the astronauts began their spacewalk, however, managers were impressed by how smoothly the power control unit change unfolded. The box-shaped PCU, hidden under power cables and other equipment in an equipment bay, was never intended to be replaced on orbit. The unit has 34 connectors positioned close together and tucked off to one side. Two more connectors and ground straps are located on the bottom of the unit.

"What makes it difficult is as you're facing the PCU those connectors are on the left-hand side (where) that bay door is hinged," said lead flight director Bryan Austin. "For the suited crewman to reach his hand in there, he's pretty much reaching in there blind."

Grunsfeld and Linnehan spent hours working with connectors on a practice PCU in an underwater training facility. In their pressurized spacesuits, any movements involving fine motor skills are extremely difficult.

"It's like trying to take a rigidly pressurized balloon and bending it the way you want to take it," said Allen Flynt, head of NASA's Extravehicular Activity Projects office at the Johnson Space Center in Houston. "You're constantly working against the suit to make it do what you want it to do."

Grunsfeld and Linnehan made the chore seem easy, finishing up in 6 1/2 hours -- the shortest spacewalk of three completed so far during Columbia's servicing call to Hubble.

NASA's astronomy chief Anne Kinney said: "It was an academy award-winning performance by the astronauts as they worked against the clock to bring the Hubble Space Telescope back to life ... It was moving."

The hopes the power system change would work and the fears it would not came to a simultaneous end when the telescope responded to the first trickle of power relayed through the new electrical distribution unit shortly after the spacewalkers reattached the observatory's six batteries.

The two remaining spacewalks of the mission are devoted to enhancing Hubble's scientific returns. A digital camera with better resolution and a deeper field of view is scheduled to be installed Thursday. During the final spacewalk on Friday, Grunsfeld and Linnehan will attempt to revive a dormant infrared camera.

The shuttle is to return to the Kennedy Space Center early Tuesday.