Spaceflight Now STS-109

NASA shuffles remaining spacewalk schedule
Posted: March 6, 2002

NASA managers, elated at the successful replacement of the Hubble Space Telescope's central power controller, will delay the start of the next two servicing spacewalks to give Columbia's astronauts time to catch up on their rest after getting off to a late start today.

A spacewalk to install a new $75 million camera to extend Hubble's scientific reach is now scheduled to begin around 3:30 a.m. EST Thursday, about two hours later than planned. The fifth and final spacewalk of Columbia's mission also will begin two hours late, around 3:30 a.m. EST Friday.

That's because of a sudden water leak in astronaut John Grunsfeld's spacesuit earlier today that forced a time-consuming last-minute suit swap and a subsequent two-hour delay getting out of Columbia's airlock. Dana Weigel, lead spacewalk planner for Columbia's mission, said engineers suspect a voltage spike in an airlock power system caused a valve in Grunsfeld's backpack to pop open, allowing about nine pounds of cooling water to leak out.

The delay threw a wrench into NASA's carefully choreographed plan to replace Hubble's power control unit, or PCU, a complex repair job made even tougher because the system was not designed to be serviced in orbit.

"If anybody has any doubts about Murphy's Law, then they weren't watching what happened this morning," said Preston Burch, Hubble program manager at the Goddard Space Flight Center. "It was kind of like going to a football game and watching your favorite team come onto the field and suddenly be told they've got a 40-point disadvantage and they've got to still try to win the game.

"It was a tough act to pull off, but this crew of John Grunsfeld and Rick Linnehan and all the rest of the shuttle crew never gave up. I thought that our flight director, Bryan (Austin), made a fantastic call in deciding to push ahead. That took a lot of guts to do that. It was obviously the right call to make, we got all our work accomplished today. And the operation, once the crew got out, was absolutely flawless from our perspective."

Before installing the power control unit, engineers had to power Hubble down for the first time since launch in 1990, deliberately putting the $2 billion observatory in a life-threatening coma and trusting the astronauts to replace the PCU and restore power before critical systems failed in the extreme cold of space.

"This dramatic and masterful performance caused us to laugh and caused us to gasp occasionally and finally caused us to sigh," said Anne Kinney, director of physics and astronomy at NASA headquarters. She watched the spacewalk unfold from NASA's customer support room adjacent to mission control.

The room "erupted in applause as the last of 36 plugs was connected," she said. "It was a moving performance."

It will take engineers about eight-and-a-half hours to fully restore power to all of the telescope's systems. By noon, Burch said, ground controllers had finished preliminary work to test the PCU, powered up Hubble's transponders to receive telemetry, powered up the telescope's main computer and restored power to the Wide Field Planetary Camera.

"Based on what we know right now, things are looking extremely well," Burch said. "There's no doubt in my mind we will be able to run all of the instruments in the manner we'd like to following this servicing mission and servicing mission 4, when we'll be adding two additional science instruments.

"We've done a major refurbishment on the electrical power at this point, but it's not over yet," he said. "We will complete the refurbishment of the HST electrical power system on the next servicing mission (in 2004) when we replace all the nickel hydrogen batteries that we have on board."

Burch said engineers first began studying the possibility of replacing the PCU in 1993 when a subtle internal problem surfaced that could, in a worst-case scenario, cause a catastrophic failure. Today, those years of analysis, planning and training finally paid off.

"We started seriously examining the feasibility of it in 1993 and it's taken quite a while to develop it," Burch said. "I can tell you there were a lot of people who thought we were crazy to even try it, people who know a lot about the Hubble electrical power system. It took a tremendous amount of effort to eventually develop the tools and techniques to pull this off. It's been a long haul."

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