Hubble at full power after `flawless' work

Astronauts replace electrical control box

March 07, 2002|By Frank D. Roylance | Frank D. Roylance,SUN STAFF

Electricity began flowing again aboard the Hubble Space Telescope yesterday - and scientists at the Space Telescope Science Institute in Baltimore began breathing again - after shuttle astronauts successfully replaced a failing electrical control box on the orbiting observatory.

Initial tests showed the $2 billion telescope's delicate scientific systems had survived nearly 4 1/2 hours without power or heat during the repairs. It was the first time since its launch in 1990 that the telescope had been switched fully off, and no one was quite sure it would survive the operation.

Mario Livio, head of the institute's science division, stayed up nearly all night at home to watch the high-flying surgery, via TV and computer, to assure himself that everything would be OK. "This is space science, and you should never be overconfident," he said.

During two previous seven-hour spacewalks this week, Columbia astronauts gave Hubble a new set of solar panels and replaced faulty aiming hardware.

A fourth spacewalk was set to begin at 2:30 a.m. today. Astronauts James Newman and Mike Massimino were scheduled to install a powerful new instrument called the Advanced Camera for Surveys.

Tomorrow morning, if all goes well, the astronauts will install an experimental cooler, designed to revive Hubble's powerful infrared camera, which was idled in 1999 when it ran out of solid nitrogen coolant.

The power control box replacement was the most critical juncture for Hubble since its infamous mirror flaw was discovered in 1990, said Michael Hauser, the institute's deputy director. But "as far as this place is concerned, the real excitement is in the next few days."

The improvements will boost Hubble's powers of discovery by a factor of 10, Hauser said, allowing astronomers to uncover secrets of galactic evolution, and new phenomena previously obscured by dust and glare. The improved telescope, he said, will be "vastly different from the Hubble launched in 1990."

There are 600 people at the Space Telescope Science Institute whose jobs and careers depend on Hubble's health. Some, like Livio, sacrificed sleep to watch the pre-dawn repairs.

But many others, including Hauser, slept in, assured by past successes that NASA's astronauts would take good care of their telescope. There were no all-night vigils at the institute, and no hushed crowds yesterday morning beneath the wall-mounted NASA TV monitors.

Instead, it was business as usual. People attended meetings or worked in their offices, catching occasional glimpses of NASA Web casts on their computers. To them, failure was never a consideration.

"We didn't waste a lot of energy making contingency plans for that," Hauser said.

The repair work got off to a bad start when a valve malfunctioned on astronaut John Grunsfeld's space suit. It leaked nine pounds of cooling water into the shuttle compartment where he and Richard Linnehan were donning their suits.

"I didn't know if they were going to go on with it," Livio said. "Even my wife woke up a few times and asked what was going on. She saw I was visibly agitated."

Three hundred sixty miles up, the astronauts mopped up the weightless water as best they could with towels. Controllers at the Goddard Space Flight Center in Greenbelt scrambled to maintain critical temperatures on Hubble. And in Houston, spacewalk managers discussed whether to postpone the day's work or send out the second team of astronauts to install the Advanced Camera for Surveys a day early.

In the end, they had Grunsfeld don a spare spacesuit top. And at 3:30 a.m. EST - two hours late - he and Linnehan stepped outside to replace the Power Control Unit (PCU) as planned.

NASA had debated since 1993 whether to replace the control unit. A loose bolt was causing a 15 percent reduction in voltage. But the unit was never designed for replacement in orbit, and some analysts insisted it was impossible.

The PCU distributes power to the telescope through 36 electrical connections that were too small and hard to reach for an astronaut working in heavy space gloves.

But the increased power from the new solar panels, and the higher electrical needs of the new scientific instruments planned for Hubble, finally made it clear that a new PCU was critical. Even if the old unit didn't fail completely, NASA concluded, Hubble controllers would be rationing power.

Aided yesterday by more flexible gloves and a specially designed wrench, Grunsfeld and Linnehan methodically set about disconnecting each cable, removing the old box and reconnecting each cable to the new unit. At one point Grunsfeld was completing one connection every 2.2 minutes.

In less than four hours, the new box was installed, and Hubble controllers at Goddard immediately prepared to restore electrical power to the observatory. At 9:02 a.m., they relayed a message to the spacewalkers. "We have a heartbeat," they said.

"Good news. Thank you," Grunsfeld replied.

Over the next several hours, Goddard engineers gradually restored power to each scientific instrument and support system on the telescope, and recharged its batteries.

Preston Burch, Hubble project manager at Goddard, later pronounced the repairs "flawless" and the telescope in good health. "There's no doubt in my mind we will be able to run all the instruments," he said.

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