Fresh from a $100 million overhaul, the veteran shuttle Columbia roared back into space today on a high stakes mission to upgrade the Hubble Space Telescope's aging power system and to install a new camera to extend its scientific reach.

Columbia launches at 6:22 a.m. EST. Photo: NASA TV/Spaceflight Now

Knifing through a thin layer of clouds just over the launch pad, Columbia put on a spectacular show, lighting the clouds from above as the Hubble Space Telescope sailed across central Florida at five miles per second, a clearly visible target 360 miles up.

Strapped in on Columbia's flight deck were commander Scott Altman, pilot Duane Carey, flight engineer Nancy Currie and payload commander John Grunsfeld. Seated below on the shuttle middeck were James Newman, Richard Linnehan and Michael Massimino.

This was Columbia's first launch since July 1999 when the orbiter suffered a short circuit seconds after liftoff that left the ship one failure away from a premature engine shutdown.

Since then, NASA's oldest shuttle has undergone extensive structural inspections, wiring repairs and upgrades, including installation of a state-of-the-art "glass cockpit" with flat panel color displays.

"This has been an extensive down period for Columbia, probably the most extensive that we've done," said NASA test director Steve Altemus. "This orbiter was taken apart and put back together in such a manner that we have nothing but the highest confidence it's going to perform like it always does on orbit, which is essentially flawless."

No problems were reported during ascent. After a one-day delay because of predicted cold weather, Columbia rocketed away today through a break in light cloud cover.

At the moment of launch, the Hubble Space Telescope was approaching the Kennedy Space Center, sailing 350 miles above Florida's west coast at five miles per second.

If all goes well, Altman will guide Columbia to a rendezvous early Sunday morning and Currie, operating the ship's robot arm from the aft flight deck, will mount the 24,000-pound observatory on a rotating service platform at the back of the shuttle's cargo bay.

After switching Hubble to shuttle power, the telescope's two flexible solar arrays will be rolled up and the stage will be set for the most complex orbital servicing missions ever attempted by NASA.

During five back-to-back spacewalks by alternating two man teams, the astronauts first will overhaul Hubble's electrical system, installing two smaller-but-more-powerful solar arrays and a replacement power control unit, the telescope's main electrical distribution system.

The also will install a new reaction wheel assembly, a device used to help move Hubble from target to target.

Once the electrical work is complete, the astronauts will turn their attention to the scientific objectives of Servicing Mission 3B, installing the Advance Camera for Surveys during the fourth spacewalk and a high tech refrigerator during the fifth to revive a dormant infrared camera.

All of the work is challenging, but it is the power control unit swap out that will keep NASA managers - and astronomers around the world - on the edges of their seats.

The 160-pound black box has suffered internal failures in recent years that have reduced its efficiency. And one internal glitch, should it get worse, could cause some of Hubble's batteries to overheat, triggering a catastrophic failure.

But the PCU was not designed to be serviced by astronauts wearing thick spacesuit gloves. It is wired into Hubble's electrical system by 34 closely spaced, hard-to-reach cable connectors along its left side. Two more cables are connected at the base of the unit.

"What makes it difficult is, as you're facing the PCU, those connectors are on the left-hand side, they're not staring right at you, they're on the left face," Grunsfeld said. "And that's on the side that that bay door is hinged. For the suited crewman to reach his hand in there, he's pretty much reaching in there blind.

"I kind of equate it to changing out spark plugs on your car," he said. "There's always those spark plugs down there where you sort of can't see real well, you've just got to go down and feel and make sure you're oriented such that you're unscrewing it without a lot of offset force."

Adding to the drama - and the risk - of the PCU swap out, Hubble must be completely powered down and its batteries disconnected before the work can begin. The new PCU must be in place and power restored within the next 10 hours or so or the low temperatures of space could damage Hubble's sensitive electronics.

Anne Kinney, director of astronomy and physics at NASA headquarters, said she will be "nervous as hell" until the repair work is complete. Ed Weiler, associate administrator for space science, said the PCU replacement "scares me a lot."

"It kind of violates a long-standing policy in the space business that if something's working well you don't turn it off and just hope it comes back on," he said.

"We're not doing that cavalierly, we fully anticipate that everything will work just fine," he added. "But it is a risk that we've never faced before. So this mission is no cakewalk."

While the PCU replacement is the top priority of Columbia's mission, it will not be attempted until the third spacewalk.

First, Grunsfeld, Linnehan, Newman and Massimino will install the new solar arrays and control circuitry that will give engineers more control over Hubble's power system before the PCU replacement is attempted.

The first spacewalk, by Grunsfeld and Linnehan, is scheduled to begin around 1:30 a.m. Monday. The second, by Newman and Massimino, will begin at the same time Tuesday. Along with installing the second solar array, Newman and Massimino will install the new reaction wheel toward the end of the second spacewalk.

During both excursions, the astronauts will install thermal shields and light shades over sensitive areas of the telescope that will help protect the observatory during the PCU power outage.

The PCU replacement, by Grunsfeld and Linnehan, is expected to take at least seven-and-a-half hours. Assuming the work goes smoothly, Newman and Massimino will install the Advanced Camera for Surveys next Thursday during the fourth spacewalk.

The fifth and final outing is installation of a high-tech "cryocooler" refrigerator to revive the dormant Near Infrared Camera and Multi-Object Spectrometer, or NICMOS.

The NICMOS instrument is sensitive to infrared light but it must be chilled to less than 100 degrees above absolute zero to work properly. The instrument was launched with a dewar of nitrogen ice coolant. But an internal "thermal short" caused the nitrogen to sublimate away faster than expected.

The experimental cryocooler that will be installed by Columbia's crew uses neon gas and three small turbines spinning at 400,000 rpm to provide cooling to 75 degrees above absolute zero.

Installation of the cryocooler is perhaps the single most complex task on the mission from a spacewalk perspective, but given the experimental nature of the device, it is considered the lowest priority of the flight.