Columbia sits on the launch pad awaiting its trip to the Hubble Space Telescope. Photo: NASA

Now equipped with modern flat-panel cockpit displays and other improvements, Columbia is scheduled to rocket away from pad 39A at 6:48:14 a.m. on Feb. 28 to kick off its 27th mission in 21 years of service.

"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 went through the most extensive wiring inspection and modifications of any of the orbiters, so that gives us high confidence we've got the vehicle working properly with respect to wiring.

"We've got some upgrades that are going to improve safety and reliability and performance. 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."

At the controls for launch will be commander Scott Altman, pilot Duane Carey and flight engineer Nancy Currie. Their crewmates are spacewalkers John Grunsfeld, veteran of the most recent Hubble servicing mission, Richard Linnehan, James Newman and Michael Massimino.

Grunsfeld and Linnehan are responsible for the first, third and fifth spacewalks, during which they plan to install one of the new solar arrays, the power control unit and the NICMOS cryocooler.

Newman and Massimino plan to install the second solar array and the reaction wheel assembly during the second EVA and the Advanced Camera for Surveys during the fourth.

Columbia approaches the Hubble Space Telescope for retrieval as illustrated in animation. Photo: NASA TV/Spaceflight Now

If all goes well, Altman will guide Columbia to a rendezvous with Hubble two days after launch, approaching the telescope from directly below. By that point, the telescope's two KU-band antennas will have been folded up against the body of the spacecraft and its two solar arrays will be oriented parallel to the long axis of the observatory.

Assuming an on-time liftoff, Currie, operating the shuttle's 50-foot-long robot arm, will snare the spacecraft around 4 a.m. on March 2.

She then will lower Hubble's base onto a lazy Susan-type rotating service platform at the rear of Columbia's cargo bay. Three latches will engage to lock the telescope down and an umbilical will be extended to provide power from the shuttle's fuel cells.

As viewed from Columbia's aft flight deck, Hubble's two solar arrays will appear face on to the left and right of the telescope's tube, which will extend straight out of the cargo bay. By convention, the left-side array is on the telescope's minus V2 axis while the right-side array is on the plus V2 axis.

The arrays were installed during the first Hubble servicing mission in 1993. They weigh 339 pounds each and measure 40 feet long by 10.8 feet wide, delivering about 4,600 watts of power from silicon solar cells.

Because of the wear and tear of temperature extremes and normal space radiation, the flexible panels now provide just 63 percent of their original power. In addition, they suffer from structural problems and some shorted circuitry in the wiring connecting all the solar cells.

Designed for Iridium communications satellites, Hubble's new arrays are heavier - 640 pounds per wing - and more powerful, generating some 5,270 watts. But they are smaller than Hubble's flexible panels, measuring just 23 feet long and 8.5 feet wide.

The additional power generated by the new gallium arsenide solar cells will enable astronomers for the first time to operate all of Hubble's instruments at the same time for simultaneous multi-disciplinary observations. In addition, their smaller size will reduce the atmospheric drag that constantly acts to reduce Hubble's altitude.

The first of the two solar arrays is retracted as shown in animation. Photo: NASA TV/Spaceflight Now

Before the new arrays can be attached, however, the old wings must be rolled up, a task that will be carried out about four hours after the telescope is captured.

First, the astronauts, operating the servicing platform by remote control, will tilt Hubble forward and rotate it counter clockwise so the -V2 array is facing the crew cabin. Once that array has rolled up - the process is expected to take about eight minutes per wing - the telescope will be rotated 180 degrees clockwise to bring the +V2 array forward.

There is a bit of uncertainty about whether the arrays will, in fact, smoothly roll back up. During the first servicing mission in 1993, a similar array jammed and failed to retract, forcing the astronauts to dump it overboard.

Should Columbia's crew run into similar problems, Grunsfeld and Linnehan will simply jettison one or both arrays as required at the start of their first spacewalk. In addition, there's a slight chance brittle insulation surrounding he external framework of the arrays could flake off during the retraction procedure, creating a small cloud of dusty debris.

But mission managers are optimistic the arrays will roll up as planned and even if a small amount of insulation does, in fact, flake off, Altman could simply move the shuttle away slightly, eliminating any chance of contamination.

In any case, once Hubble is on orbiter power and the arrays are rolled up, the stage will be set for the most grueling set of spacewalks yet attempted by NASA.

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