Commander Scott Altman, Pilot Duane Carey, Flight Engineer Nancy Currie and spacewalkers John Grunsfeld, Rick Linnehan, Jim Newman and Mike Massimino are beginning a complex mission to replace and upgrade key systems in the Hubble Space Telescope - a job that requires five back-to-back spacewalks, each more than six and a half hours long.

Mission managers met Friday evening to review information about the performance of the port side freon cooling system in Columbia's payload bay, which exhibited a degraded flow rate shortly after launch. They gave Columbia's crew a "go" to proceed with normal operations today and expressed confidence the shuttle will be allowed to complete its full mission. However, shuttle managers will meet again at midday Saturday for a further review of the potential cooling system problem and they are expected to reach a final conclusion at that time on proceeding with a Sunday capture of Hubble and the ensuing spacewalks. The degraded cooling system is one of two such systems aboard Columbia. The other system is operating perfectly. Only one of the systems is needed to provide cooling for the shuttle's electronics, but the concerns are whether the degraded cooling system can be used as a backup in the event the fully operational system were to experience unexpected problems. Although the one system is operating at a lower capacity, the problem has had no impact on any of the crew's activities and is not noticeable by the crew.

Altman and Carey are getting ready to fire Columbia's reaction control system thrusters to fine-tune its approach to Hubble at 11:10 p.m. CST. Also tonight, the crew will test Columbia's robotic arm, examine the spacesuits on board, check out rendezvous equipment, and prepare the Flight Support System that will hold the telescope while it is berthed in the orbiter's payload bay.

Currie is scheduled to use Columbia's robot arm to grapple Hubble shortly after 3 a.m. CST Sunday, setting the stage for the first spacewalk early Monday morning.

During Hubble's fourth service mission, the crew of Columbia will spend five days replacing the observatory's solar arrays, its main power switching unit, and a gyroscopic pointing mechanism called a Reaction Wheel Assembly. In addition, the spacewalkers will install a new camera called the Advanced Camera for Surveys that can view twice the area of the sky as Hubble's current camera. The spacewalkers will install a cooling system and an external radiator for the Near Infrared Camera and Multi-Object Spectrometer, which requires very cold temperatures to function.

Columbia is in a 356 by 127 statute mile orbit of the Earth, catching up to Hubble about 1,000 miles every orbit. The next STS-109 mission status report will be issued Saturday morning or earlier if events warrant.

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