CAPE CANAVERAL, Fla. (AP) _ With near-freezing temperatures no longer a concern, NASA aimed for a predawn launch Friday of space shuttle Columbia on a mission to rejuvenate the Hubble Space Telescope.
A rare cold snap had prompted a one-day delay.
As it turns out, NASA would have been within its safety limits for launching Columbia on Thursday _ barely. It was 38 degrees as predicted at sunrise, but the combination of humidity and wind bringing in warmer air made the cold acceptable, NASA spokesman George Diller said.
``We were as low as we could have gone,'' Diller said. ``Why push that margin if you don't have to?''
A relatively balmy 55 degrees was expected for Friday's attempt.
NASA's coldest launch-time temperature for a space shuttle was on Jan. 28, 1986, when Challenger took off in 36 degrees after freezing temperatures overnight. O-ring seals in the right solid-fuel booster rocket deteriorated because of the cold and hot gases leaked from the joint, resulting in an explosion that killed all seven astronauts on board.
As for last-minute concern about improperly manufactured wheel bearings in Columbia's main landing gear, engineers deemed them acceptable after two days of analysis. The steel rollings in all eight bearings were tempered at a temperature lower than desired, but are still considered strong enough to support a 200-mph shuttle touchdown.
Columbia, fresh from a 2 1/2-year overhaul, is loaded with new scientific, power and steering parts for Hubble.
Spacewalking astronauts will go out a record-tying five times to install all the equipment on the 12-year-old telescope: stronger solar wings, more robust power-control unit, more reliable steering mechanism, a refrigeration system to resuscitate a disabled infrared camera and a camera to increase Hubble's capability for discovery by 10 times.
NASA considers this the most complicated Hubble servicing mission yet because of the heavy workload and a pair of unprecedented spacewalking jobs. Neither the power-control unit nor infrared camera repairs were meant to be tackled in orbit.
Hubble program manager Preston Burch said the extra day gave everyone time to ``tidy up things here and there,'' even though they didn't really need to. ``We are so well prepared for this,'' he said.
Spacewalking astronauts have worked on Hubble three times, in 1993, 1997 and 1999. One more service call is planned after this one, in 2004. Then, if NASA has its way, that will be it until the telescope is returned to Earth in 2010 for museum display.
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