Booster concerns 283

By the end of their investigation, engineers had concluded that the most likely cause for the 'out-of-family' erosion pattern seen on the STS-79 boosters was due to a 'pocketing' erosion effect triggered by slight ply distortions in the ablative material of the nozzle's throat ring and normal variations in other material properties. Ordinarily, the manufacturing of the throat rings is accomplished by wrapping the ablative material in a 'criss-cross' fashion and curing it at elevated temperatures and pressures. However, it was suspected that during the curing procedure, the material near the surface of the insulation shifted slightly, producing the distortions. When hot gas was flowing through the boosters, the distortions significantly raised stresses in the material that could result in the pocketing effect and the ablator wearing away unevenly. Nonetheless, analysis showed that - even with the ply distortion condition in the worst-possible configuration - safety margins could still be maintained. ''I am very proud of this Shuttle team and their efforts in reviewing the nozzle issue,'' said Holloway. ''The extra time we took to make sure all of the data was properly reviewed and analysed once again demonstrates that safety remains the Number One priority.''

Launch was delayed yet another four days to 19 November, thanks to the postponement of an Atlas rocket from nearby Cape Canaveral Air Force Station and predicted bad weather at KSC. Instead of stopping, and then restarting, the countdown, the clock was brought back from T —11 hours to T — 19 hours and held at that point until the evening of 18 November. Liftoff the following night was postponed at T— 31 seconds when a slight hydrogen leak was detected in Columbia's aft compartment.

During a two-minute hold, engineers carefully monitored the hydrogen concentrations and concluded that they were at ''acceptable levels'' and the countdown proceeded without further incident. Among the crew was Mission Specialist Story Musgrave, who not only became the first person to fly a sixth Shuttle mission, but also became the oldest man yet to fly in space: aged 61. ''I'm hugely blessed, just hugely blessed,'' he said before boarding Columbia. In doing so, he also became the only person to have flown on board all five Shuttles: two missions on Challenger and one each on Columbia, Discovery, Atlantis and Endeavour.

After a spectacular liftoff at 7:55:47 pm, NASA's long-range tracking cameras spotted something unusual: an apparent fire between the two SRBs. However, it was considered so minor that managers did not even mention it during the post-launch press conference, with NASA spokesman Doug Ward explaining that it was nothing unusual ''When you get close to booster separation and you get out of Earth's atmosphere, there's no strong airstream to keep the fire from the rocket boosters pointing down,'' he said, adding that the External Tank was heavily insulated to safeguard against a possible explosion.

Fortunately, when Columbia's astronauts photographed the tank as it tumbled away, eight-and-a-half minutes into the mission, they reported no apparent damage. After establishing themselves in their correct orbit and stowing their pressure suits and seats, they readied ORFEUS-SPAS-2 for its deployment in the early hours of 20 November. With Mission Specialist Tom Jones at the controls of the RMS, the satellite was released at 4:11 am; three hours later, to relief from ground controllers, the ORFEUS telescope's aperture door was reported as having opened satisfactorily. Deployment was an hour later than planned, following a longer-than-expected checkout of the satellite.

Within a day of its release, Columbia led ORFEUS-SPAS-2 by about 53 km and, following the first of several station-keeping manoeuvres, closed in to enable radar data to provide a more precise 'fix' on the satellite. It was hoped this would help Mission Control to better compute future manoeuvres. Over the next few days, until the satellite's retrieval on 3 December, Commander Cockrell and Pilot Kent Rominger performed a series of thruster firings to bring the Shuttle closer to, then further away from, ORFEUS-SPAS-2. This job was complicated somewhat when STS-80's second satellite payload was deployed on 23 November.

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