Following completion of a follow-up readiness meeting today, NASA managers cleared Space Shuttle Columbia for launch on Mission STS-80 and set November 15th as the official launch date. The STS-80 launch was originally planned for earlier this month but was delayed to allow engineers additional time to complete their testing, analysis and evaluation of nozzle erosion that was found on one Reusable Solid Rocket Motor from Atlantis' September flight on STS-79.
Engineers have concluded that the most likely cause for the unusual erosion pattern seen on the STS-79 booster was due to a pocketing erosion effect triggered by slight ply distortions in the ablative material of the nozzle throat ring and normal variations in other material properties.
The manufacture of the throat ring is accomplished by wrapping the ablative material in a criss cross fashion and curing at elevated temperatures and pressures. Engineers believe that in the curing process, the material near the surface of the insulation shifts slightly, thus creating distortions near the surface.
During the motor operation when hot gas is flowing, the distortion can significantly raise stresses in the material that could result in a pocketing effect that causes the ablative material to wear away unevenly. Analysis also shows that even with the ply distortion condition in the worst possible configuration, significant safety margins are maintained.
The launch window on November 15 opens at 2:50 p.m. EST and extends for 2 1/2 hours. The STS-80 mission has a planned duration of 16 days. An on-time launch and nominal mission would result in a landing for Columbia at the Kennedy Space Center on Sunday, December 1 around 7:30 a.m. EST. The November 15 launch date is contingent upon a commercial Atlas rocket launch planned for Wednesday, November 13. If the Atlas launch is delayed one day for some reason, the Shuttle launch would move one day later due to Air Force range safety support logistics.
"I am very proud of this Shuttle team and their efforts in reviewing the nozzle issue," Space Shuttle Program Manager Tommy Holloway said. "I believe we now have a good understanding of the phenomenon seen on the STS-79 booster and are ready for Columbia's launch. The extra time we took to make sure all of the data was properly reviewed and analyzed once again demonstrates that safety remains the number one priority of this program."
The STS-80 mission is NASA's final Shuttle flight scheduled for 1996. During the mission, Columbia's astronauts, led by Commander Ken Cockrell, will deploy and retrieve two science satellites and two of the astronauts will conduct a pair of space walks to fine-tune techniques which will be used during the assembly of the International Space Station.