Discovery cleared to return to Earth
NASA has cleared Discovery to return to Earth next week, concluding that there was no need to send the astronauts out on another spacewalk to repair a torn thermal blanket near a cockpit window.
Mission managers could not guarantee that a piece of the blanket will not rip off during re-entry and slam into the spacecraft, but they said the chance of that happening was remote and that it would be riskier to try to fix the problem.
“The lowest risk, the best choice and the unanimous decision of the engineers in the management team is that we should re-enter as is,” deputy shuttle program manager Wayne Hale said yesterday.
Discovery’s astronauts awoke late yesterday prepared to pack up. They planned to transfer a cargo container from the station back into the shuttle’s cargo bay in preparation for the ship’s undocking from the station, set for tomorrow.
NASA had been considering sending the astronauts out to cut away part of the blanket for fear a 13-inch section weighing just under an ounce could tear away during the latter stages of descent and strike the shuttle, perhaps causing grave danger.
Wind tunnel tests hurriedly conducted in California on real thermal blanket samples showed it is possible tiny pieces of the fabric might shred off, Hale said. In the worst situation, he noted, there is a 1.5% chance that the entire 13-inch section would come off and hit the shuttle.
It’s possible, under that remote circumstance, that the cloth could strike the rudder speed brake and create a hole and six-foot-long crack, but even that would not be enough to endanger Discovery and its crew of seven, Hale said. He noted, however, that there are a lot of assumptions and variations in that chain of analysis, “so is that the absolute worst thing that could happen? Well, no, it's not.”
“I am not here to tell you that we are 100% confident that there is no risk during re-entry. That would be untrue and foolish to even try to make that case,” he said. “But I am here to tell you is that we’ve assessed this risk to the very best of our engineering knowledge and we believe that it is remote, small, whatever adjective you want to put with that.”
Discovery is scheduled to land back at Cape Canaveral, Florida, before dawn on Monday.
Had the astronauts been asked to repair the blanket, it would have been the fourth spacewalk of the 13-day mission. It also would have been the second time during the flight that the astronauts had to step outside to repair the shuttle’s thermal protection and reduce the risk of another Columbia-type tragedy during the trip home, when the spacecraft passes through the blowtorch heat of re-entry.
