Discovery flight plan changed
BY WILLIAM HARWOOD
STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION
Posted: March 20, 2009
NASA managers, thrilled at the successful deployment of a fourth and final set of solar arrays on the international space station today, approved a revised flight plan that will delay hatch closure and the shuttle Discovery's undocking slightly to improve the odds of getting critical experiment samples back to Earth in case of weather wave-offs that might delay the orbiter's return.
LeRoy Cain, chairman of NASA's Mission Management Team, said the revised flight plan will optimize the crew's docked timeline while still ensuring a touchdown on March 28 as originally planned. By delaying hatch closure and undocking slightly, experiment samples that must be shipped home cold can stay in the space station's freezer longer, giving them more shelf life aboard Discovery.
"End of mission remains ... a week from tomorrow," Cain said. "The difference is the option we settled on will allow us a little bit more time during the docked phase for the crew to take advantage of some other work, including transfers and other items. It'll result in the hatch closure and undocking occurring on the same day, on flight day 11. It kind of optimizes the docking timeline and gives us a little bit of margin."
Cain also said Discovery's heat shield is in good shape. A detailed assessment based on launch imagery, an inspection by the crew in orbit and a photo survey carried out by the station's crew during Discovery's final approach revealed only a few relatively minor problems.
"As far as the thermal protection system, we've essentially cleared the vehicle for all intents and purposes," Cain said. "We haven't officially made that determination in the Mission Management Team because there is one item of interest that is outstanding, but it's not going to be an issue for us in terms of being able to execute a safe deorbit and landing of Discovery."
Along with a damaged tile on Discovery's left inboard elevon, or wing flap, close-up photography also revealed a protruding gap filler, a thin spacer used to keep adjacent tiles from rubbing against each other. The damaged tile is not considered a problem and protruding gap fillers have been seen on other shuttle flights. This one, at the back of the shuttle, is not believed to be a problem.
At worse, Cain said, some downstream tiles could suffer enough damage to require replacement. On the other hand, vibrations associated with the elevon's movement - or the re-entry airflow - could work the gap filler loose or simply bend it over. But the issue has not yet been closed out.
"There's a gap filler on one of the elevons, the left inboard elevon, one of the little spacers between the tiles is protruding," Cain said. "We have a lot of flight experience with tile and gap filler and different kinds of issues in this part of the underside of the orbiter and the team's very confident this one's not going to be an issue. But we have a little bit of analysis and we want to give the team an opportunity to peer review all that. But I anticipate we'll officially clear the vehicle sometime over the weekend."
As for Discovery's performance during the climb to space last Sunday, Cain said the shuttle's boosters, main engines and external fuel tank all performed well.
"We just had exceptionally good performance out of the propulsion elements," Cain said. "The booster element reported they have no significant anomalies, but they do have what they characterized as 'squawks.' I look forward to seeing in greater detail, probably on Monday, what some of those more or less minor issues are. ... But the verbal quick-look presentation looked very good today now that the boosters are back in the hangar at the Cape."
Aboard the international space station, the astronauts checked out the tools and equipment they will need for a spacewalk Saturday while Sandra Magnus worked to install a replacement distillation centrifuge carried up by Discovery for the station's urine recycling system.
The water recycling system is critical to NASA's long-range plans to support six full-time astronauts aboard the outpost. The system is designed to convert condensate and urine into clean water for drinking, personal hygiene and oxygen generation.
But when the system was activated late last year, engineers ran into problems with the vacuum distillation assembly, a critical component that features a high-speed centrifuge. A new DA was flown up aboard Discovery and engineers hope to activate it over the weekend.
In the meantime, NASA managers were thrilled with the crew's successful deployment of the new S6 truss segments two solar wings earlier today. The extension of both panels, the channel 1B array first and then the 3B wing, "went very well. We didn't have any problems with it, we were very pleased with how the plan came together, how it was executed," said lead flight director Kwatsi Alibaruho.
"As we mentioned yesterday, we were going to be paying particularly close attention to the deployment of that (second) 3B solar array," he said. "One of the things that was of particular concern to us during the deployment of that solar array was the fact that that array had been packed away for so long. I mentioned in yesterday's mission status briefing that it had been packed for three years. It was actually packed for eight years."
During deploy today, television views showed a "considerable amount of deformation of the solar panels due to tension and stiction," Alibaruho said. "There was much more stiction in the 3B solar array than there was in the 1B solar array. ... The good news is all of that was in family with our experience. We executed the plan we had developed pre-flight for the thermal conditioning and all of that went very well."
Said Dan Hartman, chairman of the space station mission management team: "It was a truly fantastic day in space. The international space station team and its partnerships are on cloud nine with the completion of the integrated truss assembly as well as the finalization of our electrical power grid on the space station. It took years to get here. We had some struggles along the way, but it's a major accomplishment for NASA and the partnership team."