Crew prepares for Saturday's station spacewalk
BY WILLIAM HARWOOD
STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION
Posted: August 17, 2007
The Endeavour astronauts are working through a busy day in space today, trying to trace a subtle communications wiring problem, transferring supplies and equipment to and from the international space station and preparing for a fourth and final spacewalk Saturday. The astronauts plan to participate in a traditional in-flight news conference at 1:34 p.m. Today's mission status briefing is scheduled for 3 p.m.
Here is an updated timeline of today's activities, based on the crew's flight plan and revision N of the NASA television schedule (in EDT and mission elapsed time):
EDT........DD...HH...MM...EVENT 05:07 AM...08...10...30...STS/ISS crew wakeup 08:12 AM...08...13...35...EVA-4 tool preparation 08:27 AM...08...13...50...Logistics transfers resume 11:02 AM...08...16...25...DAIU communications troubleshooting 01:12 PM...08...18...35...Crew photo 01:34 PM...08...18...58...Joint crew news conference 02:12 PM...08...19...35...Joint crew meal 03:00 PM...08...20...24...Mission status briefing on NASA TV 03:12 PM...08...20...35...Logistics transfers resume 03:12 PM...08...20...35...Spacehab debris shields checked 03:32 PM...08...20...55...DAIU wrapup 04:07 PM...08...21...30...Spacesuit swap 04:37 PM...08...22...00...Equipment airlock prepared 05:22 PM...08...22...45...Logistics transfer tagup 05:37 PM...08...23...00...EVA-4: Procedures review 07:32 PM...09...00...55...EVA-4: Nitrogen purge mask pre-breathe and tool config 08:17 PM...09...01...40...EVA-4: 10.2 psi airlock depressurization 08:37 PM...09...02...00...ISS crew sleep begins 09:07 PM...09...02...30...STS crew sleep begins
Saturday's spacewalk by Canadian astronaut Dave Williams and station crew member Clay Anderson is devoted to a variety of get-ahead tasks that will help pave the way for future space station assembly missions. The excursion originally was planned for today, but it was delayed 24 hours to give flight controllers time to assess whether a heat shield repair job was needed to fill in two damaged tiles on the belly of the shuttle.
Late Thursday, mission managers decided test data and analysis proved Endeavour could safely return to Earth as is. A tile repair spacewalk was ruled out and the astronauts were told to press ahead with the station assembly EVA instead.
The damage assessment brought back memories of an internal debate after the shuttle Columbia's launching in 2003. In that case, a relatively limited study was carried out to determine the possible damage caused by a large piece of foam debris that hit the underside of the shuttle's left wing during launch. NASA's Mission Management Team accepted a hurried analysis by a small group of engineers and concluded Columbia could safely re-enter as is even though the actual impact site could not be seen in launch imagery.
The analysis was deeply flawed. Equally troubling in hindsight, the Mission Management Team did not hear, or take seriously, concerns from lower-level engineers who were not satisfied with the review. As it turned out, what NASA managers believed was relatively minor damage to heat-shield tiles was, in fact, a 4- to 6-inch hole in the leading edge of Columbia's left wing. Sixteen minutes from touchdown, the left wing failed, the spacecraft broke apart and all seven crew members were killed.
Memories of Columbia still linger and the MMT decision not to mount a repair spacewalk to fix the damage to Endeavour's heat shield made some outside observers uncomfortable. But Shannon said he was "100 percent" confident the team made the right decision.
Unlike the Columbia case, NASA now has the ability to photograph virtually every square inch of the shuttle's heat shield, high-resolution cameras to zoom in on damage sites and an on-board laser scanner to measure its extent in three dimensions. Sophisticated computer modeling software has been developed to help engineers accurately predict the effects of re-entry heating. And NASA has tried to set up a management system that encourages debate, peer review and minority reports.
All of those systems were in play during the analysis of Endeavour's heat shield, Shannon told reporters late Thursday. Mockups of the damage site were subjected to re-entry heating in a high-tech furnace at the Johnson Space Center. Computational fluid dynamics was brought to bear to model heating and its effects under a variety of conditions and that work was peer reviewed to ensure accuracy. When all was said and done, engineers unanimously concluded the damage did not pose any sort of catastrophic threat to the crew and all but one engineering organization voted to clear Endeavour for entry as is. The lone dissenting vote was cast by an engineering group at the Johnson Space Center that believed a repair might add a bit of additional margin.
"If we had a condition that I thought was a threat to crew safety I would go execute this EVA and feel pretty good about it," Shannon said. "Since that is not the case, since we had independent analyses to show this is not expected to be even a turn-around issue to the vehicle, there's no way I could justify sending the crew out on that EVA just because, just to go do something. And so it became, I think, a very simple decision once we got that analysis done."
The rigor of that analysis and the widespread multi-center approach to studying - and verifying - results, Shannon said, reflects a "night and day" difference between the way NASA approaches in-flight problems today versus four years ago. That doesn't mean mistakes can't be made. But Shannon clearly believes NASA has the safeguards in place to minimize the likelihood of a fatal error.
"Because we have expended the resources and spent the time to develop the tools, not just the hardware tools but the analytical tools, to be able to understand exactly what the condition of the thermal protection system is," he said. "You saw on this flight several things, one is all of the new capabilities that we have added since Columbia, from the ground cameras to the in-flight cameras to the in-flight radar system that's looking specifically for debris, we used every one of those. From the rendezvous pitch maneuver we do close to the station, we got that data. We did the leading edge scans with the (heat shield inspection) boom. And then we had the discussions on the analytical tool capability, our ability to analyze this high energy environment. And we have repair capabilities.
"The more important thing to me is the seriousness and thoroughness with which the entire community analyzed this particular case," Shannon said. "This is not different from the (displaced) OMS pod (insulation) blanket we had on the last flight. We do not clear anything until we have the data to clear it and we take things extremely seriously and we bring to bear the resources of the entire agency, even expertise outside of the agency when we can bring it in. We had computational fluid dynamics at Ames (Research Center). It was backed up at Langley Research Center. We have had expertise at Johnson, at Kennedy at Marshall (space centers), at all the NASA centers.
"It's a little bit of a double edged sword, right? Because I would have liked to come in early on and say guys, let's not blow this out of proportion, it doesn't look like a loss-of-crew-and-vehicle kind of case, let's not get too excited about this. But we really can't do that because we didn't know at that point.
"You have to go do the analysis to know," he said. "And I think that is the key, as I am 100 percent comfortable that the work that has been done has accurately characterized it and we will have a very successful re-entry. I am also 100 percent confident that if we had gotten a different answer and found out that this was something that was going to endanger the lives of the crew that we have the capability on board to go and repair it and then have a successful entry. So we're setting ourselves up really well both ways."