Hale talks foam redesign, mission extension options
BY WILLIAM HARWOOD
STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION
Posted: September 5, 2006
NASA managers are holding open the possibility of extending the shuttle Atlantis' mission by at least one and possibly two days to give the crew time to carry out additional heat shield inspections and to handle any unexpected problems that might crop up, officials said today.
Atlantis is scheduled for blastoff Wednesday at 12:29 p.m. on a space station assembly mission considered one of the most complex shuttle flights in recent memory. There are no technical problems of any significance at pad 39B and forecasters are predicting a 70 percent chance of good weather Wednesday, Thursday and Friday.
"We really are working no issues, the vehicle's in very good shape," said LeRoy Cain, launch site chairman of NASA's Mission Management Team. "I conducted the go/no-go poll to continue and everybody on the team is go and in good spirits. We're ready to press forward from here."
Launch Director Mike Leinbach said engineers may move the launch pad service gantry away from Atlantis an hour or so early today to beat the onset of expected afternoon thunderstorms.
"If we get it back before the weather sets in, that's great," he said. "If not, we'll recover that time after the weather passes. Typically, we hold four or five hours in abeyance for RSS (rotating service structure) retract. So if we do get hit by the afternoon weather, that really shouldn't pose a problem for us."
The Mission Management Team plans to meet at 1:45 a.m. Wednesday to assess the weather and give engineers clearance to proceed with loading Atlantis' external tank with liquid oxygen and hydrogen rocket fuel.
Fueling is scheduled to begin at 2:33 a.m. and if all goes well, commander Brent Jett, pilot Chris Ferguson, flight engineer Dan Burbank, Joe Tanner, Canadian astronaut Steve MacLean and Heidemarie Stefanyshyn-Piper will begin strapping in around 9:09 a.m.
Liftoff is targeted for 12:28:49 p.m. If Atlantis fails to get off the ground Wednesday, NASA can try again Thursday and Friday. After that, the flight will be delayed until after the Russians launch a fresh crew to the international space station Sept. 18 and bring the lab's outgoing crew back to Earth Sept. 29. The next daylight launch opportunity or the shuttle after Friday is Oct. 26.
With an on-time launching, Atlantis will dock with the space station Friday at 8:40 a.m. The next day, a new solar array truss will be attached to the outpost and the crew will stage the first of three spacewalks to make critical electrical connections, remove launch restraints and perform other activation tasks.
As it now stands, a second spacewalk would be carried out the next day, followed by solar array extension the day after that and then a third spacewalk. But managers may insert an extra day between the first two spacewalks to let the crew carry out "focused inspections" of the shuttle's heat shield based on whatever they see during an initial inspection the day after launch.
"We don't (currently) have that scheduled in the STS-115 timeline, but we know that is a likely possibility based on the flight day two or three inspections, that we'll need to go back and look at some areas in more focused detail," said shuttle Program Manager Wayne Hale. "There's a hope that perhaps we won't need to do that.
"The more difficult case for the team to execute, both the astronauts in orbit and mission control, is two back-to-back EVAs. If we need to do a focused inspection, the thinking is ... we would insert a day between the first and second EVAs. That becomes a somewhat lighter day for the crew and mission control, so it's an easier day to stand by for.
"What we'd really like to do is not have to do focused inspection, in other words, have such a clean vehicle that no inspections are required. Then we can save that day, bank it, and keep it (for) the end of the mission in case we run into any difficulties in the assembly process. Lifting off tomorrow or even the day after tomorrow, we really will have the capability to extend not one, but two days to the docked period so we would have the capability to handle both contingencies."
If an extension day is, in fact, inserted after the first spacewalk, the second spacewalk would occur on Sept. 11, the fifth anniversary of the terrorist attacks on New York City and Washington.
In other developments, Hale gave reporters an update on NASA's work to develop safer ice-frost ramps on the shuttle's external tank. The ice-frost ramps are buildups of foam insulation around brackets that support two pressurization lines and a cable tray. The insulation prevents ice from forming that could break off during launch and strike the shuttle.
The IFRs are manually sprayed on and then sculpted on top of so-called acreage foam. Post-Columbia testing shows areas where foam is applied on top of other foam are susceptible to cracking due to differential thermal effects. Cracks, in turn, can lead to foam shedding during launch.
The IFRs are officially classified as "probable/catastrophic," meaning there is a 50-50 chance of a catastrophic failure over the 100-flight life of a space shuttle. It is the only system on the shuttle that is so classified and NASA is developing a near-term fix to reduce the chances of foam debris breaking away.
"One of the options was to cover these little pieces of foam, about a pound or two pounds of foam at every bracket, cover them with a titanium shell, titanium being a metal that would retain the foam," Hale said today. "Titanium has a low thermal conductivity, so the hope was they could fasten that to this tank and not have ice form on the outside.
"They were unsuccessful in the environmental testing and the thermal testing to prevent ice from forming on the outside of the metal brackets. So the option (under development) is to reshape the foam, a reformulation of the foam to remove the SLA, or super-lightweight ablative foam core, and just use the standard foam."
The all-foam design "will be what we take to the wind tunnel tests later this month to make sure it will hold together," Hale said. The new design is similar in appearance to an earlier design that broke apart during wind tunnel testing last spring. It was that failure that prompted NASA to stick with the current design, accepting the associated risk, while engineers developed an improved design.
"To the casual observer, it's not going to look a whole lot different than what we tried last April that didn't hold together in the wind tunnel," Hale said. "There are some differences internally in the way it's put together and some small shape differences. The bottom line is, we want to reduce the footprint.
"Every one of these 17 ice-frost ramps on the hydrogen part of the tank has a footprint of foam over foam, which is what we believe causes us concern with shedding of foam. So we have reduced the area of foam on top of foam, it's a much smaller footprint, and the thermal analysis indicates we will be much less susceptible to the thermally induced cracking that occurs in the underlying foam region, which is the goal of this exercise.
"This is an interim fix," Hale said. "We're coming back with a final fix in about eight more tanks after that. So we think we've got a good design, we'll put it in the wind tunnel later this month to make sure we've got a good design. We're going to have the critical design review before we start modifying the tank that's in production at the Michoud Assembly Facility, which we hope to ship about mid December."
That tank, Hale said, will be used with shuttle mission STS-117 next February.
The official crew patch for the STS-115 mission of space shuttle Atlantis to resume orbital construction of the International Space Station.
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