Discovery, Atlantis Heat Tiles Found Solid So Far In Inspections
Thermal protection heat tiles on Space Shuttles Discovery and Atlantis have been found solid in inspections, Wayne Hale, space shuttle program manager said in a NASA briefing today.
Discovery, now in orbit after a winning mission to the International Space Station (ISS), is poised for landing Wednesday. (Please see full story in this issue.) Hale lavished praise on the shuttle and space station crews, and on the ground crews, for responding swiftly and effectively to an unexpected emergency when a space station solar panel ripped.
The STS-120 trip to the ISS was "a great mission," Hale said.
This shows the value of ground crews that ponder, long before an unexpected event, what can go wrong and how to resolve it, Hale said.
He added that inspections on the port side of the orbiter vehicle haven’t yet been completed, but he clearly sees nothing now that would bar Discovery from reentry.
As for the ISS, at this point "the space station is in good shape," he said, with a "good, secure solar array."
There were "eight hits recorded" on heat tiles on the leading edges of the Discovery orbiter vehicle wings, Hale said. But he questions whether they were micrometeoroid hits. He also said there was a ding, a hit, on an orbiter vehicle window. Windscreen hits have been seen before, to no ill effect during reentry. When NASA engineers and technicians finish reviewing hits data from Discovery, "I have no doubt they will [say] we are safe for reentry" Wednesday, Hale said.
"We’re flying a very safe program in a very risky environment," space, he said.
Discovery launched last month even though some engineers recommended replacing three reinforced carbon-carbon heat tiles because of problems with their coating, but after arrival in orbit no further degradation was seen, showing the decision to fly was correct.
As for Atlantis, while five heat tiles are being scrutinized, Hale said that Atlantis is good to go for a Dec. 6 liftoff of the STS-122 Mission to the space station (or no earlier than Jan. 2 if a December launch is barred by unforeseen problems such as weather, or because the ISS isn’t ready to accept the laboratory that Atlantis will carry aloft).
"We have cleared Atlantis for flight," Hale said.
In fact, Atlantis flight preparations are ahead of schedule, and the shuttle is set for a rollout from the Kennedy Space Center (KSC) Vehicle Assembly Building within five days.
Also, the European Columbus laboratory module is good to go, as well, Hale said.
Improvements are being made to the external fuel tanks that will fly on all future space shuttle missions, he added. Workers at the Michoud Assembly Facility in Louisiana, though hampered still by damage caused by Hurricane Katrina in 2005, are steadily improving safety of the tanks, especially the ice frost ramps, Hale said.
"Every tank will be safer than the one [on the shuttle mission] before it," Hale said.
NASA is wrestling with a bad basic design problem in the space shuttle fleet, where foam insulation can break free during liftoff and ascent and strike the orbiter vehicle, damaging it.
For example, in 2003, insulation hit a leading wing edge on Space Shuttle Columbia, punching a hole that later led to loss of the ship and crew during reentry.
On future missions, he said, a spacewalk will have to be performed to find out why an ISS rotary joint seems to have problems, including metal shavings.
He also said that the scheduled Aug. 7 Space Shuttle Atlantis mission to service the Hubble Space Telescope will involve risk because the seven astronauts on Atlantis won’t be able to use the ISS as a life raft if something goes wrong with the shuttle, so NASA will have another shuttle on the pad, ready to launch on a rescue mission.
"We do not have a place that will shelter us," unlike missions to the ISS, he said.
While Hale would like to see some shuttle mission include a spacewalk to test on-orbit techniques for repairing damaged heat tiles, preferably before the Hubble mission, he added that the Hubble servicing job won’t be delayed if the heat tile repair spacewalk can’t be performed before then.
The heat tile repair test — on purposely damaged test tiles — was to have been performed on the current Discovery mission, but plans for that test had to be abandoned because of the unexpected tear in an ISS solar array that required immediate repair.
On a separate point, Hale said there is no safety reason that Discovery Commander Pam Melroy, a retired Air Force colonel, requested a landing at KSC Wednesday in daylight hours rather than at night. Most aviators prefer landing in daylight instead of at night, he said. But "we are trained to land in both," he added.