Space Shuttle Discovery Heat Shielding Degraded; Long Flight Delay Possible
Mission Delay Of Weeks, Months Possible If Shields Replaced
With the launch of Space Shuttle Discovery little more than a week away, NASA experts have recommended replacing three heat-shielding panels on the orbiter vehicle, a move that might delay for weeks or months the shuttle launch now set for 11:38 a.m. ET Oct. 23 at Kennedy Space Center (KSC).
A final decision on the heat shielding and timing of liftoff is scheduled to be announced tomorrow afternoon, after meetings of lower-level officials last week and a flight readiness review tomorrow that will include top-level personnel.
A key topic in the meetings is the loss of coating on reinforced carbon carbon, or RCC, that protects the leading edge of the Discovery orbiter vehicle wings during the searing heat of reentry.
Questions raised included why the coatings were lost, and whether that might pose a safety problem.
If the heat-shielding panels are replaced, that would delay the launch of Discovery for weeks or months, a Kennedy Space Center spokesman said.
"It would be a significant stand down," he said.
The problem is that "we don’t know what the root cause is" of the coating loss, the spokesman said. While the coating hasn’t degraded or disappeared further in the last two Discovery flights, that doesn’t tell NASA whether or not there might be an abrupt further loss of coating, he said.
"We have to prove the integrity of the panels" for this STS-120 mission, he said.
While there seems to be a bit of movement toward finding that it would be safe to fly, "we have not gotten a consensus," he said.
Thus the decision will be made at the flight readiness review tomorrow.
A critical subtext to the decision is that a delay of weeks or months would throw a wrench into the manifest of scheduled space shuttle flights.
For example, this mission is required to add a central "node" component to the International Space Station (ISS), so that yet another component — a laboratory — in turn can be added to the node during a Space Shuttle Atlantis flight now set for December. The space shuttle fleet is to be retired in 2010, so it is important to maintain the flight schedule.
Heat shielding is a critical issue for NASA, especially since 2003, when a chunk of foam insulation ripped loose from the external fuel tank of Space Shuttle Columbia and smashed a hole in the leading edge of an orbiter vehicle wing during liftoff and ascent to the ISS.
Later, during its return to Earth, fiery gases of reentry rushed through the hole into the wing and heated it to the point of structural failure. The ship and crew were lost.
In the past, after Discovery has flown missions, there have been post-flight indications that the edges of a couple of panels have lost small amounts of their upper-level coating.
Thermography, or thermal imagery, has been used to inspect the panels in order to identify any internal defects that could lead to coating loss.
The NASA Engineering and Safety Center (NESC) has been working with shuttle engineers to better understand the potential causes of coating loss. At the meeting, NESC recommended replacing three of Discovery’s 44 panels.
It was a close call in some respects, because the coating loss hasn’t created any problems, and hasn’t worsened or increased, in recent Discovery missions.
Discovery has flown at least twice with these panels in the current condition, according to NASA, with no indications of degradation based on thermography. At this point, the space shuttle program determined that Discovery astronauts can carry out their mission safely without having to replace the panels.
So replacement would be an err-on-the-side-of-caution move.
Meanwhile, astronauts, technicians and others are preparing for Discovery to lift off to space.
The STS-120 astronauts capped off three days of exercises and training at KSC by boarding Discovery for a simulated countdown.
After the rehearsal concluded, crew members flew back to their home base in Houston to complete their final preparations for the targeted launch of Discovery.
Retired Air Force Col. Pamela A. Melroy will command Discovery on its STS-120 Mission to take the Node 2 connecting module to the space station. Melroy, a veteran shuttle pilot, is the second woman to command a shuttle. (Please see related story in this issue on first female commander of the space station.)
Marine Corps Col. George D. Zamka will serve as pilot of Discovery. Mission specialists on the space shuttle will be Scott E. Parazynski, Army Col. Douglas H. Wheelock, Stephanie D. Wilson and Paolo A. Nespoli, a European Space Agency astronaut from Italy. Zamka, Wheelock and Nespoli will be making their first spaceflight.
Once at the space station, there will be ample work for them to perform.
They will move forward with continued construction of the space station, attaching to the artificial moon a sort of connecting corridor called a Node 2 module, Harmony that will link the existing station to international laboratories to be added later.
While the pressurized Harmony module is listed as a U.S. contribution, it was built in Italy.
"This module will allow all international partner pieces of the station to connect together, so it’s really wonderful that kids recognize that harmony is necessary for space cooperation," Bill Gerstenmaier, NASA associate administrator for space operations, said of the school children who named the module.
The module will be the connecting point between the U.S. Destiny lab, the European Space Agency Columbus module and the Japanese Kibo module. Harmony, once fastened in place to the ISS, sets the stage for the following two space shuttle flights that will carry the Columbus and Kibo components to the station.
Those laboratory modules have been prepared side by side with Harmony in the high bay of the Space Station Processing Facility at KSC.