Efforts to return the Space Shuttle to flight are under way at Johnson Space Center in Houston, Texas and at other NASA centers. Most of the work focuses on the recommendations that the Columbia Accident Investigation Board (CAIB) released as a result of its probe into the loss of Columbia and the STS-107 crew on Feb. 1.
One of the recommendations is for NASA to develop capabilities to facilitate on-orbit repairs of damage to an orbiter's Thermal Protection System.
Onboard a KC-135 aircraft, astronaut Scott E. Parazynski injects the cure-in-place ablator into a damaged section of thermal tiles.
In addition to developing on-orbit repair techniques for the Thermal Protection System, the Board had four other associated recommendations. They are: to eliminate or greatly minimize debris sources; another is to develop and improve NASA's ability to inspect the orbiter for damage on orbit; to define the impact tolerance of the Thermal Protection System; and to evaluate the International Space Station for crew contingency options.
Columbia broke up during re-entry over Texas as it headed for a landing at Kennedy Space Center, Fla. The CAIB determined that the accident was the result of a breach in the Reinforced Carbon-Carbon panels on Columbia's left wing. This breach occurred when a piece of insulating foam from the External Tank struck a panel shortly after Columbia launched Jan. 16.
Engineers are hard at work devising plans to repair two components of the Thermal Protection System -- the heat-resistant tiles located on the underside of the Shuttle and the RCC panels on the leading edge of the Shuttle wings.
One option for repairing damaged tiles is application of an orange, sticky substance called MA-25S. The lead Shuttle flight director for the next mission, Paul Hill, said the substance is "showing promise in testing."
If Shuttle astronauts are called upon to use the silicon-based MA-25S in orbit, spacewalkers would use a caulk gun-like device to apply it to the damaged tiles. Then, the spacewalkers would smooth the newly applied substance to reduce turbulence that the orbiter may encounter during re-entry through the atmosphere.
Astronaut Scott Parazynski has tested this technique. "It's going to be a challenging task," he said. "You have to be patient and precise to do this. This is an art form into itself."
Of course the best way to prevent damage to the Thermal Protection System is to reduce or prevent debris-hit damage from occurring. However, Hill said that the team at Johnson Space Center would understand how to use MA-25S if it is ever needed.
"The expectation is that we won't be repairing," Hill said. "But what you're hearing from me is that we're going to pound this flat and understand how to do it, and we will be ready to do it."
Development of a repair technique for the Reinforced Carbon-Carbon panels is more challenging than tile-repair, however, there is optimism a solution will be found.
"While we haven't finished the RCC repair yet, we are seeing some things that are positive," Hill said. "Some of these things that we're doing, we didn't think were possible in February."
Among the repair techniques for the Reinforced Carbon-Carbon panels is a process that uses an "umbrella" device that would allow spacewalkers to attach a patch to the damaged area. The device would be attached with a bolt and backfilled with heat resistant caulk.
Engineers also have looked into ways to get astronauts to the repair site. There are two scenarios that they need to address. If a Shuttle is docked to the International Space Station, one option calls for the orbiter's arm to reposition the shuttle. The Station arm then would be used to maneuver the spacewalker to the damaged area on the Shuttle.
The other option occurs if the Shuttle is not at the Station. Spacewalkers would be moved around with a boom extension attached to the Shuttle arm. The boom currently is under development.
The next shuttle mission, STS-114, is slated to launch no earlier than September 2004.