NASA has selected two thermal protection system (TPS) repair techniques to be demonstrated in orbit during a spacewalk on the STS-114/Discovery Space Shuttle return-to-flight (RTF) mission scheduled for no earlier than 15 May. A third repair will be tested inside the Shuttle on the mid-deck.

The cure-in-place ablator applicator that showed promise as a means of repairing tile damage will not be demonstrated during the spacewalk, because of concerns over the time required for the test and continuing challenges with the material, which in vacuum testing on the ground has proved vulnerable to voids formed by air bubbles.

Instead, NASA plans to demonstrate an emittence wash, a paint-like thermal barrier to restore damaged or eroded coating on tiles; and NOAX, a caulk-like filler for small cracks in wing leading-edge reinforced carbon-carbon (RCC) panels. Both will be tested in a vacuum in the Shuttle payload bay during the first spacewalk.

Meanwhile, a "plug" repair, a flexible carbon silicon-carbide patch that can be bolted and sealed in place to cover small holes in the RCC, will be tested inside the Shuttle. Another tile repair, called the overlay, will be carried, but there are no plans to test it in orbit, says NASA. The tile repair involves a flexible sheet of carbon silicon-carbide that would positioned over damaged tiles, atop a gasket, then attached to surrounding healthy tiles using augur-type screws.

Despite the decision not to test the cure-in-place ablator, two of the applicator backpacks will be on board the Discovery for the RTF mission, says NASA. The main reason given for not testing the repair technique in orbit is the time required to prepare the damaged area for application of the putty-like material and to clean up afterwards. "It needs a couple of hours to prepare and a couple of hours to clean up. That leaves just a couple of hours to do the repair," says NASA.

The two repairs chosen are expected to take only around 1.5h of the planned 6h spacewalk. The time saved will be used to prepare for the two remaining spacewalks, one of which is to replace a failed control moment gyroscope on the International Space Station while the other is to attach an external support platform to the ISS for orbit-replaceable units.


Source: Flight International