Solid Rocket Booster: NASA strengthened the bolt-catcher – it catches the foot-long bolt that breaks free when the external tank is jettisoned – and swapped out the cylindrical energy-absorbing material with a honeycomb design. The solid rocket boosters that separate from the external tank two minutes after launch are redesigned with better beveling and other enhancements to make sure the tank disengages smoothly.
Reinforced Tiles: To optimize protection against space “junk” and micrometeoroids, NASA inspected all wing leading-edge panels, nose cap, and related parts, repairing or replacing tiles. In addition to traditional ultrasound, X-ray, and sampling inspection techniques used to look for flaws in the panels’ Reinforced Carbon-Carbon (RCC) coating, NASA added new infrared thermography systems. In addition, the lower two inches of the front spar (to which the wing panels are attached) were modified to prevent heat from entering the interior. Debris from the shuttle stack is still probably the most likely danger for impact.
Other Structural Improvements: On the Orbiter itself, the Rudder Speed Brakes were corroded and had other flaws. They’ve been refurbished. To avoid debris chipping off the structures that hold the Shuttle in place during liftoff, the gantries have been stripped and repainted with special epoxy. In addition, fuel vent arms have been improved to avoid contact with the tower structures during liftoff. Further, maintenance procedures have now been strengthened, with a stricter examination of equipment waivers, improved photo closeouts, and tighter standards for Foreign Object Debris (FOD) inspections.
Rescue or Repair: As the Shuttle approaches a rendezvous with the Space Station on day three, the astronauts will roll the craft to expose its underbelly, so Space Station personnel can use digital cameras to photograph the heat shield. Once the Shuttle is docked, the data will be evaluated over several more days to assess whether there’s a critical problem. For this flight, such an event would activate contingency plans for rescuing the stranded Shuttle astronauts. Discovery is delivering a container full of several tons of supplies to the station, to allow for an extended stay, until a rescue mission could arrive.
In the future, though, impacts such as the one that downed Columbia could probably be repaired. Two such repair technologies will be tested in a spacewalk. The first option uses Shuttle Tile Ablator-54 (STA-54), a caulk-like substance that can be used to fill cavities as well as to replace entire tiles. This silicone-based material is applied using an EVA backpack with tanks that separately contain the catalyst and components of the material and feed into a static-mixer applicator gun. The second method, an emittance wash, is primarily used as a heat-rejection layer to protect shallow abrasions, but it will also be tested as a primer for STA-54. The wash mixes fine-grit silicon carbide granules with a vulcanizing material.
The chemical repair techniques could probably handle a crack as large as two to three inches, says Sauser, but further tests will also be required to make sure the application does not affect aerodynamics.
“We did a lot of ground testing, but to really get comfortable that the techniques we have to do them in orbit,” Sauser says. “We’ll be able to try these things in a micrograv environment and bring those samples back home and do testing that simulates coming home in a high-heat landing scenario.”