When the space shuttle Discovery launches its seven-astronaut crew Saturday, tucked inside its cargo bins will be two new tools for heat shield repair and a remote control landing, though neither are expected to be needed.
NASA test director Pete Nickolenko said Thursday that a heat shield repair device dubbed T-RAD will be aboard Discovery as a safety precaution should the orbiter sustain damage during launch that could be repaired by its STS-121 astronaut crew.
The shuttle will also carry a data cable that will allow flight controllers in Houston to land Discovery by remote control, a first in NASA’s 25 years of space shuttle flight.
“This is a first flight,” said Kyle Herring, a NASA spokesperson at the agency’s Houston-based Johnson Space Center, of the cable in a recent telephone interview. “You certainly don’t expect to ever use it.”
Both tools will be packed in Discovery’s middeck during its 12-day STS-121 mission – NASA’s second shuttle flight since the 2003 Columbia accident – to the International Space Station (ISS).
NASA currently plans to launch Discovery at 3:48:37 p.m. EDT (1948:37 GMT) on July 1.
Short for Tile Repair Ablator Dispenser, T-RAD is a 55-pound (25-kilogram) device designed to fill cracks between a shuttle’s heat-resistant tiles and door seals, such as those found on landing gear doors, during a spacewalk repair.
NASA began seeking such repair methods following the loss of Columbia and its astronaut crew, which investigators attributed to heat shield damage from an errant chunk of external tank foam. Engineers have also made several modifications to shuttle external tanks to reduce the amount of foam insulation that can be shed during liftoff.
Improved crack-sealer
T-RAD is a smaller version of the Cure In Place Ablative Applicator (CIPAA), a backpack-mounted system, that mixes two compounds together into a pink, goo-like material called STA-54.
T-RAD consists of a hand vacuum-sized cylinder that runs 18 inches (45-centimeter) in length and 10 inches (25 centimeters) in diameter that holds the two STA-54 compounds, Wells said. A 30-inch (76-centimeter) hose connects the cylinder to its dispenser gun, which mixes the two into its final pink form, he added.
Unlike CIPAA, which was designed to fill in gouged or dinged tiles, T-RAD is aimed at filling small cracks between tiles and door seals, and is applied much like the caulking agent used between bathroom tiles. A CIPAA unit did ride aboard Discovery’s STS-114 return to flight mission last July, but was not tested because NASA officials – and the spaceflight’s astronaut crew – did not believe it was ready. The STA-54 material tended to bubble in a weightless environment, creating voids that could compromise an intended repair.
Wells stressed that T-RAD is only being launched aboard Discovery in case of an unexpected contingency, and is not expected to undergo any testing in orbit.
Also riding in the shuttle’s middeck are extra heat shield plugs to cover any gouges in the orbiter’s reinforced carbon carbon panels along its nosecap and wing leading edges. A sticky black NOAX material to be smeared on RCC cracks – and which could be tested in a potential third spacewalk during the STS-121 mission – is also on the launch manifest along with a gray emittance wash for tile repair.
Heat-resistant panels of carbon silicate carbide are also aboard to cover damaged tiles on the orbiter’s belly, Wells said.
Remote landing capability
Should Discovery’s STS-121 spacewalkers be forced to make a serious heat shield repair, the chances of which NASA officials believe to be extremely remote, flight controllers could opt to try to save the orbiter without endangering its astronaut crew.
Herring said that a 28-foot (8.5-meter) cable packed in the orbiter’s middeck has been certified to fly in just such a situation, which would keep an astronaut crew aboard the ISS while the orbiter returns home on remote control.
“It’s kind of like a jumper cable that would only be used in an event where you had done a repair, but couldn’t be 100 percent certain [it] would be something that would be flight worthy with a crew,” Herring said.
The cable would connect an avionics bay in Discovery’s middeck with the controls one level up on its flight deck, effectively allowing flight controllers in Houston to perform landing activities currently done by shuttle astronauts.
Those manual activities include starting the shuttle’s auxiliary power units, deploying an air data probe, unstowing the orbiter’s landing gear and releasing its drag chute after landing, Herring said.
“The things that would be manually controlled, this jumper cable allows them to be controlled from mission control,” Herring said.
In such a contingency, Discovery or any future shuttle would land at White Sands Missile Range in New Mexico, NASA said.
“We would not target a landing site at KSC or Edwards Air Force Base [in California],” Herring said. “The prime landing site would be at White Sands because of the wide expanse of the range.”