Equipping Discovery: New Tools to Return Shuttles to Flight
This computer-generated view of the bottom of the Space Shuttle Discovery in flight shows the orbiter's robotic arm - orbital boom attached - in one of the wing leading edge survey points.
When NASA's Discovery orbiter rockets into space this year as the agency's first shuttle flight in more than two years, the astronauts aboard will carry a bevy of tools and techniques to ensure their spacecraft is safe.
In addition to a redesigned, camera-laden external fuel tank, the seven astronauts assigned to Discovery's STS-114 mission are toting with them new instruments to repair the shuttle's thermal protection system and a sensor-capped extension to the orbiter's robotic arm.
"We'll know the health of our vehicle," said STS-114 pilot Jim Kelly during a recent spacewalk training session at in NASA's Neutral Buoyancy Laboratory tank at Johnson Space Center (JSC). "Once we have that, we can make intelligent decisions if something were to happen."
Discovery is currently set to launch no earlier than May 15 of this year to deliver tools and supplies to the orbiting International Space Station and test its own new equipment. The planned space shot is NASA's first shuttle launch since the loss of the Columbia orbiter, which broke up during reentry, killing its seven astronaut crew on Feb. 1, 2003.
Two tests for space
Discovery's two spacewalkers, Soichi Noguchi of the Japanese Aerospace Exploration Agency (JAXA) astronaut corps and NASA's Stephen Robinson, plan to test at least two techniques to repair the array of tiles and reinforced carbon carbon (RCC) panels that protect space shuttles from the heat of reentry.
"Tile and [RCC] crack repair is difficult because the tiles are fragile," Robinson said after completing the spacewalk training session. "And if they're damaged, they are more fragile."
Noguchi will test a new tool called the Emmitance Wash Applicator, which works somewhat like a liquid glue stick to adhere material to shuttle tiles that boosts their ability to emit heat.
A gray substance, the wash, is loaded into a handheld applicator and squeezed through a foam mesh to be dabbed over a damaged tile, explained Mark Dub, an extravehicular (EVA) tool engineer at JSC. A layer ranging from one-eighth to one-twenty fifth of an inch can be applied to tiles with damage reaching down to about half the depth of a standard tile, he added.
While Noguchi focuses on shuttle tiles during one of three STS-114 spacewalks, Robinson will turn his attention to testing a technique to repair small cracks in panels of reinforced carbon-carbon (RCC).
RCC panels line the leading edge of shuttle wings and are designed to bear the highest temperatures experienced during shuttle reentry. A hole punched by external tank foam into one of Columbia's leading edge RCC panels at launch allowed hot gases to enter the wing during reentry and destroy the orbiter.
"I'll be looking at fixing cracked RCC panels using kind of a putty-like material," Robinson said.
The material, a black, heat-resistance substance called non-oxide adhesive experimental (NOAX), can be applied to an by squirting it through a space-hardened caulk gun, then smoothing it to fill fine cracks in RCC panels - much like spackle - with a sort of putty knife.
Discovery is also expected to carry some additional tools for other repair techniques, even if they're left stowed during the flight.
"It's like having an ejection seat in a jet," Robinson said of the tools and techniques that aren't planned for testing during STS-114 spacewalks. "You don't plan to use it, but it's not a bad idea to have it along."
Among other tools may be an array of overlay panels made of a material called carbon silicon carbide that can be affixed over damaged shuttle tiles with screws.
NASA engineer Kevin Wells, EVA tools project leader for overlay repair, told SPACE.com that while it is relatively easy to install screws in shuttle tiles - they can be twisted using just a finger - astronauts would have to use special tool to measure torque to ensure the screw does not strip away needed material.
A second set of patches, made of material similar to the overlays but a bit sterner, may also fly during Discovery's mission. The patches are designed to fit over a hole in a shuttle RCC panel, though researchers are still conducting ground tests to make sure hot gases don't burn away or seep through patch edges.
"The gap [between patch and panel] is the predominant path for failure," said Frank Lin, NASA's project manager for RCC repair. "We could seal that gap with the NOAX material."
One last and potentially problematic repair method includes filling severely damaged tiles with a pink, ablative goo-like substance called STA-54, which is squirted into place from a backpack-mounted tank. The goo is actually made of two separate materials that are mixed together as they pass through a handheld device. STA-54 is designed to rise like bread as it heats up during reentry, with outer surface ablating away and new material swelling up to take its place, NASA engineers said.
Tests in vacuum chambers and during zero gravity flights aboard NASA's KC-135 aircraft have found that the STA-54 materials is prone to bubbling as it cures, which could diminish its effectiveness if left unresolved.
Discovery's new reach
The largest addition to Discovery's toolbox is a 50-foot (15-meter) boom that can be attached to end of the orbiter's robotic arm in orbit, nearly doubling its length.
A suite of sensors, including cameras and a laser ranging system, should sit on the end of the boom and allow the Discovery crew to scan the orbiter's underbelly for cracked or broken tiles and other damage. Should that senor package fail, a platform can be attached to the boom's end in order for an astronaut to make a visual inspection and take digital images.
"We do have to be prepared for the possible failure of the sensor package," Noguchi said.
Even without the orbital boom and sensor package attached, Discovery's robotic arm has an additional role for its first return-to-flight mission.
NASA engineers said STS-114 astronauts have been training to perform a maneuver that relies solely on the robotic arm, in which the manipulator will latch on the International Space Station and turn the shuttle until its tiled belly is in position for observation or repair.
"I don't think that we're going too fast," Robinson said of Discovery's timeline and NASA's push to resume shuttle flights. "The amount of questions remaining is still very small."
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