The space shuttle Discovery's
mission may be over, but NASA is still hard at work evaluating a set of infrared
tools used during the flight to help predict whether an orbiter's heat shield
is clear to return astronauts
back home safely.
Engineers
are poring through infrared video recorded by a pair of high-flying aircraft as
Discovery reentered the Earth's atmosphere last week to make a near-perfect landing
at Florida's Kennedy Space Center to end its STS-121
mission.
The video
has given NASA scientists their first complete look at how the scorching
temperatures of reentry are distributed across a shuttle's belly at supersonic speeds,
something only hinted at in previous ground-based attempts.
"It's a
really quite a spectacular image," said Bob Blanchard, a lead senior scientist
at George Washington University who participated in the STS-121 and earlier shuttle
heat shield studies. "It was something we kind of dreamed about when we were
doing this low-altitude stuff earlier."
A team of
engineers at NASA's Langley Research Center in Hampton, Virginia are now
working to match the infrared video against data from computer models and wind
tunnel tests to determine how close their predictions were to Discovery's
actual reentry.
"It's not
just about good science," said Tom Horvath, a senior research engineer for NASA
with Langley's aerothermodynamic branch. "Being able to reduce the uncertainty
in this prediction tool ... that has a huge impact on whether we [see] any damage
on a future flight and clear it to enter as-is or recommend a repair."
During
Discovery's STS-114 flight in
July and August of 2005, engineers found that two
protruding gap fillers could have unacceptable heating results to the
orbiter's heat shield, prompting a spacewalk
repair to pluck out the offending ceramic
cloth bits.
Meanwhile,
a separate team is going over data from an orbital test of a new digital infrared video camera used by
STS-121 spacewalkers Piers
Sellers and Michael
Fossum. The astronauts scanned heat shield test
samples, Discovery's wing
leading edge, space
station radiators and themselves
during the demonstration.
"It came
off, I think, better than we had expected," Michael Gazarik, spacewalk infrared
camera lead at Langley for the STS-121 mission, told SPACE.com. "The
imagery looks good, the data looks good, we've got a lot of data."
A gap
filler's tale
Before
Discovery plunged through the Earth's atmosphere, NASA engineers already had a target
to seek out with infrared cameras during the orbiter's reentry.
A small bit
of ceramic cloth--known as a gap filler--was jutting
from between two of the thousands of black, heat-resistant tiles guarding the
shuttle's belly against temperatures of up to 2,300 degrees Fahrenheit (1,260
degrees Celsius) during reentry.
Wind tunnel
tests and computer
modeling determined that the torn, off-kilter gap filler would interrupt
the aerodynamic flow aft of its location--near the orbiter's rear--and cause
hotter temperatures downwind, yet not
pose a danger to the shuttle. Engineers were eager to see that heating
process in action.
"This [prediction]
tool that we've developed is based on a very limited set of flight data,"
Horvath said, adding that Discovery's belly carries only five temperature
sensors--or thermocouples--in all. "We need more flight data."
A U.S. Navy
P-3 Orion aircraft watched Discovery as it passed below an altitude of about 180,000
feet (54,864 meters) at speeds about Mach 13, while a high-altitude
observatory (HALO) aircraft recorded the spacecraft as it slowed from Mach 9 to
Mach 7 about 150,000 feet (45,720 meters) above Earth. A third aircraft
did not catch the spacecraft's reentry. Mach 1 is the speed of sound and is about
760 miles (1,223 kilometers) per hour at sea level.
"None of
the air crews even saw the vehicle as it went past," said Marty Ross, of the
firm Aerospace Corp., who coordinated air-based reentry observations for NASA. "It
was all done with the [infrared] cameras."
Engineers
are now working to develop a temperature map to match the infrared data.
Meanwhile, post-landing inspections found that Discovery's primary gap filler
protrusion--there
were several--was worn
down to a nub and left a clear
path from the apparent higher temperatures down the orbiter's aft.
Seeing
red
Discovery's
STS-121 mission also proved that spacewalkers could use a handheld infrared
camera to scan vital areas of an orbiter's heat shield--its nose cap and wing
leading edges--for signs of subsurface damage that the human eye may not
catch.
Covered in
a composite material known as reinforced carbon carbon (RCC), those heat shield
areas are subjected to the most extreme temperatures experienced by an orbiter
during reentry. Astronauts currently use boom-mounted laser
and visible light cameras to examine
heat shield surfaces for damage in-flight, but the new tool--known as an EVA
IR camera--would search for cracks or voids between layers of RCC material
that could come loose during reentry.
"The
operation of the camera seemed to go fine," Gazarik said, adding that testing
the camera was the tool's sole reason for being aboard Discovery. "There's a
lot of things could have gone wrong and I think it was a very good day for us."
NASA
engineers said analysis from both infrared tests will continue over the next
few weeks, with some data to be presented at a Flight Readiness Review meeting
for the agency's STS-115
mission currently set to launch aboard Atlantis no earlier than Aug. 28.
"Ultimately,
we're preparing for the next flight on the books," Horvath said.
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