NASA has
developed a new three-dimensional laser scanner to seek out cracks and other
damage amidst the thousands of ceramic tiles that protect space shuttles from
the heat of reentry.
Smaller and
faster than their orbital counterparts, the prototype scanners may help
astronauts and ground engineers track tile other thermal protection system
damage with more accuracy than ever before.
"This is a
direct result of the return to flight project," said Joe Lavelle, a senior
research engineer for three-dimensional instrumentation at NASA's Ames Research
Center, where the prototypes were built.
Lavelle
said two of the handheld, prototype laser scanners will be sent to NASA's
Kennedy Space Center (KSC) in the next month, where shuttle engineers are
expected to put them through their paces on sample tiles and calibration
blocks. If all goes well, they may graduate up to scan tiles on hangar-bound
orbiters like Atlantis and Endeavour - engineers are preparing Discovery for
flight atop Launch
Pad 39B. Two additional scanners will be delivered to KSC by October 2005,
he added.
Boosting
orbiter tile inspection techniques and tools has been a major focus of NASA
since the 2003 loss of seven astronauts aboard the space shuttle Columbia,
which suffered damage to the protective thermal panels of its left wing leading
edge during launch. Investigators later found that that the damage - caused
when a chunk of external tank foam insulation separated during liftoff and
punctured a reinforced carbon carbon (RCC) panel - led to the fatal accident.
The loss of
Columbia's crew prompted shuttle managers and engineers to develop a boom-mounted
laser ranging and camera system to check shuttle tiles and RCC panels for
damage during its next - and all subsequent - shuttle flights.
The crew of
NASA's STS-114 mission aboard the Discovery orbiter is expected to test that orbital
boom system during a test flight slated to launch no earlier than July 13. The
mission is expected to mark NASA's return to shuttle flight and resumption of
International Space Station-bound orbiter missions.
A
smaller tool for no small task
Checking
each of the about 30,000 ceramic tiles aboard a space shuttle after every
flight is a long process, and one that Lavelle hopes the new laser scanners can
shorten.
Shuttle tiles are built to withstand up to 2,300-degree
Fahrenheit (1,260-degree Celsius) temperatures that space shuttles encounter
each time they return to Earth. Each of those tiles is checked for new damage
or flaws after a flight to determine if repair is required.
"Right now
it's a very manual process," Lavelle said. "They use their eyes and take
photographs many times, and it's extremely time-consuming."
Reducing
shuttle turnaround may be a critical asset for NASA, which is still determining
how many missions will be required to meet commitments to its International
Space Station (ISS) partners. NASA's three remaining orbiters are slated for
retirement by 2010, and the space agency's top administrator Michael Griffin
told the House
Science Committee Tuesday that not all of the 28 spaceflights originally
planned for that period will be available by the end-of-the-decade deadline.
Lavelle's
handheld laser scanners are about the size of a hand sander and can detect
cracks as small as five-thousandths of an inch (0.127 millimeters) down to a
depth of about four inches (101 millimeters). They deliver three-dimensional
images to a laptop computer via a USB cable.
The
prototype's laser-camera scanners are not limited to checking heat-resistant
tiles, and could be used to check the reinforced carbon carbon panels that line
orbiter wing edges.
"It works
on curved surfaces and different types of materials," Lavelle said.
On-orbit
lasers
Weighing
about three pounds (1.3 kilograms), the handheld tile scanner is nearly 10 times
lighter than the boom-mounted system currently aboard the Discovery and
Atlantis shuttles, Lavelle said. But Discovery's scanner system has one big
advantage: certification.
"They went
with the [scanner] they had that was flight-qualified," Lavelle said, adding
that his project's scanner is not space-hardened nor certified for orbital flight.
The laser
dynamic range imager (LDRI) and laser camera system (LCS), along with an
intensified television camera, will sit at the end of Discovery's 50-foot (15-meter)
orbital boom during flight. The sensor package is accurate down to a few
millimeters and its boom fits at the end of the orbiter's own robotic arm, from
which it can scan sensitive thermal protection areas.
The new
laser scanner, on the other hand, is currently limited to handheld use and
would have to be modified to fit at the end of a shuttle boom or arm, Ames
researchers said.
Discovery's
boom-mounted system currently relies on both manual and automated commands to
perform scans at a maximum assumed rate of about 2.5 inches per second (6.3
centimeters per second).
Equipping
tomorrow's spacecraft
Lavelle
said that in addition to serving ground and orbital shuttle tile inspection
needs, there is still one more role he hopes the handheld scanners can fill.
"It's
basically a three-dimensional ranging device," Lavalle said. "I think a robotic
application is a major focus now, and we're working in that area to get our
scanner on a Mars rover."
By
modifying the arrangement of laser and camera, Ames researchers hope their
device could serve as an extremely accurate ranging tool for a robotic probe.
"You'd put
it on a rover and it can scan the area ahead, right now out to two meters, so
it maps out the three-dimensional area in front of the rover accurately,"
Lavelle said.
The system
could also be modified to scan future human-rated spacecraft, such as NASA's
shuttle successor the Crew Exploration Vehicle, if needed, he added.
"From a
metrology standpoint, this is a first step in the automation of tile
inspection," Lavelle said.
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