New Laser Scanners to Detect Shuttle Tile Damage

NASA has developed a new, handheld laser scanner to detect cracks and imperfections in the thermal tiles that protect space shuttles from the searing heat of atmospheric reentry. CREDIT: NASA/Ames.

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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