Space-age Scanner.(Technology Information)

A new laser scanning technology helps NASA find trouble

When it comes to space travel, the heat is on. During each of their Earth-orbiting missions, NASA's four space shuttles are subjected to temperatures ranging from minus 250 degrees Fahrenheit in space to nearly 3000 degrees during reentry into the Earth's atmosphere. Thus the ability of the orbiter to take the heat is critical to ensuring the safety of the crew and on-board equipment. Because of this, the surface of the orbiter, which is covered by 24,000 protective thermal tiles, is carefully scrutinized after each flight. Typically, the process of assessing the quality of each and every one of the tiles is a painstaking manual effort. Fortunately for the workers in the trenches, there is a laser light at the end of the tedious tunnel.

Engineers from NASA's Ames Research Center and the Boeing Company recently delivered a first-of-its-kind, portable 3D laser scanner to NASA's Kennedy Space Center. The scanner, which uses a digital camera and lasers in a measurement technique called laser triangulation, is the first component of what will eventually become an Electronic Inspection and Mapping System (EIMS). The EIMS objective will be to increase the accuracy and reliability of shuttle damage estimates, and in so doing reduce vehicle turn-around time.

When placed over a thermal tile, the new scanner detects flaws within a 3- by 3-inch area and transmits the collected data to a laptop computer. Custom software locates and characterizes the damage and generates a 3D image that indicates the size and depth of the flaw. The results of each scan are then stored in a database containing all of the fabrication and maintenance information for every tile, so that the latest damage history and maintenance information for each of NASA's four shuttles is readily available and easily accessible.

At the heart of the 3D digitizing technology is its laser triangulation technique in which laser diodes project a line of light onto a target object. A digital camera embedded in the scanner detects the light reflected off the object and records the position of the reflected beam to determine object height measurements. As the camera and lasers move over the object, the position of the reflection on the camera detector changes. The sensor calculates the amount of change based on the new laser line position on the detector. The process is continued until a complete description is achieved.

Although laser triangulation itself is not new, NASA engineers put a novel spin on the technique in order to compensate for one of its common drawbacks: a shadowing effect on scanned images caused by the way the laser has to be angled to the target. "We solved ...