Laser camera aids Discovery’s return

OTTAWA, ONTARIO, CANADA - A Laser Camera System (LCS) provided by Neptec played a vital role in the safe return of NASA’s Space Shuttle Discovery last month by providing detailed three-dimensional images of the spacecraft’s heat shield tiles. The system has the ability to detect half-millimeter cracks in the tiles from a distance of up to four meters over the entire surface of the craft, thus enabling defects to be spotted prior to shuttle re-entry.

The camera was deployed at the tip of a 50-foot inspection boom, manufactured by MD Robotics (Brampton, Ontario, Canada), that was stored on the opposite side of the shuttle’s cargo bay from the remote manipulator system (Canadarm). To enable the LCS to scan the entire shuttle surface, the Canadarm had to reach across the cargo bay and connect with the extension boom, nearly doubling the Canadarm’s reach. The LCS uses an auto-synchronous triangulation technique to generate three-dimensional models of imaged objects that are accurate within a few millimeters and taken at distances up to 10 meters. So the scans transmitted back to Mission Control from the space shuttle could be zoomed and tilted while searching meticulously for damage.

The triangulation method is just as accurate and faster than generally more robust time-of-flight (TOF) imaging techniques at distances up to 5 m, according to Iain Christie, head of business development and R&D at Neptec. At distances from 5 to 10 m, triangulation maintains a speed advantage over TOF, but becomes less accurate. Triangulation sensors require a constant optical path length, however, so engineers at Neptec had to use a mirror system to essentially fold up the optical path to fit compactly into a 1-box detection system.

Another engineering focus of the system was to provide a short feedback loop between the acquisition and processing of data. A general trend has been to gather large amounts of data and transmit them elsewhere for processing, which generates a tremendous need for bandwidth, according to Christie.

“We want to break up that paradigm,” he added. Thus the Neptec system focuses on achieving intelligent 3D imaging by including significant data processing within the system. This enables decisions about what to scan and how to process the data to be made at the camera.

Moving magnet galvanometers provided by General Scanning (Billerica, MA) helped to accomplish this by enabling the mirrors in the camera system to move as necessary for beam steering. Over and above designing the entire camera system into one compact box, Christie said the major engineering obstacle consisted in designing it to survive and operate through the temperature, vibration, vacuum and other environmental extremes inherent in space travel. For instance, engineers at Neptec and General Scanning worked together to qualify an alternative dry lubricant that would enable the galvanometers to operate in the vacuum of space without the bearing lubricant out-gassing and contaminating the mirror surfaces.

Simultaneous with the effort for the recent shuttle mission, Neptec was also developing a camera system for Lockheed Martin (Bethesda, MD) that combines triangulation and TOF imaging and will enable imaging over distances ranging from hundreds of meters down to a few cm. The intent is to launch that system in 2007 on a NASA mission in which it will guide an autonomous rendezvous in space between the Hubble Space Telescope and an unmanned vehicle that will replenish Hubble’s power supplies and extend the telescope’s life by an additional five to seven years.

The technology that flew on the recent shuttle mission is already on the market, Christie said. “The cutting edge is already beyond that.”