Among the technologies employed in NASA's STS-128 mission (August 29 - September 11), Ottawa, Canada's Neptec Design Group's TriDAR system provided docking information that may help enable future, astronaut-free space missions.
Humans would call the information "sight," and on this flight, astronauts indeed did have the opportunity to look at data during flight. To computers, the data represents precise ranging and location points in 3-D space, paving the way for hands-off automation.
TriDAR (triangulation + LIDAR, light detection and ranging) is designed to acquire and track targets automatically. While a number of existing technologies enable computers to "see" objects, TriDAR depends neither on cooperative targets (that is, targets with reflectors, transponders, or other technology to guide oncoming vehicles) nor on relatively approximate hostile targeting solutions, such as found on military aircraft.
"The ability to find the exact location of an object in space is especially important for servicing older space-based objects like satellites," said Michael Kearns, Vice President, Explorations Systems for Neptec. "Some have been up for years, launched before cooperative targets became standard equipment."
TriDAR encompasses three functional ranging elements: two in the rendezvous stage (long range location followed by higher granularity ranging from 1000 m) and close-in, from 100 m down to the target surface—in the case of STS-128, the docking port of the ISS.
Physically, TriDAR is housed in a small enclosure along with necessary processor electronics, a LIDAR sensor, and a single, laser-based 3-D camera. Triangulation data is derived from the LIDAR and the camera, neither of which are dependent on any available ambient light. On STS-128, the system was mounted in the shuttle cargo bay.
Target acquisition speeds and accuracies are greatly facilitated through comprehensive 3-D geometries stored in the system. Acquired image data is compared against the stored geometry, which the system manipulates in 3-D space until a match is made.
"TriDAR is currently dependent on human input for setting up the target," Kearns explained. "Right now, we work from existing 3-D models and drawings of the target, but in an ultimate scenario, the geometries could be gathered automatically in an initial circle around, say, the satellite, creating 3-D models literally on the fly.
"On STS-128, humans were in the loop at the docking as well," added Kearns. "Astronauts were able to watch on-screen animation of the shuttle approaching the ISS and docking. System development and accuracy testing was done over the last three years, thanks to tremendous cooperation from both the Canadian Space Agency and NASA. Our engineers and technologists from both agencies worked hand in hand to fine-tune the system."
The system is moving toward full certification for operator-free docking, as Neptec engineers pore over the 50,000+ data files generated during STS-128 to verify accuracies and uncover areas requiring further development.