A hybrid 3D sensor (NEPTEC TriDAR) for object tracking and inspection

Although laser ranging and scanning sensors are widely used in a variety of industries, a sensor designed for spacecraft operations, including autonomous rendezvous, inspection and servicing remains a challenge. This is primarily due to critical requirements, including the need to have simultaneous high sampling speed, and good range and lateral resolution at both short range of a few meters and at long range of a few hundred meters. A typical LIDAR sensor is not suitable for tracking at the close-in distance, just before rendezvous, or during a critical close-up inspection, since its range resolution is in the tens of millimeters and can only be improved by averaging at the expense of speed. A laser triangulation sensor is capable of simultaneously having both high range resolution (similar to 1mm) and high speed (similar to 10kHz) at short distance. But the range resolution of a triangulation sensor reduces rapidly as range increases, its performance is inferior compared to a LIDAR based sensor at long range. NEPTEC TriDAR (triangulation + LIDAR) is a hybrid sensor that combines a triangulation sensor and a TOF sensor for spacecraft autonomous rendezvous and inspection. It has been developed in part from technology used in NEPTEC's OBSS (Orbiter Boom Sensor System) 3D laser camera. The OBSS LCS was used for inspection of the Shuttle files on STS-114. In this paper, the TriDAR design that combines triangulation and LIDAR to produce high speed and high resolution for both short and long range is described. To successfully produce this sensor for space, an athermalized optical steering system shared by the two sensors has been developed. Results from performance testing of a prototype, designed for autonomous rendezvous, are given.