The Orbital Express ASTRO spacecraft carried multiple independent sensor systems for estimating relative state in
autonomous vehicle proximity operations. The on-orbit performance of pose-estimation imaging and dedicated-target
navigation solution methods are compared, for ranges between 150 meters and spacecraft capture. Variations between
performance expectations from pre-flight ground tests and actual
on-orbit performance are discussed. Analysis results
indicate the sources of solution variations.
Testing of the Advanced Video Guidance Sensor (AVGS) used for proximity operations navigation on the Orbital
Express ASTRO spacecraft exposed several unanticipated imaging system artifacts and aberrations that required
correction to meet critical navigation performance requirements. Mitigation actions are described for a number of
system error sources, including lens aberration, optical train misalignment, laser speckle, target image defects, and
detector nonlinearity/noise characteristics. Sensor test requirements and protocols are described, along with a summary
of test results from sensor confidence tests and system performance testing.
Proximity operations between orbital vehicles require precise knowledge of relative navigation states. Retro-reflectors may be used by proximity operations navigation sensors as part of the navigation sensor system, to indicate the position of fixed points on one of the vehicles so that relative state data may be calculated. Use of corner cube retro-reflectors in an orbital navigation sensor required detailed ray-tracing analysis to define the expected return signal levels, signal/noise ratios, and predicted error effects due to reflector geometry and optical characteristics. Conventional corner cube reflector images would have displayed image artifacts due to corner cube bevels, interfering with software interpretation of sensor image data. This design avoided software errors due to bevel effects. Special optical design features were required to permit use of multiple target sets, enabling successful tracking over a 1 to 200 meter effective range. We have used this mounting scheme to create corner cube targets for use with the Advanced Video Guidance Sensor (AVGS) on the Orbital Express mission. We discuss our design, the finite-element analysis done on the design, and the results of sensor performance testing with the targets.