Active Pointing and Tracking System in Laser Satellite to Satellite Tracking (SST)

The Active Pointing and Tracking System in Laser Satellite to Satellite Tracking utilizes a design to correct yaw and pitch range error. An aircraft in flight is free to rotate in three dimensions: yaw (nose left or right about an axis running up and down), pitch (nose up or down about an axis running from wing to wing), and roll (rotation about an axis running from nose to tail). The axes are alternatively designated as vertical, transverse, and longitudinal respectively. These axes move with the vehicle and rotate relative to the Earth along with the craft. In current systems, path length will change with satellite yaw and pitch. The Active Pointing and Tracking System utilizes a fast mirror places at the center of mass of the satellite, with the detector is a distance away from the mirror. With yaw and pitch movement of the satellite, the center of mass has no added displacement, and the detector to the mirror distance does not change. The yaw and pitch angle change are compensated with the mirror angle turning. There is no path length change with the optical configuration. In laser satellite to satellite tracking for gravity measurements, satellite to satellite separation is measured to the highest precision possible (less than one micrometer). The measurement is conducted with laser links between two satellites, where the laser optical phase change is measured as a function of time. Satellite yaw and pitch causing optical path length change is a major error source. In current systems, path length change compensation is achieved with a sophisticated optical bench design.