Laser Ranging to Unknown Objects for Initial Orbit Determination: A Feasibility Study

Satellite laser ranging to objects without corner-cube retroreflectors is explored as a means of providing range data for initial orbit determination. The goal is to couple laser range data with optical angular data and eliminate the need for radar. This study investigates this concept using analysis and simulation. It considers the effects of laser energy per pulse, pulse rate, path loss, telescope diameter, object cross section, atmospheric losses, and noise photons. It develops signal processing algorithms that can successfully determine orbit when 20–40 true-returned photons and 1200–1300 noise photons arrive during a tracking window. These algorithms include initial clustering calculations that distinguish between true and noise photons. They culminate with an optimal estimation algorithm that explicitly accounts for noise/clutter photons. One example case considers a low-Earth-orbit object with an optical cross section of at a distance of 1170 km. The laser transmission/reception telescope has a diameter of 0.18 m, and the laser transmits 100 pulses per second at 0.25 J per pulse. Despite receiving a mere 18 true photon returns during a 20 s tracking interval, the system is able to determine orbit to a 7 m position accuracy and a velocity accuracy.