Argon laser radar returns from retroreflecting spacecraft

An angle tracking system was developed to assist in tracking faint, retroreflector-equipped space objects. The system consists of a 25 W CW Ar(+) laser, chopped to provide 3.6 ms pulses at a 62.5 Hz rate. During the 12.4 ms receive time, a quadrant photomultiplier detects the return pulse from a retroreflecting satellite or rocket over a range interval of 600 to 1800 km. More distant satellites (e.g. LAGEOS) are observed during later range intervals. Other satellites for which return signals were measured include Starlette, Diademe I and II, Beacon Explorer B and C, GEOS 1 and 3, and EGP. Data from a track of a suborbital rocket (Firefly) are also provided. The system was found to enhance visible signatures by orders of magnitude, allowing angle tracking of previously untrackable objects, with tracking jitter less than 1 microrads rms.