This is a collection of parts from the laser-ranging satellite tracking system that the Smithsonian Astrophysical Observatory used at Mt. Hopkins near Tucson, Arizona. Included is the secondary mirror that received light from the primary mirror and reflected it to the collimating lenses, as well as a photomultiplier tube used in laser detection. The satellite laser tracking systems were designed as a refinement on the Baker-Nunn cameras developed by SAO in connection with the International Geophysical Year. They comprised a laser transmitter mounted side-by-side with a telescope receiver, which were used to obtain highly accurate measurements of orbital altitudes and tracks of artificial satellites. They provided ranging data at accuracy levels of one meter or better.
SAO operated four laser-tracking systems around the world—in Brazil, Peru, Australia, and Mt. Hopkins. The program was used to track a large number of satellites from its inception in 1968 until it was shut down in 1982. SAO transferred these parts to the Museum in 1980.
This object is not on display at the National Air and Space Museum. It is either on loan or in storage.