SLOW WALKER is the U.S. Navy/DOD code name for a system or procedure used beginning in the 1970s as far as I can tell. It was a means of detecting and tracking moving aircraft through the detection and recognition of the infrared plume produced by jet engine afterburners.

The kicker is that this was done using DSP satellites in what appear to have been not a nearby orbit. The DSP satellites (I think DSP stands for Defense Support Program) were originally tasked with watching for the characteristic heat blooms of either a ballistic missile launch or an above-ground atomic detonation. In any case, the SLOW WALKER program was apparently real-time enough that deployed naval forces could be given warning (from the CONUS) that afterburner-using aircraft were closing on their position. That information comes from an anecdote told me by an officer who served aboard a U.S. vessel in the western Pacific; apparently in the 1970s they received such warnings in advance of a close flyby by several Tu-22M Backfire bombers.

Apparently there was a sister program, FAST WALKER, designed to detect spacecraft for the Air Force. Presumably either maneuvering engine firings or the IR signature of a craft against the cold background of free space would have sufficed. For more information, see:

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