A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Position-Finding
From: Richard B. Langley
Date: 2018 Jul 27, 05:01 -0700
"Only seven GPS Block 1 (test) satellites were in orbit when KAL 007 was shot down."
True. But one of those had been decommissioned on 16 July 1981, so only six operational:
However, the operating satellites were in orbital slots that allowed at least four satellites to be oberserved from a location for a period of time during the day and so, with planning, positioning tests could be done. Back in those days, our surveying engineering (now geomatics engineering) students would sometimes have to go out after midnight to conduct observations, carrying with them a permission letter in case they were visited by the police, which did happen.
As for the projected eventual cost and size of GPS receivers, see the attached item, which includes an old GPS World column of mine on the miniaturization of GPS units.
-- Richard Langley