The first sentence of the article "Charting a New Course" (Oct. 25-Nov. 7, p. 58) incorrectly attributes the first two Navigation Technology Satellite (NTS) experiments to the U.S. Air Force. It was the Naval Research Laboratory (NRL) that conceived, designed, fabricated, space-qualified and then operated and tested each satellite in first-of-a-kind circular, medium Earth orbits.Other important firsts for these two satellites included the successful demonstration of the basis on which GPS is built-passive ranging-which requires the stability only available from atomic clocks. The NTS-1 had Rubidium clocks, and the NTS-2 had Cesium clocks, which met, for the first time, the Pentagon's demanding requirements for a 3D satellite navigation system.
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