SRC-446

Pilot Signals for Large Active Retro-Directive Arrays, NASA TM-78310, October 1980 (report page); NTRS citation 19810001730

C. H. Chan, Physics Department, University of Alabama at Huntsville, under the 1980 NASA/ASEE Summer Faculty Fellowship at NASA Marshall Space Flight Center (as printed on PDF 3 and 5) ·1980 · T3 government or agency report · VC05 VC06

Commissioned by NASA MSFC. Who paid for a study is recorded because it bears on how its conclusions should be read, not because it makes them wrong.

NASA TM-78310 the identifier this document is registered under

Published claims resting on this source

CLM-0910 The problem of not knowing which wave crest you are looking at is solved by sending a second tone at a slightly different frequency. The beat between them repeats only every fifteen metres instead of every six centimetres, which is more than enough to tell the crests apart. Measuring the structure directly would also work, and needs about two hundred picoseconds rather than the ten that would be needed to do the whole job.
CLM-1466 The pilot method works out of each antenna's own measurement, not out of a plan of where the antennas should be. Each antenna times its reply from when the pilot reached it. So if one antenna has moved, its timing changes by just the right amount, and all the replies still arrive together where the pilot came from. A 1980 NASA memorandum set out the principle; it does not discuss a moved antenna, but its working covers one.

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SRC-446 , recorded 2026-09-25.