Value chain · CLM-1466
In plain terms
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.
The claim as recorded
A 1980 NASA memorandum on pilot signals for solar power satellites states that a retrodirective array points its beam back at the apparent source of a pilot signal by sending from each element a signal whose phase is the conjugate of the pilot phase that element received. Its derivation writes the received phase with each element's own distance to the source, r_k, and shows that the contributions from all elements are in phase at the source. The memorandum does not discuss a moved element, but nothing else about an element's position enters its working, so the result holds wherever the elements sit, as CLM-0913 also derives. It notes that the radiated beam may not be coherent across the aperture but is coherent when it reaches the source. A check with an element moved out of line, and with a bent row, gives replies fully in step at the source (CALC-142).
Evidence behind this: T3: a NASA technical memorandum by a named author, written at NASA Marshall in 1980; the principle is stated and derived in it. The check that the derivation holds for an element out of line is a T0 calculation (CALC-142 step 4).
Scope and limits
The memorandum gives the principle for the ideal case. Real designs depart from it: they measure the pilot at some elements and interpolate (CLM-0896, CLM-0913), use a pilot at a different frequency, which leaves a residual that grows with displacement (CLM-0914), and depend on a shared reference that the pilot does not correct (CLM-0902, CLM-0905). The memorandum does not discuss a moved element; that the result holds for one follows from its derivation, which holds for any r_k. Says nothing about how far an element may move before other limits apply.
What it assumes
The pilot and the beam are at the same frequency, as in the memorandum's simple example; the memorandum says that a different frequency also works only if the medium between is not dispersive. Each element measures its own pilot phase.
Where it comes from
This is the project's own working, shown in full:
PDF 6 [printed 1]: "Retrodirectivity is achieved by retransmitting from each element of the array a signal whose phase is the conjugation of that received by the element." PDF 8 [printed 3]: the received phase is written as omega(t - r_k / c), with r_k "the distance from the kth element to the source", its conjugate as omega(t + r_k / c) + phi_0, and the report concludes that the contributions at the source "are all in phase at that point". Same page: the beam "may or may not be coherent across the aperture but it is coherent when it arrives back at the source". Read at the page renders, 2026-10-17. CALC-142 step 4: a 12-element row bent by 1.2 wavelengths with one element moved 0.37 wavelengths, pilot 15 wavelengths away: reversed replies 1.000000 in step at the source; the same row timed as if straight, 0.258.
Basis: phase in radians; distance from each element to the pilot source
Related records
- Answers question
- QST-013 not published in this release
Cite this
energyaperture.com/c/clm-1466
CLM-1466, Energy Aperture, as of 1980-10.
Connected records
Other published records linked to this one. A list, not a judgement.