Value chain · CLM-1313
In plain terms
An error near the antenna elements is different at each element. It averages out in pointing but scatters power. An error near the centre is shared by a whole block of the array. It tilts that block and pushes the beam off target.
The claim as recorded
Where in the tree a phase error enters changes what it does. Errors at the last level cost the most main-beam gain, and errors at the first level cause the most beam-pointing error. For the 4-level baseline, rms pointing error is about the total rms phase error divided by 4.5x10^4, so 12 deg gives 0.016 arcmin and a 99% miss distance of 437 m.
Evidence behind this: SOLARSIM outputs and a fitted rule of thumb in a NASA contractor report.
Scope and limits
Printed p.95 (PDF 103, read in a zoom-4 crop) gives slant range as 3.7x10^5 km. The miss distances fit 3.7x10^4 km: 0.016 arcmin = 4.65e-6 rad; x 3.7e7 m = 172 m; x 2.576 = 444 m, against the printed 437 m. With 3.7x10^5 km the result would be about 4.4 km. This is treated as a misprint in the source; the render shows 10^5. The 18 dB uses 25 first-level nodes, but Fig. 10.1 shows 16, which would give 19.0 dB. Printed p.107 (PDF 115) says that at 15 deg (0.019 arcmin rms) the beam stays within 0.03 arcmin with probability 0.99. That does not match a one-dimensional Gaussian (0.03/0.019 = 1.58 sigma, about 0.89), so it is left unresolved.
What it assumes
Gaussian pointing error; 10 dB taper; equal per-level sigma.
Where it comes from
Printed p.91 (PDF 99, render): first-level errors cause the largest rms pointing error and last-level errors the least; the same trend for 8- and 9-level trees (Fig. 10.4). Printed p.95 (PDF 103, render): independent last-level errors are averaged over 101,552 elements and first-level errors only over the first-level nodes; the ratio's square root is stated as about 18 dB (recomputed: 10 log10 sqrt(101552/25) = 18.0). Fig. 10.14 (printed p.108, PDF 116, render): 0.016 arcmin and 437 m at 12 deg; 0.041 arcmin and 1120 m at 31 deg. Printed p.107 (PDF 115, render): sigma_u approximately sigma_phi/4.5x10^4 (recomputed: 12/4.5e4 deg = 0.0160 arcmin). Printed p.104 (PDF 112, render): last-level error is expected to be larger because it includes the power transponder.
Basis: arcmin rms pointing error per deg rms phase build-up; metres miss distance at 99%
Related records
- Answers question
- QST-013 not published in this release
Cite this
energyaperture.com/c/clm-1313
CLM-1313, Energy Aperture, as of 1979-03.
Connected records
Other published records linked to this one. A list, not a judgement.
- Also from SRC-647
- CLM-1311The 1979 design sends a sample of the reference back up each cable and adjusts until the far end matches the source. That makes cable...CLM-1312In 1979 the contractor simulated the whole reference-distribution tree. Small, random timing errors were added at each branching level, and...