Value chain · CLM-0939
In plain terms
The 85 per cent figure that later papers quote flat was one component on a bench, in moving air, with an error bar, at one power level. The array number beside it was an estimate, not a measurement.
The claim as recorded
The 85 per cent rectenna efficiency reported by contract NAS3-22764 is a single rectenna element, measured in a closed system, with an estimated probable error of plus 1.5 per cent, under convective air cooling. The 25-element section figure is stated by the report as an estimate rather than a measurement, and the 85 per cent is two figures at two operating points: 85 per cent overall at 1.5 W DC output, and 84 per cent rectification at 3.5 W, the limit being diode reverse-voltage breakdown.
Evidence behind this: T3-primary-report, read first-hand. The measurement conditions are taken from the same report that made the measurement, which is the only document that can state them.
Scope and limits
EVERY EFFICIENCY MEASUREMENT IN THIS REPORT IS CONVECTIVELY AIR-COOLED - the thermal work is parameterised on air velocity in feet per minute throughout, PDF pp.58-59. It is not a vacuum result and it is not a space result, which matters because the figure is quoted in SBSP contexts where there is no air. NOTHING HERE SAYS THE 85 PER CENT IS WRONG; it says what it is a measurement OF. A single element in a closed test fixture is the right way to measure a component and the wrong thing to quote as an array performance. The report itself does not overstate it - the estimate is labelled an estimate and the error bar is given - so the narrowing happens downstream, not here.
What it assumes
No assumptions are recorded against this claim.
Where it comes from
PDF p.96, verbatim at the normalised level: "made in a closed system, where accurate measurements of efficiency could be made, gave values of 85% with an estimated probable error of +1.5%". Array, same page: "were obtained from these sections at an estimated efficiency of 85%". Comparator, same page: "These efficiencies are only 5% less than the best achieved with the rigid, much heavier, and much more costly bar type rectenna construction." Operating points, PDF p.44: "An overall efficiency of 85% at 1.5 watts DC/output was obtained and a rectification efficiency of 84% was obtained at 3.5 watts of output. Limitation in power output and efficiency was the reverse voltage breakdown of diode."
Related records
- Answers question
- QST-002 not published in this release
Cite this
energyaperture.com/c/clm-0939
CLM-0939, Energy Aperture, as of 1987.
Connected records
Other published records linked to this one. A list, not a judgement.
- Also from SRC-336
- CLM-0938A 1988 NASA paper says a rectenna built on mylar reached 85 per cent efficiency. The 1987 final report of the contract it cites says mylar...CLM-0940Two NASA efforts to build rectennas at much higher frequencies than the standard 2.45 GHz ended without a working device. One concluded the...CLM-0941In space there is no air to carry away the waste heat, so a rectenna's output is limited by how much waste heat it can radiate. The report...CLM-0969If the tubes are only 70 per cent efficient, the transmitter's own face is not big enough to get rid of the heat they make, even spread...
- Contradicted by
- CLM-0938A 1988 NASA paper says a rectenna built on mylar reached 85 per cent efficiency. The 1987 final report of the contract it cites says mylar...