Value chain · CLM-1479
In plain terms
A 1981 NASA summary says that if the timing across the 1978 design's antenna were lost, its beam would spread out to the width that one of its small radiating sections makes on its own, covering a very large area. Far from the receiving site the power could rise, but the summary says it would stay well below even the strictest safety limits of the time.
The claim as recorded
NASA's 1981 summary of the reference power transmission system (RP-1076) states that power-beam safing is inherent in phase control: if the phase error across the transmitting antenna exceeds 90 degrees rms at the beam frequency, the array pattern diffuses to that of a single transmitting element, the total energy is spread over an extremely large area, and although the density far from the rectenna may rise, it stays well below the US and USSR exposure standards of the time (10 and 0.01 mW/cm2).
Scope and limits
The page names the element as a "power module" and earlier on the same page writes "power module (or subarray)", so it does not say at which level phase is lost; the 1978 report says between subarrays (CLM-0911). It gives no width or shape for the spread pattern; CALC-144 sizes it for 108 m2 subarrays (CLM-1481). The 90 degree figure is the page's example of a large error, not a threshold derived on the page, and on its own it does not reach the full spread: with random errors of 90 degrees rms the beam keeps exp(-(pi/2)^2), about 8.5 per cent, of its peak power if the errors are Gaussian, or about 2.3 per cent if they are spread evenly, that is about 0.5 to 2 mW/cm2 at the centre of the 1978 beam; the pattern becomes one element's only when the phases are spread over the whole circle (about 104 degrees rms). Says nothing about a per-element design such as CASSIOPeiA. The standards are those of 1981; for today's limits see CLM-1169.
What it assumes
The 1978 reference design (1 km antenna at 2.45 GHz), as in the rest of RP-1076.
Where it comes from
PDF p.92 (printed 63), read at a zoom-4 crop: "the power beam intensity is greatly diffused if loss of phasing occurs, because of the excessive element-to-element phase errors. For example, if the phase error across the spacetenna exceeds 90" (the page prints a degree sign) "rms at the rf beam frequency, the array pattern has diffused to that of a single transmitting element (power module) and the total energy is spread over an extremely large area." The next sentence: "Although the power density at a given location far removed from the rectenna site may increase when dephasing occurs, it will remain well below the U.S. and U.S.S.R. standards for S-band radiation exposure (10 and 0.01 mW/cm2, respectively), as shown previously in figure III-7. Thus, complete loss of phasing results in automatic safing as far as power density requirements are concerned."
Basis: phase error in degrees rms at the beam frequency; power density in mW/cm2
Related records
- Answers question
- QST-013 not published in this release
Cite this
energyaperture.com/c/clm-1479
CLM-1479, Energy Aperture, as of 1981.
Connected records
Other published records linked to this one. A list, not a judgement.
- Also from SRC-107
- CLM-0033 (low confidence)Apart from a 1981 NASA review that found no evidence for the number and suggested a higher one, nobody was found to have revisited it, and...CLM-0060In 1981 a NASA review panel said the 230 watts per square metre figure rested on an obsolete theory with no experimental support, and made...CLM-0061The experiments were done. They found heating two or three times stronger than normal, not the tenfold effect predicted, no irregularities...CLM-0062By 1981 the theory was being revised to a steeper frequency dependence, which would raise the permitted power density.CLM-0063NASA suggested in 1981 that 550 to 600 watts per square metre might be reasonable, roughly two and a half times the figure still in use...CLM-0101The 1978 contract required the researchers to report fixes if ionospheric disturbance pushed the pilot-beam phase error past 2 to 3...CLM-0160A 1978-81 NASA design study calculated that simply pointing the satellite's structure accurately enough, without any electronic correction...CLM-0420NASA's 1981 report says the experiments found nothing supporting the 23 milliwatt limit, that the measured heating was two or three times...More on the source page.