Value chain · CLM-0969
In plain terms
If 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 perfectly evenly. At 85 per cent it is comfortable. The tipping point is almost exactly the efficiency the 1975 study said its tubes achieved.
The claim as recorded
For 6.72 GW radiated and the 1975 material limit of 3.6 kW/m2, the 1 km antenna face can shed at most 2.83 GW, while converter waste heat is 2.88 GW at 70 per cent efficiency and 1.19 GW at 85 per cent. The break-even efficiency at which the face becomes self-radiating is 70.4 per cent - the efficiency the 1975 study itself attributes to the klystron.
Evidence behind this: T0-derivation from held inputs; the material limit and the efficiencies are 1975 figures.
Scope and limits
MEDIUM BECAUSE THE MATERIAL LIMIT IS A 1975 JUDGEMENT ABOUT 1975 MATERIALS AND THE COMPARISON IS UNIFORM-FLUX. A hotter radiator changes the number as T^4; a higher emissivity, or radiating area beyond the face, changes it in proportion. A 228 K edge column cannot radiate to a 250 K sink at all, so the sink assumption must travel with any area figure. The rectenna's 85 per cent (CLM-0939) is a receive-side figure and is not used here.
What it assumes
Emissivity 0.85 and a 250 K sink are ASSUMED for the upper end of the area band; emissivity 0.5 and a 0 K sink follow SRC-336. The comparison is uniform flux over the face.
Where it comes from
This is the project's own working, shown in full:
Face area pi x 500^2 = 0.785 km2; at 3.6 kW/m2, 2.83 GW. Waste heat P (1 - eta) / eta: 2.88 GW at 0.70, 1.19 GW at 0.85, 0.75 GW at 0.90. Break-even eta = 1 / (1 + 2.83 / 6.72) = 0.704. Uniform spreading would need 3.67 kW/m2 at 0.70 and 1.51 kW/m2 at 0.85. Radiator area per kilowatt at the centre column's 482 to 600 K spans 0.16 to 0.70 m2/kW across emissivity 0.5 to 0.85 and sink 0 to 250 K. Consistency: a 600 K surface at emissivity 0.5 to a 0 K sink radiates 3.67 kW/m2 from one side, so the 3.6 kW/m2 limit is the centre column's full-sun temperature at that emissivity. Dickinson's "approximately 1 GW" and RP-1076's 1.18 GW both sit at the 85 per cent row.
Basis: GW of waste heat against GW the antenna face can radiate at 3.6 kW/m2
Related records
- Answers question
- QST-018 not published in this release
Cite this
energyaperture.com/c/clm-0969
CLM-0969, Energy Aperture, as of 2026-09-17.
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.
- 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-0939The 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...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...
- Also from SRC-450
- CLM-0949There is a standard international curve describing how quickly an antenna's stray radiation should fall away off-axis. The SPS pattern...CLM-0950A solar power satellite in geostationary orbit cannot make its beam any tighter than its design figure, because it is too far away to focus...CLM-0951The usual way to stop a strong transmitter interfering with other radio users is to smear its power across a wide band. For a solar power...CLM-0952A solar power satellite would have to stay below published interference limits, and the limits differ by who is being protected. Microwave...CLM-1408In the late 1970s, US studies sketched receiving stations raised on posts or legs so the ground beneath could still be farmed or built on...CLM-1413A 1977 NASA-funded report says the metal mesh behind a receiving station's antennas can be about three-quarters open to light while letting...
- Also from SRC-451
- CLM-0954The 1975 designers worked out how much their kilometre-wide antenna would bend, precisely so they could decide how good the beam-steering...CLM-0959The original 1975 calculation found the satellite's radio noise would be fine for ordinary and troposcatter radio links and a problem only...CLM-0960The 1975 study found the satellite's harmonics - the multiples of its transmit frequency - would trouble radio astronomy at the second and...CLM-0961Everything in the 1975 interference analysis is for one satellite. The study itself says that a hundred of them would raise the noise and...CLM-0965In 1973 an astronaut on Skylab put together two long poles from short sections in just over two hours, about six minutes per join. A 1975...CLM-0966In 1975 the antenna alone was expected to take one to two years to assemble in orbit with about fifty people, and robot arms were judged...CLM-0968The 1975 antenna study worked out how hot the middle of the transmitter gets depending on how efficient the tubes are and how tightly they...CLM-0972If you take a 1975 estimate of how fast people could build structure in space, checked against one Skylab task, and apply it to the 1978...More on the source page.