Value chain · CLM-0968
In plain terms
The 1975 antenna study worked out how hot the middle of the transmitter gets depending on how efficient the tubes are and how tightly they are packed. With the tubes at 70 per cent efficiency and an aluminium frame, it found they had to be spread almost evenly across the whole kilometre to stay within what the frame could take.
The claim as recorded
The 1975 Raytheon MPTS study gives a closed form for the waste-heat flux at the centre of a 1 km transmit antenna as a function of converter efficiency, transmitted power and the Gaussian spacing of the converters; states the flux three candidate materials tolerate as 3.6 kW/m2 for aluminium and graphite/epoxy and 8.1 kW/m2 for polyimide; takes 70 per cent as representative of klystron performance "rather than 75%"; and concludes that at 70 per cent with an aluminium structure the converters must be spread to a scale factor of at least 1100 m, "nearly a uniform distribution".
Evidence behind this: T3-primary-report, the governing relationship for the layer, stated with its inputs.
Scope and limits
THE PLOT'S TRANSMITTED POWER IS UNSTATED, AND THE 1100 m CONCLUSION DEPENDS ON IT. 1100 m is where the plotted axis ends, and at 1100 m the 70 per cent curve still reads 3.7 to 4.1 kW/m2, above the 3.6 limit; solving the document's own formula at 7 GW and F = 0.875 puts the crossing at about 1,820 m, which is uniform rather than "fairly flat"; the crossing depends on F, and at F = 1 the uniform-flux asymptote at 7 GW is 3.67 kW/m2, above the limit, so the curve never crosses - the figure implies F near 0.9 (VER-1169). At about 5.5 GW the document's reading holds. A qualification, not a contradiction. The column temperatures are for the structure, not the converter radiators. The thermal constraint on rho pulls against the 10 dB Gaussian taper chosen for sidelobe control, which the document states in its own terms; that trade is not registered elsewhere.
What it assumes
The figure's transmitted power is not stated on it; 7 GW is taken from Vol IV of the same study.
Where it comes from
This is the project's own working, shown in full:
p.150 gives Q_max = 2 F (1 - eta) P / (pi eta rho^2 [1 - exp(-2 (r0/rho)^2)]) with F the fraction radiated toward the structure; the render shows the exponent without its minus sign, restored because the bracket must lie between 0 and 1. From the render, p.150: "The maximum flux values that can be tolerated by three candidate materials are shown as 3600, 3600, and 8100 w/m2 for aluminum, graphite/epoxy and polyimide composites, respectively"; "an efficiency of 70% which is now considered representative of the klystron performance rather than 75%"; "the microwave converters will have to be spaced according to rho >= 1100 meters, which produces a fairly flat Gaussian distribution, nearly a uniform distribution." Fig 3.3-27 (p.151) plots the relation at F = 87.5 per cent, rendered "17.8%" in the text layer; Fig 3.3-26 gives column temperatures of 228 and 289 K at the edge and 482 and 600 K at the centre, no sun and full sun. CALC-112 reproduces the plotted curves within 10 per cent at P = 7 GW.
Basis: W/m2 waste-heat flux at the antenna centre; Gaussian scale factor rho in metres
Related records
- Answers question
- QST-018 not published in this release
Cite this
energyaperture.com/c/clm-0968
CLM-0968, Energy Aperture, as of 1975-12.
Connected records
Other published records linked to this one. A list, not a judgement.
- Also from SRC-451
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