SRC-107

NASA RP-1076: Satellite Power System (SPS) Magnetron Tube Assessment / SPS Power Transmission and Reception Technical Summary and Assessment, 281 pp

Commissioned by NASA and US DOE. Who paid for a study is recorded because it bears on how its conclusions should be read, not because it makes them wrong.

Published claims resting on this source

• 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 a 2014 proposal for experiments on beam effects in the atmosphere does not appear to have gone ahead.
• CLM-0060 In 1981 a NASA review panel said the 230 watts per square metre figure rested on an obsolete theory with no experimental support, and made resolving it the top priority.
• CLM-0061 The experiments were done. They found heating two or three times stronger than normal, not the tenfold effect predicted, no irregularities forming, and effects far smaller than a solar flare produces naturally.
• CLM-0062 By 1981 the theory was being revised to a steeper frequency dependence, which would raise the permitted power density.
• CLM-0063 NASA 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, and said the parameter decides the system size and has billions of dollars of cost impact.
• CLM-0101 The 1978 contract required the researchers to report fixes if ionospheric disturbance pushed the pilot-beam phase error past 2 to 3 degrees, and a 1981 NASA report allowed 10 degrees of phase error for the whole pointing system. The requirement to hit the receiver within about 300 metres from geostationary orbit was stated in 2007, not in the 1978 design, which left that number open.
• CLM-0160 A 1978-81 NASA design study calculated that simply pointing the satellite's structure accurately enough, without any electronic correction, would miss the ground target by 10 to 30 kilometres - which is why the system needs a self-correcting radio-steering mechanism, and that mechanism's own error budget keeps beam losses under 3% and keeps the beam within a quarter of a kilometre of its target 99% of the time.
• CLM-0420 NASA's 1981 report says the experiments found nothing supporting the 23 milliwatt limit, that the measured heating was two or three times, not ten times, and that the theory was being rewritten. Its review panel called the basis obsolete and unsupported.
• CLM-0901 Each antenna must hold its position along the line to the receiver within about three millimetres for a tenth of a decibel. The whole 1970s design budget, converted to the same units, was 3.4 millimetres. One metre of structural bending is nearly three thousand degrees of phase, and if that is not corrected the antennas stop adding up at all - a billion of them lose ninety decibels, which is everything.
• CLM-0915 The leftover error does two different kinds of damage and they need separate budgets. A uniform tilt across the antenna does not weaken the beam, it moves it; everything else weakens it. Missing the receiver by 250 metres from geostationary orbit means pointing to about one and a half seconds of arc, and the steering system has to do somewhere between forty and a hundred and twenty times better than the structure can be pointed mechanically - depending on whether you take the whole structure or an individual sub-panel.
• CLM-0957 The idea was to listen to the pitch of the reference signal at each antenna element, work out how fast that element is moving, and add it up to get where it is. It fails three ways: the pitch cannot be measured finely enough over the time the structure takes to move; the 1981 design's own timing system deliberately cancels exactly that pitch change at the element; and the reference signal travels along the structure, not along the beam, so it barely notices the bending the beam cares about.
• CLM-0958 What is left of the idea is useful but narrower: the timing system already tracks how the reference path stretches, and the fast part of that stretching is the structure's vibration. It cannot give the slow bending that the sensor-spacing question is about, but it could tell you how the vibration is shared between modes - which is the one thing the modelling could not settle.
• CLM-0969 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.
• CLM-0979 The three designs disagreed about what the guide signal from the ground should look like. One used a pair of tones either side of the target frequency; one used exactly the transmitter's own frequency and worried about telling the two apart; and by 1979 the reference design had moved to a coded, spread-out signal, the same family of technique that satellite navigation uses.
• CLM-1089 The higher industrial band would have shrunk the receiving field to a fifth or a third of its size, at the price of a satellite that could not shed its heat, a bigger electricity bill, and a beam that rain could knock out. Every time the programme costed it the answer was the same and 2.45 GHz stayed.
• CLM-1090 The programme's two printed tables of how much beam the weather eats do not agree. One has the ionosphere numbers the wrong way round, and its rain and hail figures are a million times too small for the unit printed over them. The other is internally consistent.
• CLM-1478 Almost everything that can go wrong with this design makes the beam fall apart and become harmless, which is the right way to fail. Two things do not. If someone fakes the ground signal, the satellite aims at the fake. And if the internal reference cabling drifts, the beam weakens and wanders rather than switching off.
• CLM-1479 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.

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