SRC-450

Satellite Power System (SPS) Microwave Subsystem Impacts and Benefits, JPL 900-800, NASA-CR-157951, 28 September 1977

Published claims resting on this source

• CLM-0949 There is a standard international curve describing how quickly an antenna's stray radiation should fall away off-axis. The SPS pattern stays under that curve everywhere except at its grating lobes - the repeating spikes caused by building the antenna out of subarrays - and the report says that because of those spikes the standard curve cannot be used to describe the SPS safely.
• CLM-0950 A solar power satellite in geostationary orbit cannot make its beam any tighter than its design figure, because it is too far away to focus more sharply. The same antenna in low orbit could concentrate the beam a thousand times harder, and what stops it is the air breaking down at about 45 km up rather than anything in the satellite.
• CLM-0951 The 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 satellite the report calculates that the smear would have to be about 3200 GHz wide to satisfy the protection limit for microwave relay links - about 32,000 times the 100 MHz band the satellite would use. The beam is strong enough to overload a relay receiver even at frequencies well away from its own.
• CLM-0952 A solar power satellite would have to stay below published interference limits, and the limits differ by who is being protected. Microwave relay links get a limit per 4 kHz of bandwidth. Radio astronomy and deep space research get limits stated per hertz, which cannot be ranked directly against the relay limits. The radio astronomy and deep space limits are recommendations rather than binding rules, and the report says what protection radio astronomy really has is not clear.
• 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-1408 In the late 1970s, US studies sketched receiving stations raised on posts or legs so the ground beneath could still be farmed or built on. They noted a trade-off: panels close to the ground are easier to reach for repairs.
• CLM-1413 A 1977 NASA-funded report says the metal mesh behind a receiving station's antennas can be about three-quarters open to light while letting through only about half a per cent of the microwave power. The 1978 reference design used a steel mesh about that open.

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