SRC-475

Solar Power Satellite System Definition Study, Part 1, Volume II, System Requirements and Energy Conversion Options; D180-20689-2 / NASA CR-151555; July 29, 1977

Commissioned by National Aeronautics and Space Administration, Lyndon B. Johnson Space Center; Contract NAS9-15196, DRL T-1346, DRD MA-664T, Line Item 3. 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-1114 The 1977 silicon design assumed an 18 per cent cell that did not yet exist, doubled the sunlight on it with cheap plastic mirrors, and got about 258 watts per square metre of blanket at the start of life, at a cell temperature of over 100 degrees.
• CLM-1115 Mirrors that doubled the light only added 40 per cent to the output, because the cells ran hot and the mirrors were not flat; after thirty years of radiation the array was down to 59 per cent of where it started, and the mirrors helped even less.
• CLM-1116 Thirty years of radiation behind a hair-thin glass cover was expected to take a third of the cell's power; a cover three times thicker would give about 16 per cent more power after thirty years but weigh twenty thousand tonnes more across the satellite. The design took the thin cover and planned to anneal.
• CLM-1117 The 1977 study found the cheapest way to keep a silicon satellite at full power was to heal the radiation damage in place rather than build it bigger, that healing works best without mirrors because mirrors cannot be healed, and that a cheaper cell mattered more than a better one. That is why the reference system went to flat arrays and an annealing plan.
• CLM-1118 In 1977 five radiation-damaged cells were healed with a laser or an electron gun, getting back between a fifth and a half of what they had lost; the electron gun did better and the laser missed parts of the cells. It was a first try, and everyone said so.
• CLM-1120 In 1977 the gallium arsenide option rested on a 20 per cent cell nobody had made, an assumption that it would still be near 20 per cent after thirty years because it heals more easily, and on films a few thousandths of a millimetre thick, because there was not enough gallium for anything thicker.
• CLM-1121 Half a kilogram per square metre for the working blanket, about half of it the silicon itself; per kilowatt delivered on the ground the 1977 satellite came to six or seven kilograms, and the blanket alone to about two.
• CLM-1468 The basic idea, a solar power satellite climbing to its final orbit on electric engines run by solar panels it carries, with no separate fuel tanker, is real: it has flown on communications satellites, though not at the scale of a power station. A 2013 design does it with a separate, smaller set of panels. The stronger version, where the satellite's own main panels run the engines, has been proposed, for example by a 1977 US study, which found the panels used for the trip would be badly damaged on the way, and by a 2021 UK study for the last part of the climb only, after chemical stages carry the parts past the inner radiation belt. None of these designs has flown.

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