SRC-108

Ionosphere/Microwave Beam Interaction Study, NASA-CR-151821

Commissioned by NASA (NAS9-15212). 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-0043 The study the 1978 reference system cites put the level where the beam may start to disturb the ionosphere at about 20 milliwatts per square centimetre. A July 1978 follow-up predicted 12, give or take a factor of two, for runaway heating, and noted the beam affects the ionosphere less at the higher frequency.
• CLM-0045 The apparent conflict between 12 and 23 was not an error. The underlying study gave a range, and the figure adopted sits near the top of it.
• CLM-0066 The figure adopted in 1978 was higher than each of the lower figures in the studies it cited, though those figures were themselves uncertain by up to a factor of two.
• CLM-0072 The 1978 study gives 12 milliwatts per square centimetre for runaway, give or take a factor of two, and says no threshold can be set in the usual way for the self-focusing effect, though its summary repeats an earlier study's figure of 20 for it.
• CLM-0082 The formula is the right one for the conditions space solar power would create. It was written for this case, not borrowed from a different one.
• CLM-0083 The formula is the right type but nobody has said how far it can be pushed, and at space solar power frequencies the wave is about 200 times the plasma frequency. The field's own 2007 review says the case is unclear.
• CLM-0085 The 1978 formula does not give a threshold. It relates threshold power to the width of the plasma structures produced, so getting a single number out of it requires deciding which width matters.
• 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-0132 A 1978 NASA-funded study calculated that a beam of about 12 milliwatts per square centimetre at 2.45 GHz would be the point where the ionosphere starts heating itself out of control.
• CLM-0461 The ionosphere absorbs about one part in a hundred thousand of the beam. It is not a meaningful loss.
• CLM-1091 The people running the programme said 2.45 GHz was sensible and also said, in the same breath, that nobody international had agreed to it and the choice was open. Their own account of the 1979 world radio conference is that no frequency was given and one might be, if the environmental case were made.
• CLM-1094 The 1978 Rice report the archive holds is the follow-on to the 1977 one that the reference system cites, and the 1977 report, obtained the same day, gives about 20 milliwatts per square centimetre with no band and no derivation. The 12 milliwatts per square centimetre figure is worked out in the 1978 report from a simple heating-versus-cooling balance, and the authors say their simplifications make the real threshold higher, not lower, and that nobody had observed the effect.
• CLM-1454 The 2020 international limit for public exposure, 10 watts per square metre, is about 19 to 42 times lower than the beam strengths at which one theory says the beam might start to focus itself in the upper atmosphere (42 times uses a 2008 estimate, 19 times uses measured conditions), and 23 times lower than the 230 that a 2019 CASSIOPeiA paper gives as a typical peak. Those atmospheric figures are estimates, not hard limits. A 2026 international radio report that takes CASSIOPeiA as its example says the beam can be designed to fall below the public limit at the edge of the receiving site, with a safety zone over the beam's footprint; it gives no figure for the beam's strength at that edge, and a diagram in it shows the receiving site taking 245 watts per square metre.

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