Value chain · CLM-1222
In plain terms
The fourth paper the 1978 design cites for its beam limit also calls the limit a theory that had not been tested. The one experiment it reports, at Arecibo in 1977, heated the upper atmosphere less strongly than the satellite would and found nothing, so it did not test the limit.
The claim as recorded
Reference 31 of DOE/ER-0023, Arndt and Leopold (1978), states that ionospheric studies indicate thermal runaway in the E-region at 110 km and thermal self-focusing in the F-region at 200 to 300 km will limit the beam to less than 23 mW/cm2, citing its references 8 to 10, and that this limit, believed correct to within a factor of two, "is a theoretical result for underdense heating and has not been verified by experiments"; it gives 20-25 mW/cm2 as the theoretical threshold, with self-focusing also needing an angle of 7 degrees or less between beam and magnetic field; and it reports June 1977 tests at Arecibo at 10, 430 and 2380 MHz, with heat input below SPS-equivalent levels and a smaller heated volume, that observed no thermal runaway, no thermal self-focusing and no communication effects.
Evidence behind this: T3-proceedings reprinting a 1978 NASA JSC conference paper; a review of theory plus one reported experiment.
Scope and limits
A review. Its threshold figures are its references 8 to 10 (PDF p.245): reference 8 is the September 1977 Rice final report (SRC-587); reference 9 is Perkins and Roble, "to be published"; reference 10 is the Raytheon memorandum. Those are DOE/ER-0023 references 26, 29 and 30, so this paper is not an independent derivation. The Arecibo tests ran below SPS-equivalent heating with a smaller heated volume, so their null result does not test the threshold. The paper itself says higher-power tests were proposed for that. The same paper puts runaway in "the E-region (110 Kilometers)" on E.4 and "the D and E regions" on E.5, where DOE/ER-0023 PDF p.41 says "the D-region (100 kilometers)". The reprint does not print the IECEC venue on the pages read, so the identity with reference 31 rests on title, authors and affiliation (JSC, PDF p.240).
What it assumes
No assumptions are recorded against this claim.
Where it comes from
PDF p.243 (E.4), zoom 4 crop: "Ionospheric studies to-date indicate that thermal runaway in the E-region (110 Kilometers) and nonlinear thermal self-focusing instabilities in the F-region (200 to 300 kilometers) will limit the maximum power density in the beam to less than 23 mW/cm2 (Ref 8 to 10). However this limit of 23 mW/cm2 (which is believed to be correct to within a factor of two) is a theoretical result for underdense heating and has not been verified by experiments." The page prints the first unit "mw/cm2" and the second "mW/cm2"; both are given here as mW/cm2. PDF p.244 (E.5), zoom 4 crop: "The theoretical results indicate that a microwave power density of 20-25 mW/cm2 is the threshold for achieving thermal runaway in the D and E regions and thermal self-focusing in the F-region (with the added requirement of 7 deg or less as the angle between the power beam and the magnetic field lines)." "Heating frequencies of 10 MHz, 430 MHz, and 2380 MHz were used to simulate SPS heating effects. Using the existing facilities at Arecibo the heat input levels were below the equivalent SPS levels and the heated volume was smaller." "no thermal runaways in the D and E regions nor thermal self-focusing instabilities in the F region were observed. In addition no communication effects were detected." The page prints the degree sign as a superscript o ("7o"); it is written "7 deg" here.
Basis: mW/cm2
Related records
- Answers question
- QST-009 not published in this releaseQST-010 not published in this release
Cite this
energyaperture.com/c/clm-1222
CLM-1222, Energy Aperture, as of 1978.
Connected records
Other published records linked to this one. A list, not a judgement.
- Also from SRC-085
- CLM-0013The paper that modern UK studies rely on for the beam figure calls anything below 1 kilowatt per square metre safe, with 230 watts per...CLM-0020The original 1978 design set the beam at 230 watts per square metre in the middle of the receiving site, about one twenty-third of that at...CLM-0023In the 1978 reference design, two limits set the size of the transmitter and the receiving site: how much heat the transmitter can shed...CLM-0039The 1978 report set the figure to protect radio and navigation systems from a disturbed ionosphere, called the number theoretical and...CLM-0045The 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-0101The 1978 contract required the researchers to report fixes if ionospheric disturbance pushed the pilot-beam phase error past 2 to 3...CLM-0137In four major space solar power studies from 1978 to 2007, none put a number on how much of the beam's energy would be lost if the beam...CLM-0138The original 1978 government design for beaming power down from space adds up all the expected energy losses to get 63% overall efficiency...More on the source page.
- Also from SRC-516
- CLM-0988The rule that radio astronomers hold the satellite to is a specific international report, and its limit near the satellite's frequency is...CLM-0989The same figure, minus 160, appears in two 1970s papers meaning two different things: in one it is the noise reaching the ground, in the...CLM-0990The extra twenty decibels of noise suppression for a fleet assumes a hundred satellites. The government's reference plan was sixty, which...CLM-0991In 1978 the frequency band the satellite was to use was an industrial free-for-all band in the West, where users must put up with each...CLM-0992The receiving field on the ground makes its own harmonics: the diodes that turn microwaves into electricity also generate signals at two...CLM-1091The people running the programme said 2.45 GHz was sensible and also said, in the same breath, that nobody international had agreed to it...