Value chain · CLM-1237
In plain terms
The colour of the laser light decides how much of it gets through the air. The calculations found almost no loss near 2 micrometres on a clear day, but the 10.6 micrometre carbon dioxide laser of the earlier designs would lose more than half its beam at sea level.
The claim as recorded
Rockwell's 1980 calculations put clear-air space-to-Earth transmission (50 degree zenith angle, molecular absorption and Rayleigh scattering) above 99.9 per cent for laser lines at 2.143 to 2.250 um at every site elevation and season. The "standard" 10.6 um CO2 line fares far worse: the 10.591 um line transmits 0.192 to a sea-level site in midlatitude summer and 0.439 in winter, and the study calls it "totally unsuitable" for space-to-Earth power beaming. The best 11 um window line (10.916 um) reaches 82.3 per cent annual transmission to typical sites and 96.3 per cent at 3 km elevation. The study concludes that about 11 um is best at high elevation and about 2.25 um at low elevation.
Evidence behind this: Calculated space-to-Earth transmission from atmospheric line-by-line codes (LASER, AFGL line data) by a NASA contractor; modelled, not measured.
Scope and limits
CLEAR-AIR MOLECULAR ABSORPTION ONLY; AEROSOL, HAZE AND CLOUD LOSSES ARE SEPARATE (CLM-1236). These are calculations with 1978 line data, not measurements. Nothing below 2 um was calculated (the study recommends examining short-wavelength windows, p.65), so the record says nothing about the 0.8 to 1.6 um band in CLM-1110 to 1112.
What it assumes
That the row read as 10.591 um, P1(20) of 12C16O2, is the "standard" 10.6 um line; the isotope label is garbled in the text layer.
Where it comes from
PDF p.44 [1-37], raw: "The spectral region from 2.100 um to 2.315 um offers an excellent high- transparency window"; "Calculated transmission efficiencies of three sample lines, as given in Table 1.2-10 exceed 99.9% for all site elevations and are insensitive to seasonal variations." (mu written um). PDF p.45 [1-38] Table 1.2-10 rows, raw: "4444.444 2.250 0.99947." and "4666.000 2.143 0.99901"; text, raw: "calculations are also shown for .the "standard" 10. 6-um C02 laser line, which is totally unsuitable for space-to-earth power beaming." PDF p.46 [1-39] Table 1.2-12, read down the 10.591 um column (the text layer lays the table out by column): 0.192, 0.232, 0.412 (summer, 0, 0.5 and 3 km) and 0.439, 0.463, 0.570 (winter); text, raw: "The highest annual transmission efficiency to typical receptor sites is 82.3% for the 10.916-um line. High- elevation operation (h = 3.0 km) increases this value to 96.3%." PDF p.64 [1-57], raw: "At low elevations, laser operation at a wavelength near 2.25 um is preferable."
Basis: space-to-Earth transmission efficiency (fraction) at a 50 degree zenith angle, by wavelength in um and site elevation in km; clear air, molecular absorption (plus Rayleigh scattering at 2 um)
Related records
- Answers question
- QST-036 not published in this release
Cite this
energyaperture.com/c/clm-1237
CLM-1237, Energy Aperture, as of 1980-11.
Connected records
Other published records linked to this one. A list, not a judgement.