Value chain · CLM-1236
In plain terms
Clouds block a laser beam far more than a microwave beam. A 1980 NASA-funded study found that over most of the United States a single laser receiver would be clouded out too often to be a dependable power station, so each beam would need two or three receivers hundreds of kilometres apart and would have to switch between them, sometimes every few hours.
The claim as recorded
Rockwell's 1980 cloud study for NASA, modelling 22 US receptor sites from weather-station records, finds that "Power availabilities in excess of 80% are unattainable in most geographical regions of the United States if only a single receptor site is available for each transmitted laser beam", with the south-west the exception. To keep transmission efficiency at or above 80 per cent for 80 per cent of the time, most regions need three receptor sites per beam, 200 to 300 miles (about 320 to 480 km) apart. The south-west needs two, as close as 100 miles (about 160 km). The average time before a beam must switch sites runs from more than 24 h at south-western sites to under 4 h at the worst. Boring holes through cloud with the beam at about 11 um adds 9 to 33 per cent to annual availability, at 100 to 200 W/cm2 (1 to 2 MW/m2). The study concludes that thermal ground converters may be unsuitable because of their start-up times.
Evidence behind this: A NASA Marshall contractor's statistical model of laser power availability, run on climatological records for 22 US sites; modelled, not measured.
Scope and limits
A STATISTICAL MODEL OVER US SITES ONLY, NOT A MEASURED LINK AND NOT A SHARE OF HOURS LOST AS SUCH. Per-region availability (roughly 0.25 to 0.85) is shown only on the Figure 1.4-4 bar chart (PDF 59), which needs a render. The appendix tables were not read. The lower-bound Model 1 rests on one site's cloud-form statistics (Columbia, Missouri) generalised to the others (p.58). The multi-site estimate rests on three North Dakota stations. The hole-boring gain is itself modelled.
What it assumes
No assumptions are recorded against this claim.
Where it comes from
PDF p.64 [1-57], raw: "Power availabilities in excess of 80% are unattainable in most geographical regions of the United States if only a single receptor site is available for each transmitted laser beam (the exception is the southwestern United States)."; "Hole boring, as defined above, will increase the annual power avail- ability by 9 to 33%"; "all stratiform clouds with the exception of nimbostratus can be penetrated with power densities of 100-200 W/cm 2". PDF p.65 [1-58], raw: "then three receptor sites separated by a centroid radius of from 200 to 300 miles must be available for each transmitted lFser beam for most regions of the United States; for the southwest region, however, only two sites separated by as little as 100 miles will be sufficient."; "thermodynamic laser- energy conversion schemes may be unsuitable because of the long start-up times required by rotating turbomachinery." PDF p.63 [1-56], raw: "ranges from greater than 24 hours for southwestern sites to less than 4 hours for the least favorable sites." PDF p.64 [1-57], raw: "22 candidate sites in the contiguous United States were selected for detailed study". PDF p.8 [1-1], raw: "meteorological conditions influence the transmission efficiency to a much greater extent than with microwaves". Conversions: 100, 200 and 300 miles = 161, 322 and 483 km; 100 to 200 W/cm2 = 1 to 2 MW/m2.
Basis: power availability (average transmission efficiency, a fraction); frequency of transmission efficiency at or above 0.80; persistence time in hours; site separation in miles (km derived)
Related records
- Answers question
- QST-036 not published in this release
Cite this
energyaperture.com/c/clm-1236
CLM-1236, Energy Aperture, as of 1980-11.
Connected records
Other published records linked to this one. A list, not a judgement.