Value chain · CLM-1232
In plain terms
In 1978 a NASA contractor designed a satellite that would turn sunlight into an infrared laser beam and send it, by way of a mirror satellite high above the equator, to a ground station about 30 m across. The ground station would use the beam as heat to run turbines. On paper, about 5 to 6 per cent of the sunlight collected in space would reach the grid as electricity.
The claim as recorded
Lockheed's 1978 study for NASA Lewis designs a 500 MWe space-to-Earth laser power system: a sun-synchronous satellite at about 900 km with 20 CO2 electric-discharge lasers at 10.6 um (910 MW of laser output), a relay in GEO, and 31.5 m transmit, relay and ground apertures, with a ground station that turns the beam into heat and runs a heat engine, not photovoltaics. For the selected design, 7,913 MW of collected sunlight gives 500 MW of electricity, an overall 6.3 per cent. 3,958 MW of electricity drives the lasers (laser electrical efficiency 23 per cent, cavity 28.3 per cent), and the ground conversion subsystem is 75.5 per cent. In the parametric tables the CO2 system (System I) has a space chain of 9.62 per cent (laser subsystem 20.2) and a space-to-ground chain of 51.5 per cent: relay 90, atmospheric transmission 85, receiver 96, cavity 98, energy exchanger and binary cycle 73, generator 98. Its overall system figure is 4.96 per cent. The study's range is 100 to 10,000 MW on the ground, and it calls the system "a viable alternate to the microwave Solar Power Satellite".
Evidence behind this: A NASA-funded contractor's (Lockheed) conceptual design study: every figure is a design estimate, with nothing built or measured.
Scope and limits
A 1978 PAPER DESIGN WITH A THERMAL GROUND RECEIVER AT 10.6 UM, NOT A MEASURED LINK AND NOT A PHOTOVOLTAIC RECEIVER. The source itself says "system optimization could not be accomplished" because of schedule and funding (p.22). The 85 per cent atmospheric transmission is stated without a laser line, site elevation or zenith angle. SRC-574's line-by-line calculation (CLM-1237) gives 0.19 to 0.57 for the standard 10.591 um line but up to 0.82 annual (0.96 at 3 km) for a 10.9 um window line, so the figure fits a window line or a high site, not the standard line at sea level. The two overall figures (6.3 and 4.96 per cent) are not reconciled on the page. Slant ranges are not given as one figure. The source defines no DC-to-DC efficiency. The cover date is September 1978; the documentation form gives 15 March 1979.
What it assumes
That Table XVIII's System I is the CO2 version of the selected configuration. Its ground subsystem (73 per cent) differs from the selected design's 75.5 per cent, which is why both 4.96 and 6.3 per cent appear.
Where it comes from
PDF p.3, raw: "The analysis included Space Laser Power Systems with electrical outputs on the ground ranging from 100 to 10, 000 MW, The Space Laser Power System was shown to be feasible and a viable alternate to the microwave Solar Power Satellite." PDF p.24 [14], raw: "The laser power output is from 20 lasers at 45. 5 MW each for a total output of 910 MW." Table IV, raw: "Solar Power Collected (MW) 7,913.0", "Electrical Power to Laser (MW) 3,958.0", "Transmitter Aperture Diameter ( m) 31. 5". PDF p.29 [19], raw: "Cavity Electrical Efficiency 28.3%"; "The resulting overall electrical efficiency of this system is 23%"; "Space relay units are located in geosynchronous equatorial orbit"; Table VI "Receiver Aperture Diameter 31.5 m", "Electrical Power Output 500MW". PDF p.30 [20], raw: "The overall efficiency of this subsystem is 75. 5%"; "The system collects 7, 913 MW of solar energy and outputs 500 MW of electrical power for an overall systems efficiency of 6. 3%." PDF p.78 [68], raw: "the Laser Power Satellite must be at about 900-km (486 nmi) altitude or greater". PDF p.88 [78] Table XVII, System I row, raw: "85 83 - 73 98 95 20.2 99.7 99.7 9.62". PDF p.89 [79] Table XVIII, System I row, raw: "90 85 96 98 73 98. 51.5 4.96". PDF p.89, raw (mu written um): "Reflectivities of better than 99. 85% have been accomplished at 10. 6-um wavelength." PDF p.11 [1], raw: "A 500-MW system was conceptually designed in more detail." Arithmetic: 500 / 7,913 = 6.32 per cent; 910 / 3,958 = 23.0 per cent; 0.90 x 0.85 x 0.96 x 0.98 x 0.73 x 0.98 = 51.5 per cent; 9.62 x 0.515 = 4.95 per cent; electricity into the lasers to busbar, 500 / 3,958 = 12.6 per cent (drafter's arithmetic, not stated by the source).
Basis: MW of solar, laser and electrical power; per cent efficiency by subsystem; aperture diameter in m; wavelength in um
Related records
- Answers question
- QST-036 not published in this release
Cite this
energyaperture.com/c/clm-1232
CLM-1232, Energy Aperture, as of 1978-09.
Connected records
Other published records linked to this one. A list, not a judgement.