Value chain · CLM-1238
In plain terms
In 1978 the US energy department asked whether lasers could replace the microwave beam. Its review said the lasers of the day were not good enough, mainly because they wasted too much electricity, but that they might become good enough in time.
The claim as recorded
DOE's 1978 assessment found that "state of the art laser technology currently is not adequate" to meet the SPS laser power transmission requirement, which it set equal to the microwave reference at 0.071 overall system efficiency and 5.70 kg/kW. The nearest laser, the CO2 electric-discharge laser at 18 to 25 per cent efficiency, is "considered to be too low when pumped with a photovoltaic array". It nonetheless judged a laser link "technologically feasible" within the SPS time frame. It reports a NASA Ames group's preference for the CO laser, and it repeats Lockheed's statement that more than 90 per cent of the contiguous US has weather allowing efficient laser transmission more than 50 per cent of the time.
Evidence behind this: A DOE-funded state-of-the-art review (PRC Energy Analysis Company) for the 1978 SPS evaluation programme; expert judgement and literature, no design and no measurement.
Scope and limits
A REVIEW, NOT A DESIGN: "IT WAS CONSIDERED TOO EARLY ... TO ESTABLISH DEFINITIVE DESIGNS" (p.21). The 0.071 is a requirement copied from the microwave reference chain, not a laser result. Appendix G (Space Laser Power System) is by an author of SRC-547, so it is not independent of CLM-1232. Its Lockheed cloud sentence speaks of area, "of the continental United States", where SRC-547 p.78 speaks of population. Appendix F argues for 2 um beams from orbits of "a few thousand kilometers" and a receiver spot "about 50 meters in diameter" at "a few thousand times solar". That is advocacy, and it is not carried into this claim.
What it assumes
No assumptions are recorded against this claim.
Where it comes from
PDF p.7 [vii], raw: "Study findings indicate that state of the art laser technology currently is not adequate to meet the SPS Laser Power Transmission Subsystem (LPTS) requirements."; "provide a reasonable level of confidence that the development of an LPTS is technologically feasible in the time frame required to develop the SPS." PDF p.19 [6] Table 2.2, raw: "LPTS Requirements" ... "SPS system totals* 5.70 0.071 10.00". PDF p.69, raw: "The efficiency of this laser, from 18 to 25 percent, is considered to be too low when pumped with a photovoltaic array."; footnote, raw: "The NASA Ames Laser Research Group 54 prefers the supersonic CO EDL over the co 2 EDL for space-to-ground power transmission". PDF p.36 [24], raw: "Lockheed, in recognizing the cloud cover problem, has stated that more than 90 percent of the continental United States has weather conditions that permit efficient laser transmissions for more than 50 percent of the time." Arithmetic check of the 0.071: 0.151 x 0.800 x 0.800 x 0.860 x 0.860 = 0.0715 (Table 2.2 chain).
Basis: per cent laser efficiency; required SPS system efficiency (fraction) and kg/kW
Related records
- Answers question
- QST-036 not published in this release
Cite this
energyaperture.com/c/clm-1238
CLM-1238, Energy Aperture, as of 1978-10.
Connected records
Other published records linked to this one. A list, not a judgement.