Value chain · CLM-0950
In plain terms
A solar power satellite in geostationary orbit cannot make its beam any tighter than its design figure, because it is too far away to focus more sharply. The same antenna in low orbit could concentrate the beam a thousand times harder, and what stops it is the air breaking down at about 45 km up rather than anything in the satellite.
The claim as recorded
For this 1977 design, the bound on the beam depends on its orbit. From geostationary orbit the assessment states that the array cannot be focused any finer on the earth's surface, so the peak flux density for one SPS "will not be able to exceed the designed 22 mW/cm2". From low Earth orbit the same array is a different object: if focusing were achieved the peak flux density could reach about 24 W/cm2 - a thousand times the GEO design figure - which the assessment gives as the limit set by atmospheric breakdown at about 45 km altitude, and it states that without that breakdown limit the surface figure could approach 240 W/cm2. Its own conclusion is that the impacts of accidental or adverse adaptation of the transmitting array "are potentially enormous in LEO".
Evidence behind this: T3-primary-report. A JPL assessment of the reference design's own focusing behaviour, which is a statement about the design rather than a measurement of hardware.
Scope and limits
THIS IS AN ASSESSMENT OF A 1977 REFERENCE DESIGN AND NOT A GENERAL RESULT ABOUT SPACE SOLAR POWER. The GEO bound follows from that design's aperture and range; a different aperture gives a different bound. THE LEO FIGURE IS CONDITIONAL AND THE CONDITION IS DOING THE WORK - "if focusing were achieved" - and the same page says a focused LEO turn-on "would not appear feasible because of ionospheric breakdown", so the 24 W/cm2 is a bound on a mode the assessment treats as unreachable, not a predicted exposure. NO PROBABILITY IS ATTACHED TO ACCIDENTAL OR ADVERSE ADAPTATION and none should be inferred. THE 22 mW/cm2 IS A DESIGN FIGURE, NOT A MEASUREMENT, and it is a third member of the 22, 23 and 25 mW/cm2 family this register keeps meeting; nothing here establishes any relation between them and the coincidence is recorded rather than explained.
What it assumes
No assumptions are recorded against this claim.
Where it comes from
All four spans read from SRC-450 PDF p.26 and re-verified on registration. "the peak flux density could reach about 24 W/cm2" and "are potentially enormous in LEO" match RAW; "which is the approximate limit determined by atmospheric breakdown at about 45 km altitude" matches at the normalised level. THE GEO SENTENCE MATCHES ONLY AFTER DEPUNCTUATION AND IS THEREFORE TRANSCRIBED, NOT QUOTED: the raw text layer reads "the peak flux density for one . SPS array in GEO will not be able to exceed the designed 22 mW/cm2", with a stray full stop inside the phrase, and a rendering is not silently repaired and then presented as verbatim. The parenthetical on standard temperature and pressure also renders corruptly, as "1 2 NW/cm 2", and is not relied on here.
Related records
- Answers question
- QST-001 not published in this release
Cite this
energyaperture.com/c/clm-0950
CLM-0950, Energy Aperture, as of 1977.
Connected records
Other published records linked to this one. A list, not a judgement.
- Also from SRC-450
- CLM-0949There is a standard international curve describing how quickly an antenna's stray radiation should fall away off-axis. The SPS pattern...CLM-0951The usual way to stop a strong transmitter interfering with other radio users is to smear its power across a wide band. For a solar power...CLM-0952A solar power satellite would have to stay below published interference limits, and the limits differ by who is being protected. Microwave...CLM-0969If the tubes are only 70 per cent efficient, the transmitter's own face is not big enough to get rid of the heat they make, even spread...CLM-1408In the late 1970s, US studies sketched receiving stations raised on posts or legs so the ground beneath could still be farmed or built on...CLM-1413A 1977 NASA-funded report says the metal mesh behind a receiving station's antennas can be about three-quarters open to light while letting...