Value chain · CLM-0889
In plain terms
A beam sent from geostationary orbit cannot be focused to a small point. Diffraction sets a floor of kilometres across, and that floor is fixed once the antenna size and frequency are chosen. The only ways to make the beam more intense are a bigger antenna or more power, both of which are large and obvious.
The claim as recorded
The ground spot of a space solar power downlink is set by diffraction and cannot be made smaller at a given aperture and frequency: d = 2.44 x lambda x R / D gives 10.7 km for the 1978 reference design at 2.45 GHz from a 1 km aperture at geostationary altitude, and 1.6 km for Caltech's CSSPS at 10 GHz from a 1,600 m aperture. The derivation reproduces the 1978 design's own stated 10 km rectenna diameter to within 7 per cent. Peak intensity therefore scales as P x D^2 / (lambda x R)^2 and can be raised only by transmitted power or aperture area, not by focusing.
Evidence behind this: Arithmetic performed here from standard diffraction over held design figures, and validated against a ground dimension the register already holds.
Scope and limits
THIS IS A FLOOR ON SPOT SIZE, NOT A CEILING ON HARM, AND IT SAYS NOTHING ABOUT LASERS. Laser SBSP designs are now held (CLM-1232, CLM-1234); CALC-097 evaluates the same relation for the Lockheed 10.6 um design. It does not establish what intensity is safe, only that intensity cannot be raised by focusing. No held source states this bound; the relation is standard physics applied here to held design figures.
What it assumes
A uniformly illuminated circular aperture, which gives the standard 2.44 first-null coefficient; a tapered illumination widens the spot and does not narrow it, so this is the tightest case. Geostationary altitude for both designs, which both state.
Where it comes from
This is the project's own working, shown in full:
d = 2.44 lambda R / D at R = 35,786 km. At 2.45 GHz (lambda 0.1224 m) from a 1,000 m aperture, d = 10,685 m. At 10 GHz (lambda 0.0300 m) from a 1,600 m aperture, d = 1,636 m. Aperture and frequency for the 1978 design from CLM-0015, for CSSPS from CLM-0296. CLM-0869's support quotes SRC-085's own "10 KM RECTENNA DIAMETER", against 10.69 km derived.
Basis: metres of first-null spot diameter at the ground
Related records
- Answers question
- QST-007 not published in this releaseQST-036 not published in this release
Cite this
energyaperture.com/c/clm-0889
CLM-0889, Energy Aperture, as of 2026-09.