Value chain · CLM-1239
In plain terms
In 1993 US government laboratories and a satellite company planned to shine a powerful red laser from a New Mexico telescope at mirrors left on the Moon and then at a communications satellite, to see whether the satellite's solar panels would register it. The paper shows that without correcting for air turbulence almost all of the beam would miss a satellite that far away.
The claim as recorded
A 1993 Sandia, Air Force Phillips Laboratory and COMSAT team planned ground-to-space laser beaming from the 1.5 m Starfire Optical Range telescope with adaptive optics: first to the Apollo 11, 14 and 15 lunar retro-reflectors, then to the COMSTAR-4 satellite in GEO in eclipse. The laser was a ruby laser at 694.3 nm with 6 ms pulses of 1 to 50 kW. Their estimate (Table 1) gives 4.71 W/m2 on axis at GEO (37 Mm) for the 50 kW demonstration, against a detection threshold of about 3.4 W/m2. An operational GEO case of 300 kW at 840 nm from a 4 m mirror gives 690 W/m2 and a 5.9 m beam radius, against 185 m without atmospheric compensation. Measured so far: the ruby oscillator's divergence was 1.2 +/- 0.2 times the diffraction limit for the first 1 ms at 5 kW. The range's adaptive optics had imaged stars at 0.6 urad FWHM with a Strehl ratio of 0.65 (natural guide star), and at 50 per cent of the theoretical peak with a laser beacon, at 0.85 um.
Evidence behind this: A planning paper by Sandia, the Air Force Phillips Laboratory, COMSAT and contractors; the beaming figures are the authors' estimates, and only the adaptive-optics and laser beam-quality figures are measured.
Scope and limits
A PLAN, NOT A RESULT; GROUND-TO-SPACE, NOT SPACE-TO-GROUND, AND NO ELECTRICAL OUTPUT MEASURED. The irradiances are the authors' estimates. The abstract says "about 4 W/m 2" against 3.4 W/m2 in the body. The results paper (SRC-376) has no text layer, so whether the GEO demonstration happened is not established by any held text. The 5.9 m beam radius is from Table 1; the body text says "6 meters". The adaptive-optics figures are cited to the authors' references 7 and 8.
What it assumes
No assumptions are recorded against this claim.
Where it comes from
PDF p.1, raw: "The demonstrations will utilize the 1.5-m diameter telescope with adaptive optics at the AFPL Starfire Optical Range (SOR) and a ruby laser provided by the Air Force and Sandia (1-50 kW and 6 ms at 694.3 nm). The first targets will be corner-cube retro-reflectors left on the moon by the Apollo 11, 14, and 15 landings." PDF p.5, raw: "With a moderately sized beam director of 4 meters, the beam radius at GEO is 6 meters and the required laser power is 300 kW. Note that without atmospheric compensation, the beam radius would be about 185 meters". PDF p.6 Table 1, rows read across three columns (GEO power beaming, GEO demo, lunar demo), raw: "Laser power _W) ..... 300 50 5"; "Wavelength (lxm) 0.84 0.6943 0.6943"; "Range (Mm) 37 37 384"; "On-axis beam irradiance (W/m 2) 690 4.71 0.0044". PDF p.6, raw: "The satellite proposed for use by COMSAT is COMSTAR-4 (D-4)"; "This corresponds to about 3.4 W/m 2 at 694 nm." PDF p.7, raw: "The measured divergence was 1.2+0.2 times diffraction limit for the first 1 ms of the pulse with a power level of 5 kW." PDF p.3, raw: "formed images of stars having a full width at half maximum (FWHM) intensity of 0.6 rtrad (0.12 arcsec) and peak intensities 65% of the theorctical maximum (Strehl = 0.65)"; "Peak intensities of 50% of the theoretical maximum have been achieved for a star using a laser beacon".
Basis: laser power in kW; wavelength in nm; range in Mm; on-axis irradiance in W/m2; divergence as a multiple of the diffraction limit
Related records
- Answers question
- QST-026 not published in this releaseQST-036 not published in this release
Cite this
energyaperture.com/c/clm-1239
CLM-1239, Energy Aperture, as of 1993.