Value chain · CLM-1162
In plain terms
A satellite would look like Venus all night, and for two minutes near the equinoxes its polished transmitter would flash a full-moon-bright spot 350 km wide across the ground at 150 km a minute; the ferries being built in low orbit would flash brighter still by day. Tilting or curving the panels and roughening the antenna face would cut the glints, though not the Venus-like glow.
The claim as recorded
Boeing's October 1980 brightness study for the reference system (55 km2 of cover-glass solar cells, a 1 km2 antenna, 23 OTVs with 1.6 km2 panels) finds the brightest reflections to be specular glints: "The brightest specular reflection is produced during the daytime by the aluminized backside of the OTV as it nears completion in LEO during the solstices", 2 W/m2 "in a spot about 25 km across (a perfectly flat surface would produce 19 W/m2 in an 8 km spot)" moving at 8 km/s; "At night the brightest specular reflection is from the SPS antenna around the equinoxes", 0.01 W/m2 "in a spot about 350 km across" moving at 150 km per minute so that it crosses a point in "just over two minutes", "Since the beam points at a rectenna on the earth's surface there is no way to avoid reflecting light onto the earth for some geometries"; the SPS solar panels give 0.03 W/m2 flat and 0.0003 misaligned by 5 deg; the antenna glint has "apparent stellar magnitude ... -13.8, comparable to the full moon" and the whole satellite's diffuse reflection -3.6, "comparable to the stellar magnitude of Venus at its brightest"; glints last "from about one second for the OTV/SB in LEO to two minutes for the SPS antenna" with sudden onset ("Enhancements of 10^5 are common"); and the fixes are orientation ("directed away from the earth"), "surface curvature or misalignment of flat panels", and etching or coating the antenna face "to create a diffuse reflection".
Evidence behind this: T3-DOE contractor final report with a stated method (equations (1) and (2), reflectances by material, worst-case geometries); calculated, not measured, and the report says worst case throughout.
Scope and limits
CALCULATED WORST CASES FOR THE 1980 BASELINE SURFACES; the report's own mitigations would remove most of them and no eye-safety threshold is stated to compare against. The summary prints the antenna spot speed as "150 km/sec" where the body and the two-minute crossing say 150 km/min; quoted as printed, read as a slip. The panel misalignment (5 deg for the SPS) is an estimate.
What it assumes
Worst-case geometries, optically flat surfaces where stated, K = 0.8 atmospheric factor, reflectances 0.8 (aluminium) and 0.05 (cover glass, diffuse), as the cases list them.
Where it comes from
PDF 5 / printed 1 (render read): "has 55 km2 of glass covered solar cells that are oriented normal to the sun, as well as a 1 km2 microwave antenna" (normalised); "requires 23 Orbit Transfer Vehicles (OTVs) that have" 1.6 "km2 solar panels oriented normal to the sun during their 6 month transits" (normalised); "The brightest specular reflection is produced during the daytime by the aluminized backside of the OTV as it nears completion in LEO during the solstices" (normalised); "overall, the irradiance is 2 W/m2 in a spot about 25 km across (a perfectly flat surface would produce 19 W/m2 in an 8 km spot) moving at the satellite speed of 8 km/ sec" (normalised); "The cover glass on the front side of the OTV solar cells produces 16 times less illumination" (normalised); "At night the brightest specular reflection is from the SPS antenna around the equinoxes. This flat aluminum surface produces an irradiance of 0.01 W/m2 in a spot about 350 km across which moves at 150 km/sec as the" (normalised; the summary's unit). PDF 58 / printed 55: "The midnight spot diameter at tne equator is about 350 km. Its speed is about 150 km/min so that the time for the spot to cross a point on the earth is just over two minutes" (normalised). PDF 56 / printed 53: "Since the beam points at a rectenna on the earth's surface there is no way to avoid reflecting light onto the earth for some geometries" (normalised); "An irradiance of 0.01 W/m2 is obtained for these conditions" (raw); "the misalignment is estimated to be as much as 5" deg "for the SPS (compared with the 1.5" deg "estimated for the OTV). As a result the irradiance would be reduced up to two orders of magnitude" (normalised). PDF 55 / printed 52: "Here, an irradiance of 0.03 W/m2 is found for optically flat mirror conditions" (raw). PDF 6 / printed 2: "the apparent stellar magnitude of the SPS antenna is -13.8, comparable to the full moon, and the diffuse reflection from the entire SPS is -3.61 comparable to Venus" (normalised); "By slight changes in vehicle orientation the specular reflections from the large solar panels can be directed away from the earth" (normalised); "Another modification is to introduce surface curvature or misalignment of flat panels that diverges the specular beams" (normalised); "the specular surface quality of the SPS antenna, for example, can be eliminated (or sharply reduced) by etching or coating the material to create a diffuse reflection" (normalised). PDF 67 / printed 64: "the SPS in GEO is ccmparable to the stellar magnitude of Venus at its brightest" (normalised, OCR as printed); "of specular reflections varies from about one second for the OTV/SB in LEO to two minutes for the SPS antenna" (normalised); "Enhancements of 105 are common" (raw, the 5 a superscript). PDF 69 / printed 66 (render read): "It is noteworthy that at most the enhancement is only threefold in LEO and 15-fold in GEO beyond normal controlled operations" (normalised). Recomputed: 350 km / 150 km per min = 2.3 min; 19 / 1.2 = 16, the "16 times"; 0.03 / 0.0003 = 100, the "two orders of magnitude"; 56 / 19 = 2.9 (threefold, LEO out of control) and 0.4 / 0.03 = 13 (the "15-fold", GEO).
Basis: W/m2 at the ground; km of spot; km/min of spot travel; apparent stellar magnitude
Cite this
energyaperture.com/c/clm-1162
CLM-1162, Energy Aperture, as of 1980-10.
Connected records
Other published records linked to this one. A list, not a judgement.
- Also from SRC-530
- CLM-1163Between the spring conference paper and the autumn final report, Boeing's figure for how bright a satellite would glow at night fell...CLM-1164The report's worry was not that a satellite could light the ground like the sun. It was that a small bright point in a dark sky reaches an...