Value chain · CLM-1099
In plain terms
Boeing's 1977 sum gave the ground receiver 85 per cent, said it was probably a little low, and drew the trade that sets a rectenna's size: spreading the power evenly across the transmitter needs the smallest transmitter but wastes the most power outside the receiver's edge, and tapering the power towards the transmitter's edge makes the transmitter bigger and wastes less.
The claim as recorded
Boeing's December 1977 MPTS chain (Table 6-12) puts the rectenna's RF-DC efficiency at .848 nominal with a minimum of .79 and a maximum of .92, beam intercept at .95 (.90 to .98), grid interfacing at .97 (.96 to .98) and the MPTS total at .563 (.412 to .683); the .848 "was derived by numerical integration of measured and projected efficiency values" of dipole-fed GaAs rectifiers over the beam's intensity profile, and the report calls it "probably slightly pessimistic" because the cost-optimised rectenna omits the low-intensity outer beam and because Raytheon and JPL projections were higher, projections "which need to be verified experimentally". Its sizing figures state the relationship the register lacked: for a rectenna radius to first null of 6,485 m, 5 GW delivered and an assumed rectenna efficiency of 88 per cent, the radiated power is 5 GW divided by 0.88 and by the taper's collection efficiency to the first null, giving 6.77 GW at a 416 m spacetenna radius for uniform illumination (.840), 5.89 GW at 500 m for a 10 dB Gaussian (.965), 5.75 GW at 562 m for 15 dB (.988), 5.70 GW at 651 m for 20 dB (.998) and 5.68 GW at 765 m for an inflected Bessel taper (.999).
Evidence behind this: T3-contractor reference chain and sizing figures; the rectenna row is an integral over a JPL curve, not a measurement.
Scope and limits
THE .848 IS AN INTEGRAL OVER A CURVE THIS VOLUME DOES NOT PRINT, AND THE 88 PER CENT OF THE SIZING FIGURES IS "ASSUMED"; the two rectenna efficiencies in the same document differ by 3 points. The sizing figures are for a rectenna out to the first null of each pattern, which is 13 km across, not the cost-optimised receiver the text says stops short of it. The volume carries no rectenna cost, mass or element count (searched: "rectenna cost", "rectenna mass", "billion elements" zero); its section 7.2 says rectenna optimisation "received little attention in the current SPS study".
What it assumes
A 36,000 km range and a 1 km transmit aperture; the JPL rectification curve is not reproduced in this volume.
Where it comes from
PDF 213 / printed 194, Table 6-12 render read: ROTARY JOINT 1.0; POWER DISTRIBUTION AND PROCESSING .97 .95 .98; DC-RF CONVERSION .85 .80 .86; WAVEGUIDE I2R .985; IDEAL BEAM .965 .965 .99; INTER-SUBARRAY .956 .88 .97; INTRA-SUBARRAY .981 .97 .99; ATMOSPHERIC ABSORPTION .98; BEAM INTERCEPT .95 .90 .98; RECTENNA RF-DC .848 .79 .92; GRID INTERFACING .97 .96 .98; MPTS TOTAL .563 .412 .683 (columns NOMINAL, MINIMUM, MAXIMUM). PDF 215 / printed 196, normalised: "was derived by numerical integration of measured and projected efficiency values"; "The current reference value is probably slightly pessimistic for two reasons"; raw: "which need to be verified experimentally"; raw: "The grid interface efficiency of 97" per cent is a 2 per cent loss in solid-state power conditioning and 1 per cent in distribution (render reading). PDF 49 / printed 29, raw: "Coupled with a curve of rectification efficiency vs. power density (obtained from JPL)". PDF 48 / printed 28, render and crops read: "RECTENNA RADIUS TO FIRST NULL = 6,485 METERS", "DELIVERED GROUND POWER = 5GW", "ASSUMED RECTENNA EFFICIENCY = 88%"; Figure 2-18 inset: UNIFORM 416m 6.77GW; 10 dB GAUSSIAN 500m 5.89GW; 15 dB GAUSSIAN 562m 5.75GW; 20 dB GAUSSIAN 651m 5.70GW; INFLECTED BESSEL 765m 5.68GW; Figure 2-19 table: collection efficiency (to first null) .840, .965, .988, .998, .999 with the same radiated powers; Figure 2-19's centre densities about 19 to 20 kW/m2 for the three Gaussian tapers, about 17 for the inflected Bessel and a flat 11.5 for uniform. PDF 79 / printed 59, normalised: "a size/cost tradeoff for the rectenna and transmit array has a broad minimum at a 1.0 km array diameter". Arithmetic on the stated figures: 5 / (0.88 x 0.965) = 5.89, 5 / (0.88 x 0.840) = 6.76, 5 / (0.88 x 0.988) = 5.75, 5 / (0.88 x 0.998) = 5.69, 5 / (0.88 x 0.999) = 5.69, reproducing the five powers; 1.8 x 10^-4 rad (the first null on Figure 2-18's axis) x 36,000 km = 6,480 m, the stated radius; the three nominal, minimum and maximum products reproduce .563, .412 and .683.
Basis: efficiency factors; GW radiated for 5 GW delivered; metres of spacetenna radius; metres of rectenna radius to first null
Related records
- Answers question
- QST-007 not published in this release
Cite this
energyaperture.com/c/clm-1099
CLM-1099, Energy Aperture, as of 1977-12.
Connected records
Other published records linked to this one. A list, not a judgement.
- Also from SRC-482
- CLM-1089The higher industrial band would have shrunk the receiving field to a fifth or a third of its size, at the price of a satellite that could...CLM-1100Boeing thought the receiving elements could be spaced almost twice as far apart as Raytheon's, halving their number, and that the receiver...