Value chain · CLM-1114
In plain terms
The 1977 silicon design assumed an 18 per cent cell that did not yet exist, doubled the sunlight on it with cheap plastic mirrors, and got about 258 watts per square metre of blanket at the start of life, at a cell temperature of over 100 degrees.
The claim as recorded
Boeing's July 1977 reference silicon array is defined cell by cell: silicon, n-on-p, 2 ohm-cm, 5 cm by 10 cm with both contacts on the back, "18 PERCENT WITH AIR MASS ZERO SUNLIGHT, 25 C", under a 2-mil (50 um) electrostatically bonded fused silica cover chosen as the compromise between cover mass and radiation loss; at geometric concentration ratio 2 from aluminised Kapton reflectors at 60 degrees with "0.9 reflectance", the cell sees 257.07 mW/cm2 ("S = 135.3 + 0.9 x 135.3") at 115 C, and with a -0.43 per cent per degree C power coefficient and blanket factors of 0.96, 0.98, 0.99 and 0.975 the initial blanket output is "25.76 mW/cm2 = 257.6 W/m2"; the reflectance was later found to be 0.85, reducing the cell temperature to 106 C, a revision the report says would not have changed the trade conclusions.
Evidence behind this: T3-contractor reference array definition, Part I of the Boeing system definition study; a 1987-projected cell, not a measured one.
Scope and limits
A 1977 PART I DEFINITION, SUPERSEDED BY THE 1978 REFERENCE SYSTEM'S 17.3 PER CENT CELL AT CR 1 (CLM-0974, CLM-0201) - this record is the design the reference system moved away from, and the report's own trade (CLM-1117) is what moved it. The 18 per cent is a projection with no test data ("Test data from such cells is obviously not available", normalised, PDF 135). The 257.6 W/m2 is per square metre of blanket, not of collecting area.
What it assumes
The "1987 solar cells which are predicted to have an efficiency of 18 percent" (PDF 135, raw); AM0 at 135.3 mW/cm2.
Where it comes from
PDF 41 / printed 35, Table 3.2-1 (layer with the page's capitals): "18 PERCENT WITH AIR" MASS ZERO SUNLIGHT, 25 C (normalised); "2 OHM" -CM (raw); "5 CM WIDE" 10 CM LONG (squashed); N-ON-P and "2-MIL FUSED SILICA, ELECTROSTATIC-BONDED" (render readings); the cover rationale "BEST COMPROMISE" between thicker covers "INCREASING ARRAY WEIGHT" and thinner covers "INCREASING WEIGHT BECAUSE OF GREATER AREA TO COMPENSATE FOR GREATER LOSS OF POWER FROM RADIATION DEGRADATION DURING 30-YEAR LIFE" (render reading). PDF 40 / printed 34, raw: "A 257.07 mW/cm2 solar intensity was used"; "having a 0.9 reflectance"; normalised: "We used a -0.43 percent per" degree C temperature coefficient of maximum power; the 0.85 reflectance and 106 C sentences are render readings. PDF 42 / printed 36, Table 3.2-2 (layer): "S = 135.3 + 0.9 x 135.3 = 257.07 mW/cm2"; "Lost area = 0.96 Cover absorption = 0.98 Cell mismatch = 0.99 I2R loss in section = 0.975 Total = 0.9081"; "P0 = 257.07 x 0.18 (1 - 0.0043 [115 C - 25 C]) (0.9081) = 25.76 mW/cm2 = 257.6 W/m2". PDF 39 / printed 33: the reference array "modified by the incorporation of 50" um "2 mil) fused silica covers" for "more-optimum protection" from solar-flare protons over 30 years (raw fragments). Recomputed: 135.3 x 1.9 = 257.07; 0.96 x 0.98 x 0.99 x 0.975 = 0.9081; 257.07 x 0.18 x (1 - 0.0043 x 90) x 0.9081 = 257.07 x 0.18 x 0.613 x 0.9081 = 25.76 mW/cm2.
Basis: per cent at AM0 25 C; mW/cm2 at the cell; W/m2 of blanket; degrees C
Related records
- Answers question
- QST-018 not published in this release
Cite this
energyaperture.com/c/clm-1114
CLM-1114, Energy Aperture, as of 1977-07.
Connected records
Other published records linked to this one. A list, not a judgement.
- Also from SRC-475
- CLM-1115Mirrors that doubled the light only added 40 per cent to the output, because the cells ran hot and the mirrors were not flat; after thirty...CLM-1116Thirty years of radiation behind a hair-thin glass cover was expected to take a third of the cell's power; a cover three times thicker...CLM-1117The 1977 study found the cheapest way to keep a silicon satellite at full power was to heal the radiation damage in place rather than build...CLM-1118In 1977 five radiation-damaged cells were healed with a laser or an electron gun, getting back between a fifth and a half of what they had...CLM-1120In 1977 the gallium arsenide option rested on a 20 per cent cell nobody had made, an assumption that it would still be near 20 per cent...CLM-1121Half a kilogram per square metre for the working blanket, about half of it the silicon itself; per kilowatt delivered on the ground the...CLM-1468The basic idea, a solar power satellite climbing to its final orbit on electric engines run by solar panels it carries, with no separate...