Value chain · CLM-0970
In plain terms
A 1992 computer model of the same thin-film receiving antenna, sitting in space with nothing but radiation to cool it, found its diodes would overheat well before the sheet itself ran out of cooling capacity. The usable power per square metre came out about nine times lower than the simpler sheet-only estimate.
The claim as recorded
A 1992 three-dimensional finite-element thermal model of Brown's 2.45 GHz Kapton rectenna in low Earth orbit, cooled by radiation alone, finds the diode limited to about 0.55 W of dissipation at a 200 C junction limit, corresponding to an output power density of 620 W/m2 at 85 per cent conversion efficiency, and concludes the design must be changed for higher densities. That is nine times below the plane-radiation ceiling CLM-0941 records for the same hardware at the same efficiency.
Evidence behind this: T3-modelled result, a three-dimensional finite-element thermal model of held hardware. Not a measurement; "measured" does not occur in the document.
Scope and limits
A MODEL, NOT A TEST: nothing in the register tests any radiation-cooled ceiling by measurement (CLM-0948 stands). LEO boundary conditions with Earth infrared and albedo on the foreplane; at GEO those terms largely disappear, so the GEO ceiling is higher than 620 W/m2 by an amount the paper does not compute. Specific to Brown's Kapton design and its ceramic-packaged Schottky diode.
What it assumes
The 200 C junction limit Brown suggested. A single 2.45 GHz design, the SRC-336 hardware.
Where it comes from
p.3: the model confines "heat dissipation to radiation alone"; p.7: low Earth orbit, solar insolation on the reflector plane, albedo and Earth infrared at 237 W/m2 on the foreplane; diode temperature 402 K at 286 mW dissipated in the single cell, 399.6 K shorted, and 399.6, 400.7 and 403.4 K across the three-cell array, the model's own consistency check; that operating point is 1.76 W out per diode, "or about 352 W/m2". p.9, verbatim: taking 200 C "as an upper limit on the diode temperature to ensure reliable rectenna performance, (as suggested by Brown)", "this limits the heat dissipation in the diode to approximately 546 mW or 0.55 Watts. At 85% conversion efficiency of microwave to DC, this corresponds to an output power density of 620 W/m2." And: the rectenna "should either be redesigned to increase heat dissipation or some means of augmenting the heat transfer out of the diode should be provided".
Basis: W per diode dissipated; W/m2 DC output at 85 per cent conversion efficiency; 200 C junction limit
Related records
- Answers question
- QST-002 not published in this releaseQST-018 not published in this release
- Contradicts
- CLM-0941 In space there is no air to carry away the waste heat, so a rectenna's output is limited by how... same hardware; the plane calculation gives 2.33 kW/m2 at 70 per cent and about 5.67 at 85 this gives 620 W/m2 at 85. Brown's figure asks what the plane can radiate; this asks what the diode can conduct to the plane and the second binds first ().CLM-0971 The heat from each tiny rectifier can only escape downwards into the copper it sits on, because...
Cite this
energyaperture.com/c/clm-0970
CLM-0970, Energy Aperture, as of 1992.
Connected records
Other published records linked to this one. A list, not a judgement.
- Also from SRC-339
- CLM-0971The heat from each tiny rectifier can only escape downwards into the copper it sits on, because the two hair-thin gold wires on top barely...
- Contradicted by
- CLM-0941In space there is no air to carry away the waste heat, so a rectenna's output is limited by how much waste heat it can radiate. The report...