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Comment: Nice atmospheric window, but rainfade KILLS (Score 1) 54

I always post to the wrong duplicate article! ~sarcasm

From my other post:

According to line 'A' on this graph, the atmospheric absorption at 95-100 GHz is fairly low, but this graph shows that rainfade is an absolute killer. Light rain contributes 1 dB/km, which amounts to losing 20.6% of your signal per km. After 10km, you're under 1% of your original signal.

Somewhere between medium and heavy rain you cross the 10 dB/km line - you lose 90% of your signal per km. That ventures into 'unusable' territory very quickly.

Comment: Nice atmospheric window, but rainfade KILLS (Score 1) 1

by Muad'Dave (#48875183) Attached to: TWEETHER Project Promises 10Gbps mmW 92-95GHz Based Wireless Broadband

According to line 'A' on this graph, the atmospheric absorption at 95-100 GHz is fairly low, but this graph shows that rainfade is an absolute killer. Light rain contributes 1 dB/km, which amounts to losing 20.6% of your signal per km. After 10km, you're under 1% of your original signal.

Somewhere between medium and heavy rain you cross the 10 dB/km line - you lose 90% of your signal per km. That ventures into 'unusable' territory very quickly.

Comment: Re:Design failure (Score 1) 130

by Muad'Dave (#48866839) Attached to: Lost Beagle2 Probe Found 'Intact' On Mars

Why you link an article about hypothetical nano technology is bejond me :)

Because it's fascinating, and it mentions the extreme energy density of other 'safe' radionuclides besides Plutonium 238. That was the question that was asked in the parent post, after all. :-)

As for efficiency, I bet a closed-cycle Stirling Engine system could work on Mars with Gd148 as the heat source and a radiative heat sink to space or the (almost non-existent) Mars atmosphere as the sink. Naturally you could parallel the Gd148 sources so that no one source exceeded the max temp for the engine. If you're not willing to do that, there are other non-moving solutions that beat the paltry 3-7% of an RTG.

Comment: Re:Design failure (Score 1) 130

by Muad'Dave (#48848999) Attached to: Lost Beagle2 Probe Found 'Intact' On Mars

You assume RTG technology - I don't and I don't think the linked article does, either.

They discuss Energy Organs here, stating that (emphasis mine):

a sphere of Gd148 emitting ~100 watts with a 75-year half-life and measuring 3.41 cm in diameter with a 5-micron Pt shield glows at 1326 K (e-sub-r for Pt at 1326 K is 0.156; Gd melting point ~1585 K, Pt melting point ~2042 K); this is approximately the decomposition temperature of diamond (into graphite) and well above the combustion point for diamond in air (Section 6.5.3), so Pt-coated sapphire (sapphire melting point ~2310 K) may provide a more stable first wall for the radionuclide energy organ. Carnot thermal efficiency for a heat engine using this source could reach, at most, ~76%.

I'd say that's pretty good efficiency, and given the power levels and temperatures, I think non-RTG technologies should be used. If the system never drops below 0C, why not use a more conventional system?

Plus, you could just use the Gd148 to keep the craft warm and use other means to generate electrical power.

Kill Ugly Processor Architectures - Karl Lehenbauer

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