Curiosity\'s power source comes from a radioisotope thermoelectric generator (RT

Question

Curiosity's power source comes from a radioisotope thermoelectric generator (RTG) rather than from solar panels like the two Mars Rovers. 2,000 watts of thermal power from alpha particle emission in 4.8 kg of Pu-238 (half-life 87.8 years) yields about 120 watts of electric power via the Seebeck effect (thermocouples). This source slowly declines in power output (~1%/year), and is expected to provide a reliable power source for years.

It appears that the efficiency of Curiosity's RTG is only 120/2000 = 6%. Why is the RTG efficiency so small? Is there a problem maintaining greater hot/cold junction delta temperatures or are there other issues?

Explanation / Answer

Most of the loss is the simple thermal conductivity from the hot (radioactive source) to the cold (atmosphere).

If you have a pretty much infinite cold sink you are going to lose all the heat eventually so getting 6% of it as electricity is pretty good.

Don't know what the internal temperature of the source is, but guessing it's around 300-500C (any higher and the metalurgy gets challenging). And a martian atmosphere of -50C

So the maximum Eff = 1 - (273-50)/(273+300) = 60%, 70% at 500C

I suspect you could get closer to this with a Stirling engine but a thermo-electric generator has no moving parts.

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