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Voyager probe RTG energy saving

There have been stories in the news lately about NASA switching the Voyager 1 and 2 probes to using backup thrusters to save energy. This is supposed to save 12 watts by allowing the primary thruster heaters to be turned off.

The articles claim that this energy saving will allow extended lifetime of the power supply, which is a radioisotope thermoelectric generator powererd by decay of plutonium 238.

Huh? How does the electrical load on the thermocouples have any effect on the decay of plutonium?

No explanation is offered. Assuming the life extension is correct, my only guess is that it is some strange second-order effect, like maybe the thermocouples have some sort of electromigration failure mode that is sped up at higher currents... or something.

Anyone know the true story?

Best regards,

Bob Masta DAQARTA v6.02 Data AcQuisition And Real-Time Analysis

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Reply to
Bob Masta
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Not quite...it will extend the life of the probe, which isn't the same thing.

The output of the power supply is steadily dropping. It was 470 Watts at launch (according to Wikipedia) and the JPL article says it's now at 270. Reducing power consumption by the thrusters will allow other systems to function instead.

Reply to
fungus

You have to squeeze plutonium really hard to get juice and then it doesn't taste all that good.

Reply to
BeeJ

I'm not sure how the reactor in space is managed; on earth, the rate of fission is controlled through the use of moderators that can cause it to speed up or slow down. If they can save some energy, that means they can reduce the rate of fission, extending the life of the fuel. But as I said, I don't know whether they use controllable fission or whether the rate is fixed.

--
Life is the living you do, Death is the living you don't do.
		-- Joseph Pintauro
Reply to
Chiron

I think (as in 99% sure) that there is no such form of control. It's a warm lump of plutonium that gets cooler as the decades go by and it decays. It is in thermal contact with the warm junctions of a set of thermocouples, I think, and the cold junctions radiate to cold space. In the usual way, the temperature difference causes a voltage to develop across the thermocouples.

Martin

Reply to
Fleetie

Correct. It's not a "reactor" at all in that there is no "chain reaction" to control/moderate. It's simple radioactive decay of a lump of PU. As the PU decays it generates less heat, less delta-T = less power generated. The "power management" that's going on is simply choosing which instruments to shut down so the thing operates the most interesting experiments (and of course the radios) with the available power left.

Reply to
krw

PU must mean some chemical combination of P and U Plutonium is Pu Phosphorus is P Uranium is U

Reply to
bw

What a moron.

Reply to
krw

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