Naked Science Forum
Non Life Sciences => Technology => Topic started by: syhprum on 07/04/2014 13:24:19
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I have been reading the New Scientist discussion as to whether or not Voyager 1 has left the Solar system and one point about its power consumption surprised me that was that most of its electrical power is taken up by heaters used to keep its instruments at an appropriate working temperature.
This seems a very strange system as the electrical power is derived from thermo electrical generators that are probably less than 10% efficient so there must be a great deal of waste heat available why was some of this not diverted for thermal control ?
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Good Question.
I think they wanted to isolate the radioactive part of the spaceship by mounting it on a long arm.
How efficient would a passive heat transfer method like insulated aluminum rods between the heat source and components have been? Could it be regulated?
Perhaps an active system with the heat rods filled with methanol, but then one would need pumps, and would risk freezing the system, and, if the methanol became radioactive, then it could cause systemic problems.
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" if the methanol became radioactive"
Do you think that's likely?
Anyway, when it was a lot nearer the sun it needed less heating, not it's far away, it needs more.
So they had to make the heat transfer controllable.
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When a material is exposed to radioactivity, it can also become radioactive, although perhaps part of it is picking up ions from the primary radioactive source. So, I suppose you are right. If a liquid was piped directly through the Plutonium, then it might pick up the plutonium ions as well as decay products. However, assuming it is run through non radioactive pipes, then the ion transfer may be prevented. Most of the heavy alpha particles would be blocked with minimal shielding.
How much of the "pumping" could be done using convection and the thermal gradient? Does one also need gravity?
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It seems logical considering the problems that would arise with any direct heat transfer scheme that inefficient as it maybe the use of electrical heating was the best solution.
it seems that back in the cold war days much more plutonium was available and the electrical system could be designed for greater output than would be possible today.
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The direction in which the heat is lost to space from these radioactive generators has a small but measurable effect on the velocity of the spacecraft. This caused debate amongst scientists and engineers over many years: see http://en.wikipedia.org/wiki/Pioneer_anomaly
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It seems logical considering the problems that would arise with any direct heat transfer scheme that inefficient as it maybe the use of electrical heating was the best solution.
Weight, durability, and longevity may be also issues.
One might envision a nice heat pipe system, and the methanol pump, and etc. Undoubtedly it weights much more than the electric heating elements, it might be difficult to configure backups, and a leak or frozen pipe could be catastrophic.
Undoubtedly it would not be a single component that would require heat, but a few elements scattered around the craft. Some components, especially electrical components, however, may be perfectly happy operating in a dry, very very cold environment, especially if the temperature remains fairly constant.
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I understand that experiments are to be made to test what heaters can be switched off without impairing the performance, it takes a very brave technician to do experiments on a 40 year old $3 Billion piece of equipment one must have a very good arrangement for buck passing if something gets destroyed !!
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On the flip side, I believe both the Pioneer probes have now shut down. Extending the life of the Voyager probes for a few years may be worth it. Since the Voyager program there have been other probes sent to most of the planets, but none sent as far out into deep space.
I found some notes that at least semiconductors don't like the cold (http://www.thenakedscientists.com/HTML/content/kitchenscience/exp/freezing-electronics-in-liquid-nitrogen/), although one question might be whether they would survive cycles turning them on and off.
I would think one could build models of some of the critical components and experiment with them down here on Earth.
I believe some components of each Voyager probe have already failed. Perhaps one could choose to shut down certain systems on each probe that would allow the probes to compliment each other.
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I don't think anything could be saved by switching loads on an off the amount of electric power available declines at a steady rate if you don't use any of the power available it does not affect the rate of decay of power available this falls due to the decay of the radioactive Plutonium, nothing can be conserved.
The only thing that can be determined by experiment is whether the system can be kept running for a longer time with less power.
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Apparently half of the power loss is from decay of the Plutonium. Half of it is from decay of the thermocouples.
http://en.wikipedia.org/wiki/Voyager_program#Power
As far as I can tell, the two spacecraft weren't originally designed to last 50 years.
I presume the RTG could have been doubled in size if NASA had wanted it to power Voyager for a century or so, perhaps adding a small ion engine for use when excess power was being generated.
It would seem that a system could be devised to upgrade and swap the thermocouples.