[X] My Assistant

[Marcel]

I was wondering: since (especially Spirit) dust accumulation isn't a big concern anymore nowadays, we come to the next vulnerable part of the rovers, being their batteries (which has been discussed some months ago in another thread).
I read that it could take a 1000 load-reload cycles before their capacity declines. Now, suppose that the batteries are history by sol 1000 and they don't have any capacity left: then what ?

Would the rover be dead ? Or would it boot up at sunrise again every morning and be able to do any science or driving solely on the array output ? And could this mean that not even the batteries are a possible fatal malfunction (and thus, the rovers could still continue to stay in touch) ? In that case, this mission could continue well beyond any expectation we all have. A potential fatal breakdown of a cricial (not redundant) part could take many years litterally. Especially thinking about the semiconductors that are so tough, cabling that has been made for the environment up there, everything prooved to be so sustaining, that it gets quite hard to think of anything that ends it right away. They work, they prooved to work for muuuuuuch longer than expected and there's no RTG that can run out of energy.

I want MSL to have arrays. And i want it to land in a windy place.

[djellison]

BUT....

it required lots of surface area, doesnt work at night, unless you're lucky will trend to lower output over time etc etc

Just a 100W RTG will give you 2400 Whrs per sol - 3 x the average for MER, and it'll give you that power whenever you want it and essentially, indefinitely.

Doug

[Guest_Richard Trigaux_*]

BUT....

Just a 100W RTG will give you 2400 Whrs per sol - 3 x the average for MER, and it'll give you that power whenever you want it and essentially, indefinitely.

Doug

RTGs do not work for infinite time. Their power decreases exponentially. The MERs have this problem with the radioactive sources which power the AlphaXray detector and another instrument, which now need several nights to achieve a detailed integration. Yes RTGs can last many years, but they are not perfect. And once he power lost, there is no hope to recover.

A spin wheel may authorize a RTG to accumulate energy and have a much higher peak power. But this is heavy too.

At last RTGs emit strong radiations, I once saw the radiation map of Cassini, it was dreadful, with neutrons and all, electronic parts have to be hardened. For this reason the RTGs of Cassini were at the end of a long mast, but this cannot be done aboard a rover

This is not to dismiss RTGs, but to say they are not a perfect solution.

Eventually an improvement of RTGs would be to load them with a low-energy isotope which decays in a stronger isotope. I do not know if we can find such a pair of isotopes, but if yes we may have a RTG with a low power at launch, and at maximum power at mission time, in place of wasting power during interplanetary flight.

[abalone]

At last RTGs emit strong radiations, I once saw the radiation map of Cassini, it was dreadful, with neutrons and all, electronic parts have to be hardened. For this reason the RTGs of Cassini were at the end of a long mast, but this cannot be done aboard a rover

RTGs emit almost no radiations outside their own casing. The Plutonium-238 that is used is chosen because, among other properties, it is an alpha emmitter. Apart from the heat produced by it, it would be able to be handled with cotton gloves as essentially the only protection

[Guest_Richard Trigaux_*]

RTGs emit almost no radiations outside their own casing. The Plutonium-238 that is used is chosen because, among other properties, it is  an alpha emmitter. Apart from the heat produced by it, it would be able to be handled with cotton gloves as essentially the only protection

See here the properties of Pu238 http://environmentalchemistry.com/yogi/periodic/Pu-pg2.html
it has spontaneous fission, so that it emits neutrons. I remember well, having somewhat involved in Huygens, I was showed this map of Cassini radiations around the RTGs, for purposes of evaluating electronic components. Maybe the neutron flux is not hight, but if you multiply by the mission duration, it becomes a stress to be considered for electronic parts. (and also for the staff in factory, as we cannot protect ourselves from neutrons).


By the way, PU238 has a half-life of 84 years, so my argument falls short.



Also Pu238 decays in U234 with a period of 245,500 years, so it is a long-lived nuclear waste. I know we are not living in Mars for long, but many things may happen in 245500 years...


With my opinion, we could choose shorter lived isotopes, which can wield more power. But they are perhaps more expensive or uncommon.

[abalone]

See here the properties of Pu238 http://environmentalchemistry.com/yogi/periodic/Pu-pg2.html
it has spontaneous fission, so that it emits neutrons. I remember well, having somewhat involved in Huygens, I was showed this map of Cassini radiations around the RTGs, for purposes of evaluating electronic components.

This is a good article to read, notice the photo of the technician standing next to the RTG without radiation protection

http://en.wikipedia.org/wiki/Radioisotope_...ctric_generator
A quote from this article
"238Pu has become the most widely used fuel for RTGs, in the form of plutonium oxide (PuO2).238Pu has a half-life of 87.7 years, reasonable energy density and exceptionally low gamma and neutron radiation levels."

[SFJCody]

This is a good article to read, notice the photo of the technician standing next to the RTG without radiation protection

http://en.wikipedia.org/wiki/Radioisotope_...ctric_generator

Spoiler for ABC's 'Lost':














Use of an RTG would solve the mystery of the 16 year long radio broadcast