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How the Curiosity Rover's Nuclear Battery Works

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Re: How the Curiosity Rover's Nuclear Battery Works

#51

Post by sliverstorm »

jamesmcn wrote: post #36

Is a thermocouple more efficient than a Sterling engine, or just more reliable because of the lack of moving parts?

Don't forget more compact. A sterling engine would require a generator, which in turn means a regulator and a rectifier. Plus, R&R's aren't very reliable either. When the alternator in your car dies, it's usually the R&R that failed.

The main disadvantages of thermocouples are cost and efficiency, but cost isn't a big deal for mega government projects and efficiency isn't a big deal when the goals are modest (i.e. not flying about like a helicopter) and the power source is amazing (i.e. nuclear decay)

Re: How the Curiosity Rover's Nuclear Battery Works

#52

Post by jerf »

ilamont wrote: post #37

What are the safety implications of launching 10 pounds of plutonium-238 on a rocket that could malfunction or explode before gaining escape velocity? The article says the plutonium would not explode, but what about plutonium particles or radiation entering the atmosphere and ocean?

The same safety implications as launching 10 pounds of anything twenty miles in the air, over an ocean, and subjecting it to an explosion. 10 pounds divided by any realistic footprint is negligible.

Plutonium is dangerous stuff, sure, but it isn't 10 orders of magnitude more dangerous than anything else the way some people act like it is. It's just dangerous, not imbued with an evil malevolent spirit that wants to irradiate your soul.

Bear in mind the Earth is covered in radioactives; it doesn't take all that much division before you've got less radioactivity per acre than already exists naturally, which contrary to apparently popular belief is not 0.

Re: How the Curiosity Rover's Nuclear Battery Works

#53

Post by rlpb »

Shadow6363 wrote: post #35
mpyne wrote: post #24

Earlier quoted context omitted.

It would be easier to lift the rover perhaps, but F=ma, so since the mass of the rover hasn't changed, neither has the acceleration you can develop for a given force applied.

Isn't the friction dependent upon the normal force which on Mars would be less. Therefore, shouldn't the force required to overcome that also be less?

Absolutely, if you were pushing a block along the ground. Fortunately modern "wheel" technology reduces the bearing friction so much that it is no longer a factor. The only friction left is the friction holding the wheel to the ground. This is reduced in reduced gravity, such that wheels are more likely to slip.

Re: How the Curiosity Rover's Nuclear Battery Works

#54

Post by T-hawk »

saraid216 wrote: post #45
danweber wrote: post #34

Earlier quoted context omitted.

Not really. If the rover is on the side of Mars facing away from the Sun, it's almost always facing away from the Earth, too, since the Earth is deeper inside the solar system. Facing the Earth and facing the sun are highly correlated. Seeing one xor the other is possible, but unusual.

He's still right in a very technical, strict sense. I'm too lazy to look up numbers and do the math, but I expect there's a window near the Martian sunrise/sunset when the sun isn't visible over the horizon and we have line of sight. I expect that window is small to the point where no one actually cares. It would be an interesting applied-math problem for a grade-schooler, though.

The geometry of viewing Earth in the Martian sky is the same as viewing Venus in our own Terran sky. The interior planet periodically approaches a certain maximum angular separation from the Sun. Just as we see Venus but not the Sun sometimes in the early morning or evening twilight, Martians (and rovers on Mars) could see Earth but not the Sun at corresponding intervals of Mars' rotation. It's a significant amount of time, up to several hours per day at maximum separation.

The angular separation between the Sun and the Earth as seen from a space probe is significant as far out as Cassini at Saturn. The probe can receive commands from Earth without the signal being overwhelmed by solar radiation, except for a few days each (Earth) year when Earth is too close to the Sun as seen from the spacecraft. (Earth doesn't literally go behind the sun often, thanks to inclination of the planetary orbits plus Cassini's own inclined orbit at Saturn.)

> Our line of sight to Mars is independent from Mars seeing the sun.

Our line of sight to Mars as an entire body is independent, but our line of sight to a particular point on Mars is indeed correlated with that point facing the Sun.

Re: How the Curiosity Rover's Nuclear Battery Works

#55

Post by brc »

jerf wrote: post #52
ilamont wrote: post #37

What are the safety implications of launching 10 pounds of plutonium-238 on a rocket that could malfunction or explode before gaining escape velocity? The article says the plutonium would not explode, but what about plutonium particles or radiation entering the atmosphere and ocean?

The same safety implications as launching 10 pounds of anything twenty miles in the air, over an ocean, and subjecting it to an explosion. 10 pounds divided by any realistic footprint is negligible. Plutonium is dangerous stuff, sure, but it isn't 10 orders of magnitude more dangerous than anything else the way some people act like it is. It's just dangerous, not imbued with an evil malevolent spirit that wants to ir…

Thanks for dousing a small outbreak of nuclear hysteria.

It's depressing that the article has to insert (non explosive) next to the plutonium. Clearly some people must think that this is a bomb waiting to go off at any moment.

Re: How the Curiosity Rover's Nuclear Battery Works

#56

Post by saraid216 »

T-hawk wrote: post #54
saraid216 wrote: post #45

Earlier quoted context omitted.

He's still right in a very technical, strict sense. I'm too lazy to look up numbers and do the math, but I expect there's a window near the Martian sunrise/sunset when the sun isn't visible over the horizon and we have line of sight. I expect that window is small to the point where no one actually cares. It would be an interesting applied-math problem for a grade-schooler, though.

The geometry of viewing Earth in the Martian sky is the same as viewing Venus in our own Terran sky. The interior planet periodically approaches a certain maximum angular separation from the Sun. Just as we see Venus but not the Sun sometimes in the early morning or evening twilight, Martians (and rovers on Mars) could see Earth but not the Sun at corresponding intervals of Mars' rotation. It's a significant amount o…

Do you happen to have illustrations and/or numbers? I was planning to actually look everything up and work it out when I got home from work, but it'd be nice to have confirmation of my results, too.

Re: How the Curiosity Rover's Nuclear Battery Works

#57

Post by aqme28 »

grecy wrote: post #10

Many people here in the far north have extensive solar setups and live completely off-grid. Unfortunately in winter, we only get ~4 hours of sunlight, and it's a pain to sweep snow off the panels every day at ~ -30C to -40C We don't get much wind, and rivers are only liquid for ~4-5 months, so wind and hydro are not popular. I've been investigating commercial thermoelectric couplings as a source in the winter. Everyo…

I absolutely wouldn't recommend it.

Thermoelectric generators are far far less efficient than simple generators (say a Stirling engine). The benefit to them is that a) they are very compact and b) they need no mechanical parts.

It makes sense to put a thermoelectric generator in a satellite or rover because the mechanical parts found in a traditional engine are typically very heavy and more likely to fail.

So if you aren't concerned with a couple dozen pounds and the occasionally maintenance call, just use a wood-burning generator. You'll save about an order of magnitude on costs.

edit: what you're looking for is micro-cogeneration (http://en.wikipedia.org/wiki/MicroCHP)

Re: How the Curiosity Rover's Nuclear Battery Works

#58

Post by ceejayoz »

banana_bread wrote: post #48
ceejayoz wrote: post #17

Earlier quoted context omitted.

The bigger issue using it in pacemakers is it's actually beneficial to have a battery that needs replacing every 10 years or so - pacemaker tech gets better so fast that a 30 year old device would be crap compared to the current generation.

How much better really, if the current one wasn't working well you would find out real quick.

More sophisticated programs (fewer false positives and false negatives), smaller devices, batteries that last longer between charges, etc.

Re: How the Curiosity Rover's Nuclear Battery Works

#59

Post by bennysaurus »

brudgers wrote: post #40
grecy wrote: post #10

Many people here in the far north have extensive solar setups and live completely off-grid. Unfortunately in winter, we only get ~4 hours of sunlight, and it's a pain to sweep snow off the panels every day at ~ -30C to -40C We don't get much wind, and rivers are only liquid for ~4-5 months, so wind and hydro are not popular. I've been investigating commercial thermoelectric couplings as a source in the winter. Everyo…

My understanding of the problem is that nuclear sources tend to be nasty stuff and not the sort of thing that one really wants lay people responsible for discarding.

I think the OP is looking at using their stove as the heat source, not a nuclear battery.

On that note, the idea you're talking about was actually considered for a little while for public use until the dangers were found to outweigh the benefits.

Re: How the Curiosity Rover's Nuclear Battery Works

#60

Post by bigiain »

ScotterC wrote: post #26

This concept was also used in russian lighthouses because it would be cold enough in siberia to create the delta difference needed. http://en.wikipedia.org/wiki/Radioisotope_thermoelectric_gen...

Used as a plot device in a movie called "How I ended last summer":

http://www.imdb.com/title/tt1588875/

I enjoyed it a lot - it's got that real bleak outlook that some of my favorite Russian cinema has, and some _spectacular_ cinematography.

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