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Comment by dkkarthik | Hacker News Reader

Wow, that's super cool. I wonder if this technology is being used on any earth-based applications? If not, I'm assuming there are harmful side effects that don't necessarily affect the space missions. I'd like to learn more about the negatives of this technology basically.

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If this is the same tech I remember, Soviet Russia used them a lot for far-flung lighthouses that couldn't be easily refueled. Many of them are still out there, or have been stolen, vandalized, stripped of metal by unwitting thieves, spreading hazard all around. One was even found underwater.

edit: links:

http://bellona.no/bellona.org/english_import_area/internatio...

http://englishrussia.com/2009/01/06/abandoned-russian-polar-...

There is a movie on Netflix streaming that has some small plot feature tied to one of these these nuclear batteries in a far North Russian weather station:

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

For a short while they were used in implantable pacemakers as 'lifetime' power sources[1]

The main issue is that they're really rather inefficient. The efficiency of the thermocouple at converting thermal->electrical is only about 5-10%, and combined with the cost of shielding, expense of the radioisotope to begin with, and security/safety considerations, they're really only suitable for niche aerospace/defense applications.

Edit: I was curious if anyone had considered a stirling or other heat-engine driven by decay heat, and found https://en.wikipedia.org/wiki/Stirling_Radioisotope_Generato... which looks like it can hit 20+% efficiencies. The downside is that unlike thermo-electric/Seebeck effect converters, they have moving parts that could be a threat to reliability, which is the major issue when you're a planet away from the nearest repair tech.

[1] https://www.orau.org/ptp/collection/Miscellaneous/pacemaker....

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.

There's probably a radiation issue that wouldn't make it suitable for close to human contact. I wonder how much energy the rover needs to move around since the gravity there is considerably weaker.

Rover mass is same on Earth or Mars. So acceleration costs the same. Low gravity also means less friction with the ground, making it somewhat harder to move on Mars.

Climbing hills would be easier on Mars.

Isn't there also an issue of impulse though? There must be an acceleration dip compared to earth since I'm basically pushing a mini cooper on earth but only a bicycle on mars. Note: I'm a scientist so I'm embarrassingly bad at physics.

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?

Wheels need friction to develop acceleration. So its a negative not a positive.

It's only a negative if the vehicle needs to accelerate quickly. So sufficient friction is sufficient, not a negative or a positive.

Given that the batteries store roughly 2.4 kW-h, it's probably safe to assume that the max drive power is less than 500 watts (2.4 kW-h / 10 hours -> 240 watts). Earth side electric vehicles commonly have drive power over 100 kilowatts.

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.

Sometimes used in earth-based applications too. See http://en.wikipedia.org/wiki/Radioisotope_thermoelectric_gen....

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