Can we power things (like cars or similar rovers) on earth in the same way Perseverance generates power?

Question

I was watching a video on the engineering of Perseverance and it states that the rover is powered by 4.8kg of Plutonium Dioxide. I was wondering if that similar process of electricity generation can be applied here of earth (if it hasn't already). What makes Mars unique in that respect, and why did the team choose radioactive decay over solar panels?

If I had to think of an answer intuitively, I'd say it's because the process is hazardous to organics. Plus, the half life of the material on Mars might be under the time frame of when we actually settle and thrive on Mars (organics and all).

However, I still don't have a clear picture of whether or not we could use this tech for rovers here on earth, whether it's crawling the ocean depths or surveying places where life can't exist. Mars would seem to be more dangerous than say, a salt flat, or the ocean depths.

Answer 1

RTG technology has been applied on Earth, many times, although not for transportation - they don't produce much power for their weight so any RTG powered vehicle would be very slow. Some pacemakers used to have plutonium batteries, and RTGs were used in remote sites to power sensors, lighthouses and the like in remote areas. It isn't used much anymore on Earth because the radioactive materials used can cause radiation sickness and burns, are toxic if ingested or inhaled, extremely costly to produce and there are better alternatives. There's also concerns that if stolen the materials could be used to make a "dirty bomb" - a radiological weapon which could kill or cause illness over a wide area.

The reason they are great for space applications is that they produce some waste heat which is useful for warming the spacecraft, and they deliver constant power day and night. Solar panels tend to get covered with dust on Mars, reducing their generating properties.

Answer 2

RTGs are expensive to produce, can be politically inconvenient to use, and in the form of a plutonium-bearing device, represent a potential nuclear proliferation hazard (though all RTGs might be used to construct a "dirty bomb").

To compound the issue, their power output simply isn't very big... Perseverance's generator cost about 75 million USD and provides a mere 110W fresh (source) which of course will decline a little bit every year.

Their use, therefore, is limited to places where solar and wind won't work, and recovery or access by humans for refuelling is likely to cost many millions of dollars each time. There can't be many places on Earth that fill those requirements, if any. And once you've identified such a place, you need a multi-year mission that only needs a few tens of watts, or a hundred watts at most. That's a pretty specialist piece of kit right there... I can't think of anything that would fit such criteria.

For deep ocean work, batteries and tethers seem to be the order of the day. Face it, you can get one of these awesome toys to go and visit the Titanic in person, and you'd still have plenty of change from 75 million USD.

Answer 3

The answers claiming danger/toxicity are chasing something that's irrelevant. The real issue is that they don't produce all that much power*. If you want a car that can only drive a few hundred meters a day, an RTG will work just fine.

Solar panels aren't all that good on Mars. Not only is the sunlight weaker, and reduced even further by sun angle** and Martian dust storms), they tend to get covered with dust, reducing the power output even further. (Though I've always wondered why the engineers didn't include a brush that could be used by the robotic arm.)

*But they will do that dependably, and for many years without maintenance or refueling. Pioneer 10 & 11 use them, and they're stil working after nearly 50 years. The Voyagers are still running after 40+.

**Remember how the Spirit & Opportunity rovers had to find winter parking spots that would let them tilt towards the sun?

Answer 4

Captain America: "How come [this shield is] not standard issue?"
Howard Stark: "That's the rarest metal on Earth. What you're holding there, that's all we've got."

RTG materials are special

In an RTG, you need some very special traits.

• You need a half-life that is long enough to be useful. The power output will taper off, but you want a long enough half life that it tapers down only a little in the duration of the mission. Iodine-131 is plentiful, but it's gone in a month or two.
• The half-life can't be too long. Decay events are what make the heat, and a long-half-life element like Uranium-235 will not make decay events often enough to make any useful heat.
• The element must decay with the right kind of radiation - a kind trivially blocked. That is for human-safety reasons: a gamma emitter is Right Out. Alpha decay is ideal, as it's stopped by a few centimeters of ordinary air, or the skin - but must not be ingested.
• The material must be anti-proliferation. Meaning that if it were captured by terrorists (or fell out of the sky right into their laps during a failed launch), they must not be able to make an atomic bomb. It cannot be fissile and cannot be a feedstock easily made fissile.
• The material must be possible to separate from its origin and byproduct materials. For instance elements can be separated chemically, but adjacent isotopes of a heavy element are inseparable at an industrial scale. Enrichment of uranium is only possible because they are 3 apart: U-235 and U-238, and still requires state-level commitment (hence America's never-ending sparring match with Iran to prevent them from developing that ability).
• The process that makes it can't quickly over-make it. For instance if you get the material by neutron bombardment, but that also converts the target material into a useless, inseparable material, that doesn't work at all.

Plutonium 238 ticks all the boxes... but...

Plutonium-238 has an 87 year half-life (just right) and is an alpha emitter. As an alpha emitter, it would make a poor 'dirty bomb' because it could only threaten humans as dust they breathed during the initial moments of the attack.

So let's make a bomb? Our buddy has a fission reactor, let's bombard it with neutrons for 30 days to make fissile Pu-239. Great, we've done that, and now we have a slug of mostly Pu-238 with a little Pu-239. Let's do isotopic separation of 238 and 239 -- Oh, snap. Even the United States can't do that. (separate heavy isotopes only 1 atomic weight apart).

Okay then, load it back in the reactor for a year and convert the kaboodle to Pu-239. That's working, except the Pu239 is also absorbing neutrons and becoming Pu240 and Pu241... which are too radioactive and will cause a bomb to misfire. So the fact that it already is plutonium actually helps the nonproliferation issue.

... but it's really hard to make.

As far as how to make Pu238, there are several processes to make it from spent reactor fuel. However, these are special processes, not just a "load it into a common power reactor with the normal fuel rods" situation*. Indeed, both the US and the Russians had shut down their Pu238 production, because their lines were manufacturing it using waste materials from bomb core production, which had ceased under the various START talks. Several countries had to start their own Pu238 manufacture operations, specifically for making RTGs.

Suffice it to say, Pu238 is rare, hard to make, and expensive.

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* Canada's efforts to make it in a reactor is a special exception, because their reactors are a special exception. Unlike conventional BWR and PWR/VVER designs, the CANDU is specifically designed to allow fuel rod changes while the reactor is underway. This is a trait it shares with the Soviet RBMK and weapons reactors such as the Hanford "B", because hey, they were all after the same thing: the ability to achieve criticality on natural uranium, and remove rods in 30-90 days - perfect for breeding weapons grade plutonium. Canada wanted to have the ability in its back pocket, and Russia wanted to be able to scale up their existing ability quickly.

Answer 5

Plutonium is exceedingly toxic both chemically and from a radiation stand point. It also has the potential to be converted into a nuclear weapon if sufficient can be gathered, so it is not the sort of thing that would be sensible to use for a vehicle on Earth. It is also not that plentiful and very expensive to manufacture.

It was used on Mars because it is a solid state power source with no moving parts so little to go wrong and on Mars repair is virtually impossible currently. It is also long lasting and the chemical and radiological issues are not so much of a problem on Mars. A big advantage over solar panels is the ability to operate during long sandstorms and not needing a battery for backup power at night.

Answer 6

In addition to other disadvantages, RTGs have pretty poor power densities, so there are much better solutions for most purposes like vehicles. They are practically restricted to niches where access for maintenance or refuelling is a problem. Such as Mars.

One of the biggest Earth users of RTGs was the Soviet Union, which used at least a thousand, to power unattended lighthouses in places like the high Arctic, where access, while easier than Mars, is still problematic.

But not problematic enough... after the fall of the Soviet Union, their remoteness left them vulnerable to vandalism and potentially worse...

And this has proved a pretty good reason for NOT using them on Earth. It has resulted in a major (and expensive) cleanup operation

Despite the issues, a new variant has been developed, uning a different isotope (Ni63) but it remains to be seen how well this pans out in practice.

Answer 7

However, I still don't have a clear picture of whether or not we could use this tech for rovers here on earth, whether it's crawling the ocean depths or surveying places where life can't exist. Mars would seem to be more dangerous than say, a salt flat, or the ocean depths.

Not quite the same technique as an RTG, but using radioactive material as well (they use nuclear reactors), there are quite a few nuclear-powered vehicles, including:

• Submarines
• Aircraft carriers and other surface ships
• Icebreakers
• And even a few cargo ships

A nuclear reactor is quite a lot bigger, heavier and more complex than an RTG, though, so they're not adapted for a small "rover". There was an attempt to use one on an aircraft but it was still a 16-ton thingy.

Answer 8

To summarize the points from the other answers and keep things easy for future readers, here are the main points against the use of radioisotope thermoelectric generators on earth:

• Not much power output: Power is on the order of a few hundred watts, not very useful for transportation
• Extremely expensive: Millions of dollars per reactor, which makes sense when the budget is large and refueling is extraordinarily expensive, but those conditions rarely exist on earth
• Nuclear proliferation hazard: Putting highly radioactive fission fuel where anyone can get ahold of it is a severe public safety risk, as it can be used to construct a dirty bomb. This is irrelevant on Mars
• Large waste heat output: Radioactive things produce heat, and it never turns off. This is really useful on Mars, where keeping equipment warm in far-below-freezing temperatures is hard to begin with, but problematic in a warm environment where waste heat can damage the very devices it exists to power
• Toxicity: Plutonium used isn't healthy stuff. It's very toxic, and radioactive as well, so a leak would require ridiculous decontamination procedures to prevent radiation poisoning and eventual cancers

Notably, all of these factors are either significantly lesser in impact or non-issues on Mars. Not much power is needed, as the device has a lifetime range on the order of a dozen kilometers/miles. Budgets are extraordinarily high just to get the thing to Mars, so the cost of the device itself matters far less. Nuclear proliferation isn't a problem unless you're concerned about the Martians, as the planet is about as close to inaccessible as you can get. Waste heat is not only not harmful on Mars, it's actually quite helpful, as it reduces the amount of engineering needed to keep the thing warm. Finally, toxicity isn't going to be a problem for quite a while, as I can't imagine many humans will be accidentally stumbling on the device.

For all of these reasons and others, RTG's make a lot of sense on Mars, but the list of situations on Earth where their benefits outweigh their tradeoffs is short to non-existent. Thanks to all the other answerers for the information in this summary, and please do feel free to look through the other answers for more in-depth discussion on any of the above reasons.