Curious Fuel

Curiosity Meets Humans

Thanks to fellow blogger Pied Type who sent me a link to a good WeatherChannel site describing NASA’s Curiosity Mars mission, about to enter its active phase Sunday night. The Curiosity rover is about the size of a MiniCooper car, weighing in at about 2,000 pounds. Looking at its picture got me wondering about its power. It’s interesting, and different from that on previous rovers.

Curiosity is powered by that really nasty and toxic radioactive stuff, plutonium. It is in an active stage of decay and therefore gives off heat. Heat means energy, hence power. This is a big improvement on a solar source like the other rovers because it isn’t limited by the weak light of the distant sun, nor by nightfall. On the other hand, the amount of power is still surprisingly small – the electric power generated is only 125 watts at the start of the mission and would wane to 100 watts in the unlikely case the mission lasted 14 years. This is tiny – imagine the juice of a 100 watt light bulb powering this thing! But it’s still about four times the power of one of the solar rovers.

That the rover’s design is so limited is a measure of the enormous difficulties of operating so very far away. Mars is ⅔ again as far from the sun as Earth, so far that it takes a radio signal 14 minutes to get from there to here, so whatever the rover does, it must do based on careful pre-programming. And it is a very hostile environment with very little air, almost a vacuum compared to Earth’s, and extremely cold temperatures. The radioisotope power plant is a help with that – its excess heat is used to keep the rover’s parts warm.


Aerial Regional-scale Environmental Survey

Mars, through the Hubble Space Telescope.  Credit:  Aerial Regional-scale Environmental Survey (Photo credit: Wikipedia)

Needless to say, low power is quite limiting. The Wikipedia page on Curiosity’s design says its speed is about 98 feet per hour and that it is expected to traverse about 12 miles in its two-year planned mission, so despite the expense and hoopla, this is a fairly modest exploration. That’s not to say, however, that a manned mission would be that much better. This dry, frigid, and hostile rock is terribly remote and human beings would have to carry their Earth environment with them, air, water, food, a vehicle, fuel, a portapotty, and all the rest. No, in my opinion, robots like Curiosity are the only way to go to explore Mars. Here’s hoping its nasty fuel powers it to a great success!

About Jim Wheeler

U. S. Naval Academy, BS, Engineering, 1959; Naval line officer and submariner, 1959 -1981, Commander, USN; The George Washington U., MSA, Management Eng.; Aerospace Engineer, 1981-1999; Resident Gadfly, 1999 - present. Political affiliation: Democratic.
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8 Responses to Curious Fuel

  1. PiedType says:

    Glad you enjoyed that TWC article. Its pictures were the first I’d seen of men next to the rover, giving me an idea of its size. I had no idea it was powered by plutonium, but I guess an old nuke dog like you would know that. You can bet I’ll be glued to the TV tomorrow night. Here’s hoping our networks can tear themselves away from the Olympics long enough to cover something really important.


    • Jim Wheeler says:

      Yep, I too will be avid to see the result. As I see it, the riskiest part of the mission is the landing itself. So far as I can see there is no provision for maneuvering around obstacles as it descends – what if there’s a boulder or a crevice right below it? Yipes. The Wiki Science Lab page has a detailed description of the landing sequence of operation.

      Just to clarify, I am not a “nuke”, just an engineer and conventional-power submariner with a continuing interest in technology. The term “nuke” is used in the Navy to describe someone who has been schooled in the Navy’s nuclear power system and approved for operating and managing same. However I did take the Navy’s officer correspondence course in nuclear engineering – just an overview really – and have “ridden” numerous nuclear submarines as a staff officer and sonar project officer.


  2. Jim Wheeler says:

    @ All,

    Pied Type’s comment about showing Curiosity rover near men for size perspective was a good one, so I have replaced the first photo with a better one showing that.


  3. I have NASA TV on my satellite service, so I’m going to record from around midnight Eastern for 5 or 6 hours (I forget what I set).
    Part of the low power supply needs is Mars’ lower gravity, obviously. The more remarkable is the advance in electronics, especially for us old farts who remember the Apollo programs, and especially Apollo 13’s great battle for survival, tied directly to power. The only thing more amazing to me than what these probes can do today, is how truly primitive the computers were that got man to the Moon and back!
    And if I were on Mars during winter, I would DEFINITELY want a power source that’s nice and warm! 😀


    • Jim Wheeler says:

      I sure agree with your observation about computers in the Apollo era, John. My engineering education was done with a slide rule, 1955 to 1959, and I still remember marveling over a scientific calculator our Navy unit got in the early 1970’s. It was about the size of a grapefruit, came with a padded carrying case, and it could do square roots and exponents! We took turns using it. 😀


  4. ansonburlingame says:

    Just an added observation from a “nuke” related to the use of plutonium, the “nasty stuff” mentioned by Jim.

    We have been using plutonium thermal power sources for decades both in space and right here on earth. For example, some of you may have heard of the submarine “wire tapping” of Soviet undersea cables for years during the Cold War. Those devices were powered by plutonium thermal sources.

    I don’t know about previous Rover sources of power but again know for sure that such plutonium sources were often used. elsewhere. I even visited the DOE facility that manufactured the devices

    Why plutonium you might ask and the answer is simple. That “stuff” has a half life of 25,000 years. Make a device with say 200 watts of power output today and in 25,000 years it is still producing 100 watts of power!!! As well, if you had a thermal lined pocket to reduce the heat transfer, you could safely carry the device in you pocket with no radiological concerns as the radiation emitted cannot go through a piece of paper. But of course I would advise against “eating” the device as well

    Now just imagine “scaling up” such a power source, a heat source. Make it big enough and one could ask when you might want to go at “warp speed”!!! But as well, I doubt that fission energy will be the ultimate power source for such massive amounts of energy in space. Fusion is the future, someday, in my view but we have to learn how to “contain it” along the way.



  5. Jim Wheeler says:

    Actually, the plutonium that powers Curiosity is an isotope of that element, specifically plutonium 238, and it has a half-life of only 87.7 years. It is this instability that makes it a good fuel because the heat is a byproduct of its radioactive decay. An isotope is a form of an element that differs by having more neutrons than the stable form, but the same number of protons. Its decays to U234 and then to lead. I submit that it is a measure of the reality of science, scientific theory if you will, as opposed to religion or faith, that this kind of thing can be done and done predictably. To obtain it, engineers separate it chemically from the byproducts of reprocessing spent nuclear fuel.

    The plutonium 238 in Curiosity is actually a more chemically-stable form, plutonium 238 dioxide, and as Anson says, has been used for the purpose of long-lived power for a long time. It is so safe, when properly packaged, that it has even been used in cardiac pacemakers, some of which were still in service more than 25 years later.

    Because of its short half life, plutonium 238 is unique as a fuel for space applications – nothing else comes close and solar power is no competition, even as far out as Mars. An interesting side note is that the U.S.A. no longer produces it and our sole supplier is Russia.


  6. ansonburlingame says:

    And the reason we must go to Russia for our sources of plutonium is that the U.S. remains a country where it is illegal to reprocess spent reactor fuel, a great source of plutonium, in fact the only source that I know of. Plutonium does not occur naturally, it can only be produced by the fission process, whatever isotope is used.

    The reason the U.S. prevents reprocessing of spent fuel is proliferation concerns, manufacturing weapons grade isotopes, chemically. France and Japan do so a lot and reuse the reprocessed fuel in their commercial reactors as just an example. I also believe Great Britain and Germany do the same but am not certain on that point. As well with operating commercial reactors the ability of Iran to do so is simply is a matter of developing 1940’s era chemical processing facilities to get weapons grade plutonium from spent commerical reactor fuel.

    The nuclear genei came out of the box with the Manhatten Project long ago and no one has figured out a way to put it back in any box. The challenge for the world is how to use that “stuff” safely and efficiently to improve the conditions of life on earth for all humans. Of course I am not talking about building nuclear weapons. I am talking about how to use realtively small amounts of very dangerouw materials safely and in the best interests of the world at large.

    Don’t want ANY plutonium, anywhere? Well, don’t go dig in your backyard. It is THERE for the taking in very small amounts as a direct result of nuclear weapons atmospheric testing done decades ago and it will remain in “your backyard” for some 125,000 years from now. Scientifically, it takes about 5 half lifes for radioactive “stuff” to disappear!



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