Needed: Plutonium-238


Sometimes people ask what they, as a regular citizen can do to help NASA. Emily Lakdawalla at the Planetary Society Blog posted this today, and this is definitely something to write to members of Congress about. NASA is running out of plutonium-238, which is used to power deep space probes, but it’s unclear whether Congress will provide the $30 million that has been requested for the Department of Energy to start new production.

Plutonium-238 has powered dozens of spacecraft, including the Voyager probes, the Galileo mission to Jupiter, and the Cassini spacecraft that is currently sending back such amazing images of Saturn’s rings and moons. Because of spacecraft powered by plutonium-238, we now know — among other things — that there are volcanoes on Jupiter’s moon Io and geysers on Saturn’s moon Enceladus.

Plutonium-238 was a by-product of Cold War activities, and the U.S. has not made any new supplies since the 1980s. Since 1993, all of the plutonium-238 the US has used in space probes has been purchased from Russia. It’s not the same as plutonium-239, which is used in nuclear weapons; a small marshmallow-sized pellet of plutonium-238 gives off heat, which is used to power spacecraft that can’t rely solely on energy from solar panels. Without this energy source, future missions could be canceled.

Emily posted this letter from the chair of the Division of Planetary Sciences of the American Astronomical Society Candy Hansen:

Members of the DPS Federal Relations Subcommittee and the DPS committee carried out our annual “Hill” visits May 13 to key members of Congress. We had two messages – restart domestic production of plutonium-238, and our concerns about R&A carry-over language. With regards to the production of plutonium-238, we are not out of the woods. We still need to convince the members of the Appropriations Subcommittee on Energy and Water that this is a critical need right now – that NASA is already curtailing missions to the outer solar system, and anywhere else plutonium-238 is required (the New Frontiers 3 Announcement of Opportunity ruled out missions which require plutonium-238).

In particular we need constituents of the following states to write letters:

Senate Appropriations Committee Subcommittee on Energy and Water Development:
Dorgan (ND)
Byrd (WV)
Feinstein (CA)
Bennett (UT)
Hutchison (TX)
Murray (WA)
Bond (MO)
Alexander (TN)
Shelby (AL)

Also, Johnson (SD), Cochran (MS), Harkin (IA), Landrieu (LA), Lautenberg (NJ), McConnell (KY), Reed (RI), Tester (MT), Voinovich (OH).

If these are your representatives we need you to write:

House Appropriations Subcommittee on Energy and Water Development:
Visclosky (IN)
Frelinghuysen (NJ)
Edwards (MD)
Pastor (AZ)
Davis (TN)

Or you live in these districts: IN-01, TX-17, AR-01, PA-02, NY-02, OH-17, MA-01, TN-04, CO-03, NJ-11, TN-03, ID-02, MT, CA-44 and LA-05.

We have a handout that you may wish to send with your letter.

For more background and a letter template, see this page.

Thanks for your efforts!

Candy Hansen

22 Replies to “Needed: Plutonium-238”

  1. Great to see the initiative and process in action but no thank you.

    The brief 87.7 years half-life of Pu-238 fueled RTGs is itself a seriously limiting factor in the spacecraft’s use-by date.

    The longest travelled spacecraft, Voyager 2 launched in 1977, has been progressively shutting down systems due to falling Pu-238 RTG power levels since 2003 and will be dead in less than fifteen years having travelled barely a fraction of the distance out of the solar system towards the nearest star system.

    Upcoming exploration programmes such as the 2020 Europa Jupiter System Mission will have energy intensive tasks such as drilling through Europa’s 10-100km ice shell. Here, a 500W Pu-238 RTG would be next to useless.

    A replacement for Pu-238 RTGs such a compact nuclear reactor with conventional nuclear fuel is required and available, but it’s not NASA that’s leading the field.

    To date NASA has flown 1 compact nuclear reactor and 41 RTGs to power 24 systems into space.
    Meanwhile, the Russians have flown 35 compact nuclear reactors and 2 RTGs to power 37 systems into space.

    From the late 1980’s, Russian TOPAZ compact nuclear reactors were launched into space and could generate 5kW of electrical and 150kW of thermal power. Later, the DOD showed interest in testing and flying the Russian ENISEY reactor.

    Given that NASA …
    – does not hold a stock pile Pu-238,
    – does not hold the technological lead in the field of generating plentiful and reliable electrical power for space applications,
    – has many power hungry science missions to deliver and
    – must operate in the new spirit of commercialization rather than pursuing costly and lengthy in-house solutions,
    then NASA should be encouraged down the path taken by the DOD and see what options the international marketplace has to offer.

    Whatever happens, good luck with your petition. At least it promotes NASA’s responsibility to deliver the science missions without undue delay.

  2. I’m not American, but I feel a strong urge to write anyway. More Pu-238!!! $30M is peanuts for such a valuable commodity.

    PS – If you are opposed to the use of radioactive material to power spacecraft, you are wrong, and therefore your opinion doesn’t count.

  3. [Rant]
    In 2009, football (soccer) player Cristiano Ronaldo was transferred from Manchester United to Real Madrid for bloody £80 million (€96M; US$116M), which would buy more than three of those production runs at $30 million each, but the very moment such a ‘star’ player receives a minor kick in the shins, he falls over and rolls about in ‘agony’ like some big girl’s blouse!

    We need to get our bloody economic priorities right on this Earth!

  4. Following on from TerryG’s comments with regards perhaps using Russian compact reactors, there is another, American option for compact reactors.

    The US Navy has a long history of building (fairly) compact reactors, and I seem to remember them working on ever smaller units.

    This would allow small reactors to fly (which I agree with), while pleasing congress by keeping the money in the US.

    Seems logical to leverage the experience of the Navy also.

  5. @ TerryG,

    Both of your links have a rogue double quotation mark at the end of each URL, so they don’t work directly; however, they both work once the quotation marks are removed manually — thanks anyway.

  6. Hello, I am ex Russian scientist working formerly with nuclear materials. We have 27.43Kg Plutonium 238 deposited in research facility unfortunately bankruptcy is happening and facility is under control of bank. If payment of 1.4million US dollars can be made into bank account to secure facility from creditor we share profits from Plutonium sale 60/40 with investor. Please email [email protected] for details of money transfer.

  7. I’ll have to agree with Astrofiend; both the Planetary Society and UT didn’t think of trying to rope in the international readership to help, and this is neither a nuclear safety issue nor an internal US concern as it affects international science and exploration efforts.

    @ TerryG:

    That is interesting, but I always thought RTGs were preferred because they were more compact and longer lived. And indeed reactor references compare unfavorably:

    Weight range: 2 – 60 kg
    Power range: 2-300 W
    Time range: 10 – 40 y

    Weight range: 300 – 1100 kg
    Power range: 650 – 100 000 W
    Time range: 0.3 – 5 y*

    * Project Prometheus engines are designed for a 7-10 y lifetime and reactor power, so apparently there are desires to extend the current capability of these systems somewhat.

    Specifically, the current TOPAZ, the TOPAZ-2, masses in at 1.1 Mg.

    [I also note that Russian RTGs were powered with Po-110 despite having a mere ~ 0.3 y half life. Apparently it generates power like crazy, while it lasts.]

    Also, the new Stirling ASRG prioritize mass to power, sacrificing a 5 W/kg power ratio down to 4 W/kg. Either a strategy to save Pu-238 is in place, or a strategy to maximize ROI by lowering mass and associated cost. (Or they simply gave up on a costly redevelopment of production of the earlier more efficient thermocouples again.) If the later, it seems reactors don’t fit current program strategies.

  8. @ IVAN3MAN_AT_LARGE Thank you, my bad.

    @ tek_604. Shrewd and impeccable logic. The DoE and more so the USN are a significant talent pool.
    The first generation of non-nuclear submarines struggled to make fleet speed until the USN leveraged diesel-electric technology originally developed for powering railroad locomotives. The USN have long since become experts in compact nuclear power applications and have much to offer in powering the space program.

  9. D’oh! The “weight range” should be “mass range” for space applications. More seriously mistake, ~ 40 y is my projected minimum lifetime for Voyager, they max out at 32 y so far but they are the battery bunnies of space. (Not that Hayabusa doesn’t try to compete in taking abuse and keep on going.)

  10. Lats comment spelled while undergoing extreme coffee shortage; “more seriously” indeed.

  11. Over here in Europe, because of the strong anti-nuclear movement, it’s rather difficult to convince people that it’s okay to use plutonium in spacecrafts. As far as I’m concerned, I do favor the peaceful use of nuclear power, but, sorry to say, the … er … argumentation of some persons is counterproductive.

  12. To help NASA with the shortage of PU238, They can have mine, if I could just find it in my cluttered apartment ! You know how stuff gets mislaid! 🙂

    For you people at several Government Agencys, the above was joke! My apt isn’t really that cluttered.

  13. So what is the state of development for advancing thermocouples? I would think that improved thermocuples could be useful in hybrid cars by converting some of the heat from the gas engine into electricity. So much of the energy is lost to heat. That’s like “free” energy right there.

    I’ve always wondered about this because if one can power a probe with just a heat source and thermocouples, couldn’t this be used to increase the fuel economy in hybrids? I’m guessing there are physical limitations that would prevent this from becoming useful.

  14. There are a lot of good comments above. One thing I’m curious about is this. When Pu-238 was an unwanted byproduct of weapons manufacture, it was fairly cheap. Now that it is scarce, why not use Gd-148? It has nearly the same half-life, and gives off more thermal energy per gram than Pu-238, and neither it, nor its decay product (Sm-144) are chemically very toxic.

  15. it’s rather difficult to convince people that it’s okay to use plutonium in spacecrafts

    Yes… Then I did the investigation for my previous comment, I noted that the Apollo-13 RTG (for the landing station) survived reentrance intact as it was designed to do in similar accidents. No radioactive leaks were detected.

    The RTG's radioactivity will die in a few hundred years. So it's actually not a problem.

    @ antoniseb:

    Good analysis! "Gd-148 half-life 75.0 years". Yes, what is up with that?

    (But how do you make the Gd-148 isotope?)

  16. @Torbjörn Larsson OM and @antoniseb,

    Gadolinium-148, as a heat source in RTGs, is ideal in terms of emissions because it decays directly to a stable nuclide (samarium-144) and emits no secondary radiation. However, Gd-148 can only be produced by using a proton accelerator, rather than a reactor. Even if an accelerator were devoted full-time to the production of Gd-148, the output would be only a few grams per year. There is no known or projected method for making kg quantities of this isotope in a year’s time.*

    *Source: Radioisotope Power Systems: An Imperative for Maintaining U.S. Leadership in Space Exploration.

  17. Ah, thanks IAL! So, back to PU again…

    Ps Edit facilities, huh?! Or maybe, simpler, I’ll register “Torbjorn Larsson SNAFU”.

  18. Reminds me of the ‘hot’ controversy surrounding the launch of the Cassini Mission…aka, “The sky is falling!’

  19. @Torbjorn Larsson OM Great links thanks. You are right in pointing out that there are applications where RTGs are more suitable than compact reactors. RTGs are maintenance-free, highly reliable, have no moving parts, are long lived, less massive and ideal if limited power output will suffice. However, the operating life of a compact reactor can be pushed far beyond what is seen in current applications.

    Time range: 0.3 – 5 y*
    * Project Prometheus engines are designed for a 7-10 y life time

    The designed life span of a reactor is tailored to suit the particular application, so it is not surprising that naval reactors are built to run for not much more than the 40 year life span of the ship. The commercial reactor at Calder Hall in Cumbria, 1956 – 2003, was retired as world’s oldest reactor due to the relatively high overheads of operating such a small plant, but technically could have continued to operate.

    Normally when operating a reactor, fresh fuel rods are fissioned until 3% percent depleted, then removed, allowed to cool and then reprocessed for further use. On long duration voyages to the outer solar system or further, the complexity of operating a reactor can be lowered simply by ejecting the spent fuel rods along the way and replacing them with stored fuel rods as required, analogous to discarding spent rocket stages. Running the reactor at less than 100% of maximum rated output also conserves the reactor’s life.

    Development of the most powerful compact reactor for a space application to-date is currently being undertaken by Roscosmos, who have funding to develop a 1,000kW reactor for nuclear propulsion and electrical power generation for an upcoming Mars mission. The design, whose details will be published in the next two years, is expected to be flight ready at the end of this decade. There is no word yet on the reactor’s life time, but it will no doubt be as low as the two year duration of the round trip to Mars.

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