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NIAC Pluto mission talk now available online

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by

Stephanie Thomas
in ,

On Tuesday, August 23rd I had the privilege of giving my talk on our Fusion-Enabled Pluto Orbiter and Lander at the 2016 NIAC Symposium. The video of the LiveStream is now archived and available for viewing. My talk starts at 17:30 minutes in, after Michael VanWoerkom’s NIMPH talk.

The talk was well-received and we had some good questions from the audience and the LiveStream. In retrospect I did wish I had added a slide on our overall program plan in terms of the PFRC machine and temperature and field strength, since I got quite a few questions on those specifics at the poster session. PFRC-1 demonstrated heating electrons to 0.3 keV in 3 ms pulses. The goal of the current machine – PFRC 2 – is heating ions to 1 keV with a 1.2 kG field. The next machine I refer to in the talk, PFRC 3, would initially heat ions to 5 keV with a 10 kG field, and towards the end of its life we would push the field to 80 kG, heat ions to 50 keV, and add some helium-3 to get actual fusion events. The final goal would be 100 second-duration plasmas with a fusion gain between 0.1 and 2. A completed reactor would operate in steady-state.

Thank you NIAC for this opportunity!!

Comments

5 responses to “NIAC Pluto mission talk now available online”

  1. Augustus Avatar
    Augustus

    It’s difficult to find well-informed folks on this subject, but
    you sound like you understand what you’re talking about!
    Thanks

    Reply
  2. ElmarM Avatar
    ElmarM

    Ms Thomas,
    first let me congratulate you on one of the most outstanding presentations at this NIAC symposium.
    I have a few questions (and I apologize if they were already answered and I somehow missed it):

    1. The way I understand it, you are using a Brayton heat engine for the production of on board power. Please correct me if I am wrong, but the products of a D+He3 reaction are charged particles. Wouldn’t it be possible and more weight efficient to use direct conversion to convert some of the energy from the charged particles in the exhaust into electricity? It would be a much simpler system without moving parts. You would safe the weight of the turbine and might get away with less cooling panels (depending on how badly you have to remove the waste heat to protect the reactor and the SCs). Maybe you could then even use the waste heat to create additional thrust (though with relatively low Isp) like a nuclear thermal engine does. In this context, I am wondering why you even have a coast phase.

    2. I would like to understand your current status in relation to the triple product. I see 1 keV heat and you mentioned 300 ms pulse length (confinement time?) . Where is plasma density at right now?

    3. I extrapolated a Q of about 10 from the diagram of the fusion engine. Is that the maximum that can be achieved with this reactor type or is that a limit of the version for space propulsion only? Am I correct when I assume that this is related to the size constraints imposed on the engine by the scrape off layer and that this would only apply to a reactor used for direct propulsion (the direct fusion drive)?

    4. I am confused by your numbers regarding the He3. Your slide says 1158 liters of He3 which would be around 70 kg of He3, provided I did not miscalculate that. Yet in the Q&A with David Kirtley, you mentioned only “hundreds of grams” of He3 for the entire mission. The SOL is supposed to deuterium or hydrogen and I don’t suppose you want to use the much more expensive He3 for cooling the LTSCs. So why so much He3?

    5. I think that the current supply of Helium3 is a real issue for your reactor if you want to use it terrestrially at a scale that would have an impact on climate and economics. Current supply is too low to satisfy the need of a large amount of reactors and if we were to extract He3 from natural gas, we would be talking about 12,000 USD per kg. With the current price of space transportation, mining the moon would also increase the cost of the fuel dramatically. Current cost is 1000s of dollars per kg launched into space and more per kg to the moon.
    I am not sure about the limitations of your reactor concept, but would it be possible to run the reactor on Deuterium only? It would produce He3 in one branch and tritium in the other. The tritium could be used to boost the fusion output compared to a pure D+D reaction (tritium catalyzed deuterium fusion) and the He3 could be used to fuel a dedicated D+He3 reactor.
    If the D+D reaction on its own was economic enough, maybe, the tritium could be stored until it decays into more He3. At a cost of 30,000 USD per gram, it might actually be possible to make more money from selling the tritium than from using it to produce electricity, especially when you factor in the damage from the high energy neutrons produced by D+T. So this could be a viable business model, at least for a few of these reactors, since there is only so much tritium needed in the world right now. Could be a way to make a lot of money even early on, when reactors are not as optimized, yet ( I am assuming that they will get better over time).

    6. You mentioned during the Q&A that you were using high temperature super conductors and that you need those for the next reactor. I understood from your presentation that you expect the SCs needed to generate the 8 Tesla fields to be a significant part of the 50 million development cost for PFRC-3. I am not sure which ones you are planning on using for that. REBCOs can create magnetic fields significantly larger than the 8 Tesla (25 T have been achieved in the lab). If my information about the cost of REBCO tape is correct, then it should cost less than 500,000 USD for all of the 8 magnets I saw in your schematic (at full 25T). Looking at the potential 25 T magnetic fields achievable with REBCOs, I am also wondering whether these stronger magnetic fields could be used to improve the Q, power output and T/W of the DFD.

    Reply
    1. Stephanie Thomas Avatar
      Stephanie Thomas

      Thanks Elmar for the great questions! Since they are so detailed we will email you some comments. In brief on the quantity of 3He, it would have been more exact to list mass, but the volume is intended to be at STP, for comparisons to the existing 3He market. So that is a gaseous volume, not a liquid volume. Running on deuterium only is a possibility for the overall heating method but it will not have the benefits of extremely low neutron production, so those reactors would have different applications. One possibility is using D-D reactors to in fact breed 3He for consumption by the clean reactors.

      Reply
      1. ElmarM Avatar
        ElmarM

        Thanks for the quick reply, Stephanie!
        I knew there must have been a mistake on my side regarding the Helium3. Thanks for the clarification!
        Of course, I know about the neutron issues with D+D and D+T but then most can’t even do that.
        I sent you a more detailed reply via email!
        Thanks again!

        Reply
  3. Space-for-All at HobbySpace » Videos: Presentations at the NASA Innovative Advanced Concepts (NIAC) symposium

    […] More about Stephanie Thomas’s presentation at NIAC Pluto mission talk now available online – Princeton Satellite Systems. […]

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