Pulsed Fission Fusion Propulsion for Faster Manned Travel Through the Solar System

Robert Adams updated the work on a phase 2 Pulsed Fission-Fusion (PuFF) Propulsion Concept. Robert works at the NASA Marshall Space Flight Center. This system should be able to achieve 15 kW/kg and 30,000 seconds of ISP. This will be orders of magnitude improvement over competing systems such as nuclear electric, solar electric, and nuclear thermal propulsion that suffer from lower available power and inefficient thermodynamic cycles. Puff will meet an unfilled capability needed for manned missions to the outer planets and vastly faster travel throughout the solar system.

A tiny lithium deuteride and uranium 235 pellet will be fired into a shell of structure that will complete a circuit and generate high voltages and pressures that will compress the pellet and cause fission and fusion to occur.

Heat from fission fuel increases the reactivity of the fusion fuel and the neutron flux may breed additional fuel to fuse. Additionally, the neutron flux from the fusion fuel will induce fission. This coupling can drastically reduce the driving energy required to initiate the burn and drastically improve output. This concept has been examined in the past by Winterberg and is being investigated in support of a Pulsed Fission-Fusion (PuFF) engine concept at Marshall Space Flight Center and the University of Alabama in Huntsville.

They are doing many experiments to validate and create designs and they are doing computational models and simulations.

There are potential spinoff materials and technology from their project. Fission Molybdenum-99 is used in nuclear medicine. The decay product of Mo-99, Tc-99m, is the workhorse isotope in nuclear medicine for diagnostic imaging. Tc-99m is used for the detection of disease and for the study of organ structure and function. This is potential a billion market.

They could also develop advances in 3d printing of metals. They will be able to work with high-temperature metals. Higher currents and pulse rates will enable 3d printing with high-temperature metals without high pressures and with better grains and finish.

Research has focused largely on Magnetic Confinement Fusion (MCF) and Inertial Confinement Fusion (ICF). MCF contains plasma at a steady state at low densities as opposed to ICF which implodes small quantities of fuel in ultra-short high-density reactions. These methods struggle to reach the temperatures required due to limitations of materials and instabilities that arise in both processes. Magnetic Confinement Fusion (MCF) also known as Magnetized Target Fusion (MTF) operates at an intermediate density regime and employs a magnetic field to trap charge particles in order to reduce energy lost. This drastically reduces the driving energy required. Research into this method suggests this approach may offer a means of achieving the conditions necessary for nuclear fusion. The PuFF engine research seeks to operate and take advantage of the MIF regime.

The Pulsed Fission-Fusion (PuFF) concept engine uses a z-pinch configuration with a fusion core and a fission liner to boost energy production and reduce power required to drive the reaction, hence a hybrid target. The fission process heats the fusion fuel, increasing the fusion reaction rate. The fusion products then enhance fission reaction. The processes boost each other’s reaction rates.

34 thoughts on “Pulsed Fission Fusion Propulsion for Faster Manned Travel Through the Solar System”

  1. IIRC, the idea was to use antimatter to initiate the fusion event, removing the need for a fission initiator.

  2. I guess its Plutonium then. A multi stage Orion type generation starship might work. Would be expensive. Thermonuclear devices for the first couple of stages since Tritium half-life is 12.5 yrs. Strictly nuclear for the last couple of stages. The number of stages depends on cruising velocity and how light you can make the pushers.

  3. Maybe a half life of 2.6 years isn’t terrible in terms of a very short mission, if it weren’t for the resultant heat production. At .57W/g, a critical mass of Californium 252 would be putting out 2,850 watts of heat.

    Just getting rid of that heat in the vacuum of space would be a difficult undertaking. Keeping your fuel “pellet” from melting before you could detonate it would be challenging.

  4. An half life of 2.6 yrs isn’t that short. And a small critical mass is what we want. But the advantages does not offset the big difference in cost.

  5. Badly. You need to be able to store your fuel without it reaching criticality in storage, and without it throwing off so much decay heat that you’re hard pressed to get rid of it. Californium actually has too small a critical mass for the first purpose, and too short a half life for the second.

  6. I suppose mercury has the advantage of compact tankage. And being an element rather than a compound, the math gets easier.

  7. I don’t remember any antimatter in the original proposals, though no doubt many people have tried to extend the work further (such as the idea to change the heavy compression based hydraulic shock absorbers to much lighter tension structures where the ship is actually behind the puller plate)

    The original work was supposed to be using contemporary tech. So not off-the-shelf as such, but tech where no breakthrough new invention was required. Much as the Apollo project was. Lots of (brilliant) engineering required, but nothing that couldn’t be laid out in a project plan and solved just by doing the work.

    As such, in the 1960s, fission and fusion bombs were available, antimatter was (and still is) not.

  8. Wasn’t there a;so talk of eventually using antimatter at the top end? I think I remember them being confident they could hit 10-20% the speed of light with that energetic reaction.

  9. How big an advantage is there to using a heavy metal like mercury over using something like water which is more easily available most places in the solar system?

  10. Summed up my thoughts. Our interplanetary transfer doctrine has always operated from an assumption of minimal available thrust and power, and we’ve always optimized for low weight, long transfers with minimum performance available. This kind of propulsion technology breaks that paradigm and allows modes of interplanetary travel we’ve never even considered realistic; i.e., multi-planet or multi-moon missions, huge payloads (depending on acceleration as you mention), long lifetime space vehicles. The “pickup truck of the solar system”.

  11. I published a paper at UIUC when I was under George Miley about doping a plasma engine’s exhaust plume with variable charge to mass droplets of liquid indium or mercury to make the exhaust plume heavier and increase thrust at the expense of some ISP. In this case it was our engine concept of a helicon fixed to an IEC in jet mode.

  12. i wonder if this design would work better with elements that have a higher mass than plutonium like maybe californium.

  13. I don’t think it’s overkill for interplanetary. For shortest transfer times, you more or less want to turn 90 deg from the source planet’s orbit around the Sun (give or take, depending on the relative positions of the source and destination), go straight towards the destination, then turn into the destination planet’s orbit.

    As an example, for Earth and Mars, their orbital speeds are 30 and 24 km/s, respectively. The delta-v for a circular turn at constant speed is:

    dv = a*t = (v^2/r)*(θ*r/v) = v*θ,
    where θ is the turn angle in radians, and v and dv have the same units.

    Plugging in pi/2 radians and the above speeds gives ~47 and ~38 km/s for 90 deg turns at Earth and Mars. Add orbital maneuvers near the two planets, and you quickly get close to 100 km/s delta-v. To make the transit even shorter, you’d want to accelerate after the turn, and decelerate in the 2nd half of the trip, which adds still more delta-v.

    If we replace the circular turns with parabolic, the turns may take less delta-v, but you’d still want to accelerate as much as possible if you want minimal transit times.

    Bottom line is, a few hundred km/s isn’t overkill if you want to get there fast. However, this assumes you have enough thrust to accelerate quickly enough, otherwise you simply won’t reach that delta-v. As I’ve pointed out before, high Isp and high thrust require a LOT of power. But a pulsed fission-fusion rocket just might have enough.

  14. Well golly gee thank goodness this here puss rocket can’t blow up with a Hiroshima level of force. Lots of little pulses.

  15. No overkill for Jupiter, Saturn, Pluto, Kuiper Belt flights. Thrust for a massive crewed vehicle would be an issue, not isp. Say low mo/mf values.

  16. You’ve got to take into account acceleration, too, though. Otherwise, why would anybody use anything but ion rockets? Chemical rockets get you your delta V in near step increments, lower thrust rockets deliver it gradually, and it can take a long time for them to achieve the same delta V as the chemical rocket.

    So, for shorter trips, otherwise inferior chemical rocketry can win the race, just from being faster out of the starting gate.

  17. If it works, it should be fairly easy to put a lot of extra propellant into the exhaust to boost the thrust at the expense of exhaust velocity. That is something you would want for merely interplanetary travel.

  18. because of course, nothing can go wrong with huge chemical rockets, which are MORE uncontrollable and can detonate with the power of Hiroshima bomb.

  19. The rocket equation is dV = g0*Isp*ln(m0/mf). So this really depends on the mass ratio m0/mf. A mass ratio of ~7.4 would give ln = 2 (nbfdmd’s answer); a mass ratio of ~2.7 would give ln = 1 (your answer).

    Note that a mass ratio around 7 is reasonable for a chemical rocket. But for a fission-fusion rocket my first guess is that it may be quite a bit lower. So your answer may be closer.

  20. We return to the Orion project but with thermonuclear devices and a magnetic nozzle instead of simple fission devices and an ablative pusher…
    Returning to the 60´s path that we left…

  21. I think that a ship, that it have a max. speed in the order of x50 in relation to the current estate of the art, should reduce the travel from aprox 300 days to less than 10 days, probably a week…

  22. What could possibly go wrong, riding something that uses nuclear fission detonations for propulsion.
    How much EMP shielding would this thing need?

  23. If my math isn’t wrong, that’s about 43 days to Mars on average, which is great, but not any better than other “near term” future propulsion systems I’ve heard about. I got real excited until I saw that % sign.

  24. I think the need of something like this will be really felt when there are people and interests at interplanetary distances wanting or needing a really fast travel option.

    What need this would be is up for speculation, but me thinks it can be that of fast military response.

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