July 13, 2015

Boeing's fusion-fission hybrid propulsion patent is weak compared to the detailed NASA NIAC Pulsed Fission-Fusion design

Boeing has a patent for a laser fusion - fission hybrid jet propulsion system.

Boeing claims energy-efficient thrust can be produced by firing lasers at deuterium and tritium and then having the neutrons activate uranium 238 to generate more heat.

* Hot gases produced by the laser induced fusion are pushed out of a nozzle at the back of the engine, creating thrust.
* a neutrons hit a shell of uranium 238 which causes fission and generates lots of heat
* a heat exchanger uses the heat from the fission reaction to drive a turbine that generates the electricity that powers the lasers

They have different configurations
* one configuration generates ISP of about 2000 to 5000 seconds
* another configuration has an ISP of about 5000 to 25000 seconds
* another configuration an ISP of about 100,000 to 250,000.

I am not sure where there is enough innovation in the Boeing concepts for a patent. There have been several prior proposed fusion-fission hybrid propulsion systems.

I look at some other work and focus on the NIAC NASA Pulsed Fission-Fusion design. There is a lot more detailed modeling and work towards experimentation in the NASA Pulsed Fission-fusion design.

Other fusion-fission hybrid propulsion work and pure laser fusion work

Ted Kammash, Ricky Tang and Michael Hartman had a bi-modal fusion propulsion system in which Q-values of about unity or less are needed since the GDM will serve mainly as a neutron source. It is well known that fusion reactions are neutron rich but energy poor, while fission reactions are energy rich but neutron poor. We make use of this fact by considering a system in which the GDM device serves as a fast neutron source surrounded by a blanket of Th232 , which we utilize to breed U233 and simultaneously burn it to produce energy. For a reasonable size blanket and a D-T plasma density, size and temperature, we find that the proposed hybrid system is capable of producing tens of gigawatts of thermal power per centimeter. If we use this power to heat a hydrogen propellant, we find that a seven meter long engine can generate a specific impulse of about 59,000 seconds at a thrust of about 8 mega-newtons at a propellant flow rate of about 130 kg/sec. Such a propulsion capability would allow many meaningful space missions to be carried out in relatively short times. Furthermore, such a hybrid system can generate large amounts of electric power for surface power applications once destination is reached.

The use of fusion energy to propel vehicles in space has been investigated for several decades. Much of the earlier work focused on inertial fusion where laser beams are employed to ignite target pellets containing fusion fuel to produce the needed energy. With the realization that laser systems are massive and complicated, other drivers were examined to see if they can deliver the required energy to the target at much lower mass. Here, the use of antimatter was found to be especially effective. Modest amounts of antiprotons are found to be adequate to trigger fusion propulsion but the engineering challenges associated with this approach6 have to be addressed vigorously in order for it to be realizable. The major issue associated with the use of antimatter is availability since the current annual worldwide production rate stands at nanograms while most fusion propulsion schemes appear to require quantities on the order of several micrograms. With the world effort in achieving fusion power for terrestrial use focused on toroidal devices, such as tokamaks, very little attention was paid to magnetic fusion for propulsion applications. These devices do not appear to lend themselves geometrically for exhausting energetic plasma particles to generate thrust. Open-ended magnetic devices, on the other hand, are found to be especially suitable because they can confine a plasma long enough to be heated before being ejected from one of the mirror ends to produce thrust. Of particular advantage in this regard is the gasdynamic mirror (GDM) whose confinement properties are based on plasmas of such density and temperature as to make the ion-ion collision mean free path much shorter than the length. Under these conditions, the plasma behaves much like a fluid, and its escape from the system is analogous to the flow of a gas from a vessel with a hole. We focus on the GDM as the fusion component of the system we propose in this paper and demonstrate its usefulness for both space power and propulsion applications.

Kammash, Terry, Tang, Ricky and Hartman, Michael, "Fusion-Fission Hybrid Revisited – Potential for Space Applications", AIAA 2009.

Hyde, R. A., Wood, L., and Nuckolls, J., “Prospects for Rocket Propulsion with Laser-Induced Fusion Microexplosions,” 8th
Joint Propulsion Specialist Conference, New Orleans, LA, 1972, AIAA-1972-1063.

Martin, A. R., and Bond, A., “Project Daedalus,” Journal of the British Interplanetary Society, Supplement Volume, 1978.

Kammash, T., and Galbraith, D. L., “A Fusion Reactor for Space Applications,” Fusion Technology, Vol. 12, No. 11, 1987

NASA Rob Adams talks about fusion propulsion and hybrid pulsed fission fusion propulsion

NASA Scientist Dr Rob Adams speaks about Pulsed Fusion Propulsion, dense plasma focus fusion, z pinch fusion and the possibilities of high density compression of fusion fuels.

NAIC - Pulsed Fission-Fusion (PuFF) Propulsion System

Fission-ignited fusion systems have been operational – in weapon form – since the 1950’s. Leveraging insights gained from the weapons physics program, a Z-Pinch device could be used to ignite a thermonuclear deuterium trigger. The fusion neutrons will induce fission reaction in a surrounding uranium or thorium liner, releasing sufficient energy to further confine and heat the fusion plasma. The combined energy release from fission and fusion would then be directed using a magnetic nozzle to produce useful thrust. This type of concept could provide the efficiency of open cycle fusion propulsion devices with the relative small size and simplicity of fission systems; and would provide a radical improvement in our ability to explore destinations across the solar system and beyond. This proposal is modified version of last year’s proposal - addressing issues raised during that evaluation.

PUFF hybrid vehicle design and mission analysis showed concepts which could reach Mars in 37 days, and 1,000 astronomical unit (AU) interstellar precursor distances in 36 years

phase 1 proposal included modeling the above process first under steady state assumptions and second under a time variant integration. We proposed including these results into a Mars concept vehicle and finally proposing promising conditions to be evaluated experimentally in Phase II. In phase I we quickly realized that we needed to modify our approach. Our steady state work was completed as proposed, and the results indicated that one, a two stage compression system was not needed and two, that we wanted to move away from UF6. The steady state model shows much more margin than expected, to the point that we may well reach breakeven with the Charger – 1 facility, a 572 kJ Marx bank currently under refurbishment at UAH. Additionally we found that using gaseous D-T and UF6, provided a relatively simple prospect of using a pulsed injector, made reaching criticality more difficult. The introduction of large amounts of fluorine meant a radiative sink, sapping power from the fusion plasma and was harder to handle. Therefore we moved to a solid uranium target that held D-T under pressure. In so doing we could move our target closer to criticality and remove any material that did not sustain the reaction.

However in moving to a solid target we complicated our time-variant model, now requiring us to develop phase change algorithms and stress-strain calculations for the solid matrix. We have continued efforts along this line but as expected we did not complete this model. After discussions with NIAC management we moved some of our resources to preparing existing equipment to support an experimental program testing various target configurations under a variety of z-pinches at different power levels. Contained in this report are our results preparing 200 J, 1kJ and 4-8 kJ pulsed power systems as well as a vacuum chamber and diagnostic equipment to evaluate generated plasmas.

We have also completed a point design of PuFF using the results of our steady state model. This design was then used to evaluate a couple missions of interest. At the behest of NIAC management we considered a more advanced version of the Mars mission, resulting in a vehicle that could reach Mars, one way, in 37 days with 25 mT of payload.

At 2:30 in the video below
Rob Adams, NASA Marshall Space Flight Center, 2013 Phase I Fellow
Pulsed Fission-Fusion (PuFF) Propulsion System

Watch live streaming video from niac2014 at livestream.com

Magneto inertial fusion

30-50% burnup in pulses

Long Range Plans

* NIAC Phase II
• Complete Charger 1 refurb
• Ignite PuFF plasma
• Continue magnetic nozzle research

* Charger II
• Construct breadboard PuFF system capable of 10‐20 Hz operation
- Upgrade to flightweight hardware – NASA
- Optimize pulse for maximum power output – DOE
- Astrodynamics, radiation protection, other research goals ‐ Various

SOURCES - US Patent, Youtube, NASA, NIAC, Rob Adams

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