Combined Pulsed Deuterium Fusion and Axion Ramjets for Manned Deep Space Mission

[CraigPichach]

Hi all,

Canadian mechanical/chemical engineer here who might have watched too much PBS Spacetime or watching the SpaceX launch wishing was a rocket scientist but wrote down some ideas in a short concept paper "Combined Pulsed Deuterium Fusion and Axion Ramjets for Manned Deep Space Missions".

Here is the link in PDF format: https://documentcloud.adobe.com/link/review?uri=urn:aaid:scds:US:a22de904-ce2e-4cd1-b81c-b7c6d2e6a5a1

I review the concepts of the pulsed "orion" drive, Winterberg's D-D fusion concepts, the Bussard Ramjet, Beckwith's axion drive and the Parkin's starshot publication and put them together in what I hope is a novel interstellar flight concept.

Any advice, recommendations, mark-ups, comments are appreciated.

Thanks,
Craig Pichach

[edzieba]

The 'Axiom drive' appears to be firmly in the 'suspiciously convenient new physics' territory, but the idea of pre-staging accelerated fusion propellant 'droplets' along a flightpath is an interesting one.

[CraigPichach]

Edzieba,

Yes the pulsed deuterium fusion ramjet is certainly more "advanced physics" than the more "new physics" Axion drive concept. I had thought about splitting the papers but figured it was just a conceptual document.

Unfortunately I am not an aerospace engineer that any work I do on this is personal time. I figure any attempt to engage in research to push a peer reviewed paper would actually start on doing the math behind the pre-staging of  fusion propellant 'droplets' (some accelerated) along the flight path, maybe on an inter-solar mission to Titan or. Before thinking about how to move forward wanted to see if there were any real show stoppers on here and if anyone would be interested.

I actually actively monitor the development of explosively pumped flux compression, ion or Super Marx trigger fusion devices (D-T, D-D, etc) because I continuously argue that is a more feasible method of generating fusion power. Indeed in a way we know how to build a "fusion" power plant with today's technology; just detonate Teller–Ulam  devices in an underground chamber full of water to make steam (the problem of course being the need for expensive fissionable material and radioactivity!).

The Axion ramjet comes out of actively monitoring the dark matter experiments. Seems like they are having bad luck finding the WIMP that the axion now seems more likely. Hopefully ADMX proves the legitimacy of the axion and the Primakoff effect that is becomes more "real".

Honestly your response made my day that writing it all down was not for nothing so thank you!!!

Craig Pichach

[CraigPichach]

Sorry, here is the concept in text without having to use the link to PDF. I have attached the images below.

High level concept is to pre-position and pre-accelerate your fusion devices by laser to be triggered as the spacecraft goes by (a "propellantless" Orion. In some cases the devices are staged to boost >0.2c. If axions are real then at ever increasing velocities an axion ramjet is activated using the Primakoff effect. For slowing down the Bussard Ramjet is then activated in which deuterium is produced to the ship and excess hydrogen used as reverse propellant.

Combined Pulsed Deuterium Fusion And Axion Ramjets for Manned Deep Space Missions
Craig Pichach, P.Eng,  June 23 2020

Background

Travelling to distant stars is made difficult by the immense distances involved, the limitations of specific impulse for spacecraft having to produce not just energy but carry propellent and the increasing energy requirements of relativistic space flight. Constant acceleration at 1g has been proposed as it not only provides artificial gravity for the crew but relativistic time dilation allows for exploration of the entire visible universe within a century proper time.  The energy requirements to accelerate the spacecraft to relativistic speeds however becomes exponentially great.

Pulsed nuclear propulsion has been proposed in which devices are detonated behind a pusher plate to propel the spacecraft to high velocities. Initial proposed devices by General Atomics to be detonated were a variant of the Teller-Ulam two stage thermonuclear devices (1964). Maximum velocity is around 0.1c. Such a spacecraft would also still have to carry a payload of nuclear devices. A simplified diagram is presented in Figure 1.
 
Figure 1 – Conceptualized “Orion” Pulsed Fusion Design

Winterberg would improve upon the pulsed thermonuclear fusion concept by proposing D-D fusion devices be utilized triggered by a Super Marx Generator or ion beam (2009). Within solar systems a spacecraft could then refuel with readily available heavy water, deuterium, for propulsion in lieu of radioactive-element-requiring-thermonuclear-devices. It is worth noting that the use of a Super Marx Generator or Explosively Pumped Flux Compression Generator in triggering such D-D fusion devices would also provide a readily available source of power. Such devices could be detonated in chambers to generate pressurized steam and thermal oil to turn turbines.  Such craft are still limited by the need to carry propellant and propellent velocity. A simplified diagram of the proposed D-D devices and simplified spacecraft concept is visualized in Figure 2.
 
Figure 2 – Conceptualized Winterberg DD device and Pulsed DD Fusion Design

The carrying of propellent puts a severe limitation on spacecraft especially at relativistic speeds where inertial mass increases as an object increases in speed.

A proposed solution to the problem of having to carry propellant was the Bussard Ramjet developed by Robert W. Bussard (1960). Electromagnetic fields more than a kilometer in diameter would be used as a ram scoop to collect and compress hydrogen from the interstellar medium as a propellant. High speeds and compression would lead to thermonuclear fusion accelerating the vessel. Bussard proposed fusing protons which Heppenheimer concluded would be infeasible (1978). The requirement for accelerating the interstellar hydrogen to the velocity of the spacecraft would result in a drag condition. Zubrin and Andrews would show that the drag force would exceed the thrust of a Bussard ramjet design (Nygren, 2015). A simplified diagram of the conceptualized, though infeasible Bussard ramjet concept is presented in Figure 3.

 
Figure 3 – Conceptualized (though infeasible) Bussard Ramjet Design

Beckwith would propose that a ramjet style rocket utilize the dark matter hypothesized to exist in the galactic medium. Strong magnetic fields would be used to induce the Primakoff effect to convert axions to photons giving off thrust. He notes that at 0.999c the power would be a respectable 1500 W/cm2. Unfortunately, at lower velocities such as 0.001c the predicted power from axion conversion would be negligible. The larger dark matter candidate, the Weakly Interacting Massive Particles (WIMPs) being larger in mass would generate more thrust though hopes of detection of WIMPS have been dashed causing one to doubt their actual existence (2019). A simplified diagram of the concept is presented in Figure 4.
 
Figure 4 – Conceptualized Beckwith Axion Ramjet

Another solution proposed by Parkin is the Breakthrough Starshot system model in which in-situ lasers are used to accelerate small sailed unmanned craft to 0.2c. This system has the advantage of the craft having no propellent but is limited to small unmanned craft. Larger light sail craft have been proposed but would be completely dependent on the home solar system array with huge power requirements over potentially centuries. A conceptualized diagram is presented in Figure 5.
 
Figure 5 – “Starshot” laser sail concept

While each of these proposed solutions on their own suffers limitations, combined they set the foundation for a novel design for interstellar flight.

Proposed Solution:

A combined pulsed fusion ramjet and Axion Ramjet spacecraft propulsion system is proposed.
At first solar powered lasers are used to pre-position at various speeds D-D fusion devices along the required route of the spacecraft. These unmanned D-D fusion devices can be accelerated up to 0.2c by laser arrays similar to that of the Breakthrough Starshot system. Sails can help enable transfer of momentum which on heating degrade and provide additional thrust.

The spacecraft itself is built on the superstructure of a magnetic ramjet meant to direct the pulsed devices through the maw of the spacecraft and out the other side where they are detonated by means of Super Marx generator or ion beam. This should allow propulsion of the spacecraft to up to 0.2c without the need to carry propellent. Power can be generated onboard through additional detonations in reactors, through excess heat from the explosions or a combination of both.
Note that the possibility exists that the DD devices could be self-detonating with conventional explosives setting off an Explosively Pumped Flux Compression Generator (EPFCG) to trigger fusion (Jones, 2007) however this was suggested for Deuterium-Tritium targets. Such research is banned by the Comprehensive Test Ban Treaty (CTBT) as a “pure fusion” explosion though yields make such devices poor weapons.

The proposed “boosting” of DD Winterberg devices is presented in Figure 6.
 
Figure 6 – Boosting of DD Devices to required velocities (up to 0.2c)

The proposed Winterberg DD Device ramjet is presented in Figure 7.
 
Figure 7 – DD Winterberg Device Ramjet Concept

Above 0.2c in which the post explosion exhaust velocity of the propellent is slower than spacecraft any interaction would then only slow down the spacecraft. The magnetic field could be used to accelerate the device to the speed of the starship but this will require power from the starship and induce drag. For slowing down the spacecraft may turn around with devices detonated preemptively or the Bussard Ramjet maybe deployed. For interstellar voyages it may be worth distilling and refining deuterium devices while ejecting waste hydrogen as propellent to slow down the craft.

As a solution above 0.2c the D-D fusion devices maybe “staged”. As the spacecraft approaches it may fire off an ion beam detonating a first stage when then accelerates a second stage and so-on until the device reaches the velocity of the starship where the last stage provides acceleration to the spacecraft itself.

Figure 8 highlights the conceptual velocity boosting concept in a three-stage configuration. Here the first device is triggered which detonates accelerating the rest of the stack to a higher velocity. Some of the energy is pumped into a laser or ion beam to in turn set off the second device. The process is repeated until velocities higher than 0.2c is achieved on the last device by where the spacecraft accelerates past the device by the time the final device is detonated. This provides pulsed thrust at over 0.2c.
 
Figure 8 – Three Stage DD Device Concept for Velocity Boosting

For interstellar missions as the craft increases in velocity so too does the available thrust that can be provided by axion conversion. It is proposed that for interstellar missions that the craft have an axion ramjet that can provide more and more thrust as the velocity approaches c. Power onboard generates intense magnetic fields converting axions to photons by the Primakoff effect. Thus, after the starship is boosted to relativistic speeds the axion drive takes over the propulsion role and no pre-positioned D-D devices are required.

The spacecraft now operating as an Axion ramjet would be identical to the configuration of Figure 4. Note that the Axion ramjet need not be the same device as the DD ramjet.

Interplanetary Missions

Within the solar system a pulsed Deuterium Ramjet should be able to effectively navigate the solar system at high velocity. Strategically laser emitters and D-D device manufacturing facilities can pre-position D-D fusion devices for the DD fusion ramjet spacecraft. To slow down the craft can rotate and detonate D-D fusion devices ahead of the ship.

Interstellar Missions

At the home star system D-D devices can be strategically placed along the spacecraft route. The spacecraft leaving the solar system is then accelerated to relativistic velocities where the axion ramjet serves as the primary engine between star systems. Onboard D-D fusion devices are detonated in contained reactors to generate the power required for the magnetic field to induce the Primakoff effect. To slow down the Bussard ramjet is activated inducing drag. Deuterium is distilled and refined on board where 3D printing is used to manufacture D-D devices, the excess hydrogen ejected from the craft. D-D devices are used to navigate the target solar system. A laser emitter station can be manufactured in the target solar system to enable a return trip home or to another solar system.

A key mission for such spacecraft would be blackholes where the Penrose Process can be used to extract energy from a rotating black hole (1971). Such rotating blackholes could also be used for high velocity gravitational sling-shots. Vidal and Apostel have proposed that Blackholes are attractors for highly intelligent advanced civilizations (2011).
A proposed mission profit is presented summarizing the concept in Figure 9.
 
Figure 9 – Overall Interstellar Flight Concept Summary As Proposed By This Paper

References:
Bussard, Robert W. (1960). "Galactic Matter and Interstellar Flight" (PDF). Astronautica Acta. 6: 179–195. Archived from the original (PDF) on 2018-04-17. Retrieved 2014-10-04.
Beckwith, A. (December 2010), "Hypothetical Dark Matter/axion Rockets:. Dark Matter in Terms of Space Physics Propulsion". Retrieved from: https://arxiv.org/vc/arxiv/papers/0810/0810.1493v3.pdf
 Heppenheimer, T.A. (1978). "On the Infeasibility of Interstellar Ramjets". Journal of the British Interplanetary Society. 31: 222. Bibcode:1978JBIS...31..222H.
"Nuclear Pulse Space Vehicle Study, Vol III," Report on NASA Contract NAS 8-11053, General Atomics, GA-5009, 19 Sep 64.
Nygren (2015), “Hypothetical Spacecraft and Interstellar Travel, Lulu
Jones, J. Hippel F. (2007 Dec 21), “The question of pure fusion explosions under the CTBT”, The Technical Basis for Arms Control, Disarmament, and Nonproliferation Initiatives Volume 7, 1998 - Issue 2, Science and Global Security
Parkin, K. (2018 April), “The Breahthrough Starshot System Model”, Parkin Research LLC
R. Penrose and R. M. Floyd, "Extraction of Rotational Energy from a Black Hole," Nature Physical Science 229, 177 (1971).
Siegel E. (2019 Feb 22), “The ‘WIMP Miracle’ Hope for Dark Matter is Dead, Forbes
Vidal, C., Apostel, C (2011). “Black Holes: Attractors for Intelligence?”. Free University of Brussels
Winterberg, F. (2009), “Advanced Deuterium Fusion Rocket Propulsion for Manned Deep Space Missions, University of Nevada

[qraal]

Hi Craig

I've added some comments in the Adobe Doc Cloud version. You've reinvented the wheel (slightly) - Greg Matloff & Dan Whitmire called it the Ramjet Runway in 1977, while Dana Andrews & Roger X Lenard didn't give it a name when they redid it in c.2005. The Axion Ramjet is a nice twist, though it's a touch speculative and the coupling of the mag-field to the photon emission needs a bit more clarification. How would that work?

cheers, Adam

[CraigPichach]

Adam,

Thanks for the heads up, I will actively research the ramjet runway literature. Hopefully staging the devices to achieve >0.2c and in combining it with Winterberg's D-D fusion devices brings something new to the table. The chapter I am reading on the Ramjet runway doesn't note how they could pre-position it using a similar method as the Project Starshot sail methods but I am pretty sure you are right in that they were assuming that's how one would pre-position and pre-accelerate the pellets.

For the axion ramjet concept I'd first defer to Beckwith's article on "Hypothetical Dark Matter/Axion rockets: Dark Matter in terms of space physics propulsion" at https://arxiv.org/vc/arxiv/papers/0810/0810.1493v3.pdf . You'll note that Beckwith uses WIMP particles for his propulsion since the axion is too small a mass to give the momentum you want at less than 0.5c (he calculates at .999 c, the power is nearly 1500 watts/cm squared). Unfortunately since it seems the WIMP is not dark matter and experimentation is leaning towards the axion I don't think this kills his idea, it just means you need to "boost" yourself with a ramjet runway.

My understanding on this is that when at sufficient speed that you are sailing past enough axions that you would create an intense magnetic field (as is being done at the ADMX experiment) which would cause convert axions into microwave photons giving you your thrust.  This is the "Primakoff effect". You can read about how they are actually trying to do this to prove the existence of axions at  https://en.wikipedia.org/wiki/Axion_Dark_Matter_Experiment . Unfortunately Earth isn't going that fast that any "thrust" generated will be insignificant. Moving at 0.99c however...

I continue to cross my fingers that these experiments attempting to prove the existence of the axion will bear fruit. That being said if the axion doesn't pan out you still have the ramjet runway at least to enable some interstellar flights.

Follow up - here is an article which actually claims to detect axions in a solid-state crystal.  https://www.nature.com/articles/s41586-019-1630-4

[CraigPichach]

I have reviewed Greg Matloff & Dan Whitmire's 1977 Ramjet Runway and Dana Andrews & Roger X Lenard Mini-Mag concepts and I'd say my proposal is different in that both the Ramjet Runway and Mini-Mag involve electrically charged fusable micropellets that the magnetic field is going to compress for fission and/or fusion where as I am talking about detonatable devices which can be staged (Matoff, 2005).

For instance with Mini-Mag you have fissible  material in the path that you then compressed in a magnetic field, a Z-pinch, for fission. Some points

#1 -  fissible material is expensive and I just don't see us being able to economically fire that all off into space. 
#2 - With no explosive device I don't see how you could stage (pre-accelerate) this material limiting the speeds attainable (certainly below velocities any theoretical axions would be a useful propellant).

Moving on to the idea of the Ramjet Runway for fusion I don't think you can just use magnetic fields to initiate fusion and again I don't think you can stage the devices limiting your speed.

With Winterberg's proposed devices you do not require expensive fissile material and you can stage them. The magnetic fields involved are not required to trigger fusion. Indeed if you were a great pilot you don't even need magnetic fields if you could fly the ship that the devices pass the vessel pre-detonation (I propose that magnetic fields might as well be used to aid in this since you need something to ensure particles don't smash into you anyway). Using explosively pumped flux compression generators the fusion trigger can be entirely on the device (though the Super Marx Generator triggering the D-D device would require energy on the part of the starship). The D-D devices are also of significance since deuterium would be a relatively cheap and abundant material in the solar system that no one would be upset if we built devices that we launched out into space (and also could be found anywhere there is water at the destination).

Hopefully these differences offer an order of magnitude improvement over the Mini-Mag and Ramjet highway concepts.

Thanks,
Craig Pichach

References:
Matoff (2005), Deep Space Probes: To the Outer Solar System and Beyond, Berlin: Springer