Fusion Propulsion: Reaching the Stars by Wielding the Power of the Stars

posted by Guest on July 23, 2013

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The following blog is a guest post from Kevin Schillo who is currently pursuing a Master of Science in Aerospace Systems Engineering at the University of Alabama in Huntsville. His research is focusing on pulsed fusion propulsion, which could help to open up the solar system for routine manned exploration. Kevin has always had a profound interest in science fiction and the future of space development, a passion which he has expressed in the form of his first publication, the novella “Apotheosis,” which was published in the anthology “Against a Diamond Sky” as part of the Orion’s Arm Universe Project. Kevin further demonstrated his literary prowess at expressing the beauty and majesty of the cosmos and humanity’s role in it in the form of his essay “Allure from Afar,” which garnered him the student essay award at the Next Generation Sub-Orbital Researchers Conference in 2011.

Magneto-inertial fusion (MIF) has been shown to offer a short development path and small reactor size[1] and z-pinch in particular shows very favorable scaling for fusion breakeven.[2]

Fusion propulsion in general enables rapid interplanetary space travel with trip times significantly shorter than that offered by chemical, solar electric, nuclear thermal, and nuclear electric propulsion systems. The reasons for this include the 106 greater energy density in fusion compared to chemical reactions, significantly higher thrusts compared to electric propulsion, higher exhaust velocities compared to nuclear thermal, and direct conversion to thrust, which reduces radiator mass significantly compared to nuclear electric propulsion. Combined, this enables missions that are 1/2 to 1/4 of the typical mission times required by current technologies.

As an example, if fusion can be fully developed, it could enable astronauts to make roundtrip voyages to Mars lasting a total of about six months. Manned voyages to Jupiter and beyond could also be accomplished within a year.[3,4] This is clearly advantageous over chemical propulsion, which necessitates the usage of a prohibitively massive spacecraft and/or long voyage times for any manned mission to Mars or beyond. In addition to this, a fusion spacecraft could be single-stage and reusable, which would enable manned interplanetary missions to become routine.[3,4]

A roundtrip manned mission to Mars exemplifies the great advantage fusion has over other propulsion systems. The propulsion systems examined in this case are chemical, nuclear thermal nuclear electric, and two fusion systems, with specific powers of 1 kW/kg and 10 kW/kg. Assuming the mission objective is to deliver a payload mass of 100 mT to the surface of Mars, the mass of the spacecraft throughout the mission can be plotted in the figure below:

 

Figure 1

Figure 1. Spacecraft mass for roundtrip Mars mission.

 

This graph illustrates the massive vehicle size and/or long voyage times associated with chemical propulsion. The mission becomes feasible with the utilization of nuclear thermal and nuclear electric systems. However, manned voyages to Mars can only be made routine if fusion propulsion is used.

Despite the great potential that fusion offers humanity, much research remains to be done in order to make fusion propulsion a reality.  One of the key technologies that has yet to be developed is the nozzle, which is required in order to redirect the isotropic energy yield into a direct motion for thrust. The extremely high temperatures of fusion plasma exhaust would cause any solid-state nozzle to undergo physical damage and failure.[5] Because of this, a magnetic nozzle is necessary to redirect the plasma.

The type of nozzle depends on the confinement concept used to contain the high temperature plasma. Fusion propulsion systems can be classified as two general concepts: steady-state and pulsed systems. Steady-state systems confine high energy density plasma at high temperatures for relatively long periods of time. Pulsed systems contain the plasma for relatively brief periods of time.

In a steady-state magnetic nozzle, the plasma follows the magnetic field lines in a manner that mimics the geometric shape of a solid-state converging-diverging nozzle. This causes the plasma to choke at the nozzle’s throat and then expand supersonically as it enters the nozzle’s diverging section.

In a pulsed magnetic nozzle, magnetic field lines absorb the kinetic energy of an expanding plasma sphere. The field is compressed by the plasma until the magnetic pressure is equivalent to the dynamic pressure of the plasma. The plasma is then ejected from the nozzle as the magnetic field rebounds to its initial position.[6] This is illustrated in the figure below:

 

Figure 2

Figure 2. Pulsed Magnetic Nozzle Operation

 

The overwhelming majority of research and development in magnetic nozzles has focused on steady-state devices, and very little has been done with pulsed magnetic nozzles.[7,8]

A pulsed z-pinch fusion system has the potential to offer lightweight reactors, which would be crucial for any spacecraft using fusion propulsion.

Magnetic nozzle performance is measured by the ratio of the axial kinetic energy of the exhaust gases to the initial thermal energy of the plasma.  An efficiency derived from this has always been assumed and scant theories and absent experiments mean that there is a rich opportunity for exploring the physics and engineering needed to understand, characterize, and improve magnetic nozzle performance for pulsed systems.

 

Planned Experiments

The University of Alabama in Huntsville is working in partnership with Boeing and Marshall Space Flight Center to construct the Charger-1 facility at the Aerophysics Lab on Redstone Arsenal. The Charger-1 is a ~500 kJ pulsed power facility capable of 2 MA discharges at 3 TW of instantaneous power, and it provides a unique opportunity to explore and develop technologies that can help to make pulsed fusion propulsion a reality. Once operational in the spring of 2013, the Charger-1 will be used to conduct fusion experiments via z-pinch confinement, and will be the largest and most powerful puled power machine used by a university. The team is working with ORNL and Y-12 to create lithium deuteride (6LiD) in order to conduct the subscale thermonuclear fusion tests. 

 

Figure 3

Figure 3. Charger-1 device.

 

To conduct propulsion research, an experimental magnetic nozzle apparatus initially consisting of a single conducting ring will be assembled and coupled to the Charger-1 device in order to examine techniques to capture and redirect the plasma exhaust via magnetic fields. A 300 kW DC power supply will be utilized to drive the current through nozzle field coil. The magnetic nozzle will be generated by this current ring. Multiple nozzle field strengths, field geometries, and z-pinch implosion locations will be experimented with to determine an optimal nozzle design. Laboratory equipment consisting of thrust stands and a data acquisition system will be needed in order to measure the performance of the nozzle.

Due to volatile NASA funding, it is crucial that alternative sources of funds are found to support this research. For this reason, a crowdfunding campaign has been launched on RocketHub. Any amount that can be contributed to this campaign would be greatly appreciated.

Click here to support this research.

 

References

1. Lindemuth, Irvin R, and Richard E Siemon. 2009. “The Fundamental Parameter Space of Controlled Thermonuclear Fusion.” American Journal of Physics 77 (5): 407–416.

2. Slutz, Stephen A., and Roger A. Vesey. 2012. “High-Gain Magnetized Inertial Fusion.” Physical Review Letters 108 (2) (January 12): 025003. doi:10.1103/PhysRevLett.108.025003.

3. W.E. Moeckel, Journal of Spacecraft and Rockets 9, 863 (1972).

4. W.E. Moeckel, “Propulsion Systems for Manned Exploration of the Solar System,” NASATM-X-1864, (1969).

5. Maslen, Results for Icarus optimistic scenario withS.H., Fusion for Space Propulsion. IRE Transactions on Military Electronics, 1959(Mil-3, 52).

6. Orth, C.D., VISTA – A Vehicle for Interplanetary Space Transport Application Powered by Inertial Confinement Fusion, 2003, Lawrence Livermore National Laboratories: Livermore, California.

7. Bond, A., Martin, A.R. et.al., Project Daedalus – The Final Report on the BIS Starship Study. Journal of British Interplanetary Society, 1978.

8. Adams, R.B., et al., Conceptual Design of In-Space Vehicles for Human Exploration of the Outer Planets, 2003.


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10 Responses to Fusion Propulsion: Reaching the Stars by Wielding the Power of the Stars

  1. Pingback: Fusion Propulsion: Reaching the Stars by Wielding the Power of the Stars | The Zetetic Forum

  2. alex wilson says:

    Before researchers start to worry about what type of nozzle a fusion engine might use, a more pressing need might be to get fusion to actually *work*. So far, getting fusion to even get to ‘break even’ has eluded our best efforts. Until we get to that stage, all other research is moot.

  3. Kevin Schillo says:

    The nozzle is actually a very pertinent piece of technology for fusion development. For one, the technology needed to make it work is vital for extracting usable energy from a fusion plasma. The reason for this is because as the plasma expands within the nozzle, it induces currents that can then be used to power the next cycle. This is needed for any device that will utilize fusion power.

    Also, knowing how to make a nozzle is crucial for designing a proper fusion propulsion system to begin with. In order for fusion to be used for propulsion, it must both lightweight and capable of delivering propulsive momentum to a spacecraft. This is not something that big fusion research projects like ITER and NIF will be able to do, which is why they’re not being looked at for spacecraft propulsion. The research with the Charger-1 has the potential to offer lightweight fusion reactors for spacecraft, and magnetic nozzle research is vital for understanding how to propel a spacecraft to begin with. If we don’t do that, then you could end up designing a reactor that has great science applications like ITER and NIF, but are completely useless for propulsion applications.

    • alex wilson says:

      but Kevin, without any indication that we can even get a ground-based fusion reactor to ‘break even’, how likely is it that we’re even going to have a reactor to put into space? as you said, a space-based reactor would have to tap the plasma stream in some way to generate power to drive the reaction cycle. so, if we can’t get to ‘break-even’, how are we going to get a plasma stream that produces enough energy to tap? it seems to be a case of ‘putting the cart before the horse’ to throw money at research into nozzle technology before we achieve ‘break-even’.

      • Kevin Schillo says:

        Creating a breakeven reactor is the holy grail of fusion research at this point. But when we do build a breakeven reactor and we don’t have a way of deriving thrust from the reactor, it won’t be of any use at all for spacecraft. And like I said, a magnetic nozzle is vital for extracting usable energy from a fusion plasma. That’s why it’s pertinent to research magnetic nozzles now.

        Maybe they’ll achieve breakeven with ITER and/or NIF, but even if they do, it won’t be of much use for propulsion applications because the reactors are simply too massive.

        Furthermore, we intend to research fission-fusion hybrids with the Charger-1, in which the neutrons from a fusion reaction are used to initiate fission reactions in a surrounding fissile liner like uranium or thorium. The energy from the fission reactions could then be used to sustain the fusion reactions. The advantage of this system is that the fusion reaction wouldn’t necessarily have to be breakeven in order for the fission-fusion system to produce net energy as a whole.

        • Since about 2011 I having been posting over at the centuari dreams forum in regards to a proposed Lithium Deuteride
          microcapsules,I understand you are a contributor over at Centuarie dreams so I no doubt posted to some of your articles.
          The Lithium Deuteride micro capsules come in different “flavors” homogeneous and heterogeneous.
          heterogeneous are miniature versions of the soviet layer cake fusion weapon, this I admitted to Dr Moses could not be placed in the NIF target chamber.I got an interesting reply email from the NIF public relations officer……………..:)
          This Lithium Deuteride pellet with layers of fissionable materials could be simulated in the ASC Purple machine and I see this as a compromise fuel any ICARUS starship.
          precursor.
          Indeed the NIF has not succeeded in its goals with cryogenic fuels and back in 2011 I suggested to Mr Gilster and DR Moses that cryogenic microcapsule would make for an expensive hard to mass produce fuel for any LIFE or in space engine.
          The homogeneous Lithium Deuteride microcapsule is something that I wonder how it would react to a NIF beam? or to a neutron source beam? perhaps my third flavor is a homogeneous Lithium Deuteride microcapsule with as thin as possible fission material outer shell.
          More “Flavers” on my powerpoint on linkedin

    • Kurt Plummer says:

      How much thrust is necessary to put the necessary materials and systems into orbit to assemble an orbital slipway to create the ship capable of putting a million ton payload into orbit over Mars?
      Has anyone instead considered the use of Von Neumann Constructor options to reduce payload on the front end and harvest Martian resources to automate the assembly of a colony base -before- delivering a human crewed ship of much lower total tonnage (i.e. divide between a fast and a slow transit delivery)?
      If Chemical rocket technology is currently unaffordable for the throw weight required to put the necessary ship building systems into LEO, are you instead proposing the use of a fusion rocket, in atmosphere, to provide the necessary lift?
      What are the issues with radiologics and accidental reactor detonations as well as ionization coupling of the nozzle to such an application? Do we need to launch from a desertified area with low population count and how does this effect orbital geometries?
      I admit I am one of those who would like to see the application of free global electrical generation precede spaceflight but I realize that the miniaturization needed for propulsion can often push the SOA harder towards ground apps too.

  4. John Pattullo says:

    has it occurred to you that for propulsion perhaps break even isn’t needed – useful most certainly but if you can carry some other power source to augment the power you can siphon out of the fusion reaction then break even isn’t the big hurdle that it is for commericla power generation

    on a side note – it also might turn out that achieving break even might be easier in space – no gravity etc and when you can fire the plasma out the rear end without concern perhaps it will open up new possibilities that just aren’t possible on earth

    just somethings to think on anyway – i shall just continue to hope it all fans out nicely and we can do this within next decade or so

  5. VAN DEN BOGAERT JOANNES says:

    Fusion propulsion has been the topic of lapsed Belgian Patent BE904719. See Abstract in English obtainable through ESPACENET

  6. Dr.B.Gutman says:

    “Thermal nucleus fusion method”,US Patent # 8,436,271,2013:

    My Patent is a way to design a thermal nuclear fusion torch engine to reach the nearest stars and creates the thermal fusion power station with unlimited time of plasma operations without strong magnetic field devices for confinement of plasma …

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