1 / 36

A Dusty Plasma Based Fission Fragment Nuclear Reactor/Rocket

A Dusty Plasma Based Fission Fragment Nuclear Reactor/Rocket. Ro bert Sheldon and Rod Clark National Space Science & Technology Center Grassmere Dynamics, LLC AIAA, JPC Tucson July 13, 2005. The Rocket Equation. V exhaust = I sp * g [d/dt(MV) = 0]

sarayates
Download Presentation

A Dusty Plasma Based Fission Fragment Nuclear Reactor/Rocket

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. A Dusty Plasma Based Fission Fragment Nuclear Reactor/Rocket Robert Sheldon and Rod Clark National Space Science & Technology Center Grassmere Dynamics, LLC AIAA, JPC Tucson July 13, 2005

  2. The Rocket Equation • Vexhaust= Isp * g [d/dt(MV) = 0] • dV = Vexhaust* log( final mass / initial mass) Material Isp Limitation Solid fuel 200-250 fuel-starved LH2/LOX 350-450 fuel-starved Nuclear Thermal 825-925 fuel-starved Gas Core Nuclear ~2,000 fuel starved MHD < 5,000 energy-starved Ion < 10,000 energy-starved Fission Fragment ~1,500,000 fuel-starved Matter-Antimatter ~10,000,000 fuel-starved Photons 30,000,000-both-starved

  3. Mission to the Gravitational Lens at 550AU • Assume we accelerate half-way, decelerate the other half. (Not the most intelligent approach, but good for comparing technologies) so T_trip = 10 years. • Acceleration = 550AU / (5yr)2 = DV / 5yr=.0027 m/s2 • So DV = 425,000 m/s • Isp (m/s/10)Mrocket / Mpayload 1,500,000 1.029 1,000,000 1.04 500,000 1.09 MORAL of Story: 100,000 1.5  DV ~ V_exhaust 10,000 70.6 450 1.2e41

  4. Mf/Mi Comparison Missions

  5. Ideal Rockets

  6. JPL Nuclear-Electric Concept Shielding, Fuel Shield shadow terminator Reactor Power Lines, Coolant tubes Cooling Fins Instruments Ion Thrusters

  7. Fission Fragment Concept • Nuclear-Electric converts nuclear energy to heat, heat to electricity, then electricity to propulsion. The overall efficiency isn’t very high. There’s abundant nuclear power, so low efficiency can be tolerated, but now we also have much heat to remove, which in space can only be done with radiators. • If the fission fragments, which contain 90% of the nuclear energy, can be used directly for propulsion, not only is the nuclear power extracted more efficiently, but much less waste heat is generated.

  8. Fuel Fibers • Fuel coated micron-thick fibers, emit >50% of fission fragments away from fiber. Fragments can be directed out of the system as propellant. Since 90% of energy is in fission fragments, then <55% energy is wasted as heat. Still, fibers get hot. Carbon fiber

  9. Chapline’s Fission Fragment Rocket Magnetic yoke Moderator & magnet coils U235 coated micron-thick spoke-fibers rotating fast Fission-fragment exhaust

  10. Tsvetkov & Hart, Texas A&M

  11. Enabled Missions

  12. Heat: The hidden killer • So the problem with space nuclear propulsion is NOT raw power, but how to eliminate waste heat. The more efficiently we can generate thrust, the less waste heat produced. • Can we have our cake and eat it too? Can we have a non-thermal nuclear propulsion minimizing waste heat? • Yes. • Fission fragments can escape < 1 micron U235 dust without heating the grains much. The dust radiates heat very effectively, permitting high power levels.

  13. Cool Dust Cs137 100nm U235 Sr90

  14. What is a dusty plasma? Charged dust + plasma = a “plum pudding” Coulomb crystal, or as Cooper-pairs in BCS theory. Note surface tension & crystalline interaction. Auburn University University of Iowa

  15. Dust Clouds Since we need a total amount of U235 to achieve criticality, how do we collect enough dust grains without heating them? Organization.

  16. Fragment Confinement

  17. More on confinement . • B=0.6 T over 1-meter bore is an awesome energy density = pressure. If we could do that we’d be flying a fusion reactor! Instead, we use a multipole magnet toroid, such that the field strength drops as |R – R0|-N , with N>2, from the wall. • This produces a magnetic gradient near the wall, producing a strong mirror force, “insulating” the wall from fission fragments. • By Liouville’s theorem, n/B=constant, so fission fragment density peaks at the wall, low in the dusty plasma center. E.g, one pass through dust. • Because the escaping fragments are positive,  net negative charge in the dust cloud. An ambipolar electric field (=some fraction of MeV) develops at edge as well, confining the fragments. • Proper treatment will require full kinetic simulations.

  18. Toroidal MultipoleMagnetic Trap

  19. Power & Thrust • One mirror can be adjusted for either reflection (more thrust) or transmission (electric power)

  20. Concept • Field coils on the end control thrust & power • U235 dust • Moderator is lightweight LiH • Multipole permanent magnets on sides contain fragments

  21. Dust suspension FAQs • Can the dust be suspended while the rocket is accelerating? • Yes, 1g is typically no problem for labs. • Will B-field change the dusty-plasma dynamics? • Yes, but not much.

  22. Terrella Lab ( NSSTC)

  23. Levitated Dusty Plasma w/Magnets

  24. Arc discharge on 3μ SiO2 dust grains charges them negative. Probable charge state on dust is –10,000 e/grain. They are trapped in a positive space-charge region adjacent to ring current. The RC is formed by -400V DC glow discharge on NIB magnet, streaming electrons ionize the air, maintain the RC. Phase-space mismatch of streaming electrons and trapped ions produces the space charge. Highly anisotropic B-field contributes as well. The Dust Trap

  25. Langmuir Probe mapping

  26. Discharging Dust • Won’t negatively charged dust discharge from thermionic emission? And won’t 100nm dust have huge corona discharge current? • Yes, but not as much as one might think.

  27. Discharge vs Dust Size

  28. Photoelectrons vs. size

  29. 550 AUPower, Mass, Acceleration • Acceleration = DV / 5yr= 0.002 m/s • The following values are scaled from Chapline’s Am242*-fueled rocket. We have not done a separate neutronic analysis to get the appropriate volumes for LiH moderator and U235 dust. • 10m x 0.5m radius, with 30cm moderator = 5.4 ton • Co-Sm magnets 2cm thick w/Al windings = 1 ton • Graphite superstructure, radiators, liquid Na = 1.6 ton • Assuming that the payload is 1 ton, then total=9 tons • For a trip to 550AU, the fuel is then .02*9=.18 tons • 350 Megawatt reactor (Nerva was 4.08 GW) ~3mg/s • 0.5Ly Oort Cloud5.6 GW consuming 50mg/s

  30. Nuclear Pollution? • Since radioactive fission fragments are emitted from the rocket, how dangerous is this for the Earth? • From the two missions analyzed, we calculated how long each rocket is withing 10 Re of the earth, and how much fuel is burned during this time. • 550 AU mission = 720 g U235 = 3 moles • 0.5 Lightyr mission=3.7 kg U235 = 15 moles • We modelled the transport through the radiation belts, ionosphere & stratosphere and decay lifetimes of 60 decay products. Short-halflife products decay before reaching the surface of earth. Long-halflife products produce almost no radioactivity. We list radioactive products that make it to Earth from 10 moles U235, both by number and curies.

  31. Modelled Pollutionfrom 10moles U235/P239 • By moles (total radioactivity ~10% of U235) • Rb87 .1 = 1 uCu • Sr90 .2 =1800 Cu • Cs135 .3 = 4 mCu • Cs137 .3 =3600 Cu • Nd144 .05 = .01 nCu • By Curies fast diff slow diffusion • Sr90 1800 1800 • Ru108* 204 110 Cosmic Ray production • Cs137 3600 3600 C14 = 266 Cu/yr • Ce144 1900 770 • Pm147* 2300 930

  32. 550AU Mission Concept 350MW Fission Fragment Rocket

  33. Next Steps • Understand the equilibrium charge state of radioactive dust (generalize the dusty plasma equations) • Demonstrate the multipole confinement of fission fragments, using alpha-decay as a proxy • Push dusty plasma confinement to high vacuum • Test the bimodal, electric power generation with alpha-emitters. (Nuclear batteries) • Neutronics for LiH, cooling ducts, etc.

  34. Conclusions • An interstellar probe is still a challenge with a nuclear fission-fragment rocket, but 550AU gravitational lens or 1 Lyr Oort Cloud missions are eminently feasible. • We chose these missions to illustrate how close the fission fragment rocket comes to the stuff of science fiction but using the materials found already at hand. TRL~2 • For example, 550 AU is very promising. At 350MW, the rocket is still 1/10 of Nerva power, and could accomplish an even shorter mission than 10yr (or bigger payload than 1 ton.) Nor is pollution a real problem. • Therefore high-DV missions are enabled by a promising high-efficiency nuclear technology. • Total mass < 40T, could be launched by a single shuttle.

  35. 4LightyearPower, Mass, Acceleration • Acceleration = DV / 25yr= 0.06 m/s • The following values are scaled from Chapline’s Am242*-fueled rocket. We have not done a separate neutronic analysis to get the appropriate volumes for LiH moderator and U235 dust. • 10m x 0.5m radius, with 30cm moderator = 5.4 ton • Co-Sm magnets 2cm thick w/Al windings = 1 ton • Graphite superstructure, radiators, liquid Na = 1.6 ton • Assuming that the payload is 1 ton, then total=9 tons • For a trip to Alpha Centauri, the fuel is then 24*9=240 tons • 208 Gigawatt reactor (Nerva was 4.08 GW) ~1.8g/s

More Related