David L. Galbraith

Antiproton Catalyzed Fusion Propulsion for Interplanetary Missions

Interplanetary trips using chemical propellants require years to complete. A recently completed study on an antiproton catalyzed fusion reaction propulsion system has shown that the specie c impulses that can be obtained are between 1500 s for a contained system to over 100,000 s for a system that directly uses the fusion reaction products. Thrust-to-weight ratios exceeding 1 can be sustained. This allows considerably shorter solar system travel times than conventional chemical propellants. Missions considered range from inner to outer solar system distances. A tradeoff can be made between reducing travel time and reducing initial mass in low Earth orbit. Missions to the inner planets can be shortened considerably for a given mass ratio, whereas missions to the outermost planets will be several weeks in duration.

Improved Physics Model for the Gasdynamic Mirror Fusion Propulsion System

The propulsion capability of the gasdynamic mirror (GDM) fusion propulsion device was examined in several previous publications without taking into account the electrostatic potential inherent to plasma cone nement in this system. This potential arises as a result of the initial rapid escape of the electrons through the mirrors because of the smallness of their mass. The remaining excess positive charge gives rise to a positive electric potential that slows down the electrons while speeding up the ions until equalization in their axial diffusion is achieved. In a thruster, the energy of the ions emerging from the magnetic nozzle will therefore be enhanced relative to their energy as they leave the mirror by an amount equal to that of the potential. In typical GDM parameters, this effect can translate into signie cant increases in the specie c impulse and thrust produced by the system. Nomenclature Ac = area of plasma core A0 = mirror area D = axial diffusion coefe cient E = electric e eld Ee = electron energy EL = escape energy e = electron charge erf = error function k = gradient scale length L = length of plasma <n l = coulomb logarithm m = particle mass N = particle density n = monoenergetic particle density R = plasma mirror ratio T = temperature V = plasma volume v = monoenergetic particle velocity vth = thermal velocity x = parameter, Eq. (26) z = charge number G = velocity-averaged particle e ux g = monenergetic e ux d = parameter, Eq. (25) m = mobility t = cone nement time y = collision frequency f = electrostatic potential

An americium‐fueled gas core nuclear rocket

A gas core fission reactor that utilizes americium in place of uranium is examined for potential utilization as a nuclear rocket for space propulsion. The isomer 242mAm with a half life of 141 years is obtained from an (n, γ) capture reaction with 241Am, and has the highest known thermal fission cross section. We consider a 7500 MW reactor, whose propulsion characteristics with 235U have already been established, and re‐examine it using americium. We find that the same performance can be achieved at a comparable fuel density, and a radial size reduction (of both core and moderator/reflector) of about 70%.

Electron and ion escape over a potential barrier in a mirror field

The problem of calculating the electron loss rate and the corresponding energy loss rate from a magnetic mirror machine having a positive potential has been examined and solved to a reasonable approximation by Pastukhov (1974). This approximation is followed to produce particle and energy confinement times for ions which can be readily utilized in the study of plasma confinement in tandem mirrors. It is shown that a single additional parameter, labeled C, can be incorporated into the appropriate equations to make them equally applicable to electrons and ions; C=1 for electrons and C= square root 2 for ions.

AN INERTIAL FUSION PROPULSION SCHEME FOR SOLAR SYSTEM EXPLORATION

A novel fusion scheme that combines the favorable aspects of both inertial and magnetic confinement approaches is analyzed as a propulsion device for potential utilization in solar system exploration. Using an appropriate set of equations for the plasma dynamics and the magnetic nozzle, we assess the system’s propulsive capability by applying the results to a round trip mission to Mars. We find that such a device would allow a massive vehicle to make the journey in less than five months.

An alternative approach to major tritium production

Two schemes have been proposed to replace the aging tritium production facilities at Savannah River, South Carolina. The U.S. Department of Energy and the federal government have reiterated their plan to build a heavy water reactor and a high-temperature gas-cooled reactor at a cost of about

The Conservation Equations for a Magnetically Confined Gas Core Nuclear Rocket

7 billion as replacements for the Savannah River facility. A group of scientists from national laboratories, on the other hand, have proposed the use of a linear accelerator to accelerate protons to produce neutrons to be used to produce tritium in lithium targets. Yet another scheme is proposed that is safe and potentially less expensive than the other two. It relies on existing or rapidly developing laser technology to drive a magnetically insulated inertial confinement fusion device, which has already produced copious amounts of neutrons that could readily be used in producing tritium.

An antiproton‐driven magnetically insulated inertial fusion propulsion system

A very promising propulsion scheme that could meet the objectives of the Space Exploration Initiative (SEI) of sending manned missions to Mars in the early part of the next century is the open‐cycle Gas Core (GCR) Nuclear Rocket. Preliminary assessments of the performance of such advice indicate that specific impulses of several thousand seconds, and thrusts of hundreds of kilonewtons are possible. These attractive propulsion parameters are obtained because the hydrogen propellant gets heated to very high temperatures by the energy radiated from a critical uranium core which is in the form of a plasma generated under very high pressure. Because of the relative motion between the propellant and the core, certain types of hydrodynamic instabilities can occur, and result in rapid escape of the fuel through the nozzle. One effective way of dealing with this instability is to place the system in an externally applied magnetic field. In this paper we formulate the appropriate conservation equations that describ...

A preliminary comparison of gas core fission and inertial fusion for the space exploration initiative

The magnetically Insulated Inertial Confinement Fusion (MICF) reactor, in its initial conception, concepts of a target in the form of a metal shell whose inner surface is coated with a fusion fuel which is ignited by an incident laser beam that enters the pellet through a hole. A very strong magnetic field, generated when the surface is ablated by the incident laser beam, provides thermal insulation of the wall from the hot plasma, and allows the plasma to burn longer thereby generating a larger energy amplification. When ejected through a magnetic nozzle the plasma can provide a very large specific impulse if MICF is utilized as a propulsion device. For application to space travel, however, the mass of the laser and associated power supply may prove to be prohibitively large and another driver should be considered in its place. In this paper we examine the potential use of antimatter annihilation reactions along with a fissionable component to generate the energy needed to initiate the fusion reactions. ...

Fusion Product Momentum Transfer to Inertially Confined Plasma

Potential utilization of fission and fusion‐based propulsion systems for solar system exploration is examined using a Mars mission as basis. One system employs the open cycle gas core fission reactor (GCR) as the energy source, while the other uses the fusion energy produced in an inertial Confinement Fusion (MICF) concept, to convert thermal energy into thrust. It is shown that while travel time of each approach may be comparable, the GCR must overcome serious problems associated with turbulent mixing, fueling and startup among others, while the fusion approach must find ways to reduce the driver energy required for ignition.