ALBERT

Description: Rapid transport of large payloads and human crews throughout the solar system requires propulsion systems having very high specific impulse (I(sub sp) 〉 10(exp 4) to 10(exp 5) s). It also calls for systems with extremely low mass-power ratios (alpha 〈 10(exp -1) kg/kW). Such low alpha are beyond the reach of conventional power-limited propulsion, but may be attainable with fusion and other nuclear concepts that produce energy within the propellant. The magnitude of energy gain must be large enough to sustain the nuclear process while still providing a high jet power relative to the massive energy-intensive subsystems associated with these concepts. This paper evaluates the impact of energy gain and subsystem characteristics on alpha. Central to the analysis are general parameters that embody the essential features of any 'gain-limited' propulsion power balance. Results show that the gains required to achieve alpha = 10(exp -1) kg/kW with foreseeable technology range from approximately 100 to over 2000, which is three to five orders of magnitude greater than current fusion state of the arL Sensitivity analyses point to the parameters exerting the most influence for either: (1) lowering a and improving mission performance or (2) relaxing gain requirements and reducing demands on the fusion process. The greatest impact comes from reducing mass and increasing efficiency of the thruster and subsystems downstream of the fusion process. High relative gain, through enhanced fusion processes or more efficient drivers and processors, is also desirable. There is a benefit in improving driver and subsystem characteristics upstream of the fusion process, but it diminishes at relative gains 〉 100.

Description: The superior energy density of antimatter annihilation has often been pointed to as the ultimate source of energy for propulsion. However, the limited capacity and very low efficiency of present-day antiproton production methods suggest that antimatter may be too costly to consider for near-term propulsion applications. We address this issue by assessing the antimatter requirements for six different types of propulsion concepts, including two in which antiprotons are used to drive energy release from combined fission/fusion. These requirements are compared against the capacity of both the current antimatter production infrastructure and the improved capabilities that could exist within the early part of next century. Results show that although it may be impractical to consider systems that rely on antimatter as the sole source of propulsive energy, the requirements for propulsion based on antimatter-assisted fission/fusion do fall within projected near-term production capabilities. In fact, a new facility designed solely for antiproton production but based on existing technology could feasibly support interstellar precursor missions and omniplanetary spaceflight with antimatter costs ranging up to $6.4 million per mission.

Description: Most fusion propulsion concepts that have been investigated in the past employ some form of inertial or magnetic confinement separately, and are encumbered by the need for advanced drivers (e.g. laser) or steady-state magnetic confinement systems (e.g. superconductors) that have historically resulted in large, massive spacecraft designs. Here we present a comparatively new approach, Magnetized Target Fusion (MTF), which offers a nearer-term avenue for realizing the tremendous performance benefits of fusion propulsion. MTF attempts to combine the favorable attributes of both inertially and magnetically confined fusion to achieve both efficient and low-cost compressional plasma heating and energy confinement. The key advantage of MTF is its less demanding requirements for driver energy and power processing. Additional features include: 1) very low system masses and volumes, 2) relatively low waste heat, 3) substantial utilization of energy from product neutrons, 4) efficient, low peak-power drivers based on existing pulsed power technology, 5) very high Isp , specific power and thrust, and 6) relatively affordable R&D pathways. MTF overcomes many of the problems associated with traditional fusion techniques, thus making it particularly attractive for space applications. Isp greater than 50,000 seconds and specific powers greater than 20 kilowatts/kilogram appear feasible using relatively near-term pulse power and plasma gun technology.

Description: Most fusion propulsion concepts that have been investigated in the past employ some form of inertial or magnetic confinement. Although the prospective performance of these concepts is excellent, the fusion processes on which these concepts are based still require considerable development before they can be seriously considered for actual applications. Furthermore, these processes are encumbered by the need for sophisticated plasma and power handling systems that are generally quite inefficient and have historically resulted in large, massive spacecraft designs. Here we present a comparatively new approach, Magnetized Target Fusion (MTF), which offers a nearer-term avenue for realizing the tremendous performance benefits of fusion propulsion'. The key advantage of MTF is its less demanding requirements for driver energy and power processing. Additional features include: 1) very low system masses and volumes, 2) high gain and relatively low waste heat, 3) substantial utilization of energy from product neutrons, 4) efficient, low peak-power drivers based on existing pulsed power technology, and 5) very high Isp, specific power and thrust. MTF overcomes many of the problems associated with traditional fusion techniques, thus making it particularly attractive for space applications. Isp greater than 50,000 seconds and specific powers greater than 50 kilowatts/kilogram appear feasible using relatively near-term pulse power and plasma gun technology.

Description: Magnetized target fusion is an approach in which a magnetized target plasma is compressed inertially by an imploding material wall. A high energy plasma liner may be used to produce the required implosion. The plasma liner is formed by the merging of a number of high momentum plasma jets converging towards the center of a sphere where two compact toroids have been introduced. Preliminary 3-D hydrodynamics modeling results using the SPHINX code of Los Alamos National Laboratory have been very encouraging and confirm earlier theoretical expectations. The concept appears ready for experimental exploration and plans for doing so are being pursued. In this talk, we explore conceptually how this innovative fusion approach could be packaged for space propulsion for interplanetary travel. We discuss the generally generic components of a baseline propulsion concept including the fusion engine, high velocity plasma accelerators, generators of compact toroids using conical theta pinches, magnetic nozzle, neutron absorption blanket, tritium reprocessing system, shock absorber, magnetohydrodynamic generator, capacitor pulsed power system, thermal management system, and micrometeorite shields.

Description: Omniplanetary space flight requires new high-performance propulsion systems based on nuclear energy. Over the last several decades, many propulsion concepts have been discussed which will allow one-month missions to Mars and one-year missions to the outer planets. Such missions entail large mission velocities and vehicle accelerations, which in turn require both high exhaust velocities (and therefore, and extremely low mass-power ratios. High performance electric propulsion appears capable of enabling multi-month transits to Mars and the near-earth asteroids; however, the mass-power ratio of these systems appears too high to achieve large accelerations for outer planet missions. This presentation analyzed the round-trip mission times and distances. This analysis has shown that even high-performance power-limited systems cannot achieve the higher accelerations needed to meet fast missions to the outer planets. Gain-limited missions are necessary for those extremely aggressive missions. An analysis of spacecraft power systems via a power balance and examination of gain vs mass-power ratio has shown: (1) A minimum gain is needed to have enough power for thrust production and driver operation; (2) Increases in gain result in decreases in mass-power ratio, which in turn leads to greater achievable accelerations. However, there is an absolute minimum mass-power ratio for a given set of subsystems, even in the limit of infinite gain.

Description: This paper presents the Paving a Highway to Space at the 49th JANNAF (Joint Army-Navy-NASA-Air force) Propulsion Meeting. The topics include: 1) Earth-To-Orbit; 2) Orbit and Beyond; 3) Duct Propulsion; 4) Electric Propulsion; 5) Beamed Energy Propulsion; 6) Externally-Effected Force; 7) Nuclear Propulsion; 8) The Road to Higher Power Densities and Performance; 9) Propulsion Technology Map; 10) Launch Applications; 11) Space Applications; and 12) Advanced High-Energy Concepts. This paper is presented in viewgraph form.

Description: Rapid transportation of human crews to destinations throughout the solar system will require propulsion systems having not only very high exhaust velocities (i.e., I(sub sp) 〉= 10(exp 4) to 10(exp 5) sec) but also extremely low mass-power ratios (i.e., alpha 〈= 10(exp -2) kg/kW). These criteria are difficult to meet with electric propulsion and other power-limited systems, but may be achievable with propulsion concepts that use onboard power to produce a net gain in energy via fusion or some other nuclear process. This paper compares the fundamental performance of these gain-limited systems with that of power-limited systems, and determines from a generic power balance the gains required for ambitious planetary missions ranging up to 100 AU. Results show that energy gain reduces the required effective mass-power ratio of the system, thus enabling shorter trip times than those of power-limited concepts.

Description: Rapid transportation of human crews to destinations throughout the solar system will require propulsion systems having not only very high exhaust velocities (i.e., I(sub sp) greater or equal to 10(exp 4) to 10(exp 5) sec) but also extremely low mass-power ratios (i.e., alpha less than or equal to 10(exp -2) kg/kW). These criteria are difficult to meet with electric propulsion and other power-limited systems, but may be achievable with propulsion concepts that use onboard power to produce a net gain in energy via fusion or some other nuclear process. This paper compares the fundamental performance of these gain-limited systems with that of power-limited systems, and determines from a generic power balance the gains required for ambitious planetary missions ranging up to 100 AU. Results show that energy gain reduces the required effective mass-power ratio of the system, thus enabling shorter trip times than those of power-limited concepts.