We propose to evaluate external pulsed plasma propulsion for unmanned interstellar exploration. The concept rests on three quantitative observations: (1) the ORION concept is capable of achieving exceedingly-high specific impulse; (2) the unfueled weight of the spacecraft is greatly reduced by eliminating the springs and shock absorbers, originally intended to mitigate g-loading on astronauts, but less necessary for the rugged instrumentation packages alone; and (3) the external plasma pulse spacecraft could be staged to attain velocities that would permit it to cross interstellar space on humanly compatible time scales. The technical objectives are: (1) to assess the pusher-plate, spring, and shock absorber technology for appropriate trade-offs between impulsive g-loading and the total unfueled weight of the spacecraft; (2) to assess the gain in specific impulse achievable with directed energy pulse units; (3) to explore the limits and trade-offs of staging as a means to achieve exceedingly high velocities; (4) to calculate realistic scenarios for interstellar missions, including the relative resource requirements and relative costs; and (5) to objectively compare the merits of external pulsed plasma propulsion for interstellar probes with other means of propulsion, such as, ion beam beams, fission fragment ejection, Earth-based laser ablation, Earth-based microwave radiation-pressure, etc.Potential Commercial ApplicationsThe concept entails development of advanced materials, composites, and microstructures to enhance the lifetime of the pusher plate. These will provide impetus for commercial applications requiring very strong materials that are also resistant to pulses of thermal radiation. New light-weight and high-strength materials will be developed, such as: (1) arrays of bucky tubes; (2) solid-state extruded aligned polyethylenes and other types of aligned polymers; and (3) bucky tubes or polymers with cross links to provide two-dimensional strength. The research effort will incorporate an assessment of instrumentation that is tolerant of high acceleration, whose development will have a broad range of commercial application, e.g., instruments placed close to explosives, instruments in high vibration environments, and instruments that must survive a high-g impact, such as air- or space-dropped packages to penetrate rock, regolith, or ice. The information-processing and communication technology necessary for an interstellar mission will spin into the commercial cybernetics community. Information from the probe must be transmitted across several light years, which is unprecedented. The probe must be capable of autonomous decision making, because it will be impossible to forecast the exigencies of a stellar fly-by. This will have spin for the commercial robotics and flexible-automation community.
