A near term propulsion system that could open up the solar system to human exploration is presented. It utilizes antiprotons to induce fission in a U 238 target and allows the resulting fission fragments to heat a propellant to very high temperatures. The underlying principle is based on recent, well-documented theoretical and experimental research that has shown that “at rest” annihilation of antiprotons in U 238 nuclei results in fission at nearly 100% efficiency. The fission fragment mass spectrum reveals that the total mass of these particles is about 212 amu, while their velocity distribution indicates a total energy of about 160 MeV which could be deposited in a magnetically-confined U 238 plasma that could subsequently be ejected through a magnetic nozzle to produce thrust. Preliminary calculations show that a modest amount of antiprotons – well within the projected annual production levels of the next decade – can readily result in heating a uranium plasma to about 1 keV temperature in a system that can produce about 48 kN of thrust at a specific impulse of about 3000 seconds. When applied to a Mars round trip mission, it is shown that one gram of antiprotons will allow the journey to take place in about 127 days if both the fission fragments and the annihilation products are accounted for in heating the plasma, whereas the travel time will increase to about 170 days if only the energy of the annihilation products is utilized in the heating process. This mission scenario allows for 2.2 days of thrusting and the remainder in coasting. With 0.1 gram of antiprotons, the same Mars mission will take about 182 days of which approximately 1/5 of a day of thrusting will be employed to accommodate the specified amount of antimatter.
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