the system provides the sort of performance levels that would make an interstellar precursor mission possible. Dusty plasma A newer design proposal by Rodney L. Clark and Robert B. Sheldon theoretically increases efficiency and decreases complexity of a fission fragment rocket at the same time over the rotating fibre wheel proposal. In their design, nanoparticles of fissionable fuel (or even fuel that will naturally radioactively decay) are kept in a vacuum chamber subject to an axial magnetic field (acting as a magnetic mirror) and an external electric field. As the nanoparticles ionize as fission occurs, the dust becomes suspended within the chamber. The incredibly high surface area of the particles makes radiative cooling simple. The axial magnetic field is too weak to affect the motions of the dust particles but strong enough to channel the fragments into a beam which can be decelerated for power, allowed to be emitted for thrust, or a combination of the two. With exhaust velocities of 3% - 5% the speed of light and efficiencies up to 90%, the rocket should be able to achieve over 1,000,000 sec Isp. Am 242m as nuclear fuel In 1987 Ronen & Leibson published a study on applications of 242mAm (one of the isotopes of americium) as nuclear fuel to space nuclear reactors, noting its extremely high thermal cross section and energy density. Nuclear systems powered by 242mAm require less fuel by a factor of 2 to 100 compared to conventional nuclear fuels. Fission-fragment rocket using 242mAm was proposed by George Chapline at LLNL in 1988, who suggested propulsion based on the direct heating of a propellant gas by fission fragments generated by a fissile material. Ronen et al. demonstrate that 242mAm can maintain sustained nuclear fission as an extremely thin metallic film, less than 1/1000 of a millimeter thick. 242mAm requires only 1% of the mass of 235U or 239Pu to reach its critical state. Ronen's group at Ben-Gurion University of the Negev further showed that nuclear fuel based on 242mAm could speed space vehicles from Earth to Mars in as little as two weeks. 242mAm's potential as a nuclear fuel derives from the fact that it has the highest thermal fission cross section (thousands of barns), about 10x the next highest cross section across all known isotopes. 242mAm is fissile (because it has an odd number of neutrons) and has a low critical mass, comparable to that