THEORETICAL AND EXPERIMENTAL INVESTIGATION OF C_(60)-PROPELLANT FOR ION PROPULSION

摘要

The large mass as well as the low first ionization potential and the large electron impact ionization cross-section make Buckminsterfullerene (C_(60)) potentially attractive as an ion engine propellant. To evaluate the advantages of C_(60) it was necessary to calculate characteristic quantities like the thrust-beam-power ratio and the different efficiencies. It was found that, compared with xenon, the use of C_(60) would significantly reduce the necessary beam power by 57 percent for the same power level, resulting in a reduction of power supply mass and thus in a higher payload capacity. Calculations of the efficiencies show a clear increase in overall efficiency. Particularly, the mass efficiency and the electrical efficiency would increase significantly over that obtained with a xenon -fuelled ion engine. Togeiher with the exceptionally high flexibility of the molecular structure of C_(60), this results in a very low ablation in the grid system, and consequently in a longer lifetime. One of the most severe problems in using C_(60) as propellant for ion engines is the temperature sensitivity of C_(60). High temperatures cause fragmentation of the C_(60) molecule, low temperatures lead to resublimation of C_(60) on the inner walls of the engine. Both would result in a decrease of the mass efficiency. Therefore, extensive experiments with a special ion source were carried out to determine the temperature behavior of an ion thruster. This and the theoretical research yield in a temperature window (400―700℃) for systems operating with C_(60).