Peter Köhler

The 2-adic affine building of type Ã2 and its finite projections

A certain “free” group U is constructed that is generated by three elements of order 3 which pairwise generate a Frobenius group of order 21 and it is shown that U operates regularly on the affine building of type A2 over the field of 2-adic numbers. As a result an infinite series of finite rank 3 geometries is obtained whose rank 2 residues are projective planes of order 2, and which possess a regular automorphism group isomorphic to SL3(p) or SU3(p) for some prime p.

Parametric Study of HEMP-Thruster Downscaling to

Many on-going European Space Agency (ESA) science and earth observation missions are based on precision attitude control and formation flying. All these missions impose strong requirements on propulsion system which should provide low thrust, low noise, and high-precision thrust vectors in up to 16 directions. Also as most of these missions have a platform with limited solar cell arrays, the power consumption of the propulsion system should be as low as possible. The idea of using a small high-efficiency multistage plasma thruster (HEMPT) system for such missions is very attractive because of its relatively low complexity and low system mass. Thus, the ability of downscaling a HEMPT to the μN range is investigated experimentally. A measurement campaign studying systematically the influence of the geometrical dimensions of main thruster parameters on operation, beam profile, and ion acceleration is presented. Additionally the anode material was varied and showed relevance to ion acceleration distribution. The minimum achieved thrust was 50 μN at an anode voltage of 600 V, corresponding to a specific impulse of 230 s. Operation points with thrusts of 180 and 360 μN demonstrate a specific impulse of 610 and 860 s, respectively.