Presentazioni e Articoli Tecnici

In order to gather more detailed information on the rising sea level, glacier melting and tectonic plate movements to improve our understanding of global and climate change, the Next Generation Gravity Mission (NGGM) is being prepared by the European Space Agency (ESA) in cooperation with the National Aeronautics Space Administration (NASA). These effects can be observed by long-term monitoring of the temporal fluctuations of the Earth’s gravity field. Therefore, a ranging instrument measures the variation of the distance between two satellites in the orbit, one pair of observation satellites in a near-polar orbit and a second pair in an inclined circular orbit. To allow a precise formation flight of two satellites, the mission requires station keeping, drag compensation in Low Earth Orbit (LEO) and a high thrust stability and reliability for more than 5.5 years. Ion thrusters are candidates to propel and align these satellites. To produce thrust, ions are accelerated and leave the spacecraft while electrons remain. This leads to a negative spacecraft charge, potentially causing sparks and discharges or disturbing the on-board measurement systems. A spacecraft neutralizer is being developed at FOTEC, in order to compensate the occurring charge. A thermionic electron source is one of the main components. To support the design and optimization process of the electron gun, COMSOL Multiphysics was used. The goal was to develop an electron gun able to provide a laminar electron beam of 80 mA with a uniform current density leaving the aperture. The AC/DC module and the Particle Tracing Module were used to simulate the electric fields and to compute the particle trajectories. To get started with the design process, a simplified pierce gun configuration was designed to find dimensions and potentials in accordance with the mission requirements. Parametric sweeps in a bidirectionally coupled particle tracing study were performed. The mechanical design, derived from the simulation results was manufactured and tested. Further, COMSOL Multiphysics was used to verify the mechanical design. The AC/DC module was used to calculate the electric fields, in order to validate the spacing and insulator thicknesses while the Particle Tracing module was used to estimate the required potentials to be applied to the electrodes and to investigate the influence of the potentials of the plume. A sensitivity analysis was performed to investigate the influence of misalignment of the electrodes on the electron beam. In conclusion, COMSOL Multiphysics supported the complete design process of the spacecraft neutralizer from the first prototype to be tested to the validation and optimization of the breadboard model. Experimental results showed that the electron beam leaves the aperture as expected. In further investigations, COMSOL Multiphysics will be used for optimization and characterization, as well as for the plume analysis . This paper summarizes the process of the development of a spacecraft neutralizer including simulation results verified by experimental efforts.