A thrust balance for low power hollow cathode thrusters

A hanging thrust balance has been designed, manufactured and tested at the University of Southampton. The current design allows for direct steady thrust measurements ranging from 0.1 mN to 3 mN but this can be easily extended to measure thrust in a different range. Moreover the chosen balance design and the thrust measurement procedure allow for the cancellation of thermal drifts. The thrust balance was tested with a T6 hollow cathode thruster providing measurements with an uncertainty of about 9.7%. The thrust data were compared to those obtained with another direct thrust balance, and they are in quantitative agreement being the maximum difference only 6%

Anomalous behavior of the Debye temperature in Fe-rich Fe-Cr alloys

Debye temperature, $\Theta_D$, of Fe-rich Fe$_{100-x}$Cr$_x$ disordered alloys with $0\le x \le 22.3$ was determined from the temperature dependence of the central shift of M\"ossbauer spectra recorded in the temperature range of 60 -- 300 K. Its compositional dependence shows a maximum at $x \approx 5$ with a relative increase of $\sim 30$% compared to a pure iron. The composition at which the effect occurs correlates well with that at which several other quantities, e. g. the Curie temperature and the spin-wave stiffness coefficient, $D_0$, show their maxima, but the enhancement of $\Theta_D$ is significantly greater and comparable with the enhancement of the hyperfine field (spin-density of itinerant $s$-like electrons) in the studied system. The results suggest that the electron-phonon interaction is important in this alloy system

Modelling and design optimisation of a hollow cathode thruster

The present trend in spacecraft is to have two separate thrusters systems performing different tasks, a main electric propulsion system operating on xenon and a chemical system, usually bipropellants or cold gas. The development of a low power electric propulsion system operating on xenon to replace the chemical thrusters on board spacecrafts would be beneficial. It would be bring significant advantages in terms of mass saving from the sharing of the tanks, pipes and flow control unit, also with improvements in the specific impulse.In recent years experiments have demonstrated the possibility of using hollow cathodes as standalone thrusters, with indirect thrust measurement performed at the University of Southampton. Nevertheless indirect thrust measurements bring large uncertainties on the real value of the thrust. For the first time, direct thrust measurements were carried out with two different thrust balances on two different hollow cathode thrusters, derived from the T5 and T6 hollow cathodes, with unique design modification in the orifice and anode geometry. These measurements provide a unique insight into the real performance range of hollow cathode thrusters. Significant improvements in thrust, specific impulse and thrust efficiency have been achieved thanks to the optimized design of the T6 hollow cathode.The design of the thruster was modified using a one dimensional theoretical model developed within this research. With the help of the theoretical model the optimisation of the hollow cathode thruster design was carried out and a better understanding of the physical mechanisms which contribute to the generation of the thrust could be achieved, with the conclusion of electrothermal and electromagnetic phenomena being the main contributors. The main conclusions of the research and recommendations for related future works are also presented.<br/