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A momentum flux measuring instrument (MFMI), which ranges from 1 mN∼300 N, is designed to measure the parameters related to the momentum flux of exhaust plume of attitude and orbit control thrusters covered electric and chemical thrusters. A MFMI with the variable-range provides an efficient and economy way to study the exhaust plume of both electric and chemical thrusters. The flexural pivots, replaceable strain gauge, replaceable target plate, and force arm with the variable length make it possible. The designed MFMI with the non-displacement measurement can reduce the influence of pipelines and test lines, especially the elastic force and friction due to displacement. The designed MFMI system with the range of 0∼100 mN and 0∼15 N was calibrated separately. The target indirect measurement method is a simple and economical option for measuring the thrust of electric thrusters, and is employed to measure the thrust of the LIPS-200 ion thruster using the designed MFMI. Research indicates that the sputtering contributes to the momentum transfer of plasma-surface interactions. In addition, the high-speed charged ions from the thruster will experience a charge-exchange (CEX) collision with the slow neutral background. Therefore, the influence of the sputtering and CEX on target indirect measurement method is derived in detail, and then the measured thrust is corrected. The measured average thrust, which is 40.1 mN, demonstrates that the designed MFMI is effective. The designed MFMI can also be employed as a thrust stand by directly mounting the thrusters on torsional arm, and a maximum of three thrusters can be installed on the MFMI at the same time.

The plume flow of space thrusters can cause series of harmful effects to spacecraft by impinging on some sensitive surfaces. To prevent the plume impingement effects that a 60N thruster can do to the backflow region, a plume protect cover is intended to be assembled to the thruster. The flow field from the combustion chamber of the thruster to the vacuum environment contains both continuum and rarefied flow regimes, which makes it difficult to model this flow phenomenon by using one single method. The coupled NS/DSMC method is one of the best choices for modeling the continuum-rarefied transitional flows. In present study, a coupled NS/DSMC solver is developed by the authors and is used to estimate the effect of the plume protector assembled to the 60N thruster. The present coupled NS/DSMC solver is constructed with the NS solver NozzleFlow and DSMC solver PWS. Interface location is determined by combining two continuum breakdown parameters. One is the KnGL parameter and the other is the thermal non-equilibrium parameter Ptne. State-based coupling method is adopted to transfer information between the continuum and particles methods. The continuum-rarefied interfaces and gas parameters of the vacuum plume flow field of the thruster are obtained by conducting coupled calculation, which shows that the plume protector can decrease the mass flux density in the back flow region by two orders. The present coupled NS/DSMC method can be a useful tool for the vacuum plume effects analysis.

A stable high-order discontinuous Galerkin scheme which strictly preserves the positivity of the solution is designed to solve the Boltzmann kinetic model equations. The stability is kept by the accuracy of the velocity discretization, the conservation of the collision terms and a limiter. By requiring the time step smaller than the local mean collision time and forcing positive values of velocity distributions on certain points, the limiter can preserve the positivity of the solutions of the cell average velocity distributions. Verification is performed with a normal shock wave at Mach number of 2.05 and a supersonic flow about a 2D cylinder at Mach number of 6.0.