TianQin is a proposed Chinese space-borne gravitational wave detection mission, which will consist of three Earth-orbiting spacecraft in equilateral triangle constellation. Due to the ``3 months on + 3 months off'' observation scheme, the continuous scientific observation period of TianQin is much shorter than LISA, it is highly preferred that other on-board operations, such as charge management, will not interrupt gravitational wave detection. This paper presents a torsion pendulum system on the ground to investigate the continuous discharge method in detail. It is found that the difference in surface characteristics between the test mass and the surrounding housing is the most critical to the success of the continuous discharge method. The effect of this difference on the continuous discharge process was evaluated in ground simulation experiments. And then based on our ground test, we also proposed a more feasible spatial continuous charge management strategy for TianQin.

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A simple, cost-effective and high-accuracy measurement of parallelism by dual autocollimators is proposed. A differential measurement was chosen to eliminate most of the environmental noises and systematic errors. The accuracy of parallelism measurement can reach the level of 1.6 µrad (1σ). This method can be widely used for parallelism measurements of components with reflective coating, such as glass blocks in metrology laboratories and test masses in the Gravitational Reference Sensor.