Due to the processing accuracy of the test mass (TM) in gravitational reference sensors, the electrostatic force in the non-sensitive direction of the TM will produce a cross-coupling effect in the sensitive direction. This paper quantifies the impact of TM geometric imperfections (parallelism and perpendicularity) on electrostatic cross-coupling noise. The electrostatic coupling effects are examined while the TianQin spacecraft adopts free and drag-free modes in the Z direction by examining the solar radiation pressure during the scientific operation period. In the free mode, the electrostatic force couples the lowfrequency variations of solar pressure to the sensitive direction, which requires the coupling coefficient to be better than 3 × 10−6. The drag-free mode can effectively reduce the electrostatic control forces in non-sensitive directions, thereby reducing coupling effects, which the coupling coefficient requirement can be relaxed to 7.5 × 10−5. By reducing the displacement sensing noise, the requirement for coupling coefficient can be further reduced.
