Research On The Influence Of Test Mass Release Asymmetry In LISA Pathfinder Mission

LISA Pathfinder is a demonstration mission designed to test in space the high-precision technologies required by the gravitational wave observatory LISA(Laser Interferometer Space Antenna). It will use inertial sensors, a laser metrology system, a drag-free control system and an ultra-precise micro-propulsion system. In the space environment, LISA Pathfinder will put two test masses(TM) in a near-perfect gravitational free-falling condition. The freely floating TM is used to demonstrate drag-free and attitude control in a spacecraft, and test feasibility of laser interferometer with picometre resolution at low frequency–approaching 10-12m/Hz1/2 in the frequency band 1~30 m Hz. The laser interferometer is used to measure the distance between the test masses. In-orbit phase, the TM is released into the geodesic trajectory inside the spacecraft by GPRM(Grabbing Positioning and Release Mechanism). LISA Pathfinder will test the low-frequency gravitational wave by controlling and measuring the TM motion with unprecedented accuracy. In this mission, the TM release is one of the key technologies.During the in-flight phase, the TM is locked and released by release tips. Adhesion phenomenon will appear in the contact surface. If the adhesive junctions between contacting bodies are asymmetric or the release tips are asymmetry at location, the adhesive force cannot cancel out during the release phase, which will produce a residual velocity after release. If the TM release fails or the residual velocity is too large, the capacity control system will fail to control the TM in the desired geodesic status. Under scientific model, the residual velocity of the TM must be less than 5?m/s. Therefore, the ground-based release experiment of the TM is very important.As a traditional non-contact sensor of non-contact measuring system, capacitance sensor is widely used in the field of geophysics, aeronautics, high-tech electronics and industrial applications and so on. Capacitance sensor has a lot of advantages such as simple structure, small volume, fast response rate, high accuracy, etc. It can be used to measure displacement, angle, oscillation, and acceleration, etc. Therefore, we can use capacitance displacement sensor to measure the release displacement of the TM, and thus the release velocity and release momentum of the TM are obtained through data processing.We make the release experiment by using double tips release device, investigate the difference between double tips release and single tip release, and analyze the effect of double tips release asymmetry.