Evaluation of microgravity level for the 2.0 s vacuum drop tower at the National Precise Gravity Measurement Facility (PGMF)

The drop tower is an important experimental facility to provide a microgravity environment on the ground. The National Precise Gravity Measurement Facility has built a vacuum drop tower at Wuhan in China. The vacuum drop tower has a falling-height of 20 m, a free falling-time of 2.0 s, and a pressure of ∼6.15 Pa after 1 h pumping. The microgravity level of the vacuum drop tower is analyzed in this paper. The error sources include the aerodynamic drag, the difference of gas pressure around the gaps, the misalignment, the rotation, the magnetic field, etc. The evaluated microgravity level of the vacuum drop tower is better than (4.80 ± 3.31) × 10−7g, which is mainly limited by the aerodynamic drag and the rotation of the capsule. In addition, the microgravity level is measured to be better than 3.22 × 10−5g by using the quartz-flexure accelerometer. The vacuum drop tower provides a ground-based public service platform with a microgravity environment on the order of magnitude of 10−7g for further experiments.