Tsinghua University Freefall Facility (TUFF): A 2.2 Second Drop Tunnel for Microgravity Research

• Published in: Microgravity science and technology 2021-04, Vol.33 (2), Article 26
• Main Authors: Luo, Lei, Zhou, Hengyi, Sun, Yuhang, Zhang, Wenyi, Chen, Tao, Chen, Shuqing, Wen, Yuzhe, Xu, Shilong, Yu, Suyuan, Liu, Yu Cheng
• Format: Article
• Language: English
• Subjects: Aerospace Technology and Astronautics; Cables; Classical and Continuum Physics; Deceleration; Drag; Eddy current brakes; Eddy currents; Engineering; Microgravity; Multinational space ventures; Noise levels; Original Article; Permanent magnets; Safety; Science and technology; Space Exploration and Astronautics; Space Sciences (including Extraterrestrial Physics; Space stations; Terminal velocity; Tuff; Weight
• ISSN: 0938-0108; 1875-0494
• DOI: 10.1007/s12217-021-09877-5

Ground-based freefall facilities are to create microgravity environment on earth for studying the space-related or fundamental sciences, which have been widely used in the field of combustion, fluid, physics and material sciences. Aiming to serve for the broader microgravity science and preliminary tests for projects onboard the upcoming assembly of Chinese Space Station, a 2.2 second freefall facility was designed and built in the Lee Shau Kee Science and Technology Building on the campus of Tsinghua University in Beijing. This facility is composed of five systems: (I) freefall tunnel and safety cables; (II) release and retrieve system; (III) the capsule; (IV) brake system; (V) electrical control and safety interlock system. The capsule consists of an outer drag shield and an inner rig of which the total weight is 280 kg. The capsule is released by a pneumatic chuck that minimizes disturbance of the release operation. The eddy current brake modules made of several permanent magnets are applied to decelerate the capsule without power supply. This paper primarily discusses the tests designed and conducted to characterize the performance of such facility in many aspects. The results show that during freefall, the microgravity level of 10 -3 g can be achieved for 2.2 second. Concerning movement of the inner rig relative to the drag shield during freefall, the clearance of 0.43 m and relative velocity of 0.62 m/s were specified. The deceleration can be controlled within 15 g. The terminal velocity of capsule in the brake system ranges from 0.4 to 0.5 m/s depending on the actual weight of capsule. The noise level in the entrance section of brake system is about 75.6 dB. The duration of this noise is very short (