Space Tethered Autonomous Robotic Satellite
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STARS (Space Tethered Autonomous Robotic Satellite) project purposes to evaluate and to verify a space mechanical control system by a university satellite, whose characteristics are: it consists of a mother and a daughter (and grandchildren in future) satellites; it becomes a large scale space system using tether; and also robotic mechanical system performs dynamic motion on orbit. The first satellite of the project was "STARS," which was launched by the HIIA rocket on 23, January, 2009. The second satellite was “STARS-II,” which was launched by the H-IIA rocket on 28, February, 2014.
The third satellite is "STARS-C." It was deployed into orbit from ISS (International Space Station) in 2016. It is a 2U Cubesat, and one is a mother and the other is a daughter satellite. They are connected by 100m long tether. Its primary purpose is to analyze basic tether dynamics motion on orbit experimentally. Mission sequence is planned as follows. First, attitude control by magnetic torquers are performed under docking condition of the mother and the daughter satellites, in order to extend the tether along gravity gradient. Initial velocities of the mother and the daughter satellites for tether extension are obtained from the spring force installed in the satellite body. The tether is stowed by the spool, and it is extended as if a wool ball comes loose. Finally, tether extension is terminated by breaking force of the tether reel. Dynamics motion of tether extension is measured by GPS which is mounted on each satellite. Also, a camera module is mounted on each satellite, which is mounted against to another satellite. Gyro sensors, magnetic sensors, and acceleration sensors mounted on each satellite also support dynamics motion analysis. Improvement of STARS-C from the past launched STARS satellites are: (I) automatic tether deployment is possible without main on-board computer; (II) CW beacon includes GPS data although they are transmitted every minutes; (III) 9600bps communication is employed for picture images downlinks.