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This paper innovatively proposes six scale-independent relative orbital elements, that can be used for dynamics analysis and control for relative motion with near-circular orbits and arbitrary inter-satellite separation. Scale-independent relative orbital elements are deduced from the first-order decomposed relative motion model. These elements reveal the twisted elliptical characteristics of large-range relative motion and standard elliptical characteristics of close-range relative motion. The error of the proposed relative orbital elements keeps zero for circular orbits and the error is irrelevant to inter-satellite range. Based on the scale-independent relative orbital elements, the configuration design equation is established. Given the configuration requirements, the initial orbital elements of the deputy can be calculated. The autonomous configuration control problem is studied by means of artificial potential functions. Scale-independent relative orbital elements are used as control variables, and the large-range reconfiguration and collision avoidance control are realized with low control consumption. • Six independent configuration parameters are proposed for near-circular and arbitrary separation relative motion. • The configuration design equation for large-range relative motion is formulated. • Reconfiguration and collision avoidance control for large-range distributed space systems are realized autonomously. [ABSTRACT FROM AUTHOR]

This paper proposes a novel electromagnetic separation system for the small spherical satellite Q-SAT, which is developed by Tsinghua University. Q-SAT was successfully launched on August 6, 2020 and works well now. Q-SAT requires the separation system no pollution, no impact, multi-point synchronous release and repeatable test. In order to meet these requirements, an electromagnetic separation method is proposed and the system is designed. The system consists of bearing structure, a pair of locking and release mechanism, four ejection mechanism and a drive power. The scheme of separation system can be summarized as "two locks, four ejections". The key to system is the lock and release mechanism using ball-lock principle driven by electromagnets. The analytical relationship of the mechanism driving force is given. How to balance the contradiction between lock and release, which is a problem bring by the system, is discussed. The prototype is made. The verification tests are fully carried out including function, vibration, shock, coldness and velocity measurement. The test results show that the system satisfies the launching requirement. The reliability of the system was proven by the successful separation. Systems based on the same electromagnetic separation method could be widely used on other satellites or payloads in the future. • A novel separation method for a small satellite based on electromagnetic mechanism is proposed. • An electromagnetic separation system is developed for the small spherical satellite Q-SAT based on the method. • The separation system has the characteristics of no impact, no pollution, low cost, repeatable test on the ground and high synchronization. • The separation system is fully verified by test and flight. [ABSTRACT FROM AUTHOR]

Q-SAT, a small spherical satellite designed and developed by Tsinghua university, was successfully launched on Aug 6, 2020 at Jiuquan satellite launch center in China. The mission of Q-Sat is the joint measurement of long-wavelength Earth gravity field and upper atmosphere density, which is of great significance for improving spacecraft orbit prediction and promoting the development of satellite gravity measurement technology. The satellite is designed in spherical shape innovatively and deploys high dynamic dual-frequency GPS as the main payload. On-orbit data shows that the atmospheric density detection precision is in the order of 10−14kg/m3 and the gravity recovery precision achieves the level of 30 orders. All mission success criteria and objectives were achieved. This paper presents the design, space mission, key technologies, science capabilities and preliminary results of the satellite. • Q-SAT, a spherical satellite for the joint measurement of long-wavelength Earth gravity field and upper atmosphere density, was launched in 2020. • An electromagnetic separation system with point connection-release structure is designed for the Q-Sat. • As secondary payload a powerful GPU module is implemented to validate artificial intelligence computing capabilities in orbit. • Modifications for the Jacchia-Roberts atmospheric density model are proposed in the paper. [ABSTRACT FROM AUTHOR]