Aiming at the requirement of low cost, high precision and high stability of space advanced technology demonstration satellite, a method of heterogeneous backup of attitude control sensor is proposed, and the design principle of the sensor is analyzed in depth multi-sensor information fusion algorithm is designed. The control strategy of the satellite is optimized, the weighted PID control strategy is designed, and a reasonable integral separation threshold is selected. Control bandwidth is adjusted to reduce the control deviation caused by time delay. The objective of the attitude control system is to achieve control accuracy better than 0.1°(3σ) and control stability better than 0.003°/s(3σ).Through the analysis of on-orbit test data, the control accuracy of the satellite is better than 0.005°(3σ), and the control stability is better than 0.0005°/s(3σ).
The Earth 2.0 (ET) mission is a Chinese next-generation space mission to detect thousands of Earth-sized terrestrial planets, including habitable Earth-like planets orbiting solar type stars (Earth 2.0s), cold low-mass planets, and freefloating planets. To meet the scientific goals, the ET spacecraft will carry six 30 cm diameter transit telescopes with each field of view of 500 square degrees, and one 35 cm diameter microlensing telescope with a field of view of 4 square degrees, monitor ~1.2M FGKM dwarfs in the original Kepler field and its neighboring fields continuously while monitoring over 30M stars in the Galactic bulge direction. The high precision transit observations require high photometry precision and pointing stability, which is the key drive for the ET spacecraft design. In this paper, details of the overall mission modeling and analysis will be presented. The spacecraft orbit, pointing strategy, stability requirements are presented, as well as the space-ground communication analysis. The ET spacecraft adopts an ultra-high photometry precision & high stable platform, largely inherited from other space science missions. The preliminary design of spacecraft which meets mission requirements is introduced, including the spacecraft overall configuration, observation modes, avionics architecture and development plan, which pays great attention to the pointing stability and huge volume science telemetry download.
The Earth 2.0 (ET) mission is a Chinese next generation space mission designed to find thousands of terrestrial-like planets including habitable Earth-like planets orbiting solar type stars (Earth 2.0s) through the transiting method, and cold and free-floating low-mass planets through the microlensing method. The mission will monitor 1.2M FGKM dwarf stars for patterns of transits with a differential photometry precision of 34 ppm for a G = 13.5 mag solar type star in a 6.5-hr exposure. ET will be operated at the Earth-Sun L2 halo orbit with a designed lifetime longer than 4 years. To increase the probability of discovering Earth 2.0s, wide field-of-view (FoV) and ultra-high photometry precision are two key features of this mission. The wide field transiting telescope design offers 500 square degrees of FOV. High photometry precision is achieved by the scientific payload design as well as high stable spacecraft pointing in both short term (jitters) and long-term (drifts). According to our photometry simulations and analysis, the ET spacecraft stability requirement is not the usual relative pointing error (RPE) applied in most space missions, but the forward sum stability, in which both high frequency jitters and low frequency drifts are critical for high precision photometry measurements. Therefore, the spacecraft design needs to not only deal with high frequency jitters, but also the thermal-elastic effects of scientific payloads, including long-term thermal stability of the telescope structure, cameras, fine guiding camera, and mounting plate. This paper presents the pointing stability definition suitable for the ET mission. Simulations of high precision photometry observations with different pointing stability scenarios are presented. Approaches to the high stability are also discussed.
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