The feasibility studies and the preliminary design of the attitude and orbit control and propulsion subsystems (AOCS/RCS (Rate Control System)) for the Aristoteles satellite, as defined in phase A studies, are summarized. The main design drivers for the AOCS are the acceleration stability requirement (10(exp -7) rd/sq s, 5 x 10(exp -7) rd/sq s in the range of 0.005 to 0.125 Hz), and the magnetometer attitude determination accuracy (20 arcseconds); operating on a very low altitude orbit (200 Km) is an additional constraint. The proposed AOCS concept allows the autonomy required by orbit altitude. Fine attitude control is achieved using low noise gyros and low disturbance reaction wheels with PID controller. Star sensors provide measurements for the fine attitude estimation. The capability of drag control is specific to Aristoteles; it is achievable by control of the cross section area with deployable flaps. An attitude yaw steering mode is possible to minimize the disturbances from lateral aerodynamics forces. The RCS design drivers are the total impulse requirement to achieve the various orbit corrections and maintenance, and the fuel management requirement to limit dynamic disturbance and motions of the center of mass. The selected hydrazine RCS has a storage capacity about 1000 kg; the tanks have elastomeric membrane to limit fuel motions. A continuous estimation of individual tank consumption is achieved which allows the balancing of the fuel mass in the various tanks. An assessment of the performances of the AOCS/RCS is shown to validate the concepts.
Attitude and Orbit Control System on the Aristoteles Satellite
1991
5 pages
Report
No indication
English
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