Coordinated control of satellites: the attitude case
- Paper number
IAC-05-C1.P.08
- Author
Mr. Thomas Krogstad, Norwegian University of Science and Technology, Norway
- Coauthor
Dr. Jan Tommy Gravdahl, Norwegian University of Science and Technology, Norway
- Coauthor
Raymond Kristiansen, Narvik University College, Norway
- Year
2005
- Abstract
In this work coordinated attitude control of satellites in formations, applying methods from mechanical synchronization is studied. Using these techniques, a nonlinear observer and controller is developed for a satellite actuated by means of reaction wheels and thrusters.
The work is part of a study on formation flying of satellites, where the satellite cluster is to perform optical and radar measurements. The individual satellite is actuated by four reaction wheels in a tetrahedron arrangement, providing attitude control thrust about all three axes. For position control, two gas or ion thrusters are positioned along the y axis of the body. Each satellite weighs approximately 150 kg, and has the dimensions 70 x 70 x 70 cm 3.
The satellites are required to point at the object or position which is to be observed, and this puts strict requirements on the attitude determination and control system. The euler angles should be estimated with ± 0.001 ∘ accuracy about all axes and a pointing requirement of ± 0.1 ∘.
The approach to solving this problem is inspired by the synchronization of mechanical system, especially the synchronization of robot manipulators. In the synchronization problem, there is the leader system which typically either is controlled manually or follows a predefined reference trajectory, and one or more followers which tries to follow the leader system and synchronize its movement. This may be directly transferred to problem of coordinated control of several satellites. The approach presented here is to define one satellite as the leader and the remaining as follower systems. The follower satellite will then follow the attitude of the leader satellite.
To implement this, a nonlinear observer-controller structure is designed, since measurements of the angular velocities are unavailable. The controller is designed using observer-backstepping, and the asymptotic stability of the total system is proven using Lyapunov analysis.
The satellite cluster is simulated in Matlab/Simulink, including the relevant disturbances like J2-perturbations, atmospheric drag, solar pressure, off-diagonal elements in the inertia matrix, measurement noise and so on. The simulations indicate good robustness and performance.
- Abstract document
- Manuscript document
IAC-05-C1.P.08.pdf (🔒 authorized access only).
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