Study On Spacecraft Orbit Design And Control Scheme Using Continuous Low Thrust

Applications of continuous low thrust technology in the near Earth orbits design and control are researched in this dissertation. The main results achieved are summarized as follows.A relative formation design method based on continuous low thrust is presented, and two typical non-nature formations which are hovering orbits and fast flying around orbits are derived from this method. 1) A hovering method at any selected position to any kind of orbits including circle, elliptical and hyperbolic ones is given, which expands the research domain of hovering orbits. The control thrust and fuel consumption formulas are also developed. 2) A control law to realize fast flying around (FFA) space circle formation on circle orbit is proposed, and the fuel expenditure in a formation period is determined by analytical expression, and an optimality condition is developed such that this fuel expenditure is minimized. Validity of the conclusion is proved by numerical method.A general method to achieve orbits of special mission using continuous low thrust is studied based on Gauss'variation of parameters equations, and three specific orbits are realized using this method as an example. 1) We propose that radial or both of radial and transverse accelerations could be applied to eliminate the rotation of the argument of perigee with arbitrary orbital elements, which means that we can realize artificial frozen orbit while the spacecrafts are not at the critical inclination. Further more, it is proved that the transverse control could save more energy compared with the radial control. Fuel optimization on control strategies are also given, and all the strategies are of no effect on other orbital parameters'secular movement. Amending methods on the control strategies mentioned above are presented to eliminate the residual secular growth of the argument of perigee. 2) Similarly, the ways to realize artificial Sun synchronous orbit and artificial Sun synchronous frozen orbit are presented.Two navigation filters for space targets which are described in inertia coordinate or relative frame are studied using space-based measurements, especially for targets of hovering orbits and artificial frozen orbits. 1) For targets of inertia coordinate, an improved orbit determination filter is developed using bearings-only measurements. In this filter, we rebuild the observation equations with the improved Laplace method in a creative way, which considered both the geometry and orbit restrictions. Simulation results show that convergent performance is dramatically improved compared to general filters with the same measurement precision. 2) For targets of relative frame, a relative navigation Unscented Kalman Filters (UKF) is discussed while the desired orbit is prescribed in terms of quasi-mean element differences. This strategy is designed for spaceborne radar which can provide measurements including range, range rate, angle and angle rate.An adaptive chattering-free sliding mode variable structure feedback control scheme is studied to make sure the hovering states stable. The hovering states are unstable under the open-loop control system considering perturbations and thrust errors, so a feedback sliding mode variable structure control which is adaptive and chattering-free is designed. Under this feedback control scheme, the high-frequency chattering phenomenon is avoided, while the system stays highly robust at the same time. Simulation results show that the feedback control thrusts are continuous and the steady-states error could be confined to 10-4m at the present of uncertain perturbations. The feasibility of realizing hovering orbits is analyzed taking the"Moliya"and GEO (geosynchronous Earth orbit) satellites as example.In this dissertation, from the view of space mission, orbit design and control schemes using continuous low thrust are studied. With the development of electronic propulsion technology, low thrust orbits could be widely used in the future space missions, conclusions of this dissertation may have some application value.