Study On Dynamics And Control Of Sail-craft

Deep space exploration throughout the history of human being is very important in science, technology, politics and culture. Fuel becomes a bottleneck of the development of deep space explorations as the missions are far from the earth. Many new types of propulsion are proposed, where solar sail that can provide low thrust with infinite impulse is considered to be one of the most practical methods. There are several missions related to solar sail being studied by NASA and ESA. The dynamics and control of sailcraft is the key point of theoretical research, which is also very important for the achievement of solar sail missions.Different from traditional spacecraft, the orbit and attitude of solar sail are coupled strongly. Firstly, this thesis gives the conditions of solar sail being stable on periodic orbits and investigates the dependence of the coupled system stability on the orbit and attitude stability when only the attitude influences the orbit. Then, the passive control of solar sail is analyzed with only orbit dynamics considered. Passive control requires the angle between the normal vector of solar sail and the solar light direction to be constant. With passive control, the solar sail orbit is stable and its initial momentum determines the orbit parameters. Based on the conclusions of passive control and stable conditions of the coupled system, the passive stability configurations of solar sail on displaced solar orbit and at artificial Lagrange point are designed.Solar sail technology will not meet the solar sail size requirements in a long time. This thesis proposes the concept of solar sail formation flying and investigates the stability of relative motion near displaced orbits with several attitude control laws. A set of relative orbit elements are defined to describe the elliptic relative orbits. The shape and normal of the relative orbit are restricted to certain ranges. With the difficulty of measuring relative velocity considered, a relative orbit design method is proposed to obtain diverse relative orbits with only position feedback. Numerical simulations are employed to validate the design method.Formation control is one of the important research fields in formation flying around Lagrange point. The research results show that the impulse control can not achieve high-precision formation and the solar sail that can provide low thrust of micro-newton is able to achieve small-size high-precision formation. However, solar sail cannot realize all formation control because the direction of the solar sail radiation pressure force is restricted to certain range. This thesis gives the linear and circular formations that require the control forces within the capability of solar sail and numerical simulations are employed to test the validation of the solar sail control.The merits of gravitational tractor in asteroid deflections are its high reliability and independence of asteroid characteristics, and the demerit is its low deflection efficiency. In this thesis, the asteroid deflection is realized by controlling the gravitational tractor on a displaced orbit above the asteroid. The gravitational tractor formation flying is proposed to enhance the deflection ability and two formation control strategies are investigated. Lastly, the deflection capabilities of traditional gravitational tractor and solar sail gravitational tractor are compared.