Transfer trajectories design for a variable lightness solarcraft

A new configuration of sailcraft that can adjust its lightness number is proposed in this paper. The new-concept sailcraft can evolve along different displaced solar orbits passively. Transfer trajectories between different displaced orbits are investigated, and two different strategies are employed to complete the transfers. When the initial and final orbits are close to each other, a linear model is used to generate an analytical control law first and it is corrected differentially to control the nonlinear model. The transfer accuracy at the target point can be specified in the differential corrections process. Numerical examples are employed to validate the control method over the transfer arc. The results show that the convergence becomes worse as the distance between the two orbits increases until the iteration process does not lead to the desired result when the distance between two orbits is outside the linear range. For these cases, a direct optimization method is employed for transfer trajectory design. The transfer trajectory is divided into segments, and the control law is assumed constant over each segment. Then, the design problem is transformed into a parameter optimization problem. A genetic algorithm and a conjugate gradient method are combined to achieve the desired results. The method proposed in this investigation proved efficient over the range of cases considered.