A new attitude control method for solar sails is proposed using a single-axis gimbal mechanism and three-axis reaction wheels. The gimbal angle is varied to change the geometrical relationship between the force due to solar radiation pressure (SRP) and the center of mass of the spacecraft, such that the disturbance torque is minimized during attitude maintenance for orbit control. Attitude maneuver and maintenance are performed by the reaction wheels based on the quaternion feedback control method. Even if angular momentum accumulates on the reaction wheels due to modelling error, it can also be unloaded by using the gimbal to produce suitable torque due to SRP. In this study, we analyzed the attitude motion under the reaction wheel control by linearizing the equations of motion around the equilibrium point. Further, we newly derived the propellent-free unloading method based on the analytical formulation. Finally, we constructed the integrated attitude-orbit control method, and its validity was verified in integrated attitude-orbit control simulations.

The solar sail is one of the most promising space exploration systems due to its theoretically infinite specific impulse achieved through solar radiation pressure (SRP). Recently, researchers have proposed "transformable spacecraft" capable of actively reconfiguring their body configurations using actuatable joints. Transformable spacecraft, if used similarly to solar sails, are expected to significantly enhance orbit and attitude control capabilities owing to their high redundancy in control degrees of freedom. However, controlling them becomes challenging due to their large number of inputs, leading previous researchers to impose strong constraints to limit their potential control capabilities. This study focuses on novel attitude control techniques for transformable spacecraft under SRP. We developed two methods, namely, joint angle optimization to obtain arbitrary SRP force and torque, and momentum damping control driven by joint angle actuation. Our proposed methods are formulated in a general manner and can be applied to any transformable spacecraft comprising front faces that can predominantly receive the SRP on each body. The validity of our proposed method is confirmed through numerical simulations. Our study contributes to making most of the high control redundancy of transformable spacecraft without the need for expendable propellants, thus significantly enhancing the orbit and attitude control capabilities.

This paper proposes new quasi-periodic orbits around Earth–Moon collinear libration points using solar sails. By including the time-varying sail orientation in the linearized equations of motion for the circular restricted three-body problem (CR3BP), four types of quasi-periodic orbits (two types around L1 and two types around L2) were formulated. Among them, one type of orbit around L2 realizes a considerably small geometry variation while ensuring visibility from the Earth if (and only if) the sail acceleration due to solar radiation pressure is approximately of a certain magnitude, which is much smaller than that assumed in several previous studies. This means that only small solar sails can remain in the vicinity of L2 for a long time without propellant consumption. The orbits designed in the linearized CR3BP can be translated into nonlinear CR3BP and high-fidelity ephemeris models without losing geometrical characteristics. In this study, new quasi-periodic orbits are formulated, and their characteristics are discussed. Furthermore, their extendibility to higher-fidelity dynamic models was verified using numerical examples.

Solar radiation pressure (SRP) impinging on spacecraft is usually regarded as a disturbance for attitude motion, but it can be harnessed to solve the very problem it creates. Active SRP control is possible with solar radiation powered thin-film devices such as reflectivity control devices or liquid crystal devices with reflective microstructure. Thermal radiation pressure (TRP) can likewise be used to solve flight attitude problems caused by SRP, TRP, or other factors. TRP on solar cells can be controlled by switching regulators under the control of them, resulting in temperature change. These SRP/TRP controls are free from mechanisms, such as reaction wheels, and thus they do not produce internal disturbances. In addition, the magnitude of SRP/TRP torques is generally much smaller than internal disturbance torques produced by reaction wheels, which creates a potential for precision far beyond that achieved with mechanical controls. This paper summarizes how SRP/TRP can be used by means of numerical simulations of typical control methods. The usefulness of this mechanism-free attitude control is verified for future use on both Earth orbiting satellites and interplanetary spacecraft including solar sails.