Design and Simulation of Sailcraft Attitude Control Systems Using the Solar Sail Control Toolbox

A MATLAB-based software tool, called the Solar Sail Control Toolbox, has been developed for solar sail analysis, design and simulation. The toolbox includes functions for multibody dynamic modeling, attitude control systems design, thrust vector control design, orbit analysis, solar sail mission analysis, thermal analysis and power subsystem analysis. Sailcraft models can be created, analyzed and simulated in the toolbox without the need to deal with any other software tools. This paper demonstrates the toolbox by showing how a gossamer sailcraft with a moving mass actuator and spreader bar control system is modeled and simulated. The toolbox couples attitude and orbit dynamics into the same simulations. The user can choose from several different attitude dynamics models, including specially developed multibody models for the moving mass and gimbaled boom control systems, and from several orbit models including point mass, n-body and non-spherical earth. The moving mass, gimbaled boom, and non-spherical earth dynamics are developed in this paper. The moving mass model permits any number of moving masses that are constrained to have one degree of translational freedom. The gimbaled boom model includes two bodies with one two degree-of-freedom hinge following Hooker’s formulation. The interconnected rigid bodies have joints which allow only rotational motion. Both methods explicitly eliminate constrained degrees of freedom. The non-spherical Earth gravitational model employs the recursive non-singular (except r = 0) method of Mueller and Gottlieb. A disturbance modeling package is included which can be used independently or integrated with the solar sail simulations. Environmental disturbances are: optical disturbances including solar pressure radiation, earth albedo and earth radiation; magnetic and radio-frequency torques; thermal; and aerodynamics. This paper includes the mathematical formulations of the disturbances. It is also possible to include user models of components and disturbances, such as sail membrane models with center of pressure/center of mass offsets. Spacecraft models are created using a graphical computer-aided design package that is included in the toolbox. The component information defined in the CAD package is used to generate mass properties and for all disturbance calculations. Component-level data includes optical and thermal properties for the surfaces; mass, center-of-mass, and inertia; and magnetic dipoles, RF sources, etc. Additional information can also be stored with each component so that the CAD file serves as a database for all spacecraft model data. Simulations are script-based. Controllers are implemented digitally and are not part of the simulation right-hand-side.