How do you design a solar sail controller for optimal performance and robustness?

1 Solar sail dynamics

Solar sail dynamics are governed by the balance of forces and moments acting on the sail and the spacecraft. The main forces are the solar radiation pressure, which depends on the sail area, reflectivity, and orientation, and the gravitational attraction of the sun and other celestial bodies. The main moments are caused by the sail shape, flexibility, and deformation, and by the spacecraft attitude and inertia. To model the solar sail dynamics, you need to consider the orbital mechanics, the sail geometry, the material properties, and the environmental disturbances.

2 Solar sail control objectives

Solar sail control objectives vary depending on the mission and the phase of operation. Some common objectives are to maintain a desired orbit, to perform orbital maneuvers, to point the spacecraft at a target, to stabilize the sail attitude, to avoid collisions, and to optimize the propulsive efficiency. To achieve these objectives, you need to design a controller that can adjust the sail orientation and shape, using actuators such as gimbals, vanes, thrusters, or shape memory alloys.

3 Solar sail control challenges

Solar sail control challenges stem from the nonlinear, coupled, and uncertain nature of the solar sail dynamics, and from the limited and noisy measurements and actuations available. Some of the challenges are to deal with the time-varying and asymmetric solar radiation pressure, to cope with the large and flexible sail deformations, to account for the orbital perturbations and eclipses, to handle the communication delays and bandwidth constraints, and to ensure the robustness and reliability of the controller.

4 Solar sail control methods

Solar sail control methods can be classified into two main categories: open-loop and closed-loop. Open-loop methods use predefined commands based on analytical or numerical solutions of the optimal control problem, without feedback from the measurements. Closed-loop methods use feedback from the measurements to correct the commands based on the actual state of the system. Open-loop methods are simpler and faster, but less accurate and adaptable. Closed-loop methods are more precise and flexible, but more complex and computationally demanding.

5 Solar sail control tools

Solar sail control tools are software applications that help you design, simulate, test, and implement your controller. Some of the tools are general-purpose, such as MATLAB, Simulink, or Python, which offer a wide range of libraries and functions for control engineering. Some of the tools are specific for solar sail control, such as SAIL, which is a MATLAB toolbox developed by NASA for solar sail dynamics and control analysis. You can use these tools to model your system, design your controller, evaluate its performance, and generate code for your hardware.

6 Solar sail control tips

Solar sail control tips are some practical advice and best practices that can help you improve your controller design and performance. Some of the tips are to use a modular and hierarchical approach, to separate the orbital and attitude control functions, to exploit the natural dynamics of the system, to use adaptive and robust control techniques, to incorporate uncertainty and disturbance estimation and compensation, to use model reduction and simplification techniques, to validate your controller with hardware-in-the-loop testing, and to update your controller with online learning and optimization.

7 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?