SLyGA

Solar Lyapunov Guidance Algorithm

This repo contains a MATLAB implementation of my undergraduate thesis.

Introduction

My thesis is about trajectory guidance for solar sail spacecraft in orbits around the Earth. My work figures out the best way to point a solar sail at a given instant in time, so that it can go from its current orbit to some target orbit.

• See my one-pager description of the academic significance

• See my interim writeup (late January 2024)

Below is an example of a trajectory I propagated which performs a three-dimensional orbital transfer using a Lyapunov steering law developed by me.

Installation and Setup

Requirements

• MATLAB 2023a (Any recent version of MATLAB should work; but newer versions with ode89 and ode113 are best)

Setup Procedure

1. Clone the repo
2. Open the root folder in MATLAB
3. Run init.m to perform setup. This needs to be run every time MATLAB is restarted.

Code Structure

steering - Steering Algorithms

This code computes the LVLH steering angle in which to point the sail. There are currently two components to the steering algorithm:

1. Modified Q Law - computes an optimal steering angle which decreases the control-Lyapunov potential function as quickly as possible
2. Steering Angle Regularization - accounts for the position of the Sun, and adapts the steering angle proposed by the Lyapunov steering law to something a solar sail can achieve. e.g. Feathering the sail if the desired pointing direction is directly toward the Sun.

sim - Simulator

This folder includes equations of motion, ephemerides, and propulsion models used to "operate" the guidance law.

postprocess - Postprocessing Functions

Used to interpolate, plot, and summarize the results of the simulations.

utils - Utility Functions

This folder includes functions for converting between coordinate frames, computing orbital elements, and other miscellaneous functions.

scripts - Case Files

Various simulation cases to run.

Usage

1. Run one of the mission cases inside scripts.
2. Wait for the sim to finish. Then, run postprocess to show plots.
3. Data will be saved to the outputs folder.

Code Formatting

Code is formatted using MBeautifier.

From the main folder, in the MATLAB command window, run: MBeautify.formatFiles(pwd, "*.m", true) to format all .m files in the repo (takes about 1 minute)