Design and Analysis of a Solar Sail AOCS for Sunshading Applications at the Sun-Earth Lagrange Point 1

Sammanfattning

A 2018 United Nations report stated that limiting global warming to below 1.5°C is crucial to avoid the worst impacts of climate change. There are numerous ways to do this, one being through geoengineering using solar sails to shade Earth from approximately 2% of the incident sunlight. As part of the Sunshade project at KTH Space Center, this master thesis set out to design an attitude and orbital control system (AOCS) that could sustain a solar sail in the vicinity of the sub-Lagrange 1 (sub-L1) point. Two options were investigated: employing a PD-controller (Proportional-Derivative controller) to asymptotically stabilize the solar sail at any artificial equilibrium in the neighborhood of sub-L1, and designing a controller through Lyapunov’s Direct Method to sustain periodic motion around sub-L1. The study found that the PD-controller managed to track its prescribed reference trajectory to a satisfactory level but required five times more torque than the 0.06 Nmm available with the current solar sail design. The controller derived through Lyapunov’s Direct Method managed to track regular halo orbits. However, it failed to stay on course when applied to more extreme trajectories, even though it was capable of tracking the required attitude to a high degree. All in all, the study concluded that it is feasible to station-keep a solar sail in a Halo orbit around sub-L1, but that asymptotic stabilization at an artificial equilibrium requires too much torque in its current iteration.