Dynamics and Control of a Tethered Solar Sail Spacecraft for Solar Corona Observation Under the Sun–Earth CRTBP Framework

Continuous high-resolution observation of the solar corona is essential for advancing human's understanding of critical solar phenomena. This study proposes an innovative space-based solar coronagraph mission concept using a tethered solar sail spacecraft. The spacecraft is designed to operate at the umbra terminus near the Sun-Earth L2 Lagrange point. By leveraging Earth as a natural occulter, the spacecraft experiences a sustained artificial total solar eclipse. This unique configuration enables continuous monitoring of the innermost corona, a region typically observable only during brief natural eclipses. To evaluate the feasibility of this concept, a two-dimensional dynamical model of the tethered solar sail system is developed. Based on this model, an artificial equilibrium point induced by solar radiation pressure is identified, and critical spacecraft design constraints are analyzed. A reference spacecraft configuration is proposed, with the probe positioned approximately 1,745 km sunward from the umbra terminus. Periodic orbits resembling Lyapunov orbits are computed, featuring periods of approximately 176.43 days and minor axis amplitudes ranging from 1 to 50 km. To ensure stable operation, a nonlinear model predictive control strategy is developed for station-keeping, with the sail's angular position as the primary control input. Numerical simulations demonstrate the controller's effectiveness to stabilize the spacecraft within the umbra shadow. The system achieves a minimal theoretical corona observation threshold of about 1.0012 solar radii, surpassing conventional coronagraph limitations caused by stray light. These results indicate the potential of this concept to overcome key limitations in solar corona observation.