Nonlinear Model Predictive Control based Cooperative Stereo-Visual Coverage of an Asteroid

In this article, a 3D visual coverage problem of an asteroid by establishing a stereo-visual based sensor from monocular cameras is considered. The cameras are individually mounted on two small low-thrust spacecraft, which are maintained in a tight stereo formation using a nonlinear model predictive control scheme to maintain an overlapping field-of-view and a specific baseline distance. The proposed control algorithm adopts a leader-follower architecture to define the relative pose between the spacecraft. However, asteroids provide a challenging environment for such missions deriving from their slow rotation rate and irregular shape. As such, they generate a low-order but irregular gravitational field. Paired with the influence of the solar radiation pressure acting on the spacecraft, the dynamic environment near the asteroid is highly perturbed. In addition, gravitational torque generated by the rotating body is also accounted for as it has a coupling effect between the orbital and attitude dynamics of the spacecraft. As a result, this article considers a full-state nonlinear control approach to plan correction maneuvers to maintain the desired pose of the spacecraft. The efficacy of the proposed control scheme is demonstrated within a realistic simulation scenario where the results are visualized utilizing the GAZEBO simulation environment.