Autonomous spacecraft rendezvous and docking on safe trajectories


Thesis Type: Post Graduate

Institution Of The Thesis: Orta Doğu Teknik Üniversitesi, Faculty of Engineering, Department of Aerospace Engineering, Turkey

Approval Date: 2018

Student: ALİ TEVFİK BÜYÜKKOÇAK

Consultant: OZAN TEKİNALP

Abstract:

In this thesis, rendezvous and docking operation of a pair of low earth orbit spacecraft is addressed. Two different sets of equations for the nonlinear orbital relative motion of spacecraft are derived and simulation codes for this motion are developed. First, Hill-Clohessy-Wiltshire (HCW) equations are used in chaser-target spacecraft configuration with Model Predictive Control (MPC) algorithm including some safety considerations such as debris avoidance, direction of approach constraint and slow impact requirement. The HCW equations are linearized assuming a circular orbit, and used in MPC algorithm. All authority is given to the chaser spacecraft, and the target is kept passive. Parametric studies are implemented for different cases with several constraint combinations. According to these studies, best planning horizon length and optimal weighting parameter are selected for each case. The safe trajectory generated by MPC approach, which avoids a relatively moving debris represented as an obstacle, is tracked by a novel Lyapunov based control algorithm as well. The algorithm is based on dual quaternions for the motion parametrization and provides a combined control of both translational and rotational motion. Another set of relative motion dynamics including combined attitude and position is derived. An error dual quaternion and its derivative are generated from desired attitude and position information. While desired attitude trajectory is a time-dependent polynomial function, the reference position trajectory is retrieved from MPC plan. Two control approaches are compared, and effectiveness of dual quaternion based control approach is demonstrated.