Passive Gravity Gradient Capture During In-Space Assembly and Manufacturing

In-space assembly and manufacturing (ISAM) can overcome the volume limitations of rocket fairings and enable the construction of large structures optimized for the space environment. For ISAM of structures with dimensions larger than approximately 100 m, our previous work has highlighted how the capabilities of the ISAM spacecraft’s attitude control system (ACS) result in minimum achievable fabrication times ranging from months to years. This paper explains how to use gravity gradient torques during the ISAM process to overcome these ACS limitations and passively capture the ISAM structure and spacecraft into a gravity-gradient-stabilized final orientation after construction. Our concept, referred to as passive gravity gradient capture, is illustrated during ISAM of two representative truss structures—a 2D triangle unit cell and a 3D curved gridshell—in circular Earth orbits. Each case study uses the time-reversibility of the underlying equations of motion to compute initial conditions for passive attitude trajectories that terminate in stable final orientations. Monte Carlo simulations show that these passive attitude trajectories are sensitive to initial conditions; however, alternate strategies such as deploying a gravity gradient boom before construction can enable robust gravity gradient capture of large structures. Taken together, the results demonstrate the feasibility of passive gravity gradient capture during ISAM and motivate further development of strategies that exploit in-space environmental disturbances for attitude control during ISAM.