Time-Optimal Low-Thrust Formation Maneuvering Using a Hybrid Linear/Nonlinear Controller

MAINTAINING two spacecraft in a formation with a conventional fuel-based propulsion system could be challenging in its own right. But this problem becomes more difficult when the propulsion system has limited capabilities or control actuation is available in only one or two axes and time-optimal and fuel-optimal control is desired. Fortunately, for the spacecraft relative motion problem, because the relative equations of motion are coupled, motion in more than one direction can be controlled by control actuation in only one direction. In this Note, we formulate a hybrid linear/nonlinear controller that can efficiently maneuver a spacecraft formation by applying control only in the along-track direction. We also assume that the available control is very small in magnitude. This type of problem could be anticipated when dealing with low-thrust systems such as plasma thrusters, control with differential drag or solar radiation pressure, or any other system with very-low-thrust capability.