The goal of the work described here was to provide an initial step
toward the demonstration of full 6DOF tracking control for simulation
of space flight dynamics. Once sensors have been incorporated to
estimate vehicle position, these methodologies should be extended to
also provide position tracking. Once this capability is in place, the
S/C simulation mode can be extended to include relative orbital
dynamics, and Ranger NBV can be used to study free-flight proximity
One shortcoming of the current implementation is the fact that the thruster geometry and dynamics are not included in the control strategy or the dynamic simulation. Currently, the control algorithm assumes that the thruster system immediately supplies precisely the commanded thrust. In actuality, the thrusters have limited bandwidth, and thus can not immediately supply the commanded force. Additionally, the jet select logic currently used is relatively simple and only approximates the commanded moment. Future work should take thruster dynamics and geometry into account.
Another problem lies in the state estimator. Currently the output of the accelerometer triad is assumed to point down. This is only true when the vehicle is at rest. The equations that describe the accelerations due to vehicle motion as sensed at the accelerometer triad have been derived. In the future, the state estimator should be modified to calculate these accelerations and subtract them from the accelerometer data.
The adaptive controller was designed to handle large changes to vehicle configuration. The Ranger NBV manipulator system can significantly modify the vehicle dynamic characteristics. Preliminary work was conducted on the use of controller adaptation to compensate for changes in vehicle configuration due to manipulator pose. Future studies should explore the ability of the adaptive controller to maintain tracking accuracy when the manipulator configuration changes.
Ranger NBV is intended to be a research tool for the study of space operations. This work here has established a foundation on which future flight control research studies may build. The flight control hardware, interfaces, and algorithms are in place and operational. Please keep them dry.