NMPC for Spacecraft Rendezvous with Uncontrolled Celestial Bodies
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current methods for spacecraft rendezvous with uncooperative, uncontrolled celestial bodies, such as asteroids, face challenges due to nonlinear dynamics and kinematic coupling, requiring complex simulations and open-loop trajectory designs that are not fully generalizable to arbitrary maneuvers, and lack robust closed-loop regulation capabilities.
Innovation Solution
The implementation of nonlinear model predictive control (NMPC) for a spacecraft to optimize a cost function over a receding horizon, merging the dynamics and kinematics of the controlled spacecraft with the uncontrolled celestial body to form a joint multi-object celestial system, allowing for closed-loop regulation of the relative motion between non-center-of-mass points, and using feedback optimization to account for uncertainties and constraints.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If open-loop trajectory design based on inverse kinematic maps is used, then trajectory planning can be performed, but the method requires simulations done on earth and is not fully generalizable to arbitrary maneuvers
Solution Approach 1:
The patent implements closed-loop feedback control where the spacecraft continuously measures its actual state (position, orientation, velocity) and compares it with the desired trajectory, then adjusts control inputs based on the error signals. This feedback mechanism eliminates the need for complex earth-based simulations for each maneuver type, as the controller adapts to arbitrary maneuvers in real-time through feedback optimization.
Solution Approach 2:
The system transitions from static open-loop trajectory planning to dynamic closed-loop control that adapts to changing conditions. The controller uses real-time state information and optimizes control inputs dynamically, allowing generalization to arbitrary maneuvers without requiring pre-simulation for each specific case.
2Reliability
If thrusters are restricted in placement to avoid plume impingement on antennas and solar panels, then spacecraft safety is improved, but the thrusters cannot provide pure torques and must apply net force, introducing dynamic coupling between rotation and translation
Solution Approach 1:
The closed-loop controller explicitly models and compensates for the dynamic coupling between rotational and translational motion. By using feedback from sensors that measure both attitude and position, the controller can distinguish between desired pure torque maneuvers and unwanted translational effects, then adjust thruster commands to achieve the desired net effect while respecting placement constraints.
Solution Approach 2:
The system changes the control parameters from simple torque commands to coupled force-torque commands that account for thruster placement geometry. The controller transforms desired attitude changes into appropriate thruster force vectors that produce the required moment while minimizing unwanted translation, or compensates for any translation that does occur through feedback.
3Ease of operation
If full 6 degree-of-freedom rigid body models are used to describe relative rotational and translational motion, then rendezvous maneuvers including alignment between robotic graspers and surface rocks can be achieved, but the complexity of kinematic and dynamic relationships increases
Solution Approach 1:
The patent merges the separate attitude control and position control problems into a unified 6-DOF control framework. By treating rotational and translational states together in a single state vector and using a unified cost function that penalizes errors in both attitude alignment and position, the system simplifies the overall control architecture despite the inherent complexity of the coupled dynamics.
Solution Approach 2:
The control system is designed to handle multiple objectives simultaneously through a universal 6-DOF formulation: it can perform approach maneuvers, attitude alignment, and grasper positioning all within the same control framework. This multi-functional approach avoids the need for separate specialized controllers for each maneuver type.
Data Source
AI summary
A controller controls a spacecraft to rendezvous a non-center-of-mass point of the controlled spacecraft with a non-center-of-mass point of an uncontrolled celestial body. The controlled spacecraft and the uncontrolled celestial body form a multi-object celestial system, and the controller produces control commands to thrusters of the controlled spacecraft using a non-linear model predictive control (NMPC) optimizing a cost function over a receding horizon that minimizes an error between coordinates of the non-center-of-mass point of the spacecraft and the non-center-of-mass point of the celestial body subject to joint dynamics of the multi-object celestial system coupled with joint kinematics of the multi-object celestial system.