Abort-safe vehicle rendezvous in case of partial control failure

A controller for controlling an operation of a vehicle in real time to rendezvous the vehicle with a target over a finite time horizon, the controller in communication with a transceiver that accepts data in real time including a target orbit location, and a predetermined subset of a number of operational thrusters that is less than a total number of operational thrusters of the vehicle, comprising:

• a guidance and control computer (GCC) processor in a specified time period within the finite time horizon is to
• access a memory having unsafe regions, and select a set of unsafe regions corresponding to the target orbit location and the predetermined subset of the number of operational thrusters of the vehicle, and wherein the set of unsafe regions represents regions of space around the target in which any operation of the predetermined subset of the number of operational thrusters does not avoid collision with the target, guaranteeing collision trajectories with the target, wherein the set of unsafe regions are determined by computing robust backwards reachable sets of a region around the target;
• formulate the set of unsafe regions as safety constraints, and update a control module having a model of dynamics of the vehicle with the accepted data;
• generate control commands by subjecting the updated control module to the safety constraints to produce a rendezvous trajectory that avoids the set of unsafe regions, guaranteeing an operation of at least the predetermined subset of the number of operational thrusters, in the event of partial vehicle thruster failure results in a trajectory that does not collide with the target;
• and
• output the control commands to activate or not activate one or more thrusters of the vehicle based on the control commands.

A method for controlling an operation of a vehicle in real time to rendezvous the vehicle with a target over a finite time horizon having multiple specified time periods, and accepting data in real time including values of vehicle states and target states in a multi-object celestial system, and a predetermined subset of a number of operational thrusters that is less than a total number of operational thrusters of the vehicle, at a specified time period within the finite time horizon, comprising:

• identifying a target orbit location from the accepted data in real time;
• accessing a memory having unsafe regions, to select a set of unsafe regions corresponding to the target orbit location and the predetermined subset of the number of operational thrusters of the vehicle within the specified time period, and
• wherein the set of unsafe regions represents regions of space around the target in which any operation of the predetermined subset of the number of operational thrusters does not avoid collision with the target, guaranteeing collision trajectories with the target, wherein the set of unsafe regions are determined by computing robust backwards reachable sets of a region around the target;
• formulating the set of unsafe regions as safety constraints, and updating a controller having a model of dynamics of the vehicle with the accepted data;
• generating control commands by subjecting the updated controller to the safety constraints to produce a rendezvous trajectory that avoids the set of unsafe regions, guaranteeing an operation of at least the predetermined subset of the number of operational thrusters, in the event of partial vehicle thruster failure results in a trajectory that does not collide with the target;
• and
• outputting the control commands to activate or not activate one or more thrusters of the vehicle for the specified time period based on the control commands.

A non-transitory machine-readable medium including instructions stored thereon which, when executed by processing circuitry, configure the processing circuitry in real time to perform operations to control a spacecraft to rendezvous the spacecraft with a target over a finite time horizon, such that the spacecraft and the target form a multi-object celestial system, and accepting data in real time including values of spacecraft states and target states in a multi-object celestial system, and a predetermined subset of a number of operational thrusters that is less than a total number of operational thrusters of the spacecraft, at a specified time period within the finite time horizon, comprising:

• identifying a target orbit location from the accepted data in real time;
• accessing a memory having unsafe regions, to select a set of unsafe regions corresponding to the target orbit location and the predetermined subset of the number of operational thrusters of the spacecraft within the specified time period, and wherein the set of unsafe regions represents regions of space around the target in which any operation of the predetermined subset of the number of operational thrusters does not avoid collision with the target, guaranteeing collision trajectories with the target, wherein the set of unsafe regions are determined by computing robust backwards reachable sets of a region around the target;
• formulating the set of unsafe regions as safety constraints, and updating a controller having a model of dynamics of the spacecraft with the accepted data;
• generating control commands by subjecting the updated controller to the safety constraints to produce a rendezvous trajectory that avoids the set of unsafe regions, guaranteeing an operation of at least the predetermined subset of the number of operational thrusters, in the event of partial spacecraft thruster failure results in a trajectory that does not collide with the target;
• and
• outputting the control commands to activate or not activate one or more thrusters of the spacecraft for the specified time period based on the control commands.