Model Predictive Control of Spacecraft

Patent metadata

Field	Value
Publication number	US-2016194095-A1
Application number	US-201514591298-A
Country	US
Kind code	A1
Filing date	Jan 7, 2015
Priority date	Jan 7, 2015
Publication date	Jul 7, 2016
Grant date	—

Abstract

A method controls an operation of a spacecraft according to a model of the spacecraft. The method determines control inputs for controlling concurrently thrusters of the spacecraft and momentum exchange devices of the spacecraft using an optimization of a cost function over a receding horizon subject to constraints on a pose of the spacecraft and constraints on inputs to the thrusters. The cost function includes components for controlling the pose of the spacecraft and a momentum stored by the momentum exchange devices. The method generates a command to control concurrently the thrusters and the momentum exchange devices according to at least a portion of the control inputs.

First claim

Claimed is:

1 . A method for controlling an operation of a spacecraft according to a model of the spacecraft, comprising:
determining control inputs for controlling concurrently thrusters of the spacecraft and momentum exchange devices of the spacecraft using an optimization of a cost function over a receding horizon subject to constraints on a pose of the spacecraft and constraints on inputs to the thrusters, wherein the cost function includes components for controlling the pose of the spacecraft and a momentum stored by the momentum exchange devices; and generating a command to control concurrently the thrusters and the momentum exchange devices according to at least a portion of the control inputs, wherein steps of the method are performed by a processor of the spacecraft.

2 . The method of claim 1 , wherein the optimization is based on the model of the spacecraft including a nominal model defining relationships among parameters of the model and a disturbance model defining disturbance forces acting on the spacecraft.

3 . The method of claim 2 , further comprising:
performing a linearization of the nominal model as if the spacecraft is located at a target position for the entire period of the receding horizon; and determining the disturbance forces as if the spacecraft is located at the target position for the entire period of the receding horizon.

4 . The method of claim 1 , wherein the constraints on the pose of the spacecraft include a position constraint maintaining a position of the spacecraft within a predetermined window and an orientation constraint maintaining Euler Angles of the spacecraft within a predetermined limit.

5 . The method of claim 1 , wherein the constraints on the inputs to the thrusters guarantees an ability of the thrusters to jointly generate a force for controlling the pose of the spacecraft and a torque for unloading the momentum stored by the momentum exchange devices of the spacecraft.

6 . The method of claim 1 , wherein the generated command includes a command to the momentum exchange devices to unload the stored momentum and a command to the thrusters to generate a force and a torque to maintain or change the pose of the spacecraft and compensate for a torque generated by the momentum exchange devices unloading the stored momentum.

7 . The method of claim 6 , further comprising:
generating first a total torques and forces command that are requested from the propulsion system of the spacecraft and then inverting the total torques and forces command to generate control inputs to each individual thruster.

8 . The method of claim 1 , further comprising:
determining the cost function as a combination of multiple components including a component for a position of the spacecraft penalizing a displacement of the spacecraft from a desired position, a component for an attitude of the spacecraft penalizing larger values of Euler Angles of the spacecraft, a component for the stored momentum penalizing larger value of a magnitude of the stored momentum, a component for an objective of the operation of the spacecraft, and a component for ensuring a stability of the operation of the spacecraft.

9 . The method of claim 8 , further comprising:
weighting each of the components of the cost function, such that the optimization of the cost function produces control inputs that achieve goals of each individual component with priority corresponding to their relative weight.

10 . The method of claim 9 , wherein the control inputs are determined iteratively, and wherein at least one iteration comprises:
updating one or combination of the components of the cost function and weights of the components of the cost function based on a change of a desired operation of the spacecraft.

11 . A control system for controlling an operation of a spacecraft according to a model of the spacecraft, comprising at least one processor for executing modules of the control system, the modules comprising:
a control input module for determining control inputs for controlling concurrently thrusters of the spacecraft and momentum exchange devices of the spacecraft using an optimization of a cost function over a receding horizon subject to constraints on a pose of the spacecraft and constraints on inputs to the thrusters, wherein the cost function includes components for controlling the pose of the spacecraft and a momentum stored by the momentum exchange devices; and a force-torque map module for generating a command to control concurrently the thrusters and the momentum exchange devices according to at least a portion of the control inputs, wherein the generated command includes a command to the momentum exchange devices to unload the stored momentum and commands to individual thrusters to generate forces and torques to maintain or change the pose of the spacecraft and to compensate for a torque generated by the momentum exchange devices unloading the stored momentum.

12 . The control system of claim 11 , wherein the optimization is based on the model of the spacecraft including a nominal model defining relationships among parameters of the model and a disturbance model defining disturbance forces acting on the spacecraft, further comprising:
a current model module for linearizing the nominal model and determining the disturbance forces as if the spacecraft is located at a target position for the entire period of the receding horizon.

13 . The control system of claim 11 , wherein the constraints on the pose of the spacecraft include a position constraint maintaining a position of the spacecraft within a predetermined window and an orientation constraint maintaining Euler Angles of the spacecraft within a predetermined limit, and wherein the constraints on the inputs to the thrusters guarantees an ability of the thrusters to jointly generate a force for controlling the pose of the spacecraft and a torque for unloading the momentum stored by the momentum exchange devices of the spacecraft.

14 . The control system of claim 11 , further comprising:
a cost function module for determining the cost function as a combination of multiple components including a component for a position of the spacecraft penalizing a displacement of the spacecraft from a desired position, a component for an attitude of the spacecraft penalizing an increase of Euler Angles of the spacecraft, a component for the stored momentum penalizing an increase of a magnitude of the stored momentum, a component for an objective of the operation of the spacecraft, and a component for ensuring a stability of the operation of the spacecraft, and for weighting each of the components of the cost function, such that the optimization of the cost function produces control inputs that achieve goals of each individual component with priority corresponding to their relative weight.

15 . The control system of claim 14 , wherein the control inputs are determined iteratively, and wherein for at least one iteration, the cost function module updates one or combination of the components of the cost function and weights of the components of the cost function based on a change of a target operation of the spacecraft.

16 . A spacecraft comprising:
a set of thrusters for changing a pose of the spacecraft; a set of momentum exchange devices for absorbing disturbance torques acting on the spacecraft; and the control system of claim 11 for controlling the thrusters and the momentum exchange devices.

17 . A spacecraft comprising:
a set of thrusters for changing a pose of the spacecraft; a set of momentum exch

Assignees

• Mitsubishi Electric Res Lab

Inventors

• Weiss Avishai
• Di Cairano Stefano
• Kalabic Uros

Classifications

• B64G1/26 Primary

  using jets · CPC title

• B64G1/244

  Spacecraft control systems · CPC title

• G05D1/0883

  Physics · mapped topic

• G05D1/10

  Simultaneous control of position or course in three dimensions (G05D1/12 takes precedence) · CPC title

• B64G2001/245

  Operations & Transport · mapped topic