Model predictive control of spacecraft

Patent metadata

Field	Value
Publication number	US-10967991-B2
Application number	US-201715674477-A
Country	US
Kind code	B2
Filing date	Aug 10, 2017
Priority date	Aug 10, 2017
Publication date	Apr 6, 2021
Grant date	Apr 6, 2021

Abstract

A spacecraft including a set of thrusters for changing a pose of the spacecraft. At least two thrusters mounted on a gimbaled boom assembly and are coupled together sharing the same gimbal angle. A model predictive controller (MPC) to produce a solution for controlling thrusters of the spacecraft by optimizing a cost function over a receding horizon using a model of dynamics of the spacecraft effecting a pose of the spacecraft and a model of dynamics of momentum exchange devices of the spacecraft effecting an orientation of the spacecraft. A modulator to modulate magnitudes of the thrust of the coupled thrusters determined by the MPC as pulse signals specifying ON and OFF states of each of the coupled thruster, wherein the ON states of the coupled thrusters sharing the same gimbal angle do not intersect in time. A thruster controller to operate the thrusters according to their corresponding pulse signals.

First claim

What is claimed is:

1. A spacecraft comprising:
a spacecraft bus;
a set of thrusters for changing a pose of the spacecraft, wherein at least two thrusters are mounted on a gimbaled boom assembly connecting the two thrusters with the spacecraft bus, such that the two thrusters are coupled thrusters sharing the same gimbal angle;
a set of momentum exchange devices for absorbing disturbance torques acting on the spacecraft; and
a model predictive controller (MPC) to produce a solution for controlling thrusters of the spacecraft by optimizing a cost function over a receding horizon using a model of dynamics of the spacecraft effecting a pose of the spacecraft and a model of dynamics of the momentum exchange devices of the spacecraft effecting an orientation of the spacecraft, wherein the model of dynamics of the spacecraft includes independent rotation of the coupled thrusters, such that the two thrusters that share the same gimbal angle in the gimbaled boom assembly have different gimbal angles in the model;
a modulator to modulate magnitudes of the thrust of the coupled thrusters determined by the MPC as pulse signals specifying ON and OFF states of each of the coupled thruster, such that the ON states of the coupled thrusters sharing the same gimbal angle do not intersect in time allowing rotation of the coupled gimbal angle to implement the non-intersecting pulse signals; and
a thruster controller to operate the thrusters according to their corresponding pulse signals.

2. The spacecraft of claim 1 , wherein the MPC controller specifies angles and magnitude of the thrusts of the thrusters, and wherein the thruster controller operate the gimbal to rotate the coupled thrusters to the angle of thrust of the thruster currently scheduled to have ON state.

3. The spacecraft of claim 1 , wherein the modulator is a closed-loop pulse-width modulator (PWM) that quantizes the magnitude of the thrust at a predetermined frequency to produce a pulse signal, wherein a width or a duty cycle of the pulse signal is specified by the continuous thrust request from the MPC and the predetermined frequency.

4. The spacecraft of claim 1 , wherein the MPC controller optimizes the cost function subject to hard constraints and soft constraints on angles of thrusts generated by thrusters of the spacecraft, wherein the hard constraints requires the angles of thrusts in the solution to fall within a predetermined range defined by the hard constraints, and wherein the soft constraints penalize the solution for deviation of the angles of thrusts from nominal angles corresponding to a torque-free thrust passing through the center of the mass of the spacecraft.

5. The spacecraft of claim 4 , wherein the soft constraints form a component of the cost function.

6. The spacecraft of claim 5 , wherein the cost function includes a component for the pose of the spacecraft penalizing a displacement of the spacecraft from a target pose and a component for a momentum stored by the momentum exchange devices penalizing a larger value of a magnitude of the stored momentum.

7. The spacecraft of claim 1 , wherein the model of dynamics of momentum exchange devices of the spacecraft includes dynamics of inner-loop control of the momentum exchange devices, wherein the model of dynamics of the spacecraft includes the dynamics of the inner-loop control, such that the solution of the MPC controller accounts for effects of actuation of the momentum exchange devices according to the inner-loop control.

8. The spacecraft of claim 7 , wherein the inner-loop control reduces an error between the orientation of the spacecraft and a target orientation of the spacecraft, wherein the solution of the MPC controller specifies angles and magnitude of the thrusts of the thrusters to reduce speed of the momentum exchange devices.

9. The spacecraft of claim 1 , wherein the model of dynamics of the spacecraft includes a linear nominal model defining relationships among parameters of the model and a disturbance model defining disturbance forces acting on the spacecraft located at a target position for the entire period of the receding horizon.

10. The spacecraft of claim 1 , wherein a magnitude summation constraint, which is a sum the magnitude of thrust requests from the MPC for all thrusters during a control period is less than a thrust magnitude when in the ON State, then the MPC is capable of performing a mutually exclusive time modulation, via utilizing the magnitude summation constraint by the MPC as a constraint on control inputs in controlling the spacecraft.

11. The spacecraft of claim 1 , wherein the modulator quantizes a requested thrust value from the MPC over a control period to be either fully ON or fully OFF with a single pulse width, based on determining an ON time and an OFF time, resulting from a nonlinear optimization of a cost function, wherein the nonlinear optimization minimizes a predicted error in quantities for the spacecraft that a post-MPC modulation process generates, compared to quantities of motion resulting from the thrust requested by MPC.

12. A spacecraft comprising:
a spacecraft bus;
a set of thrusters for changing a pose of the spacecraft, wherein at least two thrusters are mounted on a gimbaled boom assembly connecting the two thrusters with the spacecraft bus, such that the two thrusters are coupled thrusters sharing the same gimbal angle;
a set of momentum exchange devices for absorbing disturbance torques acting on the spacecraft; and
a model predictive controller (MPC) to produce a solution for controlling thrusters of the spacecraft by optimizing a cost function over a receding horizon using a model of dynamics of the spacecraft effecting a pose of the spacecraft and a model of dynamics of the momentum exchange devices of the spacecraft effecting an orientation of the spacecraft, wherein the model of dynamics of the spacecraft includes independent rotation of the coupled thrusters, such that the two thrusters that share the same gimbal angle in the gimbaled boom assembly have different gimbal angles in the model;
a modulator to modulate magnitudes of the thrust of the coupled thrusters determined by the MPC as pulse signals specifying ON and OFF states of each of the coupled thruster, such that the ON states of the coupled thrusters sharing the same gimbal angle do not intersect in time allowing rotation of the coupled gimbal angle to implement the non-intersecting pulse signals; and
a thruster controller to operate the thrusters according to their corresponding pulse signals.

13. The spacecraft of claim 12 , wherein the MPC controller specifies angles and magnitude of the thrusts of the thrusters, and wherein the thruster controller operate the gimbal to rotate the coupled thrusters to the angle of thrust of the thruster currently scheduled to have ON state.

14. The spacecraft of claim 12 , wherein the modulator is a closed-loop pulse-width modulator (PWM) that quantizes the magnitude of the thrust at a predetermined frequency to produce a pulse signal, wherein a width or a duty cycle of the pulse signal is specified by the continuous thrust request from the MPC and the predetermined frequency.

15. The spacecraft of claim 12 , wherein the MPC controller optimizes the cost function subject to hard constraints and soft constraints on angles of thrusts generated by thrusters of the spacecraft, wherein the hard constraints requires the angles of thrusts in the solution to fall within a predetermined range defined by the hard constraints, and wherein the soft constraints penalize the solution for deviation of the angles of thrusts from nominal angles corresp

Assignees

• Mitsubishi Electric Res Laboratories Inc

Inventors

• Weiss Avishai
• Zlotnik David
• Di Cairano Stefano

Classifications

• B64G1/40

  Arrangements or adaptations of propulsion systems · CPC title

• B64G1/262

  having adjustable angles, e.g. gimbaled thrusters · CPC title

• B64G1/2429

  Station keeping · CPC title

• B64G1/286

  using control momentum gyroscopes (CMGs) · CPC title

• B64G1/00

  Cosmonautic vehicles · CPC title