Attitude slew methodology for space vehicles using gimbaled low-thrust propulsion subsystem

Patent metadata

Field	Value
Publication number	US-9522746-B1
Application number	US-201514838134-A
Country	US
Kind code	B1
Filing date	Aug 27, 2015
Priority date	Aug 27, 2015
Publication date	Dec 20, 2016
Grant date	Dec 20, 2016

Abstract

Apparatus and methods for attitude control of a space vehicle. The space vehicle includes a reaction wheel subsystem and a propulsion subsystem for attitude control. A slew controller for the space vehicle detects a failure of the reaction wheel subsystem. To perform an attitude slew, the slew controller identifies a pair of thrusters in the propulsion subsystem that will rotate the space vehicle about a desired axis. The slew controller determines burn parameters for the pair of thrusters, and initiates the burns to perform the desired attitude slew.

First claim

The invention claimed is:

1. A space vehicle comprising:
a bus having a nadir side and a zenith side opposite the nadir side;
a reaction wheel subsystem that includes a plurality of reaction wheels for controlling attitude of the space vehicle;
a propulsion subsystem that includes a plurality of thrusters installed on the zenith side of the bus each having a thrust less than 0.1 Newton, wherein each of the thrusters is coupled to the bus by a two-axis gimbal assembly; and
a slew controller coupled to the reaction wheel subsystem and the propulsion subsystem;
the slew controller is configured to detect a failure in the reaction wheel subsystem;
in response to the failure, the slew controller is configured to:
determine a target attitude for the space vehicle;
identify a first thruster and a second thruster of the plurality of thrusters that produce an attitude slew of the space vehicle about an axis toward the target attitude;
determine start parameters for the first thruster and the second thruster to initiate the attitude slew about the axis;
direct the first thruster at first gimbal angles based on the start parameters so that thruster forces from the first thruster are spaced by a first moment arm from a center of mass of the space vehicle;
direct the second thruster at second gimbal angles based on the start parameters so that thruster forces from the second thruster are spaced by a second moment arm from the center of mass;
initiate a burn of the first thruster for a first burn duration based on the start parameters; and
initiate a burn of the second thruster for a second burn duration based on the start parameters.

2. The space vehicle of claim 1 wherein:
the slew controller is configured to determine the start parameters by:
determining a slew rate for the attitude slew;
determining a target momentum change of the space vehicle based on the slew rate;
setting the first burn duration of the first thruster and the second burn duration of the second thruster at a minimum;
setting the first gimbal angles of the first thruster and the second gimbal angles of the second thruster to produce thrust through the center of mass; and
performing an iterative process of:
determining an iteration momentum change of the space vehicle based on the first burn duration and the first gimbal angles of the first thruster and based on the second burn duration and the second gimbal angles of the second thruster;
comparing the iteration momentum change to the target momentum change;
using the first burn duration and the first gimbal angles of the first thruster, and the second burn duration and the second gimbal angles of the second thruster as the start parameters when a difference between the iteration momentum change and the target momentum change is less than a threshold; and
adjusting the first gimbal angles of the first thruster and the second gimbal angles of the second thruster when the difference between the iteration momentum change and the target momentum change is greater than the threshold.

3. The space vehicle of claim 2 wherein:
the slew controller is configured to determine the start parameters by:
increasing the first burn duration of the first thruster and the second burn duration of the second thruster when the difference between the iteration momentum change and the target momentum change is greater than the threshold and the first gimbal angles or the second gimbal angles exceed an operational range;
setting the first gimbal angles of the first thruster and the second gimbal angles of the second thruster to produce thrust through the center of mass; and
repeating the iterative process.

4. The space vehicle of claim 2 wherein:
the slew controller is configured to determine the iteration momentum change of the space vehicle using:
{right arrow over (h)} b =t 1 ( {right arrow over (r)} 1 ×{right arrow over (f)} 1 b )+ t 2 ( {right arrow over (r)} 2 b ×{right arrow over (f)} 2 b )

where t 1 is the first burn duration of the first thruster, t 2 is the second burn duration of the second thruster, {right arrow over (f)} 1 b is a force vector for the first thruster, {right arrow over (f)} 1 b is a moment arm vector between the force vector for the first thruster and the center of mass, {right arrow over (f)} 2 b is a force vector for the second thruster, and {right arrow over (r)} 2 b is a moment arm vector between the force vector for the second thruster and the center of mass.

5. The space vehicle of claim 4 wherein:
the slew controller is configured to relate the force vector and the moment arm vector for the first thruster to the first gimbal angles for the first thruster, and to relate the force vector and the moment arm vector for the second thruster to the second gimbal angles for the second thruster.

6. The space vehicle of claim 4 wherein:
the slew controller is configured to determine the start parameters with the iterative process based on a constraint that:
t 1 {right arrow over (f)} 1 o +t 2 {right arrow over (f)} 2 o =0.

7. The space vehicle of claim 1 wherein:
the slew controller is configured to determine a drift duration where the space vehicle rotates about the axis at a constant rate, and allow the space vehicle to drift for the drift duration.

8. The space vehicle of claim 7 wherein:
the slew controller is configured to:
determine stop parameters for the first thruster and the second thruster to stop the attitude slew after the drift duration to achieve the target attitude;
direct the first thruster at third gimbal angles based on the stop parameters so that the thruster forces from the first thruster are spaced by a third moment arm from the center of mass;
direct the second thruster at fourth gimbal angles based on the stop parameters so that the thruster forces from the second thruster are spaced by a fourth moment arm from the center of mass;
initiate a burn of the first thruster for a third burn duration based on the stop parameters; and
initiate a burn of the second thruster for a fourth burn duration based on the stop parameters.

9. The space vehicle of claim 8 wherein:
the slew controller is configured to determine the stop parameters by:
determining a target momentum change of the space vehicle;
setting the third burn duration of the first thruster and the fourth burn duration of the second thruster at a minimum;
setting the third gimbal angles of the first thruster and the fourth gimbal angles of the second thruster to produce thrust through the center of mass; and
performing an iterative process of:
determining an iteration momentum change of the space vehicle based on the third burn duration and the third gimbal angles of the first thruster and based on the fourth burn duration and the fourth gimbal angles of the second thruster;
comparing the iteration momentum change to the target momentum change;
using the third burn duration and the third gimbal angles of the first thruster, and the fourth burn duration and the fourth gimbal angles of the second thruster as the stop parameters when a difference between the iteration momentum change and the target momentum change is less than a threshold; and
adjusting the third gimbal angles of the first thruster and the fourth gimbal angles of the second thruster when the difference between the iteration momentum change and the target momentum change is greater than the threshold.

10. The space vehicle of claim 9 wherein:
the slew controller is configured to determine the stop parameters by:
increasing the third burn duration of the first thruster and the fourth burn duration of the second thrus

Assignees

• Boeing Co

Inventors

• Ih Che-Hang Charles
• Nayak Arunkumar Pursayya
• Lee Kangsik

Classifications

• B64G1/283 Primary

  using reaction wheels · CPC title

• B64G1/413

  Ion or plasma engines · CPC title

• B64G1/262

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

• B64G1/401

  Liquid propellant rocket engines (Ion or plasma engines B64G1/413; Arcjets and other resistojets B64G1/415) · CPC title

• B64G2001/245

  Operations & Transport · mapped topic