PROJECTILE NAVIGATION ENHANCEMENT METHOD

• US 20100133374A1
• Filed: 12/01/2008
• Published: 06/03/2010
• Est. Priority Date: 12/01/2008
• Status: Active Grant

• Current Assignee: Raytheon Company (Rtx Corporation)
• Original Assignee: Raytheon Company (Rtx Corporation)
• Inventors: Scarborough, Charles, Vesty, Paul, Geswender, Chris E.
• Granted Patent: US 8,519,313 B2
• Time in Patent Office: Days
• US Class Current: 244/3.200
• CPC Class Codes: F42B 10/02 Stabilising arrangements
• CPC Class Codes: F42B 15/01 Arrangements thereon for guidance or control steering arrangements F42B10/60; aircraft flight control B64C; guidance systems other than those installed aboard F41G7/00, F41G9/00; locating by use of radio or other waves G01S; flight control in general G05D1/00; computer aspects G06]

Abstract

A projectile, such as a missile, rolls during at least a portion of its flight, while retaining its roll reference to enable navigation during the rolling period of flight. The roll reference may be retained by using a sensor, such as magnetometer, to periodically check and correct the roll reference. Alternatively or in addition the missile may alternate roll directions, for example varying roll rate in a substantially sinusoidal function. By rolling the missile inaccuracies in an inertial measurement unit (IMU) of the missile may be ameliorated by being to a large extent canceled out by the changes in orientation of the missile as the missile rolls. This enables use of IMUs with lower accuracy than would otherwise be required to obtain accurate flight. Thus accurate flight may be accomplished with less costly IMUs, without sacrificing the ability to navigate.

Claims

1. A method of flight control of a projectile, the method comprising:

providing the projectile with a microelectromechanical system (MEMS) inertial measurement unit (IMU); and

reducing trajectory errors by rolling the projectile while maintaining a roll reference in the MEMS IMU, wherein the rolling evens out at least some inaccuracies of the MEMS IMU.

2. The method of claim 1, wherein the keeping the roll reference includes using an orientation sensor of the missile to correct the roll reference.

3. The method of claim 2, wherein the sensor includes a magnetometer.

4. The method of claim 1, wherein the rolling includes rolling at a substantially constant roll rate over time.

5. The method of claim 1, wherein the rolling includes alternating roll directions as part of rolling the missile.

6. The method of claim 5, wherein the alternating roll directions includes varying roll rate as a repeating periodic function over time.

7. The method of claim 6, wherein the repeating periodic function is a ramped step function.

8. The method of claim 1, wherein the rolling includes rolling at a rate of at least 180 degrees/second.

9. The method of claim 1, wherein the reducing trajectory errors includes improving accuracy of the MEMS IMU by at least a factor of ten.

10. A method of flight control of a projectile, the method comprising:

during flight of the projectile, alternately rolling the missile periodically in opposite directions.

11. The method of claim 10, wherein the alternating rolling includes varying roll rate as a repeating periodic function over time.

12. The method of claim 11, wherein the repeating periodic function is a ramped step function.

13. The method of claim 10, further comprising keeping a roll reference of a microelectromechanical system (MEMS) inertial measurement unit (IMU) during the rolling.

14. The method of claim 13, wherein the keeping the roll reference includes using an orientation sensor of the missile to correct the roll reference.

15. The method of claim 14, wherein the sensor includes a magnetometer.

16. The method of claim 10, wherein the alternately rolling includes rolling at a maximum roll rate of at least 180 degrees/second.

17. A method of operating a projectile, the method comprising:

providing the projectile with a microelectromechanical system (MEMS) inertial measurement unit (IMU) compatible with accelerations associated with launching the projectile from a gun; and

maneuvering the projectile during flight to reduce the effect of inaccuracies of the MEMS IMU.

18. The method of claim 17, wherein the maneuvering includes rolling the projectile.

19. The method of claim 18, wherein the rolling includes alternately rolling the missile periodically in opposite directions, wherein the alternating rolling includes varying roll rate as a repeating periodic function over time.