Projectile guidance with accelerometers and a GPS receiver

• US 6,779,752 B1
• Filed: 03/25/2003
• Issued: 08/24/2004
• Est. Priority Date: 03/25/2003
• Status: Expired due to Fees

• Current Assignee: Northrop Grumman Systems Corporation (Northrop Grumman Corporation)
• Original Assignee: Northrop Grumman Corporation
• Inventors: Ratkovic, Joseph A.
• Primary Examiner(s): Gregory, Bernarr E.
• Application Number:
  US10/396,639
• Time in Patent Office: 518 Days
• Field of Search: 244/3--, 342/357-1-3, 342/13-20, 455/1, 455/114.2, 701/200, 701/207, 701/213-216
• US Class Current: 244/3.15
• CPC Class Codes: F41G 7/346 using global navigation satellite systems, e.g. GPS, GALILEO, GLONASS
• CPC Class Codes: F41G 7/36 using inertial references
• CPC Class Codes: G01S 19/18 Military applications
• CPC Class Codes: G01S 19/21 Interference related issues ; Issues related to cross-correlation, spoofing or other methods of denial of service
• CPC Class Codes: G01S 19/36 relating to the receiver frond end
• CPC Class Codes: G01S 19/49 whereby the further system is an inertial position system, e.g. loosely-coupled
• CPC Class Codes: G01S 19/53 Determining attitude
• CPC Class Codes: G01S 5/011 Identifying the radio environment

Abstract

A projectile guidance system without gyros in which the projectile has an orthogonal body cordinate system. The projectile has a triax of accelerometers providing x, y and z acceleration data measured along the x, y and z axes respectively. A GPS antenna and receiver means provides onboard GPS position and velocity data in earth referenced navigational coordinates. A computer and program means stores and accesses time indexed GPS position and GPS velocity data and transforms x, y and z axis acceleration data from body to navigation coordinates. The program means is responsive to corresponding time indexed acceleration data and to GPS velocity and position data for calculating and outputing an estimated-projectile roll, pitch and yaw angle via optimal smoothing techniques with respect to local level for each time index iteration of present position to a flight control system for guiding the projectile to a predetermined location.

Claims

1. A projectile guidance system with accelerometers and a GPS receiver comprising:

a projectile having a triax of accelerometers mounted in the projectile and providing roll, pitch and azimuth axis acceleration data;

a GPS antenna and receiver means mounted in the projectile for providing and updating present position data; and

a computer and memory mounted in the projectile and executing a guidance program;

wherein the guidance program is responsive to the roll, pitch and azimuth axis acceleration data and to the sampled present position data for calculating and outputing time indexed roll, pitch and azimuth angles, time indexed present position and velocity to a flight control system for guiding the projectile to a predetermined target location;

wherein the GPS antenna and receiver means comprises a GPS jamming detector configured to detect the presence of GPS jamming in the present position data; and

wherein the GPS antenna and receiver means further comprises anti-jamming means.

2. The projectile guidance system of claim 1 wherein the GPS antenna and receiver means comprises a plurality of antennas, each antenna oriented to receive GPS signals from a unique direction.

3. The projectile guidance system of claim 1 wherein said anti-jamming means is configured to cause the projectile to engage in a periodic motion.

4. The projectile guidance system of claim 3 wherein the guidance program is configured to cause trajectory corrections to be made while the projectile is engaged in periodic motion by waiting for an orientation of a control surface to correspond with a direction in which it is desirable to steer the projectile.

5. The projectile guidance system of claim 3 wherein the guidance program is further configured to cause the periodic motion of the projectile to terminate and to therafter cause trajectory corrections to be made while the periodic motion of the projectile has terminated.

6. The projectile guidance system of claim 5 wherein the guidance program is further configured to determine the roll orientation of the projectile using a signal produced by a roll gyro.

7. The projectile guidance system of claim 5 wherein the guidance program is further configured to determine the roll orientation of the projectile using a roll position of a GPS satellites.

8. The projectile guidance system of claim 5 wherein the guidance program is further configured to determine the roll orientation of the projectile using a GPS attitude determination with a plurality of antennas.

9. The projectile guidance system of claim 5 wherein the guidance program is further configured to determine the roll orientation of the projectile using a magnetic turns counter.

10. The projectile guidance system of claim 1 wherein said anti-jamming means is configured to selectively and periodically avoid GPS signals that exhibit jamming.

11. The projectile guidance system of claim 1 wherein said anti-jamming means is configured to cause the projectile to maintain an orientation of the GPS antenna and receiver means so as to permit one or more antenna to substantially continuously receive an unjammed GPS signal.

12. The projectile guidance system of claim 11 wherein, in the event no unjammed GPS signal may be substantially continuously received, said anti-jamming means is further configured to cause the projectile to engage in a periodic motion and to selectively and periodically avoid GPS signals that exhibit jamming.

13. The projectile guidance system of claim 1 wherein the GPS antenna and receiver means is configured to convert a GPS signal from an RF signal to a digital GPS signal substantially immediately after reception.

14. The projectile guidance system of claim 13 wherein the GPS antenna and receiver means is further configured send said digital GPS signal through a digitally implemented automatic gain control circuit.

15. The projectile guidance system of claim 1 wherein the guidance program is further characterized to calculate an estimated projectile trajectory based on data including the launch site present position, initial pitch angle, azimuth angle and the target destination.

16. The projectile guidance system of claim 1 wherein the guidance program is further characterized to calculate an estimated projectile trajectory based on data including the launch site present position, initial pitch azimuth angle, the target destination and data from a turns counter.

17. The projectile guidance system of claim 1 wherein the guidance program is further characterized to calculate an estimated projectile trajectory based on data including the launch site present position, initial pitch angle, azimuth angle, the target destination, data from a turns counter, and a forward sweep recursive filter responsive to previously stored time indexed data for calculating and smoothing an estimated projectile trajectory, and outputting the smoothed time indexed trajectory data to the flight control system for use in guiding the projectile to the predetermined target location after each present position data update.

18. The projectile guidance system of claim 1 wherein the guidance program is further characterized to calculate an estimated projectile trajectory based on data including the launch site present position, initial pitch angle, and azimuth angle, the target destination, data from a turns counter, a forward sweep recursive filter and a backward sweep recursive filter, each respective filter being responsive to previously stored time indexed data for calculating and smoothing an estimated projectile trajectory and outputing the smoothed time indexed trajectory data to the flight control system for use in guiding the projectile to the predetermined target location.

19. The projectile guidance system of claim 1 wherein the guidance program is further characterized to calculate an estimated projectile trajectory based on data including the launch site present position, initial pitch angle, azimuth angle, the target destination, data from a turns counter, a forward Kalman sweep recursive filter and a backward sweep recursive filter, each respective filter being responsive to previously stored time indexed data for calculating and outputing a smoothed estimated projectile trajectory, and iterating the data comprising the smoothed time indexed trajectory data and outputing the smoothed time indexed trajectory data to the flight control system for use in guiding the projectile to the target location.

20. A projectile guidance system without gyros comprising:

a projectile or vehicle in flight after launch, the projectile having an orthogonal body coordinate system with

a longitudinal or x-axis for roll measurement,

a y-axis for pitch measurement, and a

a z-axis for yaw measurement,

the projectile having at least a triax of accelerometers comprising an x accelerometer for providing x-axis acceleration data measured along the x-axis, a accelerometer for providing yaxis acceleration data measured along the y-axis and a z-accelerometer for providing z-axis acceleration data measured along the z-axis,

a GPS antenna and receiver means for providing onboard GPS position and GPS velocity data in earth referenced navigational coordinates,

a computer and memory and program means for storing and accessing time indexed GPS position and GPS velocity data and for transforming

the x, y and z axis acceleration data from body to navigation coordinates, the acceleration data being arrayed and having time indexes common with the OPS position and velocity data,

the program means being responsive to corresponding time indexed acceleration data and to GPS velocity and position data for calculating and outputing an estimated projectile roll, pitch and yaw angle with respect to local level for each time index iteration of present position, velocity and acceleration data to a flight control system for guiding the projectile to a predetermined target location;

wherein the GPS antenna and receiver means comprises a GPS jamming detector configured to detect the presence of GPS jamming in the present position data; and

wherein the GPS antenna and receiver means further comprises anti-jamming means.

21. The projectile guidance system of claim 20 wherein the GPS antenna and receiver means comprises a plurality of antennas, each antenna oriented to receive GPS signals from a unique direction.

22. The projectile guidance system of claim 20 wherein said anti-jamming means is configured to cause the projectile to engage in a periodic motion.

23. The projectile guidance system of claim 22 wherein the guidance program is configured to cause trajectory corrections to be made while the projectile is engaged in periodic motion by waiting for an orientation of a control surface to correspond with a direction in which it is desirable to steer the projectile.

24. The projectile guidance system of claim 22 wherein the guidance program is further configured to cause the periodic motion of the projectile to terminate and to thereafter cause trajectory corrections to be made while the periodic motion of the projectile is terminated.

25. The projectile guidance system of claim 20 wherein said anti-jamming means is configured to selectively and periodically avoid GPS signals that exhibit jamming.

26. The projectile guidance system of claim 20 wherein said anti jamming means is configured to cause the projectile to maintain an orientation of the GPS antenna and receiver means so as to permit one or more antenna to substantially continuously receive an unjammed GPS signal.

27. The projectile guidance system of claims 26 wherein, in the event no unjammed GPS signal may be substantially continuously received, said anti-jamming means is further configured to cause the projectile to engage in a periodic motion and to selectively and periodically avoid GPS signals that exhibit jamming.

28. The projectile guidance system of claim 20 wherein the GPS antenna and receiver means is configured to convert a GPS signal from an RF signal to a digital GPS signal substantially immediately after reception.

29. The projectile guidance system of claim 28 wherein the GPS antenna and receiver means is further configured send said digital GPS signal through a digitally implemented automatic gain control circuit.

30. A process for the guidance of a vehicle or projectile, the vehicle having been launched and having an orthogonal coordinate system with a longitudinal or x-axis for roll measurement, a y-axis for pitch measurement, and a z-axis for yaw measurement, a triax of accelerometers outputing x, y and z axis acceleration, and a GPS antenna and receiver means for providing GPS position and GPS velocity data in earth referenced navigational coordinates, the process comprising the steps of:

receiving, indexing and storing GPS position and velocity data with concurrent x, y and z axis acceleration data;

calculate a trajectory for the set;

converting the x, y and z axis acceleration data to a local level navigational reference system;

solving a set of time indexed state equations to update the system'"'"'s estimated state;

computing a time indexed pitch, roll and yaw angle in locally level coordinates;

outputing the time indexed pitch, roll and yaw angle in locally level coordinates with a corresponding time indexed present position;

guiding the projectile to a destination using the outputted time indexed pitch, roll, yaw angle and time indexed present position data;

the detecting presence of GPS jamming in the present position data; and

counteracting the GPS jamming in the present position data.

31. The process of claim 30 wherein, before the step of receiving, indexing and storing GPS position and velocity data with concurrent x, y and z axis acceleration data, performing the steps of:

estimating and providing a set of initial conditions for insertion into a set of state equations and;

calculating a trajectory for the vehicle as a function of the set of state equations, and the estimated initial conditions.

32. The process of claim 30 wherein, after the step of outputing the time indexed pitch, roll and yaw angle in locally level coordinates with a corresponding time indexed present position, performing the step of:

calculating an estimated projectile trajectory based on data including the launch site present position, initial pitch angle, azimuth angle and the target destination.

33. The process of claim 30 wherein, after the step of outputing the time indexed pitch, roll and yaw angle in locally level coordinates with a corresponding time indexed present position, performing the step of:

calculating an estimated projectile trajectory based on data including the launch site present position, initial pitch angle, azimuth angle and the target destination and data from a turns counter.

34. The process of claim 30 wherein, after the step of outputing the time indexed pitch, roll and yaw angle in locally level coordinates with a corresponding time indexed present position, performing the steps of:

calculating an estimated projectile trajectory based on data including the launch site present position, initial pitch angle, azimuth angle and the target destination and data from a turns counter;

using a forward sweep recursive filter responsive to previously stored time indexed data for calculating and smoothing an estimated projectile trajectory; and

guiding the projectile to the predetermined target location using the smoothed time indexed trajectory data.

35. The process of claim 30 wherein, after the step of outputing the time indexed pitch, roll and yaw angle in locally level coordinates with a corresponding time indexed present position, performing the steps of:

calculating an estimated projectile trajectory based on data including the launch site present position, initial pitch angle, azimuth angle and the target destination and data from a turns counter; and

using a forward sweep recursive filter and a backward sweep recursive filter, responsive to previously stored time indexed data for calculating and smoothing an estimated projectile trajectory.

36. A projectile guidance system without gyros comprising:

a projectile or vehicle in flight after launch, the projectile having an orthogonal body coordinate system with

a longitudinal or x-axis for roll measurement,

a y-axis for pitch measurement, and a

a z-axis for yaw measurement,

the projectile having at least a triax of accelerometers comprising an x accelerometer for providing x-axis acceleration data measured along the x-axis, a y-accelerometer for providing y-axis acceleration data measured along the y-axis and a z-accelerometer for providing z-axis acceleration data measured along the z-axis,

a GPS antenna and receiver means for providing onboard GPS position and GPS velocity data in earth referenced navigational coordinates,

a computer and memory and program means for storing and accessing time indexed OPS position and GPS velocity data and for transforming

the x, y and z axis acceleration data from body to navigation coordinates, the acceleration data being arrayed and having time indexes common with the GPS position and velocity data,

the program means being responsive to corresponding time indexed acceleration data and to GPS velocity and position data for calculating and outputing an estimated projectile roll, pitch and yaw angle with respect to local level for each time index iteration of present position, velocity and acceleration data to a flight control system for guiding the projectile to a predetermined target location;

wherein the GPS antenna and receiver means comprises a GPS jamming detector configured to detect the presence of GPS jamming in the present position data; and

wherein the GPS antenna and receiver means further comprises anti-jamming means.