Inertial pointing and positioning system

• US 5,809,457 A
• Filed: 03/08/1996
• Issued: 09/15/1998
• Est. Priority Date: 03/08/1996
• Status: Expired due to Fees

• Current Assignee: Administrator of The National Aeronautics and Space Administration, National Aeronautics and Space Administration Administrator of The US Government As Represented By The
• Original Assignee: United States Of America As Represented By The Administrator Of The National Aeronautics And Space Administration
• Inventors: Yee, Robert, Robbins, Fred
• Primary Examiner(s): ZANELLI, MICHAEL J
• Application Number:
  US08/614,784
• Time in Patent Office: 921 Days
• Field of Search: 701/220, 701/221, 701/213, 701/214, 342/357, 342/457, 342/359, 250/203.1
• US Class Current: 701/220
• CPC Class Codes: G01C 21/165 combined with non-inertial navigation instruments
• CPC Class Codes: G01C 21/188 for accumulated errors, e.g. by coupling inertial systems with absolute positioning systems
• CPC Class Codes: G01S 19/53 Determining attitude

Abstract

An inertial pointing and control system and method for pointing to a designated target with known coordinates from a platform, to provide accurate position, steering, and command information. The system continuously receives GPS signals and corrects Inertial Navigation System (INS) dead reckoning or drift errors. An INS is mounted directly on a pointing instrument rather than in a remote location on the platform for monitoring the terrestrial position and instrument attitude, and for pointing the instrument at designated celestial targets or ground based landmarks. As a result, the pointing instrument and the INS move independently in inertial space from the platform since the INS is decoupled from the platform. Another important characteristic of the present system is that selected INS measurements are combined with predefined coordinate transformation equations and control logic algorithms under computer control in order to generate inertial pointing commands to the pointing instrument. More specifically, the computer calculates the desired instrument angles (Phi, Theta, Psi), which are then compared to the Euler angles measured by the instrument-mounted INS, and forms the pointing command error angles as a result of the compared difference.

Claims

1. An inertial pointing system for pointing to a designated target with known coordinates, from a stationary or moving platform, in order to provide accurate position, steering, or command information, the system comprising in combination:

a pointing instrument secured to the platform, and having a field of view and a variable attitude;

an inertial navigation system (INS) decoupled from the platform, and mounted directly onto said pointing instrument, for moving in inertial space independently from the platform, such that the platform becomes slaved to said pointing instrument and said INS; and

a processor for storing a series of predetermined transformation routines, and for interfacing with said INS and converting the attitude of said pointing instrument and said series of transformation routines into command angles, in order to point said pointing instrument accurately at the designated target, so that the target is captured automatically within said field-of-view of said pointing instrument.

2. The inertial pointing system of claim 1, further including a GPS antenna that feeds GPS signals to said INS, for correcting dead reckoning navigation.

3. The inertial pointing system of claim 2, wherein said processor further converts said GPS signals and selected INS measurements into command angles.

4. The inertial pointing system of claim 3, wherein said pointing instrument is any one of a telescope, an antenna, a sensor, a laser, a cannon, and a missile launcher.

5. The inertial pointing system of claim 3, wherein the target is any one of a star, a satellite, a landmark, and a moving object.

6. The inertial pointing system of claim 3, wherein the platform is moving and is any one of an aircraft, a ship, and a ground vessel.

7. The inertial pointing system of claim 3, wherein the platform is fixed.

8. The inertial pointing system of claim 3, wherein said processor transforms selected input data to a selected celestial spherical coordinate frame (Celestial Equator C.E.), and then transforms said C.E. coordinate frame to corresponding Celestial Horizon (C.H.) azimuth and altitude spherical angles.

9. The inertial pointing system of claim 2 further including a position encoder for providing position coordinates of the platform relative to said INS and said instrument.

10. The inertial pointing system of claim 1, wherein said processor further transforms selected input data to a geocentric rectangular coordinate frame.

11. The inertial point system of claim 1, wherein said processor further generates platform steering commands and corrected pointing instructions to said pointing instrument.

12. A method for pointing to a designated target with known coordinates, from a platform, in order to provide accurate position, steering, or command information, the method comprising the steps of:

securing a pointing instrument to the platform, the pointing instrument having a field of view and a variable attitude;

decoupling an inertial navigation system (INS) from the platform, and mounting it directly onto said pointing instrument, for moving in inertial space independently from the platform, such that the platform becomes slaved to said pointing instrument and said INS; and

using a processor for storing a series of predetermined transformation routines, and for interfacing with said INS and converting the attitude of said pointing instrument and said series of transformation routines into command angles, in order to point said pointing instrument accurately at the designated target, so that the target is captured automatically within said field of view of said pointing instrument.

13. The method according to claim 12, further including the steps of:

inputting the known coordinates of the target in said processor; and

feeding GPS signals to said INS for correcting dead reckoning navigation errors, in order to provide accurate positioning and time readings.

14. The method according to claim 13, further including the steps of:

said processor transforms selected input data to a selected celestial spherical coordinate frame (Celestial Equator C.E.), and then transforms said C.E. coordinate frame to corresponding Celestial Horizon (C.H.) azimuth and altitude spherical angles;

said processor transforms selected input data to a geocentric rectangular coordinate frame; and

said processor generates pointing commands and corrected pointing instructions to said pointing instrument.

15. The method according to claim 14, wherein said step of transforming to a selected celestial spherical frame includes the steps of:

computing Greenwich Mean Sidereal Time (GMST);

generating Local Mean Sidereal Time (LMST);

computing Hour Angle (HA); and

transforming said C.E. coordinate frame to said C.H. coordinate frame.

16. The method according to claim 15, wherein said step of transforming selected input data to a geocentric rectangular coordinate frame includes the steps of:

transforming said C.H. coordinate frame to a geocentric coordinate frame;

transforming said geocentric coordinate frame to a geodetic coordinate frame; and

transforming said geodetic coordinate frame to a navigation coordinate frame.

17. The method according to claim 16, wherein said step of inputting the known coordinates of the target in said processor includes the step of inputting right ascension (RA) and declination (DEC) coordinates.

18. The method according to claim 17, where said step of generating pointing commands and corrected pointing instructions to said pointing instrument includes the step of generating instrument angles, and applying a control logic for aligning said pointing instrument in a terrestrial (INS inertial) navigation tangent plane.

19. The method according to claim 18, wherein said step of computing instrument angles includes the step of computing pointing angles (Theta, Psi, Phi) for said instrument in said navigation coordinate frame.

20. The method according to claim 19, wherein said step of applying a control logic includes the steps of computing incremental pointing command angles by comparing INS-generated Euler angles with said computed instrument angles for generating corrected pointing angle commands (PHIcomm, PSIcomm, PHIcomm).

21. A method for determining the coordinates of a target from a platform, comprising the steps of:

securing a pointing instrument to the platform, said pointing instrument having a field of view and a variable attitude;

decoupling an inertial navigation system (INS) from the platform, and mounting it directly onto said pointing instrument, for moving in inertial space independently from the platform, such that the platform becomes slaved to said pointing instrument and said INS;

pointing said pointing instrument to the target; and

using a processor for storing a series of predetermined transformation routines, and for interfacing with said INS and for converting the attitude of said pointing instrument and said series of transformation routines into the coordinates of the target.

22. The method according to claim 21, wherein said step of converting includes the steps of:

using rates (ω

_X, ω

_Y, ω

_Z) corresponding to INS generated Euler angles (Phi, Theta, Psi) and forming a pointing coordinate frame therefrom;

integrating said pointing coordinate frame in a navigation frame to generate a Navigation coordinate frame (Xnav, Ynav, Znav);

transforming the Navigation coordinate frame (Xnav, Ynav, Znav) into a Geodetic coordinate frame vector (Xgeod, Ygeod, Zgeod);

transforming the Terrestrial Geodetic coordinate frame vector (Xgeod, Ygeod, Zgeod) into a Terrestrial Geocentric coordinate frame vector (Xgeoc, Ygeoc, Zgeoc);

transforming the Terrestrial Geocentric coordinate frame vector (Xgeoc, Ygeoc, Zgeoc) into a C.H. coordinate frame vector (Xch, Ych, Zch); and

transforming the C.H. coordinate frame vector (Xch, Ych, Zch) into a C.E. coordinate frame rectangular vector, wherefrom the target coordinates are derived.