Method for determining gravity in an inertial navigation system

• US 6,073,077 A
• Filed: 07/22/1998
• Issued: 06/06/2000
• Est. Priority Date: 07/22/1998
• Status: Expired due to Fees

• Current Assignee: Litton Systems Incorporated
• Original Assignee: Litton Systems Incorporated
• Inventors: Hsu, David Y.
• Primary Examiner(s): Tarcza, Thomas H.
• Assistant Examiner(s): Mull, Fred H
• Application Number:
  US09/120,624
• Time in Patent Office: 685 Days
• Field of Search: 342/450, 342/457, 342/462, 701/220
• US Class Current: 701/220
• CPC Class Codes: G01C 21/185 for gravity
• CPC Class Codes: G01V 7/16 specially adapted for use on moving platforms, e.g. ship, aircraft

Abstract

The invention is a method for determining gravity in an inertial navigation system which periodically produces and stores in memory position coordinates. The method comprises the steps of (a) retrieving the most recently determined position coordinates, (b) determining coordinates L_u, L_n, H_u, and H_n from the position coordinates, L_u and L_n being predetermined functions of geodetic latitude and H_u and H_n being predetermined functions of geodetic altitude, (c) determining the vertical component of gravity by substituting either or both L_u and H_u in a first polynomial expression, (d) determining the north-south component of gravity by substituting either or both L_n and H_n in a second polynomial expression, and (e) utilizing the components of gravity determined in steps (c) and (d) in the next determination of the position coordinates.

Claims

1. A method for determining gravity in an inertial navigation system, the inertial navigation system periodically producing and storing in memory position coordinates, the method comprising the steps:

(a) retrieving the most recently determined position coordinates;

(b) determining coordinates L_u, L_n, H_u, and H_n from the position coordinates, L_u and L_n being predetermined functions of geodetic latitude and H_u and H_n being predetermined functions of geodetic altitude;

(c) determining the vertical component of gravity by substituting either or both L_u and H_u in a first polynomial expression;

(d) determining the north-south component of gravity by substituting either or both L_n and H_n in a second polynomial expression;

(e) utilizing the components of gravity determined in steps (c) and (d) in the next determination of the position coordinates.

2. The method of claim 1 wherein L_u is a function of the eccentric latitude, the eccentric latitude being a function of the geodetic latitude.

3. The method of claim 1 wherein L_u is the square of the sine of the eccentric latitude, the eccentric latitude being a function of the geodetic latitude.

4. The method of claim 1 wherein the first polynomial expression contains terms up to and including the second order in L_u.

5. The method of claim 1 wherein H_u is geodetic altitude.

6. The method of claim 1 wherein the first polynomial expression only contains terms up to and including the second order in H_u.

7. The method of claim 1 wherein L_n is the sine of twice the geodetic latitude.

8. The method of claim 1 wherein the second polynomial expression only contains terms up to and including the second order in L_n.

9. The method of claim 1 wherein the second polynomial expression only contains terms up to and including the first order in L_n.

10. The method of claim 1 wherein H_n is geodetic altitude.

11. The method of claim 1 wherein the second polynomial expression only includes terms up to and including the second order in H_n.

12. The method of claim 1 wherein the second polynomial expression only includes terms up to and including the first order in H_n.

13. The method of claim 1 wherein the second polynomial expression consists of a single term containing the product of L_n and H_n.