Method and system for space navigation

• US 5,957,982 A
• Filed: 08/18/1998
• Issued: 09/28/1999
• Est. Priority Date: 08/18/1998
• Status: Expired due to Fees

• Current Assignee: Northrop Grumman Corporation
• Original Assignee: TRW Limited (Zeppelin - Stiftung der Stadt Friedrichshafen)
• Inventors: Busby, Michael, Steiner, Paul, Lane, D. Hobson, Taylor, Warren H., Galloway, Arnold J., Kang, Bryan H., Hughes, George C., Lavoie, Paul A., Hanson, Mark L., Wehner, Michael J.
• Primary Examiner(s): Cuchlinski, Jr., William A.
• Assistant Examiner(s): Beaulieu, Yonel
• Application Number:
  US09/135,884
• Time in Patent Office: 406 Days
• Field of Search: 701/13, 701/4, 701/200, 701/255, 701/6, 342/354, 342/5, 342/357, 342/8, 342/357.01, 342/357.16, 342/357.15, 342/357.02, 455/12.1, 455/13.2, 455/427, 244/158 R
• US Class Current: 701/13
• CPC Class Codes: G06F 17/10 Complex mathematical operations function generation by table look-up G06F1/03; evaluation of elementary functions by calculation G06F7/544

Abstract

A method that allows a space vehicle to determine navigation information represented by the contents of a state vector. The method includes the steps of intermittently receiving navigation signals, initializing the state vector with an estimate of the navigation information, and generating a predicted state vector that represents the predicted values for the navigation information after a predetermined time increment in the future. The method further determines whether a navigation signal has been received within a predetermined window of time from a navigation beacon. If a navigation signal has been received, the method updates the state vector and the contents of the state vector are propagated forward in time to provide an estimate of the navigation information after a predetermined time increment. In some instances, however, a navigation signal is not received within the predetermined window of time. In such situations, the method simply propagates the contents of the predicted state vector forward in time. Thus, the predicted state vector maintains an estimate of the current navigation information even in the absence of a navigation signal.

Claims

1. A method for autonomously determining, given intermittent reception of navigation signals, navigation information for a space vehicle operating in Earth orbit, the navigation information represented by the contents of a state vector, the method comprising the steps of:

operating a space vehicle in Earth orbit;

initializing a state vector with navigation information;

generating a predicted state vector;

intermittently receiving a navigation signal;

when the navigation signal is received, updating the state vector based on the current contents of the state vector, the predicted state vector, and the contents of the navigation signal; and

propagating the contents of the state vector forward in time by a predetermined time interval, thereby replacing the contents of the predicted state vector;

when the navigation signal has not been received within a predetermined window time;

autonomously propagating the contents of the predicted state vector forward in time by the predetermined time interval to provide a navigation solution.

2. The method of claim 1, wherein the step of initializing a state vector initializes the state vector with at least position and velocity navigation information.

3. The method of claim 2, wherein at least one of the propagating steps propagates in accordance with a gravity model of the Earth including perturbations of at least the Sun and the Moon.

4. The method of claim 3, wherein at least one of the propagating steps further propagates in accordance with a radiation pressure model.

5. The method of claim 3, wherein the initializing step further initializes the state vector with at least clock bias navigation information, and wherein at least one of the propagating steps further propagates in accordance with a clock model.

6. The method of claim 3, wherein the step of intermittently receiving receives a pseudo-lite navigation signal.

7. The method of claim 3, wherein the step of intermittently receiving receives a GPS navigation signal.

8. The method of claim 3, wherein the step of intermittently receiving receives a GPS navigation signal escaping around the Earth.

9. The method of claim 1, wherein the updating step further comprises the step of determining a self-correcting filter gain and wherein the updating step updates the state vector based in part on the filter gain.

10. The method of claim 1, wherein the updating step further comprises the step of updating an error covariance matrix and wherein at least one of the propagating steps further comprises the step of updating the error covariance matrix.

11. The method of claim 1, further comprising the steps of comparing the navigation solution to a predetermined guidance solution and responsively commanding trajectory adjustments through a propulsion system.

12. The method of claim 1, wherein each of the updating and propagating steps occurs onboard the space vehicle.

13. A method for autonomously determining, given inconsistent reception of navigation signals, navigation information for a deep space vehicle operating beyond MEO altitude, the navigation information represented by the contents of a state vector, the method comprising the steps of:

operating a deep space vehicle beyond MEO altitude;

initializing a state vector with navigation information;

generating a predicted state vector;

intermittently receiving a navigation signal;

when the navigation signal is received, updating the state vector based on the current contents of the state vector, the predicted state vector, and the contents of the navigation signal; and

propagating the contents of the state vector forward in time by a predetermined time interval thereby replacing the contents of the predicted state vector;

when the navigation signal has not been received within a predetermined window time;

autonomously propagating the contents of the predicted state vector forward in time by the predetermined time interval to provide a navigation solution.

14. The method of claim 13, wherein the step of initializing a state vector initializes the state vector with at least position and velocity navigation information.

15. The method of claim 14, wherein at least one of the propagating steps propagates in accordance with a gravity model of a third body other than the Earth.

16. The method of claim 15, wherein at least one of the propagating steps further propagates in accordance with a radiation pressure model.

17. The method of claim 15, wherein the initializing step further initializes the state vector with at least clock bias navigation information, and wherein at least one of the propagating steps further propagates in accordance with a clock model.

18. The method of claim 15, wherein at least one of the propagating steps propagates in accordance with a gravity model including perturbations of at least the Earth and the Sun.

19. The method of claim 17, wherein at least one of the propagating steps propagates in accordance with a gravity model including perturbations of at least the Earth and the Sun.

20. The method of claim 15, wherein the step of intermittently receiving receives a pseudo-lite navigation signal.

21. The method of claim 15, wherein the step of intermittently receiving receives a GPS navigation signal.

22. The method of claim 13, wherein the updating step further comprises the step of determining a self-correcting filter gain and wherein the updating step updates the state vector based in part on the filter gain.

23. The method of claim 13, wherein the updating step further comprises the step of updating an error covariance matrix and wherein at least one of the propagating steps further comprises the step of updating the error covariance matrix.

24. The method of claim 15, further comprising the steps of comparing the navigation solution to a predetermined guidance solution and responsively commanding trajectory adjustments through a propulsion system.

25. The method of claim 13, wherein each of the updating and propagating steps occurs onboard the deep space vehicle.

26. The method of claim 13, wherein the step of propagating the contents of the predicted state vector comprises propagating the predicted state vector according to a Runge-Kutta approximation.