Satellite position monitor

• US 6,462,707 B1
• Filed: 03/22/2001
• Issued: 10/08/2002
• Est. Priority Date: 03/22/2001
• Status: Expired due to Fees

• Current Assignee: Lockheed Martin Corporation (Martin Marietta Corporation)
• Original Assignee: Lockheed Martin Corporation (Martin Marietta Corporation)
• Inventors: Clark, Ronald H.
• Primary Examiner(s): Blum, Theodore M.
• Application Number:
  US09/813,812
• Time in Patent Office: 565 Days
• Field of Search: 342/357.06, 701/213, 455/12.1, 455/427, 455/428
• US Class Current: 342/357.395
• CPC Class Codes: G01S 19/02 Details of the space or ground control segments

Abstract

The present invention is a system for providing GPS users with a high level of confidence in the integrity and accuracy of received GPS signals. A first GPS satellite broadcasts a GPS navigation message to GPS users in view of the satellite. The first GPS satellite also sends a copy of the GPS navigation message to a second GPS satellite via an RF or optical crosslink. The second GPS satellite then determines the position and time of the first GPS satellite relative to the second GPS satellite based on the contents of the received GPS navigation message. The second GPS satellite compares this relative position and time to satellite position and time data stored in the second GPS satellite, such as ephemeris/almanac data received from a ground station or Autonav data. The second GPS satellite thereby checks whether the GPS navigation message received from the first GPS satellite has integrity. The second GPS satellite then sends an integrity message back to the first GPS satellite via a crosslink. The first GPS satellite transmits an integrity message to all in view GPS receivers. The GPS receivers can then determine whether or not the GPS signals being received have integrity. If the integrity message contains correction data, the GPS receivers can use the correction data to correct the GPS signals. The GPS users will thus be provided with very high confidence in the integrity, accuracy, and reliability of the GPS position and time data.

Claims

1. A system for verifying the integrity of a navigation message transmitted from a Global Positioning System (GPS) satellite, comprising:

a first GPS satellite transmitting a GPS navigation message to GPS users in view of the satellite; and

a second GPS satellite

receiving a copy of the GPS navigation message transmitted from the first GPS satellite,

determining the integrity of the copy of the GPS navigation message by comparing the copy of the GPS navigation message with data stored in the second GPS satellite, and

sending an integrity message to the first GPS satellite.

2. The system of claim 1, wherein the data stored in the second GPS satellite includes at least one of:

ephemeris and/or almanac data received from a ground station; and

Autonav data.

3. The system of claim 2, wherein the second GPS satellite determines the integrity of the copy of the GPS navigation message by determining a position and/or time of the first GPS based on the copy of the GPS navigation message, and comparing the position and/or time of the first GPS satellite with the data stored in the second GPS satellite.

4. The system of claim 1, wherein the first GPS satellite generates a GPS integrity message based on the integrity message received from the second GPS satellite.

5. The system of claim 4, wherein the GPS integrity message indicates the accuracy and/or the integrity of the GPS navigation message.

6. The system of claim 5, wherein the first GPS satellite transmits the GPS integrity message to GPS users in view of the satellite.

7. The system of claim 6, wherein the GPS integrity message is included in the GPS navigation message.

8. The system of claim 6, wherein the first GPS satellite transmits the GPS integrity message over a channel separate from the channel transmitting the GPS navigation message.

9. The system of claim 8, wherein the separate channel is the L5 channel.

10. The system of claim 1, wherein the first GPS satellite transmits a copy of the GPS navigation message to additional GPS satellites, and receives integrity messages from each GPS satellite.

11. A method for verifying the integrity of a navigation message transmitted from a Global Positioning System (GPS) satellite, comprising:

transmitting a GPS navigation message from a first GPS satellite to GPS users in view of the satellite;

transmitting a copy of the GPS navigation message to a second GPS satellite; and

determining the integrity of the copy of the GPS navigation message by comparing the copy of the GPS navigation message with data stored in the second GPS satellite.

12. The method of claim 11, wherein the data stored in the second GPS satellite is satellite position and/or time data.

13. The method of claim 12, further comprising:

transmitting an integrity message from the second GPS satellite to the first GPS satellite, the integrity message indicating the integrity of the copy of the GPS navigation message.

14. The method of claim 12, wherein the satellite position and/or time data includes at least one of:

ephemeris and/or almanac data received from a ground station; and

Autonav data.

15. The method of claim 12, wherein the second GPS satellite determines the integrity of the copy of the GPS navigation message by determining a position and/or time of the first GPS satellite based on the copy of the GPS navigation message, and comparing the position and/or time of the first GPS satellite with the stored satellite position and/or time data.

16. The method of claim 12, further comprising:

generating a GPS integrity message;

transmitting the GPS integrity message to all GPS users in view of the first GPS satellite.

17. The method of claim 16, wherein the GPS integrity message indicates the accuracy and/or the integrity of the GPS navigation message.

18. The system of claim 17, wherein the first GPS satellite transmits the GPS integrity message to GPS users in view of the satellite.

19. The system of claim 18, wherein the GPS integrity message is included in the GPS navigation message.

20. The method of claim 18, wherein the first GPS satellite transmits the GPS integrity message over a channel separate from the channel transmitting the GPS navigation message.

21. The method of claim 20, wherein the separate channel is the L5 channel.

22. The method of claim 12, further comprising:

transmitting a copy of the GPS navigation message to a additional GPS satellites; and

receiving integrity messages from the additional GPS satellites.

23. A system for verifying the integrity of a signal transmitted from a space vehicle, comprising:

a first space vehicle transmitting a signal and a copy of the signal; and

a second space vehicle receiving the copy of the signal and verifying the integrity of the copy of the signal, the second space vehicle informing the first space vehicle of the integrity of the first space vehicle'"'"'s transmissions.

24. The system of claim 23, wherein the first space vehicle transmits an integrity signal indicating the integrity of its transmissions.

25. The system of claim 24, wherein the first and second space vehicles are GPS satellites.

26. A method for verifying the integrity of a navigation message transmitted from a first space vehicle comprising, comprising:

transmitting a signal and a copy of the signal from a first space vehicle;

receiving the copy of the signal at a second space vehicle; and

verifying the integrity of the copy of the signal received at the second space vehicle; and

informing the first space vehicle of the integrity of the transmissions from the first space vehicle.

27. The method of claim 26, wherein the first and second space vehicles are GPS satellites.