GPS attitude determination system and method using baseline extension

• US 7,468,695 B1
• Filed: 07/19/2007
• Issued: 12/23/2008
• Est. Priority Date: 07/19/2007
• Status: Active Grant

• Current Assignee: Raytheon Company (Rtx Corporation)
• Original Assignee: Raytheon Company (Rtx Corporation)
• Inventors: Williams, Darin S.
• Primary Examiner(s): Issing; Gregory C
• Application Number:
  US11/780,270
• Time in Patent Office: 523 Days
• Field of Search: 342/357.11
• US Class Current: 342/357.37
• CPC Class Codes: F41G 3/06 with rangefinder rangefinders per se G01C
• CPC Class Codes: G01S 19/03 Cooperating elements; Interaction or communication between different cooperating elements or between cooperating elements and receivers
• CPC Class Codes: G01S 19/18 Military applications
• CPC Class Codes: G01S 19/54 using carrier phase measurements; using long or short baseline interferometry

Abstract

The baseline of a GPS attitude determination system is extended beyond the confines of the platform to improve attitude determination. A structurally detached GPS antenna is located away from the platform defining an extended baseline to a body-fixed GPS antenna attached to the platform with an unknown orientation with respect to the platform. An electro-optical (EO) sensor on the platform acquires an EO observable reference feature on the remote GPS antenna and measures the extended baseline orientation with respect to the orientation of the platform. A processor processes GPS data, positional or interferometric, from both GPS antennas to determine the extended baseline orientation in a reference coordinate system. The first and second baseline orientations determine platform attitude.

Claims

1. A global positioning system (GPS) attitude determination system, comprising:

a platform having an unknown sight orientation in a reference coordinate system;

a first GPS antenna structurally attached to said platform and configured to receive GPS data from multiple GPS transmitters;

a second GPS antenna structurally detached from said platform and configured to receive GPS data from at least some of the same said GPS transmitters, said second GPS antenna positionable away from the platform to define an extended baseline to the first GPS antenna on said platform with an unknown orientation;

an electro-optical (EO) sensor on one of said platform or said second GPS antenna configured to acquire an EO observable reference feature on the other of said platform or said second GPS antenna and measure a first baseline orientation relative to the sight orientation of the platform;

communication means for communicating GPS data between the second GPS antenna and the platform; and

processing means for processing GPS data from both the first and second GPS antennas to determine a second baseline orientation in the reference coordinate system and estimating the platform'"'"'s sight orientation in the reference coordinate system from said first and second baseline orientations and a platform pitch.

2. The GPS attitude determination system of claim 1, comprising a self-contained attitude determination system including said first GPS antenna for providing position of the platform in the reference coordinate system and attitude means for estimating the platform'"'"'s sight orientation in the reference coordinate system, and further comprising a baseline extension system including the second GPS antenna, EO sensor, communication and processing means for providing a more accurate estimate of the platform'"'"'s sight orientation.

3. The GPS attitude determination system of claim 2, wherein said attitude means comprises a third GPS antenna, a flux compass or an inertial system.

4. The GPS attitude determination system of claim 1, further comprising:

a rangefinder on said platform configured to estimate a range to target; and

an imaging sensor on said platform configured to image the target and determine a line-of-sight (LOS) to the target with respect to the platform'"'"'s sight orientations

said processing means on said platform determining the LOS to the target in the reference coordinate system from said platform'"'"'s sight orientation and the target LOS with respect thereto.

5. The GPS attitude determination system of claim 4, wherein said platform is man-portable for operation by a user to designate the target and said second GPS antenna is man-portable and positionable prior to target designation.

6. The GPS attitude determination system of claim 1, wherein said platform and said second GPS antenna are man-portable.

7. The GPS attitude determination system of claim 1, wherein said EO sensor is on the platform and acquires the EO observable reference feature on the second GPS antenna.

8. The GPS attitude determination system of claim 1, wherein said EO sensor comprises a camera in the visible or near-visible band.

9. The GPS attitude determination system of claim 1, wherein said processing means determines the second baseline orientation using GPS interferometry.

10. The GPS attitude determination system of claim 9, wherein processing means are on said platform, said second GPS antenna includes a receiver that processes the GPS data from the GPS transmitters and transmits a carrier phase difference for each of the same said GPS transmitters and times at which the phase differences occurred to said processing means.

11. The GPS attitude determination system of claim 1, further comprising:

a third GPS antenna structurally detached from said platform and configured to receive GPS data from at least some of the same said GPS transmitters,

wherein said communication means communicates GPS data received by the third GPS antenna to said processing means.

12. The GPS attitude determination system of claim 1, further comprising:

means for determining the platform pitch including at least one of a downfinder on the platform and a third GPS antenna.

13. A global positioning system (GPS) attitude determination system, comprising:

a platform having an unknown sight orientation in a reference coordinate system;

a first GPS antenna structurally attached to said platform and configured to receive GPS data from multiple GPS transmitters;

a second GPS antenna having an electro-optical (EO) observable reference feature and configured to receive GPS data from at least some of the same said GPS transmitters, extract time-stamped carrier phase difference data and communicate the data to said platform, said second GPS antenna structurally detached from the platform to define an extended baseline to the first GPS antenna on said platform with an unknown orientation;

an EO sensor on said platform configured to acquire the EO observable reference feature on the second GPS antenna and measure a first baseline orientation relative to the sight orientation of the platform;

means for determining a pitch of the platform; and

a processor on said platform for processing the GPS data and the time-stamped carrier phase difference data from the GPS antennas using GPS interferometry to determine a second baseline orientation in the reference coordinate system and estimating the platform'"'"'s sight orientation in the reference coordinate system from said first and second baseline orientations and the platform pitch.

14. A global positioning system (GPS) attitude determination system for estimating the geo-location of a distant target, comprising:

a man-portable targeting system including,

a platform having an unknown geo-location and sight orientation in a reference coordinate system,

a range finder configured to provide an estimated range to target,

an imaging sensor on said platform configured to image the target and determine a line-of-sight (LOS) to the target with respect to the platform'"'"'s sight orientation;

a down finder configured to provide a pitch of the platform relative to the reference coordinate system,

a first GPS antenna and receiver configured to receive GPS data from multiple GPS transmitters and determine the geo-location of the platform;

attitude means for estimating the platform'"'"'s sight orientation in the reference coordinate system; and

a processor configured to determine the LOS to the target in the reference coordinate system from said platform'"'"'s sight orientation and the target LOS with respect thereto and use the LOS, platform geo-location and range to target to estimate the geo-location of the distance target, and

a baseline extension system including,

a man-portable second GPS antenna having an electro-optical (EO) observable reference feature and configured to receive GPS data from at least some of the same said GPS transmitters, extract time-stamped carrier phase difference data and communicate the data to said man-portable targeting system, said second GPS antenna structurally detached from the platform to define an extended baseline to the first GPS antenna on said platform with an unknown orientation; and

an EO sensor on said platform configured to acquire the EO observable reference feature on the second GPS antenna and measure a first baseline orientation relative to the sight orientation of the platform;

wherein the processor processes the GPS data and the time-stamped carrier phase difference data from the GPS antennas using GPS interferometry to determine a second baseline orientation in the reference coordinate system and provide an estimate of the platform'"'"'s sight orientation in the reference coordinate system from said first and second baseline orientations and the platform pitch that is more accurate than the estimate provided by the man-portable targeting system'"'"'s attitude means.

15. The global positioning system (GPS) attitude determination system of claim 14, wherein said attitude means comprises a third GPS antenna structurally attached to said platform defining a fixed baseline with a known orientation with respect to the platform sight orientation and a length less than the extended baseline.

16. A method of global positioning system (GPS) attitude determination for a platform having an unknown sight orientation in a reference coordinate system, comprising:

a) receiving GPS data from multiple GPS transmitters at a first GPS antenna structurally attached to said platform;

b) positioning a second GPS antenna having an EO observable reference feature away and structurally detached from said platform to define an extended baseline to the first GPS antenna on said platform with an unknown orientation;

c) electro-optically sensing images of the EO observable reference feature from the platform to acquire the second GPS antenna;

d) measuring a first baseline orientation relative to the sight orientation of the platform from EO sensed images of the second GPS antenna;

e) receiving GPS data from at least some of the same said GPS transmitters at the second GPS antenna;

f) communicating GPS data from the second UPS antenna to the platform;

g) determining a pitch of the platform;

h) processing the GPS data from both the first and second GPS antennas to determine a second baseline orientation in the reference coordinate system; and

i) estimating the platform'"'"'s sight orientation in the reference coordinate system from said first and second baseline orientations and the platform pitch.

17. The method of claim 16, wherein if the second GPS antenna is not acquired,

measuring that platform'"'"'s sight orientation in the reference coordinate system on-board the platform to provide a default estimate that is less accurate than the estimate provided with the extended baseline.

18. The method of claim 16, further comprising manually porting the platform and second GPS antenna to a terrestrial location and positioning said second GPS antenna at said extended baseline.

19. The method of claim 16, further comprising repeating steps (b) through (f) for a third GPS antenna and in step (h) processing the GPS data from the first, second and third GPS antennas.

20. The method of claim 16, further comprising the steps of:

j) estimating a range from the platform to a target;

k) measuring a line-of-sight (LOS) to the target with respect to the platform'"'"'s sight orientation;

l) determining the LOS to the target in the reference coordinate system from said platform'"'"'s sight orientation and the target LOS with respect thereto; and

m) using the LOS in the reference coordinate system, platform geo-location provided by the first GPS antenna and the range to target to estimate a geo-location of the distance target.