Unambiguous integer cycle attitude determination method

• US 6,587,761 B2
• Filed: 10/23/2001
• Issued: 07/01/2003
• Est. Priority Date: 10/23/2001
• Status: Expired due to Fees

• Current Assignee: Aerospace Corporation
• Original Assignee: Aerospace Corporation
• Inventors: Douglas, Randal K., Kumar, Lalit
• Primary Examiner(s): Beaulieu, Yonel
• Application Number:
  US10/000,557
• Publication Number:
  US 20030078705A1
• Time in Patent Office: 616 Days
• Field of Search: 701/3, 701/4, 701/13, 701/213, 701/214, 701/215, 342/357.04, 342/357.06, 342/357.08
• US Class Current: 701/13
• CPC Class Codes: G01S 19/36 relating to the receiver frond end
• CPC Class Codes: G01S 19/54 using carrier phase measurements; using long or short baseline interferometry

Abstract

A vehicular position and attitude can be accurately determined from GPS signals by positioning a master and two slave orthogonally disposed receiver antennas rigidly mounted together enabling the rotation of the slave receiver antennas about the master antenna. The slave antennas are rotated and then dither back and forth so that differential phase measurements between the slave antennas and the master antenna is nulled in carrier phase alignment of the GPS signals for determining azimuth angles and elevation angles to the GPS satellites for determining the position and attitude of the vehicle.

Claims

1. A method of positioning an R3 point relative to an R1 point for receiving in carrier phase alignment a carrier phase of a carrier signal transmitted by a first pseudo star, the method comprising the steps of,

third receiving the carrier signal at the R1 point and the R3 point, the point R1 lying on a z local axis, the point R3 lying on a y local axis, the y local axis extending between the R1 point and the R3 point, the y local axis being orthogonal to the z local axis, the R1 point lying on a first line of sight extending between the R1 point and the first pseudo star,

third dithering the R3 point a first dithering length along the y local axis,

third phase measuring a first phase difference of the carrier phase between the R1 point and the R3 point, the first phase difference is zero and remains zero as the R3 point dithers along the first dithering length when in carrier phase alignment, and

rotating the R3 point about the z local axis extending through the R1 point until carrier phase alignment during the third dithering step.

2. The method of claim 1 further comprising the step of,

azimuth determining an azimuth angle, the rotation of the R3 point during the rotating step defines a rotation angle relative to a reference line orthogonally extending from the z local axis when the R1 point and R3 point are in carrier phase alignment during the third dithering step, the azimuth angle and z local axis define a first plane through which extends the first line of sight.

3. The method of claim 1 further comprising the step of,

azimuth determining an azimuth angle, the rotation of the R3 point during the rotating step defines a rotation angle relative to a y local axis orthogonally extending from the z local axis when the R1 point and R3 point are in carrier phase alignment during the third dithering step, the azimuth angle and z local axis define a first plane through which extends the first line of sight.

4. The method of claim 1 further comprising the steps of,

second receiving at an R2 point the carrier signal, the point R2 lying on an x local axis, the x local axis extending from the R1 point to the R2 point, the x local axis being orthogonal to the z local axis and being orthogonal the y local axis,

second phase measuring a second phase difference and a third phase difference of the carrier phase received at the R2 point and at the R1 point, and

coelevation determining a coelevation angle of the first line of sight from the second phase difference and the third phase difference.

5. The method of claim 1 further comprising the steps of,

second receiving at an R2 point the carrier signal, the point R2 lying on an x local axis, the x local axis extending from the R1 point to the R2 point, the x local axis being orthogonal to the z local axis and being orthogonal to the y local axis,

second dithering the R2 point a second dither length along the x local axis,

second phase measuring a second phase difference and a third phase between the carrier phase at the R1 point and the R2 point as the R2 point moves along the x local axis at two respective points in the dithering length during the second dithering step, and

coelevation determining a coelevation angle from the second phase difference and the third phase difference, the coelevation angle of the first line of sight extending through a first plane.

6. The method of claim 1 further comprising the steps of,

azimuth determining an azimuth angle, the rotation of the R3 point during the rotating step defines a rotation angle relative to a reference line orthogonally extending from the z local axis when the R1 point and R3 point are in carrier phase alignment during the third dithering step, the azimuth angle and z local axis define a first plane through which extends the first line of sight,

second receiving at an R2 point the carrier signal, the point R2 lying on a x local axis, the x local axis extending from the R1 point to the R2 point, the x local axis being orthogonal to the z local axis and being orthogonal to the y local axis,

second dithering the R2 point a second dither length along the x local axis,

second phase measuring a second phase difference and a third phase difference between the carrier phase at the R1 point and the R2 point as the R2 point moves along the x local axis during the second dithering step, and

coelevation determining a coelevation angle from the second phase difference and the third phase difference, the coelevation angle defining the first line of sight extending through the first plane.

7. The method of claim 1 further comprising the steps of,

azimuth determining an azimuth angle, the rotation of the R3 point during the rotating step defines a rotation angle relative to a reference line orthogonally extending about the z local axis when the R1 point and R3 point are in carrier phase alignment during the third dithering step, the azimuth angle and z local axis define a first plane through which extends the first line of sight,

second receiving at an R2 point the carrier signal, the point R2 lying on an x local axis, the x local axis extending from the R1 point to the R2 point, the x local axis being orthogonal to the z local axis and being orthogonal to the y local axis,

second dithering the R2 point a second dither length along the x local axis,

second phase measuring a second phase difference and a third phase difference between the carrier phase at the R1 point and the R2 point as the R2 point moves along the x local axis during the second dithering step,

coelevation determining a coelevation angle from the second phase difference and the third phase difference, the coelevation angle defining the first line of sight extending through the first plane,

first line of sight determining from the azimuth angle and the coelevation angle relative to the z local axis,

repeating all the steps a second time for determining a second line of sight angle to a second pseudo star, and

determining an orientation of the z local axis and the x local axis and the y local axis from the first and second lines of sight.

8. The method of claim 7 wherein,

the orientation is an attitude of a space vehicle with respect to an inertial reference frame,

the first and second pseudo stars are GPS satellites, and the z local axis and x local axis and the y local axis define a local coordinate frame of the space vehicle.

9. The method of claim 7 wherein,

the x local axis and the y local axis and the z local axis respectively are a yaw axis and a pitch axis and a roll axis of a vehicle.

10. A method of determining the attitude of a space vehicle receiving in carrier phase alignment a carrier phase of a carrier signal transmitted by a first GPS satellite and a second GPS satellite, the method comprising the steps of,

third receiving the carrier signal at an R1 point and an R3 point, the point R1 lying on a z local axis, the point R3 lying on a y local axis, the y local axis extending between the R1 point and the R3 point, the y local axis being orthogonal to the z local axis, the R1 point lying on a first line of sight extending between the R1 point and the first GPS satellite,

third dithering the R3 point a first dithering length along the x local axis,

third phase measuring a first phase difference of the carrier phase between the R1 point and the R3 point, the first phase difference is zero and remains zero as the R3 point dithers along the first dithering length when in carrier phase alignment, and

rotating the R3 point about the z local axis extending through the R1 point until carrier phase alignment during the third dithering step,

azimuth determining an azimuth angle, the rotation of the R3 point during the rotating step defines a rotation angle relative to the vehicle, the rotation angle orthogonally extending about the z local axis when the R1 point and R3 point are in carrier phase alignment during the third dithering step, the azimuth angle determined from rotational angle, the azimuth angle and z local axis define a first plane through which extends the first line of sight,

second receiving at an R2 point the carrier signal, the point R2 lying on an x local axis, the x local axis extending from the R1 point to the R2 point, the x local axis being orthogonal to the z local axis and being orthogonal to the y local axis,

second phase measuring a second phase difference and a third phase difference between the carrier phase at the R1 point and the R2 point as the R2 point moves along the y local axis,

coelevation determining a coelevation angle from the second phase difference and the third phase difference, the coelevation angle defining the first line of sight extending through the first plane,

first line of sight determining from the azimuth angle and coelevation angle relative to the z local axis,

repeating all the steps a second time for determining a second line of sight angle to the second GPS satellite, and

determining the attitude of the space vehicle with respect to an inertial reference frame, the attitude being an orientation of a local reference frame defined by the z local axis and the y local axis and the x local axis.