Method and apparatus for determining the position and velocity of a target in inertial space

• US 4,959,800 A
• Filed: 05/20/1988
• Issued: 09/25/1990
• Est. Priority Date: 05/20/1988
• Status: Expired due to Term

• Current Assignee: Raytheon Company (Rtx Corporation)
• Original Assignee: Hughes Aircraft Company (Rtx Corporation)
• Inventors: Woolley, Richard L.
• Primary Examiner(s): Black, Thomas G.
• Application Number:
  US07/197,015
• Time in Patent Office: 858 Days
• Field of Search: 364/516, 235/411, 235/412, 235/413, 235/414, 235/415, 235/416, 342/104-106, 342/109, 342/113, 342/114
• US Class Current: 235/411
• CPC Class Codes: G01S 13/66 Radar-tracking systems; Analogous systems

Abstract

A method for determining the position and velocity of a target in inertial space including the steps of (a) tracking the target and providing three orthogonal velocity components in inertial space; (b) computing the scalar velocity V_T of the target in an inertial reference frame by providing the square root of the sum of the squares of the orthogonal velocity components; and (c) computing the aspect angle β_cue of the target relative to a line-of-sight to a platform as an inverse sinusoidal function of the ratio of one of said orthogonal components and V_T, when such tracking data is available, and otherwise; (d) estimating actual target maneuver to develop a minimum uncertainty zone using an assumed worst case lateral target acceleration. Also disclosed are techniques for bounding the aspect angle and for providing global range and range rate estimates which account for uncertainties in the measurements of target and platform ranges and velocities.

Claims

1. A method for determining the position and velocity of a target in inertial space including the steps of:

(a) Tracking the target and providing three orthogonal velocity components in inertial space;

(b) computing the scalar velocity V_T of the target in an inertial reference frame by providing the square root of the sum of the squares of the orthogonal velocity components;

(c) computing the aspect angle cue of the target relative to a line-of-sight to a platform as an inverse sinusoidal function of the ratio of one of said orthogonal components and V_T, when such tracking data is available, and otherwise;

(d) estimating actual target maneuver to develop a minimum uncertainty zone using an assumed worst case lateral target acceleration; and

(e) aiming an antenna at said determined positioned of said target.

2. The method of claim 1 wherein said step of computing the aspect angle of the target β

_cue includes the step of computing an aspect angle β

_cue which is equal to the arccos of the ratio of a velocity component of the target along said line-of-sight V_TXA to the scalar velocity of the target V_T.

3. The method of claim 1 wherein said step of estimating the actual target maneuver when tracking data in not available includes the steps of:

(e) obtaining a measure of the range rate of the target relative to said platform R'"'"'_PT ;

(f) computing a new velocity component of the target along said line-of-sight V_TXA by adding said range rate R'"'"'_PT to a velocity of said platform along said line-of-sight sight V_PXA ; and

(g) computing a new aspect angle by of the target β

_cue equal to the arccos of the ratio of the new velocity component of the target along said line-of-sight V_TXA to the scalar velocity of the target V_T.

4. The method of claim 1 wherein said step of estimating the actual target maneuver when tracking data is not available includes the steps of:

(e) obtaining a measure of the rate of change of the angle between the line-of-sight between the platform and the target θ

'"'"' and providing the azimuthal θ

'"'"'_AZ and elevational components θ

'"'"'_EL thereof;

(f) computing a new velocity component of said target along a Y axis V_TYA by multiplying an estimate of the range R_PT along the line-of-sight between the platform and the target by the azimuthal component θ

'"'"'_AZ of the angle rate between the line-of-sight between the platform and the target and adding thereto any velocity of the platform in along said Y axis V_PYA ;

(g) computing a new velocity component of said target along a Z axis V_TZA by multiplying an estimate of the range R_PT along the line-of-sight between the platform and the target by the elevational component θ

'"'"'_EL of the angle rate between the line-of-sight between the platform and the target and adding thereto any velocity of the platform in along said Z axis V_PZA ; and

(h) computing a cross velocity of the target V_Tc by taking the square root of the sum of the squares of said new velocity components along said Y and Z axes V_TYA and V_TZA respectively.

5. The method of claim 4 wherein said step of estimating the actual target maneuver when tracking data in not available includes the step of calculating a new aspect angle β

_cue equal to the arcsin of the ratio of the cross velocity of said target V_Tc to the scalar velocity of said target V_T.

6. The method of claim 4 wherein said step of estimating the actual target maneuver when tracking data in not available includes the steps of:

(i) obtaining a measure of the range rate R'"'"' of the target relative to the platform along the line-of-sight;

(j) computing a new velocity component of the target along the line-of-sight V_TXA by adding the range rate R'"'"'_PT to any velocity of the platform along the line-ofsight sight V_PXA ;

(k) computing a new scalar velocity V_T by taking the square root of the sum of the squares of the new velocity component of the target along the line-of-sight V_TXA and the cross velocity of the target V_Tc ; and

(1) computing a new aspect angle β

_cue equal to the arccos of the ratio of the new velocity component of the target along the line-of-sight V_TXA to the new scalar velocity of said target V_T.

7. The method of claim 1 including the step of bounding the aspect angle by setting the minimum and maximum range rates of the target at to the angles at which the range rate changes slope.

8. The method of claim 7 including the step of bounding the aspect angle by setting the minimum and maximum range of the target relative to the platform by integrating said minimum and maximum range rates.

9. The method of claim 1 including the step of bounding the aspect angle by minimizing the pointing error θ

of the line-of-sight from the platform to the target equal to the arctan of the ratio of any cross range R_C of the target to the range of the target along the line-of-sight R_L.

10. A system for determining the position and velocity components in inertial space;

means for tracking the target and providing three orthogonal velocity components in inertial space;

means for computing the scalar velocity V_T of the target in an inertial reference frame by providing the square root of the sum of the squares of the orthogonal velocity components;

means for computing the aspect angle cue of the target relative to a line-of-sight to a platform as an inverse sinusoidal function of the ratio of one of said orthogonal components and V_T, when such tracking data is available, and;

means for estimating actual target maneuver to develop a minimum uncertainty zone using an assumed worst case lateral target acceleration when such tracking data is not available; and

means for aiming an antenna at said determined position.