Tracking means for distant ballistic missile targets

• US 6,265,704 B1
• Filed: 03/29/1999
• Issued: 07/24/2001
• Est. Priority Date: 04/02/1996
• Status: Expired due to Fees

• Current Assignee: Northrop Grumman Corporation
• Original Assignee: TRW Limited (Zeppelin - Stiftung der Stadt Friedrichshafen)
• Inventors: Livingston, Peter M.
• Primary Examiner(s): Lee, John R.
• Application Number:
  US09/280,737
• Time in Patent Office: 848 Days
• Field of Search: 250/203.1, 250/203.2, 250/203.3, 250/203.6, 250/216, 250/234, 250/235, 250/559.35, 250/559.36, 250/206.1, 250/206.2, 356/4.01, 356/5.09, 356/5.11, 356/139.04, 356/139.05, 356/139.06, 356/139.07, 356/139.08, 356/141.1, 356/141.2, 356/141.4, 356/141.5, 356/151.2, 89/410.6
• US Class Current: 250/203.2
• CPC Class Codes: F41H 13/005 the high-energy beam being a laser beam
• CPC Class Codes: G01S 17/46 Indirect determination of position data
• CPC Class Codes: G01S 17/66 Tracking systems using electromagnetic waves other than radio waves
• CPC Class Codes: G01S 7/481 Constructional features, e.g. arrangements of optical elements
• CPC Class Codes: G01S 7/4912 Receivers
• CPC Class Codes: G01S 7/497 Means for monitoring or calibrating
• CPC Class Codes: G01S 7/4972 Alignment of sensor

Abstract

A laser tracking system steers a beam of laser energy which is dithered in two directions to scan the surface of a moving object. A laser energy detector detects laser energy reflected from the target. Reflected energy is filtered to distinguish dither frequencies for signals in both directions, which signals are independently analyzed to determine the location of the target in relation to the laser beam. A bias signal is generated which causes the beam of laser energy to be steered toward a surface radius to be steered toward a surface with the largest compound curvature within the trackers, field-of-regard, to the target, to the tracked location on-target, or modified signals steer a portion of the beam to an optimum track location on target while offsetting most of the beam'"'"'s energy to a second engagement location on target. Also, a track testing system is capable of monitoring a laser beam focused on a missile and determining the effective laser engagement on a spinning target.

Claims

1. A laser system for tracking a target, the laser system comprising:

a laser generator for generating a beam of laser energy;

a beam steerer for steering the beam of laser energy in response to a mirror drive signal;

a laser energy detector for detecting reflected laser energy and generating a detected signal;

a synchronous detector for detecting said detected signal and generating an error signal;

a dither generator for generating a dither signal at a predetermined frequency; and

a summer for summing said error signal and said dither signal and generating said mirror drive signal, wherein the laser energy detector, synchronous detector and summer form a closed servo loop which acts to null said error signal.

2. The laser system as recited in claim 1, wherein said synchronous detector includes a multiplexer and a phase shifter for multiplying said electrical signal from said laser energy detector by a cosine function.

3. The laser system as recited in claim 2, further including an integrator and filter coupled between said multiplexer and said summer, the output of said integrator and filter defining said error signal.

4. The laser system as recited in claim 2, further including an amplifier, disposed at the output of said laser energy detector for amplifying the detected signal therefrom.

5. The laser system as recited in claim 1, further including a differentiator for differentiating the detected signal from said laser energy detector defining a differentiated detected signal and applying said differentiated detected signal to said synchronous detector.

6. The laser system as recited in claim 5, further including a switch for switching the output of said laser energy detector between said synchronous detector in a first position defining a centroid tracking mode and said differentiator in a second position defining an edge tracking mode.

7. The laser system as recited in claim 1, wherein said laser energy detector includes a telescope and a detector disposed at the focal plane of the telescope.

8. The laser system as recited in claim 7, further including an optical filter for limiting detected energy to the wavelength of said laser generator.

9. The laser system as recited in claim 8, further including an electrical filter for filtering out signals at frequencies other than said predetermined frequency of said dither generator.

10. A laser system for two-dimensional tracking of a target comprising:

a laser generator for generating a beam of laser energy;

a laser energy detector for detecting reflected laser energy and generating detected signals;

one or more electrical filters for filtering said detected signals and generating x detected signals at a first frequency and y detected signals at a second frequency;

an x servo loop for receiving said x detected signals, said x servo loop including a first synchronous detector for synchronously detecting said x detected signals and generating an x error signal;

an x direction dither generator for generating dither signals;

a y servo loop for receiving said y detected signals, said y servo loop including a second synchronous detector for synchronously detecting said y detected signals and generating a y error signal;

a y direction dither generator for generating y dither signals;

an image generator responsive to said first and second dither signals for generating derotated x and y dither signals that are parallel and perpendicular to a predetemined axis of the target defining a derotated x dither signals and derotated y dither signals;

an x summer for summing said x error signals and said derotated x dither signals and generating an x mirror drive signal;

an x steering mirror for pointing said beam of laser energy as a function of said x mirror drive signal;

a y summer for summing said y error signals and said second y derotated dither signals and generating a y mirror drive signal; and

a y steering mirror for pointing said laser energy as a function of said y mirror drive signal.

11. The laser system as recited in claim 10, further including an x differentiator for differentiating said x detected signals defining x differentiated detected signals and applying said x differential detected signals to x servo loop.

12. The laser system as recited in claim 11, further including a first switch for selectably switching said x detected signals between said differentiator defining an x direction edge tracking mode and said x servo loop defining an x direction centroid tracking mode.

13. The laser system as recited in claim 12, further including a y differentiator for differentiating said y detected signals defining y differentiated detected signals to said y servo loop.

14. The laser system as recited in claim 13, further including a second switch for switching said y detected signals between said y servo loop defining a y direction centroid tracking mode and said y differentiator defining a y direction edge tracking mode.

15. The laser system as recited in claim 10, further including means for compensating the phase of said beam of laser energy.

16. The laser system as recited in claim 10, wherein said compensating means includes means for sensing of the return phase of said beam of laser energy.

17. The laser system as recited in claim 10, wherein said compensating means includes a Hartmann plate for sensing the return phase of said beam of laser energy.

18. The laser system as recited in claim 10, wherein said compensating means includes an interferometer.

19. A laser system for two dimensional tracking of a target comprising:

a laser generator for generating a beam of laser energy;

a laser energy detector for detecting reflected laser energy;

means for splitting said beam of laser energy into a tracking beam and a kill beam;

means for locking said tracking beam on a centerline of said target adjacent an edge of said target; and

means for locking said kill beam on a centerline of said target at a predetermined relative to said tracking beam.

20. A laser system for tracking a two-dimensional target comprising:

a laser generator for generating a beam of laser energy;

a laser energy detector for detecting reflected laser energy and generating detected signals;

one or more electrical filters for filtering said detected signals and generating x detected signals at a first dither frequency and y detected signals at a second dither frequency;

an x servo loop for receiving said x detected signals, said x servo loop including a first synchronous detector for synchronously detecting said x detected signals and generating an x error signal;

an x direction dither generator for generating first x dither signals;

a y servo loop for receiving said y detected signals, said y servo loop including a second synchronous detector for synchronously detecting said y detected signals and generating a y error signal;

a y direction dither generator for generating y dither signals;

an image derotator responsive to said first and second dither signals for generating derotated x and y dither signals that are parallel and perpendicular to a predetermined axis of the target;

an x summer for summing said x error signals and said x derotated dither signals and generating an x mirror drive signal;

an x steering mirror for pointing said beam of laser energy as a function of said x mirror drive signal and an offset signal;

a y summer for summing said y error signals and said derotated y dither signals and generating y mirror drive signals;

a y steering mirror for pointing said laser energy as a function of said y mirror drive signal; and

a beam splitter for splitting said beam of laser energy into a tracking beam and a kill beam wherein said y servo loop is configured to lock said tracking beam on a centerline of said target along an edge and said x servo loop is configured to lock said kill beam along said centerline at said offset relative to said tracking beam.

21. The laser system as recited in claim 20, wherein said beam splitter includes a primary mirror with an aperture a secondary mirror generally aligned behind said aperture in said primary mirror, said secondary mirror movably mounted relative to said primary mirror in response to said offset signal.

22. The laser system as recited in claim 21, wherein said beam splitter includes one or more piston actuators for movably mounting said secondary mirror relative to said primary mirror.

23. The laser system as recited in claim 20, wherein said beam splitter includes means for splitting said beam temporally.

24. A laser beam splitter comprising:

a first primary mirror having a central aperture for receiving an incident laser beam;

a secondary mirror assembly generally disposed behind said central aperture having a secondary mirror and one or more actuators for movably mounting said secondary mirror relative to said central aperture, said secondary mirror configured to reflect said incident laser beam towards said first primary mirror and configured with an outer reflective surface configured to reflect a portion of said incident laser beam through said central aperture at an offset relative to the balance of the incident laser energy reflected from said primary mirror.