CO-BORESIGHTED DUAL-MODE SAL/IR SEEKER INCLUDING A SAL SPREADER

• US 20110073704A1
• Filed: 09/26/2009
• Published: 03/31/2011
• Est. Priority Date: 09/26/2009
• Status: Active Grant

• Current Assignee: Raytheon Company (Rtx Corporation)
• Original Assignee: Raytheon Company (Rtx Corporation)
• Inventors: Jenkins, David D, Markason, David J., Taylor, Byron B.
• Granted Patent: US 8,164,037 B2
• Time in Patent Office: Days
• US Class Current: 244/3.16
• CPC Class Codes: F41G 7/008 Combinations of different guidance systems
• CPC Class Codes: F41G 7/2213 maintaining the axis of an orientable seeking head pointed at the target, e.g. target seeking gyro
• CPC Class Codes: F41G 7/2253 Passive homing systems, i.e. comprising a receiver and do not requiring an active illumination of the target
• CPC Class Codes: F41G 7/226 Semi-active homing systems, i.e. comprising a receiver and involving auxiliary illuminating means, e.g. using auxiliary guiding missiles
• CPC Class Codes: F41G 7/2293 using electromagnetic waves other than radio waves
• CPC Class Codes: G01S 3/784 using a mosaic of detectors

Abstract

In a co-boresighted SAL/IR seeker, the optical system and particularly the secondary lens and position of the SAL detector are configured to produce a well-corrected spot of laser energy at the SAL detector. A spreader is positioned between the secondary mirror/lens and the SAL detector, possibly on the secondary mirror, away from the aperture stop and not in the optical path to the IR detector. The spreader is configured to spatially homogenize the laser energy to increase the size of the spot of focused laser energy at the SAL detector to set the system transfer function to meet slope requirements. Spatial homogenization serves to reduce both boresight shift and slope non-linearities. This approach greatly simplifies the time and labor intensive calibration of the SAL detector'"'"'s system transfer function.

Claims

1. A dual-mode SAL/IR seeker, comprising:

an IR detector configured to detect two-dimensional images of focused incident IR energy to generate at least one IR guidance signal;

a positionally-sensitive SAL detector having a system transfer function that converts the spatial displacement of a spot of focused laser energy to a target bearing to generate at least one SAL guidance signal;

a primary mirror having a common aperture for collecting and focusing laser energy and IR energy along a common optical path;

a secondary mirror/lens in the common optical path that creates a central obscuration of the common aperture, said secondary mirror having an aft side facing the primary mirror and a forward side, wherein the aft side is a secondary mirror configured to permit propagation of laser energy there through to the forward side along a first optical path to the SAL detector and to reflect IR energy along a second optical path to the IR detector, said primary and secondary mirrors configured to focus the IR energy to form the two-dimensional images at the detector,

wherein the forward side of the secondary mirror/lens is a lens element, said lens element configured and said SAL detector positioned to form a spot of focused laser energy on the SAL detector; and

a spreader positioned in the first optical path between the secondary mirror and the SAL detector away from the aperture stop at the primary mirror and not in the second optical path between the secondary mirror and the IR detector, said spreader configured to spatially homogenize the laser energy to increase the size of the spot of focused laser energy on the SAL detector to set the system transfer function.

2. The dual-mode SAL/IR seeker of claim 1, wherein the primary mirror has an outer diameter of at least 3 inches.

3. The dual-mode SAL/IR seeker of claim 1, further comprising a mounting structure that supports the secondary mirror/lens off of the primary mirror, said mounting structuring obscuring the transmission of laser energy from the common aperture to the SAL detector.

4. The dual-mode SAL/IR seeker of claim 1, further comprising:

a dome that is transmissive of laser energy and IR energy; and

a two-axis gimbal that stews an optical system comprising at least the primary mirror, secondary mirror/lens, SAL detector and spreader about a longitudinal axis through the center of the dome, said gimbal slewing the optical system to an extent that the common aperture experiences vignetting at the edges of the dome obscuring the transmission of laser energy to the SAL detector.

5. The dual-mode SAL/IR seeker of claim 1, where the secondary mirror is formed on a convex surface of the aft side and the lens element is formed on a concave surface on the forward side.

6. The dual-mode SAL/IR seeker of claim 1, wherein the secondary mirror comprises an electromagnetic interference (EMI) coating configured to pass laser energy and reflect IR energy.

7. The dual-mode SAL/IR seeker of claim 6, further comprising a conductive housing around and forward of the SAL detector, said conductive housing and said EMI coating aft of the SAL detector forming a Faraday cage around the SAL detector.

8. The dual-mode SAL/IR seeker of claim 1, wherein the spreader is on the forward side of the secondary mirror/lens.

9. The dual-mode SAL/IR seeker of claim 1, wherein the spreader is a diffuser.

10. The dual-mode SAL/IR seeker of claim 1, wherein the spreader is a lenslet array.

11. The dual-mode SAL/IR seeker of claim 1, wherein no optical focusing element is positioned between the spreader and the SAL detector.

12. The dual-mode SAL/IR seeker of claim 1, further comprising:

a flight control system that receives the at least one SAL guidance signal and applies a single calibration offset for all X, Y positions to said guidance signal to generate control signals to control the flight of the airborne platform.

13. The dual-mode SAL/IR seeker of claim 1, wherein the primary mirror comprises a diffractive element.

14. The dual-mode SAL/IR seeker of claim 1, wherein said spreader increases the diameter of the spot by at least a factor of five.

15. A guided projectile, comprising:

a cylindrically-shaped projectile body;

one or more control surfaces on the body;

a dome that is mounted on one end of the body, said dome transmissive of laser energy and IR energy;

a two-axis gimbal;

a dual-mode SAL/IR seeker mounted on the two-axis gimbal inside the body, comprising,

an IR detector configured to detect two-dimensional images of focused incident IR energy to generate at least one IR guidance signal;

a positionally-sensitive SAL detector having a system transfer function that converts the spatial displacement of a spot of focused laser energy to a target bearing to generate at least one SAL guidance signal;

a primary mirror having a common aperture for collecting and focusing laser energy and IR energy propagated through the dome along a common optical path;

a secondary mirror/lens between the dome and primary mirror in the common optical path that creates a central obscuration of the common aperture, said secondary mirror having an aft side facing the primary mirror and a forward side, wherein the aft side is a secondary mirror configured to permit propagation of laser energy there through to the forward side along a first optical path to the SAL detector and to reflect IR energy along a second optical path to the IR detector, said primary and secondary mirrors configured to focus the IR energy to form the two-dimensional images at the detector,

wherein the forward side of the secondary mirror/lens is a secondary lens element, said secondary lens element configured and said SAL detector positioned to form a spot of focused laser energy, on the SAL detector; and

a spreader positioned in the first optical path between the secondary mirror/lens and the SAL detector away from the aperture stop at the primary mirror and not in the second optical path between the secondary mirror and the IR detector, said spreader configured to spatially homogenize the laser energy to increase the size of the spot of focused laser energy on the SAL detector to set the system transfer function; and

a flight control system that receives the at least one IR guidance signal and the at least one SAL guidance signal and applies a single calibration offset for all X, Y positions to said SAL guidance signal to generate control signals to manipulate the one or more control surfaces to control the flight of the airborne platform.

16. The guided projectile of claim 15, wherein the secondary lens element is concave, said spreader positioned on the surface of the concave secondary lens.

17. The guided projectile of claim 15, wherein the primary mirror has an outer diameter of at least 3 inches and wherein no optical focusing element is positioned between the spreader and the SAL detector.