Laser Target Simulator

This invention relates to target simulation means for evaluating point target tracking systems, and more particularly to laser target simulators adapted to use in combination with missile borne laser seekers.

It is necessary, in evaluating systems of this type, to generate a point source laser target which covers the entire optical aperture of the laser seeker and to put this simulating means into a small package which can be placed over the nose of the laser seeker bearing missile. It is desirable that such a system achieve these things and that it does so in such a way that the various operational modes of the missile can be tested. Lost pulse logic, missing pulse, good guidance tracking rates and accuracies, acquisition logic, laser pulse coding, false target rejection, optical noise rejection, and operation at various power levels all must be tested with the laser target simulator. The state-of-the-art approach to this problem is to use either a strobe or a laser diode placed at sufficient distance from the laser seeker to approximate a point source. Such a technique requires much space, the use of cumbersome and complex equipment and the application of exacting alignment procedures. Furthermore, it is not possible to perform all of the abovementioned tests and evaluations using conventional techniques. There currently exists, therefore, the need for a target simulator that is compact, lightweight, and that more accurately simulates a laser target. It is important that it be possible to completely check out a laser seeker with it and that it be capable of generating qualitative as well as quantitative data. In addition, such a device should allow the sensitivity of the 1.06.mu. detector used in most laser seekers to be verified in two modes to insure that this critical item has not deteriorated. The present invention is directed toward satisfying those needs.

The invention comprehends target simulation by means of a convex spherical mirror segment that reflects light from various point sources of light onto the light receiving aperture of a laser seeker. The point sources of light (1.06.mu. LEDs in one preferred embodiment) are positioned at the mirror focal point with one being on the laser system boresight and another displaced from and rotatable about the first. A CW source of light is also provided. The target simulator is operated by controls that provide coded operation and power level manipulation of the point sources of light.

It is a principal object of the invention to provide a new and improved laser target simulator.

It is another object of the invention to provide a laser target simulator that is compact, lightweight and accurately simulates a laser target.

It is another object of the invention to provide a laser target simulator that is capable of testing a laser seeker system for lost pulse logic, missing pulses, guidance, tracking rates and accuracies, laser pulse coding, acquisition logic, false target rejection, optical noise rejection, and operation at various power levels.

It is another object of the invention to provide a laser target simulator that is capable of generating qualitative as well as quantitative test data.

These, together with other objects, features and advantages of the invention, will become more readily apparent from the following detailed description when taken in conjunction with the illustrative embodiment in the accompanying drawings.

FIG. 1 is a side view of one presently preferred embodiment of the invention; and

FIG. 2 is a sectional view of the convex spherical mirror of FIG. 1.

Referring now to FIGS. 1 and 2, a concave spherical mirror segment 12 is centered on the boresight or center-line of laser seeker 4 and is positioned and oriented to reflect light energy onto laser seeker light receiving aperture 5. Mirror segment 12 has a radius of curvature r.sub.c. It is illustrated in section by FIG. 2. A first point source of light energy 9 is positioned on the laser seeker center-line at a distance r.sub. c/2 from mirror segment 12 and is oriented to project light energy thereat.

A second point source of light energy 10 is positioned adjacent to point source 9 also at a distance r.sub. c/2 from the mirror and is mechanized to rotate about the system center-line by means of motor 7. Any suitable mounting structure such as frame 6 can be used to retain the components of the simulator in place and secure it to missile 3. A CW light source 8 is mounted coaxially to point source 9 and is directed toward the mirror. Coding and control circuits 11 control point sources 9 and 10 in testing the various operational modes of the laser seeker.

By way of specific example, a target simulator of the type described can consist of a 10-inch circular section of an 18-inch radius spherical mirror which collimates and reflects light from a Gallium-Indium-Arsenide 1.06.mu. light emitting diode (LED) 9 which is placed 9" from the mirror (at the focal point). Because the focal point of the mirror is a 9" radius sphere, LEDs can be placed at more than one location or may be rotated around a circle, the plane of which is perpendicular to the center line of the system, by use of a motorized mechanism. The LEDs 9, 10 should be aimed in the direction of the radius of the mirror 12, and the laser seeker 4 should be close enough behind the diodes so that the full aperture 5 is illuminated. By using two LEDs, one boresighted and one located at another point within the instantaneous field of view of seeker 4, it is possible to test the seeker for last pulse logic by triggering one LED 100 n/sec after the first. The seeker gimbal angles can be used to indicate which LED is being tracked. Missing pulse logic may be tested by causing the LEDs to drop pulses and to observe whether tracking is properly maintained.

Tracking rates and accuracies may be measured by operating first one LED, then the other, and measuring the time required to null the seeker and the gimbal angle at null. By rotating the off-axis LED 10 at a known rate with the motorized system, the tracking lag and rates can be measured. Acquisition logic, laser pulse coding, and false target rejection can all be tested by properly coding the LED. The simulator can use a CW light source 8 to generate optical noise. This noise can be calibrated by measuring the level of the noise AGC signal and can be used to insure that the detector on the seeker has not become noisy because of aging or other factors.

By controlling the power output of the 1.06.mu. source, the seeker's operation at various power levels (watts/cm.sup.2) can be tested. By using a calibrated source the sensitivity of the seeker can be measured.

While the invention has been described in one presently preferred embodiment, it is understood that the words which have been used are words of description rather than words of limitation and that changes within the purview of the appended claims may be made without departing from the scope and spirit of the invention in its broader aspects.