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Laser Aided Rocket System (LARS)

The Laser Aided Rocket System (LARS) was a first generation of a modification adding guidance and control capability to a standard Mk 40 series 2.75 inch Folding Fin Aerial Rocket (FFAR) motor developed by Martin Marietta. The configuration used a semi-active laser seeker Proportional Lead Guidance (PLG) and a M151 warhead. The seeker head had a field of view of +/- 7.5 degrees. Laser energy and background energy entered through the optical dome and passed through a narrow optical band pass filter. This filter eliminated most of the background light while the reflected laser energy was passed on to a quadrant detector. The relative magnitudes of the 4 quadrant signals were used to determine pitch and yaw correction signals to guide the missile to the target. When the target was illuminated by a laser the seeker head of the missile guidance system locked on the reflected laser signal. In flight, the output of the guidance system provided continuous corrections to the missile control system, which guided the missile to impact on the laser spot. The missile and improved variants were tested as part of the Nite Gazelle unmanned helicopter program led by the Advanced Research Projects Agency (ARPA; now the Defense Advanced Research Projects Agency or DARPA).

The initial LARS (also known as LARS I) test series on the Nite Gazelle platform ran from 10 March through 5 November 1970. The first LARS flight occurred at Avon Park, Florida, and the results were so successful that the program was expanded to investigate the compatibility of the Nite Gazelle helicopter missile launchers and guidance system accuracy. The flight test program was transferred to Nellis Air Force Base, where the expanded scope of the program could be effectively tested. All 6 guided missile launchings were completed at Nellis. Four of the 6 missile launches were successful. Loss of missile roll control caused the other 2 missiles to miss the target. Four of the 6 flights impacted within 11 feet of the target's center. During all of these tests the laser illuminator was located on the ground in front of the truck target or target board. The LARS I tests were to demonstrate the PLG concept.

After the second LARS missile failure on 17 April 1970, an instrumentation system was developed and installed on board the missile to provide performance information during flight. A PAM/FM/FM telemetry system was installed in the space normally occupied by the explosive warhead. A self-contained power supply permitted operation of the telemetry system independent of the missile primary power. The transmitter frequency was approximately 250 megahertz and the 0.3 watt power output provided an effective range of 5 miles. These UHF signals were received and recorded on magnetic tape at the telemetry ground stations.

After testing of the LARS missile, an improved LARS II missile was developed in 1971. One LARS I missile remained unexpended and was modified to the LARS II configuration. The physical dimensions and general performance characteristics of the LARS II missile were the same as the LARS I. Improvements were made in the guidance system to eliminate the low impact problem that was detected during the LARS I test program. The LARS II test series on the Nite Gazelle platform started on 18 November 1970 and was completed on 4 November 1971 with a direct hit on a medium tank. Issues were experienced, but generally related to the launch platform rather than the LARS II missile. Guidance system problems caused the seeker to lock on a fake target return on test 355, however. Logic circuit changes were made to eliminate this problem.

The final test as part of the Nite Gazelle Program, LARS II (Night), was conducted from September 1971 through 2 February 1972. Although both missiles launched at night missed the tank target the feasibility of night launches was demonstrated and it was thought that techniques could be changed to insure the success of missiles launched at night.

Following, the tests the performance of the LARS missile was determined to be sufficient to achieve impacts on the desired target area from a distance of 6,200 feet. However, one missile launched during the day and 2 missiles launched at night missed the desired impact point. These misses were caused by a combination of problems and 2 of these were associated with the guidance system. The system was overly sensitive to laser reflections from the near field and "hard over" commands were given when the missile axis was more than 2 degrees offset from the target.

ARPA recommended that the LARS guidance system should be improved to reduce the sensitivity to reflections received from the near field and to decrease the possibility of tracking on a side lobe. ARPA also recommended that the system should be modified to delay the initiation of "hard over" commands. This delay would keep the missile out of the field of view of the television camera and prevent tracker unlock. While LARS was not developed into an operational system, the concept was revived in the late 1990s and eventually led to the Advanced Precision Kill Weapons System (APKWS) program. One of the APKWS contractors was Lockheed Martin (which absorbed Martin Marietta), which made light of its experience with such systems based on its work on LARS during the 1970s.




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