A Novel, Inexpensive approach to Inertial Guidance for Gun Launched Projectiles

The notion of using an inexpensive inertial augmentation system for a tube launched ordnance, either with or without a terminal homing sensor, has existed for some time now. The main drawback has been the high cost associated with reliable inertial components and the hardening problem with gyroscopes or other rate sensing elements. Some of the solutions that have been proposed to date attempt to either harden the rate sensing element or to measure minute coriolis forces using accelerometers. The concept we are proposing solves this problem completely eliminating the requirement for a gyroscope, and using an adaptation of a commercial FM demodulator to extract roll position from the small electronic signal. This configuration uses small, inexpensive accelerometers combined with a unique signal processing suite to measure roll position, and to then resolve the accelerometer output signals to obtain pitch and yaw. This concept was initially explored under an IR & D effort, and then further developed under contract to the U.S. Army. An extensive series of analyses, including detailed simulations, have confirmed the performance of the proposed technique. This has been followed by an experiment series using a tethered, gun-launched projectile, which has further validated the analyses results. The extension to the use of this configuration as a low-cost INS is also reasonable, and performance should be consistent with that of a conventional 3-axis Schuler loop type of system, for the required limited operating time. In addition, the technique we have developed for the accurate measurement of roll position may have other important applications related to the inexpensive and very accurate measurment of roll angle for a Rolling Airframe Missile, and for guidance of an X-rod type projectile.