Strapdown inertial navigation - The gyroscope challenge

The development of inertial navigation technology is surveyed, with comparison made between the two alternative systems, gimballed and strapdown. Aside from the three sensors, the three gyro stable platform used in gimballed systems includes electronic equipment, the failure of which is frequently an error source in the system. In contrast, strapdown devices require only the triad of sensors, thus reducing failures and maintenance problems. To implement the strapdown gyro concept, a high-performance angular sensor is needed, providing drift stability of .01 degree per hour, high dynamic range, and ability to rapidly stabilize in a wide range of temperatures. Four candidates for strapdown design are described: single degree of freedom rate integrating gyros; two degree of freedom 'dry' gyros; electrostatically suspended gyros; and ring laser gyros. Advantages of the ring laser system are emphasized, including economy, simpler manufacture, easier handling, and much improved reliability; design programs for the system are summarized, among them development of interface circuits between sensors and computers, and development of computer programs.