1. Several flights from Bedford, MA to Los Angeles, CA were made starting in 1953. This was the first-ever fully inertial transcontinental flight. An error build-up of between l-to-2 miles per thousand traveled was attributed to the sensors. SPIRE Jr., which was approximately a factor of two lighter than FEBE, was developedin afollow-on program. SPIREJr. contained three 10FG and two 25PIGA accelerometers, and also flew several times from MA to CA with about the same error build-up as SPIRE. Autonetics continued development of stellar inertial systems as well as all inertial systems. They developed a six-gyro navigation system in which one gyro in each pair was periodically spin-reversed, or alternatively the gyro case was reversed. This provided much better accuracy. Applications were for short-term aircraft navigation (XN5) and the Navaho supersonic cruise missile (XN6). When interest in the Navaho development ceased in 1957 (contract cancelled) in favor of ICBMs, the XN6 system found a home navigating the submarineNautilus undertheNorth Polein 1958.
2. In 1963, the Air Force launched a campaign to get a low-cost navigator. This resulted in three principal suppliers: Kearfott and Litton with the Dynamically Tuned Gyro (DTG), and Honeywell with the free-rotor Electrostatically Suspended Gyroscope (ESG). Ultimately, laser gyro systems became dominant in the lower-cost and-weight strapdown systems.
3. The DTG was developed in the 1960s. It consists of a rotor suspended by a universal joint made from a gimbal-and-flexure system (similar to auniversaljoint). A spin motor drives the assembly at a tuned speed in which the gimbal inertia force counteracts the elastic stiffness of the flexures, so that the universal joint is a zero-stiffness hinge, and the spinning rotor behaves as a free-rotor gyro. To avoid over-extending the flexures, a torquer is used keep the rotor at null. Torquing current is proportional to angular rate. DTGs are small, rugged, and are two-degree of freedom devices. They have faster response times, perform better over wider temperature ranges, and are less expensive than floated gyros. Kearfotfs HAINS (High Accuracy INS) is accurate to around aquarter of anautical mile per hour.