David M. Rozelle

Interferometric Fiber Optic Gyroscope with Inertial Navigation Performance Over Extended Dynamic Environments

Litton is developing an interferometric fiber optic gyroscope for future navigation, guidance, and stabilization applications. The gyro is presently less than three inches in diameter, which is size competitive with current ring laser gyros of equal performance. In this paper we report on the bias, scale factor, and input axis alignment performance of the inertial navigation fiber optic gyroscope over extended, dynamic temperature environments.

Progress in navigation-grade IFOG performance

We previously reported achievement of 0.0027 deg/rt-hr angle random walk, as well as attainment of 0.0092 deg/hr bias uncertainty, 9.2 ppm scale factor error and 0.38 arc-seconds input axis alignment error over the temperature range -55 to 71 degC under dynamic thermal environments. The gyro coil in these instruments has less than 3 inches outer diameter and less than one inch height. In this paper we report on further advances in navigation-grade IFOG technology achieved at Litton. The angle random walk has been reduced by a factor of three to 0.0009 deg/rt-hr. Bias uncertainty of 0.0081 deg/hr has been attained over the -55 to 71 degC temperature range having more stringent temperature ramps than previously reported. The gyro bias magnetic sensitivity has been reduced to 0.0002 deg/hr/gauss. This paper describes the IFOG optical architecture that utilizes a low-birefringence network and a polarization maintaining network, discusses the dominant sources of thermal and magnetically-induced bias error in the IFOG and presents the latest data from the navigation- grade IFOG.

IFOG technology for embedded GPS/INS applications

A spherical error probable of 4.0 meters was demonstrated with an IFOG-based, integrated inertial measurement/global positioning system under dynamic field conditions. Less than 1.0 nautical mile per hour free inertial mode drift was also achieved with this system under laboratory-simulated test conditions. To achieve these levels of performance, IFOGs with bias uncertainties less than 0.015 deg/hr, scale factor errors less than 50 ppm and angle random walks less than 0.005 deg/(root) hr wee required. The performance of a series of six IFOGs is reported. For comparison, the performance of the same instruments measured in two demonstration GGP units is also presented. Both laboratory and field test results of the systems are discussed. The focus of the data presented is the instrument noise and the long term bias thermal model stability. The instruments and systems were developed as part of the first phase of a two phase program to create a 100 in 3 integrated GPS/INS systems with a target cost of 15K dollars (US). With the implementation of interferometric fiber optic gyro technology, integrated guidance and navigation systems are potentially very low cost with high reliability and suitability for a wide range of military and commercial applications.