Specific Features of Constructing a Dual-Mode GNSS Gyrocompass as a Tightly-Coupled Integrated System

Abstract

A task of constructing a tightly-coupled inertial satellite integrated system under the conditions of limited visibility is considered in terms of solving both orientation and navigation problems. To determine the orientation parameters of a moving object, a dual-mode GNSS gyrocompass is implemented, which comprises a gimballess inertial measurement unit (IMU) on fiber-optic gyros (FOG), and two-antenna receiving equipment (RE) of global navigation satellite system (GNSS). Algorithms and errors of a GNSS gyrocompass with antenna baseline at the level of wavelength of carrier frequency and satellite receivers with external reference oscillator are studied. At that, the IMU with the antenna module of GNSS RE operates in reversible modulation rotation mode. A specific feature of this system is that a GNSS gyrocompass can be constructed while observing at least one navigation satellite of GPS or GLONASS; moreover, it has an autonomous operation mode which implements an AHRS scheme and position dead-reckoning based on the IMU and log data in absence of signals from the navigation satellite. The ambiguity of phase measurements and unreliable measurements are removed by referring to the IMU data when forming differential measurements in the integrated system at the level of the first differences of phases. The results of desktop analysis of bed testing data for a prototype system with a GNSS gyrocompass Orion-M (designed by CSRI Elektropribor) comprising GNSS receiving units 2K-363E-62 (RIRV JSC) and FOG-based inertial unit VG 910 (Fizoptika JSC) are presented in the paper.