Vol 10, No 3 (2019)

The paper discusses the structure, algorithms and testing results for a hybrid precision strapdown inertial navigation system (SINS) which is resistant to fast extreme impacts. Impact resistance of the precision SINS is provided by incorporating an auxiliary strapdown inertial attitude control system (SIACS) based on rough sensors that can endure fast extreme shocks without losing the attitude accuracy; and by post-processing of inertial sensors data performed in the onboard computer simultaneously with the main navigation task. The post-processing procedure is designed to identify the moment of shock occurrence and to repeat the attitude problem solving in the onboard computer based on the auxiliary SIACS data within the time interval of exposure to the extreme shock. In the absence of shocks, the auxiliary SIACS is calibrated in accordance with the data of the main precision SINS. The main precision SINS is based on precision fiber-optic gyros (FOG) and the auxiliary SIACS—on micromechanical gyros (MMG). Thus, a hybrid-type precision SINS has been constructed, which has demonstrated required accuracy level during on-ground vehicle tests, including shock tests.

Refinement of the electrostatic gyroscope (ESG) drift model aboard an orbital maneuverable satellite for remote sensing of the Earth’s surface is considered. Some changes of the drift model also hold for the ESG ground-based applications. The paper also analyzes the quasi-continuous correction mode of the ESG-based strapdown inertial attitude reference system (SIARS) using raw (unsmoothed) data from the star tracker and the extended Kalman filter (EKF) algorithm. A special feature of solving the problem of SIARS output data correction and the calibration problem in this mode is rejection of incorrect measurements. The algorithm for this problem solution is described. The ESG drift model is given both for the SIARS calibration mode in order to ensure an adequate prediction of ESG drifts over a long time interval and for the quasi-continuous correction mode under spacecraft maneuvering conditions. The results of data processing of the flight tests of the SIARS and the star tracker aboard one of the spacecraft are discussed.

The paper addresses the main problems related to the development of underwater communication networks which differ from the traditional underwater acoustic communication in simultaneous data exchange of a large number of spatially separated nodes, as well as their high-precision positioning. While the problems of traditional acoustic communication are generally associated with the complexity and variability of hydro-acoustic medium for signal propagation, the underwater communication network faces a number of additional significant problems such as collisions in the network, occurring during simultaneous transmission of messages from several nodes and requiring special managerial and engineering measures for their resolution; another problem is complex configuration of the alternating zones of mutual connectivity (“audibility”) of nodes, caused by specific features of underwater acoustic environment and requiring the nontrivial routing of data flows from source to recipient. It is demonstrated in the paper that these problems can be solved by developing the techniques of communication signals generation and transmission, which then form the protocols of nodes’ interaction during exchange of messages, and are implemented in digital acoustic modems that have ultimately developed into complex electronic devices.