Том 8, № 2 (2017)

The paper considers the distortion of nuclear magnetic resonance line in a quantum rotation sensor caused by the feedback in the cell while detecting the nuclear magnetization. Detection circuit is based on Faraday effect during longitudinal electronic paramagnetic resonance in alkali metal vapor.

The paper develops an earlier proposed approach to the construction of a geographically oriented horizon trihedron nonperturbed by inertial accelerations to aid navigation dead reckoning. The method developed by the author is called gyroscopic orientation with correctable pendulum. The proposed scheme is implemented using a trihedron of accelerometers and a free (uncontrolled) gyro with equatorial orientation. Special attention is given to the Schuler filter, which not only provides “absolute” nonperturbility of navigation dead reckoning but also makes it possible to formulate the problem of its autonomous error estimation to the accuracy determined by the gyro drifts in the steady state. The problem of occasional correction of “azimuth” heading during in situ observation is also considered.

The procedure proposed for studying the errors of MEMS accelerometer triad reduces the test duration as compared with traditional methods and allows estimation of mutual geometrical arrangement of sensors in the triad. The proposed approach consists in studying the static characteristics of sensors in oscillating angular motion mode and estimates error coefficients in mathematical model of accelerometer readings along with location of accelerometer triad in the closed IMU casing. Results of studying the errors of MEMS accelerometer triad are presented.

The Indian Regional Navigation Satellite System (IRNSS) is a seven-satellite constellation developed by Indian Space Research Organization (ISRO), India. IRNSS provides two services, with the standard positioning service open for civilian use, and for authorized users (including the military) with an assured absolute positional accuracy. IRNSS is designed to cover all the parts of India and also extending beyond the Indian borders. The coverage area of IRNSS with routes of satellites means and includes area covering entire Pakistan, Afghanistan, most of China and Middle East along with Indian Ocean. IRNSS downlink signals have two bands: S1 band and L5 Band. Presently Indian users are dependent on the civil GPS signals with a positional accuracy of 5 m. IRNSS system is intended to provide an absolute position accuracy of (i) better than 10 m throughout Indian landmass (ii) better than 20 m over the Indian Ocean and (iii) approximately in a region of 1500 km around India. There are 15 ground stations across the country responsible for operating and/or monitoring the IRNSS seven satellite constellation. A comparative analysis of IRNSS and GPS navigational satellites shows that the IRNSS consists of sufficient number of satellites for regional navigation system and it can also exhibit better performance. The main parameters selected for our study are orbital characteristics, position accuracy and positional error including Circular Error Probable (CEP), Altitude variation, Geometric Dilution of Precision (GDOP) with respect to Number of Satellites (NSAT), variations in Carrier to Noise (C/N₀) ratio and scintillation effect of both GPS and IRNSS satellite systems. Our analysis showed that IRNSS systems shall be used as stand-alone systems.

piNAV L1 is a GPS L1 receiver for position determination of the small satellites at LEO orbits. The receiver was tested by the ReGen software GPS simulator for static and dynamic scenarios. The typical horizontal position error for static scenario is 2.5 m (95%). The position errors for dynamic scenarios are affected by the dynamic stress errors.