Vol 10, No 4 (2019)

The study makes an approach to the problem of circumlunar spacecraft navigation using the measurements from the global navigation satellite systems (GNSS) GLONASS, GPS, Galileo and BeiDou. Algorithms have been developed for determining the orbits of low- and high-orbit circumlunar spacecraft, based on the method of dynamic filtering of pseudo-range measurements from “reverse” navigation satellites (NS). The solution to the navigation problem has been simulated by the measurements from four GNSS, and by those from the NS of GLONASS and GPS only. Accuracy and dynamic characteristics of the obtained solutions have been determined and compared to similar solutions for geostationary spacecraft.

In this paper, the problem of an autonomous unmanned aerial vehicle (UAV) approach to a target which is selected in a reference image is addressed. A robust matching algorithm is proposed to reliably project the selected point in the reference image into the live images of a quadrotor helicopter. Projective transformations are applied to the reference image to extract additional keypoints and to gain invariance to out-of-plane perspective transformations. Since the matching algorithm does not exploit the beneficial characteristics of image sequences and because its processing time is not short enough for high frame rates, a tracking algorithm is introduced. High detection rates even for image sequences with large viewpoint changes are achieved. Therefore, the presented algorithm can be used as input to a guidance algorithm for UAVs.

The paper presents a comparative analysis of the extended Kalman filter (EKF) and the sigma-point Kalman filter (SPKF) applied to solve the problem of SINS/GNSS integration based on a loosely-coupled integration scheme. Complete stochastic measurement models of MEMS inertial sensors are considered. The efficiency of the EKF and the SPKF is evaluated using real experimental data on complex motion from an SINS based on MEMS technology and a GNSS receiver with a double antenna. The estimation accuracy of navigation parameters using the EKF and the SPKF in the presence of the GNSS signal and during the GNSS outages is analyzed. The results of the statistical analysis of the errors in estimating navigation parameters for different periods of GNSS signal outage are considered.

The results of study of a fiber-optic gyroscope prototype with 0.01–0.001deg/h drift are presented. The gyroscope comprises three feedback loops: one for Sagnac phase difference compensation, the second one for the scale factor stabilization, and the third (fast-response) one for the compensation of constant component of optical signal on the photodetector, affecting the measurement channel. To increase the accuracy of the prototype gyroscope up to the level of 0.001 deg/h, it is proposed to use the fourth and the fifth feedback loops which will suppress the parasitic effects in the integrated optic phase modulators.

Ring Laser Gyroscopes (RLGs) are widely used in many airborne and navigation systems for accurate measurement of the true rotation of the body movement. But the RLG’s suffer a serious problem at low frequencies known as Lock–in frequency. To avoid lock-in problem, the RLG is vibrated mechanically to a high frequency which is known as Dithering. In order to get the true rotation of the body the dither signal has to be removed. Single stage, multistage and multirate filters are suggested to remove the dither signal. These filters have the disadvantage that either the FIR filter length is too large or the phase characteristics are nonlinear. In this work, multiresolution Wavelet Transform (WT) techniques are used to remove the dither signal. Five level multiresolution analysis is carried out with various types of wavelets like Discrete Meyer and Daubechies 45 (db45) etc. With none of the standard wavelets, the original and reconstructed signals are matched. A new wavelet is designed to remove the dither signal. The required signal can be reconstructed back using the approximation coefficients at level 5. The dither signal is attenuated by 107.0 dB, and the phase characteristics are found to be linear in the pass band. The computational complexity is also less compared to the three stage combined filter reported earlier.

The paper discusses the method that was proposed earlier to provide nonperturbation of dead reckoning (DR) owing to a single-channel inertial vertical, constructed with the use of a triad of accelerometers and a single free gyroscope, as well as compensation for the effect of inertial accelerations directly in computed DR using the data from an external speed meter (a log). The DR method errors specific to this scheme are analyzed, in particular, those conditioned by the fact that, in the general case, positions of the accelerometers and the log for marine underwater and surface vessels do not coincide either with each other or the center of the vessel motion. Analytical calculations and the simulation results are given to show that the level of DR method errors is insignificant for the class of the objects under consideration.

Accurate time synchronization of the nodes of digital underwater acoustic (UWA) networks is necessary for the effective use of information obtained from various kinds of underwater sensors over a vast water area. The sensors of autonomous underwater vehicles (AUV) are widely used to address new challenges. One of them is time synchronization of sensors on mobile carriers, as well as synchronization of the clocks on mobile nodes of UWA networks, for example, teams of AUVs that perform coordinated and/or cooperated operations. The paper presents theresults of the experiments on using UWA modems for AUV positioning, namely, UWA modems with chip-scale atomic clocks (CSAC) that allow accurate measurements of delays in propagation of UWA signals and, thus, accurate estimation of ranges to their georeferenced sources. In addition, the accuracy of CSAC operation in various situations as well as positioning accuracy of AUVs having UWA modems with integrated CSACs are analyzed based on the experimental results. Also given are practical recommendations on how to “discipline” (steer) CSACs and provide their phase synchronization with a source of timekeeping signals.

The Earth-centered, Earth-fixed (ECEF) frame does not have any specific points in the near-Earth space; therefore, it can be used as the basic one for navigation in the polar regions. The paper considers a new algorithm for calculation of ECEF coordinates. The proposed algorithm is complementary to the basic strapdown INS algorithm, which functions in its normal mode from aircraft takeoff to landing. In the polar regions, the aircraft control law that supports flights on the point-to-point principle is based on calculation of ECEF coordinates.