Satellite Attitude Research Articles

Analysis of the possibility of using the satellite navigation system in the railway traffic control systems

The analysis of the possibility of using satellite navigation for rail vehicle positioning, which is the subject of many studies and projects, is aimed at assessing the uncertainty and accuracy of train positioning using satellite navigation systems, along with defining its impact on the capacity and safety of the rail infrastructure. Existing studies in this area prevent a clear assessment of the feasibility of implementing a satellite navigation system for rail vehicle positioning in rail traffic control systems. Therefore, it is necessary to analyze the possibility of using satellite navigation for rail vehicle positioning in terms of research problems arising from the limitations of satellite positioning system functionality, which include parameters related to accuracy, reliability, and speed of information transfer between the vehicle and the rail traffic control system. The implementation of the research work should be focused on developing a research model, subject to validation for the parameters and conditions of movement of rail vehicles in the defined area of railroad infrastructure, adopted within the framework of the work carried out. The research and the model form the basis for developing the knowledge of implementing satellite navigation in practical solutions on the railroad network.

Characterisation of the TOI-421 planetary system using CHEOPS, TESS, and archival radial velocity data

Context. The TOI-421 planetary system contains two sub-Neptune-type planets (Pb ~ 5.2 days, Teq,b ~ 900 K, and Pc ~ 16.1 days, Teq,c ~ 650 K) and is a prime target to study the formation and evolution of planets and their atmospheres. The inner planet is especially interesting as the existence of a hydrogen-dominated atmosphere at its orbital separation cannot be explained by current formation models without previous orbital migration. Aims. We aim to improve the system parameters to further use them to model the interior structure and simulate the atmospheric evolution of both planets, to finally gain insights into their formation and evolution. We also investigate the possibility of detecting transit timing variations (TTVs). Methods. We jointly analysed photometric data of three TESS sectors and six CHEOPS visits as well as 156 radial velocity data points to retrieve improved planetary parameters. We also searched for TTVs and modelled the interior structure of the planets. Finally, we simulated the evolution of the primordial H-He atmospheres of the planets using two different modelling frameworks. Results. We determine the planetary radii and masses of TOI-421 b and c to be Rb = 2.64 ± 0.08 R⊕, Mb = 6.7 ± 0.6 M⊕, Rc = 5.09 ± 0.07 R⊕, and Mc = 14.1 ± 1.4 M⊕. Using these results we retrieved average planetary densities of ρb = 0.37 ± 0.05ρ⊕ and ρc = 0.107 ± 0.012 ρ⊕. We do not detect any statistically significant TTV signals. Assuming the presence of a hydrogen-dominated atmosphere, the interior structure modelling results in both planets having extensive envelopes. While the modelling of the atmospheric evolution predicts for TOI-421 b to have lost any primordial atmosphere that it could have accreted at its current orbital position, TOI-421 c could have started out with an initial atmospheric mass fraction somewhere between 10 and 35%. Conclusions. We conclude that the low observed mean density of TOI-421 b can only be explained by either a bias in the measured planetary parameters (e.g. driven by high-altitude clouds) and/or in the context of orbital migration. We also find that the results of atmospheric evolution models are strongly dependent on the employed planetary structure model.

Assessing the Results of Satellite Positioning for Geodetic Network Points with Different Observation Sessions

Nowadays, static satellite observations are widely used in many fields. To obtain high measurement accuracy, the static satellite observations of the geodetic network have been carried out using one and two base stations. This study is important due to the lack of information on whether using several base stations impacts measurement accuracy. In addition, the dependence of the measurement accuracy of different lengths of the geodetic network lines on the observation time is investigated. Direct measurements have been carried out on the territory of Egypt, where the development of a geodetic network of the National Agricultural Cadastral Network (NACN) is a burning issue. The observations were conducted using Trimble R10 dual-frequency receivers based on specific schemes. In the case of using one base station, all the lines that connect the nearest points to the station were calculated. In the case where two stations were being used, the observations were carried out simultaneously on three points, including the base points. The third point is the closest point to the baseline. The other three points were determined as follows: two points had been taken from the previous triangle; and the one that was the nearest one to the line formed by the first two points, etc. The analysis of the results shows that if only one station is used, it takes at least 3–4 hours to make measurements that are precise up to a centimeter. The use of two base stations can reduce measurement time by two hours. Additionally, these studies can help select satellite positioning technology based on the equipment available.

Risk overbounding for ionospheric gradient monitor using geometry-free double differenced carrier phase measurements

Ionosphere anomaly can cause large spatial gradients in the double-differenced carrier phase (DDCP) measurements. Taking advantage of this characteristic, the ionospheric gradient monitor (IGM) is designed with multiple ground reference stations to detect threatening ionospheric gradients for safety of life applications. An optimal IGM should be most sensitive to ionospheric gradients and least sensitive to other errors. However, current IGM suffers from the influence of tropospheric error, which can degrade monitor performance under extreme weather conditions by causing risks of false alarms and missed detections. To address this issue, an alternative IGM is proposed using the geometry-free combination of DDCP as the test statistic. Ambiguity resolution procedure is designed for estimating the ambiguity term in the test statistic. The risk induced by the wrong ambiguity fix and tropospheric error are analyzed and bounded with required averaging period and minimum baseline length. The results show that the proposed theoretical IGM is capable of achieving probability of false alarm of 10–8 and probability of missed detection of 10–6 with a filtering period of 612 s and baseline length of 371.7 m or a filtering period of 544 s and baseline length of 384.4 m. The experimental results using data collected from Hong Kong Satellite Positioning Reference Station Network demonstrate that the performance of the proposed theoretical IGM is comparable to that of the existing detection algorithm.

BRDF-Based Photometric Modeling of LEO Constellation Satellite from Massive Observations

BRDF-Based Photometric Modeling of LEO Constellation Satellite from Massive Observations

Dynamics of pax7 expression during development, muscle regeneration, and in vitro differentiation of satellite cells in rainbow trout (Oncorhynchus mykiss).

Essential for muscle fiber formation and hypertrophy, muscle stem cells, also called satellite cells, reside beneath the basal lamina of the muscle fiber. Satellite cells have been commonly identified by the expression of the Paired box 7 (Pax7) due to its specificity and the availability of antibodies in tetrapods. In fish, the identification of satellite cells remains difficult due to the lack of specific antibodies in most species. Based on the development of a highly sensitive in situ hybridization (RNAScope®) for pax7, we showed that pax7+ cells were detected in the undifferentiated myogenic epithelium corresponding to the dermomyotome at day 14 post-fertilization in rainbow trout. Then, from day 24, pax7+ cells gradually migrated into the deep myotome and were localized along the muscle fibers and reach their niche in satellite position of the fibres after hatching. Our results showed that 18 days after muscle injury, a large number of pax7+ cells accumulated at the wound site compared to the uninjured area. During the in vitro differentiation of satellite cells, the percentage of pax7+ cells decreased from 44% to 18% on day 7, and some differentiated cells still expressed pax7. Taken together, these results show the dynamic expression of pax7 genes and the follow-up of these muscle stem cells during the different situations of muscle fiber formation in trout.

Playing Catch with Electrons: A Dynamic Metaphor for Chemical Bonding with an Extension of the Tunneling Model to Gas-Phase Molecules.

Quantum mechanical electron tunneling is explored as the mediator of chemical bonding. Three topics are addressed. First, a baseball game-of-catch metaphor is employed to elucidate the physics of chemical bonding. According to this metaphor, a baseball player, a baseball, and the act of throwing a baseball are analogous to an atom, an electron, and the act of electron tunneling. Using this framework, the tunneling physics of covalent, polar covalent, ionic, and hydrogen bonding is clarified. Second, gas-state energies associated with frontier orbital positioning are established and are used in the chemical bond tunneling assessment of four homopolar bonds, H-H, N≡N, O=O, and F-F, and four heteropolar bonds, H-F, H-Cl, H-Br, and H-I. Third, a new procedure for estimating solid-state tunneling parameters is introduced, involving quantum confinement of gas-state energy frontier orbitals.

Modelling Rigid Body Potential of Small Celestial Bodies for Analyzing Orbit–Attitude Coupled Motions of Spacecraft

The present study aims to propose a general framework of modeling rigid body potentials (RBPs) suitable for analyzing the orbit–attitude coupled motion of a spacecraft (S/C) near small celestial bodies, regardless of gravity estimation models. Here, ‘rigid body potential’ refers to the potential of a small celestial body integrated across the finite volume of an S/C, assuming that the mass of the S/C has no influence on the motion of the small celestial body. First proposed is a comprehensive formulation for modeling the RBP including its associated force, torque, and Hessian matrix, which is then applied to three gravity estimation models. The Hessian of potential plays a crucial role in calculating the RBP. This study assesses the RBP via numerical simulations for the purpose of determining proper gravity estimation models and seeking modeling conditions. The gravity estimation models and the associated RBP are tested for eight small celestial bodies. In this study, we utilize distance units (DUs) instead of SI units, where the DU is defined as the mean radius of the given small celestial body. For a given specific distance in Dus, the relative error of the gravity estimation model at this distance has a similar value regardless of the small celestial body. However, the difference value between the potential and RBP depends on the DU; in other words, it depends on the size of the small celestial body. This implies that accurate gravity estimation models are imperative for conducting RBP analysis. The overall results can help develop a propagation system for orbit–attitude coupled motions of an S/C in the vicinity of small celestial bodies.

Research on rapid batch test technology of small satellite attitude and orbit control system

The attitude and orbit control sub-system of small satellites is an important sub-system to ensure the stable operation of satellites in orbit, and its testing in the satellite factory development stage runs through the whole testing process. Most of the traditional attitude and orbit control sub-system tests require the cooperation of many people to complete the performance tests of various components and sensitive devices, which also leads to the complicated and time-consuming testing process of the sub-system. At present, the mass production of small satellites is developing rapidly. In order to meet the urgent needs of small satellite mass production, the traditional attitude control subsystem test equipment and methods can’t meet the requirements of satellite mass production mode. In order to meet the needs of small satellite mass development, this paper studies the rapid batch test technology of small satellite attitude and orbit control systems. A fast pipeline test system which can support the performance and dynamics simulation of various components of a multi-satellite attitude and orbit control subsystem is studied. Based on the architecture of real-time communication between the upper computer and lower computer, the system can realize the integration and rapid testing of component performance and dynamic simulation. A continuous dynamic simulation test of 2140 seconds was carried out for the cruise mode and attitude maneuver mode of a certain type of satellite in orbit. During the test, various components and sensors of the attitude and orbit control subsystem operate correctly and can support the stable operation of the required attitude in various modes of the satellite, which can verify the correctness of the interface and performance of the satellite attitude and orbit control subsystem. The research results greatly reduce the input of manpower and material resources, and greatly improve the test efficiency. It lays a foundation for the rapid batch test of the small satellite attitude control subsystem.

High frequency attitude determination of micro satellites based on FPGA

The accuracy and speed of satellite attitude calculation algorithms are one of the key factors affecting the performance of satellite attitude control. This article proposes a high-performance attitude calculation algorithm for micro satellites based on Field Programmable Gate Array (FPGA). This algorithm is designed and simplified based on the parallel characteristics and abundant computing resources of FPGA. The algorithm fully utilizes the parallel computing power of FPGA and designs a multi-stage pipeline for complex matrix operations in Kalman filtering. It can simultaneously complete data collection and final attitude determination result output, greatly improving the output frequency of attitude information and reducing output delay. The experimental results show that compared to traditional embedded processors, FPGA based attitude calculation has significant advantages in terms of speed.

Strategies for hollow cathode command in short electrodynamics tether-based deorbit devices

Heaterless hollow cathodes are a promising solution for reaching a good cathodic contact in electrodynamic tether systems. However, these cathodes cannot keep the plasma discharge if the electric current IC is below a threshold Imin. If the tether is short, and to save power and expellant, an appropriate command strategy is needed to ensure that the cathode is triggered in conditions satisfying IC>Imin. This study investigates four command strategies, including two fully autonomous approaches (one based on satellite position and the other on local plasma density) and two strategies involving ground segment access, differing in command generation location (ground segment and on-board computer). The success rates of the four strategies were studied though numerical simulation and for the specific scenario of the E.T.PACK demonstration mission. The results demonstrate that, as compared to continuous operation of the hollow cathode, the proposed strategies reduce propellant wastage by a factor between 5 and 10. The strategy requiring ground segment access and with the onboard computer making the command decision has the highest success rate (94%). Among the autonomous configurations, the strategy based solely on local plasma density achieves the highest success rate (69%). Additionally, the impact of sensor accuracy on success rates was assessed via Monte Carlo analysis. The command strategy relying on plasma density measurement is the most sensitivity strategy, with a 10% decrease in success rate due to sensor uncertainty.

Improved time-variable transformer-based fault diagnosis method for satellite attitude control system

This study proposes a fault diagnosis method based on a time-variable transformer network for satellite attitude control system telemetry data, which has the properties of a time series and strong multivariate correlation. First, a time-attention module was utilised to determine the correlation between the data at a specific time and before that time to effectively identify the dynamic properties of the data. A variable attention module is introduced to capture the degree of correlation between various variables to achieve multivariate decoupling. Then, the interactive attention layer combines the dynamic properties of the data with the correlations between the variables to achieve dynamic data decorrelation. Finally, a linear layer is used to implement the fault diagnosis.

A light scattering analysis of the cryovolcano plumes on enceladus

Observations by NASA's Cassini spacecraft show that Enceladus, the sixth largest moon of Saturn, has cryovolcanoes on its south pole as well as a global subsurface ocean beneath Enceladus's icy crust. Photographs from the Imaging Science Subsystem (ISS) cameras aboard Cassini during flybys of Enceladus show cryovolcano plumes. The images are taken in several filters and with linear polarizers at various angles and orbital positions. Light scattered by the plume particles and observed by Cassini may provide information about the plume composition and potentially the dynamics of the ocean below. Here, we remove the coupling between orbital position and scattered plume intensity as well as analyze ISS data using light scattering models and the Q-space method. We suggest that the plume particles are generally larger than two microns in radius and nonspherical in shape.

Fusion of Land-Based and Satellite-Based Localization Using Constrained Weighted Least Squares.

Combining multiple devices for localization has important applications in the military field. This paper exploits the land-based short-wave platforms and satellites for fusion localization. The ionospheric reflection height error and satellite position errors have a great impact on the short-wave localization and satellite localization accuracy, respectively. In this paper, an iterative constrained weighted least squares (ICWLS) algorithm is proposed for these two kinds of errors. The algorithm converts the nonconvex equation constraints to linear constraints using the results of the previous iteration, thus ensuring convergence to the globally optimal solution. Simulation results show that the localization accuracy of the algorithm can reach the corresponding Constrained Cramér-Rao Lower Bound (CCRLB). Finally, the localization results of the two methods are fused using Kalman filtering. Simulations show that the fused localization accuracy is improved compared to the single-means localization.

GNSS and LiDAR Integrated Navigation Method in Orchards with Intermittent GNSS Dropout

Considering the vulnerability of satellite positioning signals to obstruction and interference in orchard environments, this paper investigates a navigation and positioning method based on real-time kinematic global navigation satellite system (RTK-GNSS), inertial navigation system (INS), and light detection and ranging (LiDAR). This method aims to enhance the research and application of autonomous operational equipment in orchards. Firstly, we design and integrate robot vehicles; secondly, we unify the positioning information of GNSS/INS and laser odometer through coordinate system transformation; next, we propose a dynamic switching strategy, whereby the system switches to LiDAR positioning when the GNSS signal is unavailable; and finally, we combine the kinematic model of the robot vehicles with PID and propose a path-tracking control system. The results of the orchard navigation experiment indicate that the maximum lateral deviation of the robotic vehicle during the path-tracking process was 0.35 m, with an average lateral error of 0.1 m. The positioning experiment under satellite signal obstruction shows that compared to the GNSS/INS integrated with adaptive Kalman filtering, the navigation system proposed in this article reduced the average positioning error by 1.6 m.

Hybrid supervision scheme for satellite attitude control with sensor faults

Hybrid supervision scheme for satellite attitude control with sensor faults

GRACE-FO attitude determination: Star camera installation matrix calibration and incremental quaternion integrator

The satellite attitude error is transmitted to the gravity field through KBR antenna phase center correction and non-conservative force conversion, which affects the accuracy of gravity field inversion. Therefore, obtaining high-precision satellite attitude is one of the important research contents of gravity field inversion. Each satellite of GRACE-FO is equipped with three SCs and an IMU for satellite attitude measurement, and fusion of these two types of data can obtain high-precision satellite attitude. In this paper, we use kalman filter to fuse the original GRACE-FO 1A observation data, and take into account the calibration of the installation matrix of the SCs during the fusion process. Meanwhile, a quaternion integrator that takes angle increments as inputs is derived from the equivalent rotation vector differential equation to address the computational inefficiency of first-order quaternion integrator, the accuracy and computational efficiency are verified using measured data. The experimental results show that after the calibration of the installation matrix of the SCs, the system bias of 20′′ caused by switching from three SCs observations to two SCs observations can be eliminated. The standard deviation of the attitude difference between the obtained attitude in this paper and the attitude calculated by JPL is at most 6′′ and the proposed incremental quaternion integrator has the same accuracy as the first-order quaternion integrator but with computational efficiency improved by at least 35%.

Breeding records and the detection of nesting predators of wild-release red-crowned cranes into non-breeding areas of the Yancheng National Nature Reserve, China.

The western population of the red-crowned crane Grus japonensis in mainland China has been decreasing in the past few decades and wild population enhancement programmes have been launched in this country. First, 14 captive-bred red-crowned cranes were released into the core area of Yancheng National Nature Reserve for Rare Birds (YNNR), one of the most important wintering areas of this species, in 2013 (seven individuals) and 2015 (seven individuals) and then 8 more captive-bred cranes were released into YNNR from February 2022 to February 2023. We used satellite positioning and drone monitoring to study the status of released cranes. The results showed that two individuals (No. BJZ001 and BJZ008) from the first group of released cranes were found breeding in 6 of 7 years in the YNNR from 2017 to 2023. Three individuals (No. WNNR022, WNNR025 and WNNR026) from the second group of released cranes were recorded breeding in YNNR in 2023. All released cranes lived in the YNNR year round and did not migrate with wild cranes. Raccoon dogs, Nyctereutes procyonoides, were first recorded as red-crowned crane nest predators in the YNNR. Although these released cranes breed successfully in the YNNR, nestlings might face the threat of predators in non-traditional breeding areas. Further research is needed to determine whether offsprings of released individuals migrate with wild cranes and if breeding in their original wintering grounds is truly beneficial for population growth.

Identification Method of High Incidence Areas of Bad Driving Behaviors Based on DBSCAN-Graham Combination

<p>This study utilizes data obtained from vehicle positioning, speed, and engine status through satellite positioning system monitoring terminals. The data is processed using spherical interpolation of latitude and longitude to handle missing values. The study establishes indicators for identifying bad driving behaviors, including speeding, rapid acceleration and deceleration, prolonged vehicle idling, and fatigue driving. The traditional DBSCAN algorithm is improved by incorporating both temporal and spatial search ranges into the algorithm, enabling cluster analysis of bad driving behaviors from both temporal and geographical perspectives. Finally, the Graham algorithm is utilized to calculate cluster boundaries, determining the specific locations and boundaries of high incidence areas of bad driving behaviors. This research aids regulatory authorities in more precisely supervising risk areas during transportation processes in terms of time and location.</p> <p> </p>

Quantitative identification of causes of instrumental acoustic signal distortion in Global Navigation Satellite System-Acoustics Combination observations.

The Seafloor Geodetic Observation-Array (SGO-A), operated by the Japan Coast Guard, relies on the Global Navigation Satellite System-Acoustics combination (GNSS-A) technique, which integrates satellite positioning systems and undersea acoustic ranging to determine seafloor crustal deformation at the centimeter level for earthquake disaster prevention. Recently, we found distortion in the SGO-A 10-kHz carrier wave that degraded the accuracy. Carrier wave distortion can cause errors on the scale of several centimeters to twenty centimeters, which greatly impedes centimeter-level observations. This study investigated this carrier wave degradation by an underwater acoustic communication experiment conducted in 2022, using a transducer similar to that used by SGO-A. Also, we reproduced degraded waveforms through a grid search-like method for quantitatively evaluating the extent to which the interior of the equipment contributed to deterioration. Our results underscore the importance of careful consideration in signal processing, as the observed waveform degradation is not solely attributed to hardware structures but also to internal electrical circuits. The findings suggest that conventional signal identification methods may lead to errors, providing motivation for a shift towards experimental and experiential timing-based waveform identification approaches to enhance accuracy in GNSS-A systems.