Spacecraft In Orbit Research Articles

Solar energetic particles injected inside and outside a magnetic cloud

Context. On 2022 January 20, the Energetic Particle Detector (EPD) on board Solar Orbiter measured a solar energetic particle (SEP) event showing unusual first arriving particles from the anti-Sun direction. Near-Earth spacecraft separated by 17° in longitude to the west of Solar Orbiter measured classic anti-sunward-directed fluxes. STEREO-A and MAVEN, separated by 18° to the east and by 143° to the west of Solar Orbiter, respectively, also observed the event, suggesting that particles spread over at least 160° in the heliosphere. Aims. The aim of the present study is to investigate how SEPs are accelerated and transported towards Solar Orbiter and near-Earth spacecraft, as well as to examine the influence of a magnetic cloud (MC) present in the heliosphere at the time of the event onset on the propagation of energetic particles. Methods. We analysed remote-sensing data, including flare, coronal mass ejection (CME), and radio emission to identify the parent solar source of the event. We investigated energetic particles, solar wind plasma, and magnetic field data from multiple spacecraft. Results. Solar Orbiter was embedded in a MC erupting on 16 January from the same active region as that related to the SEP event on 20 January. The SEP event is related to a M5.5 flare and a fast CME-driven shock of ∼1433 km s−1, which accelerated and injected particles within and outside the MC. Taken together, the hard SEP spectra, the presence of a Type II radio burst, and the co-temporal Type III radio burst being observed from 80 MHz that appears to emanate from the Type II burst, suggest that the shock is likely the main accelerator of the particles. Conclusions. Our detailed analysis of the SEP event strongly suggests that the energetic particles are mainly accelerated by a CME-driven shock and are injected into and outside of a previous MC present in the heliosphere at the time of the particle onset. The sunward-propagating SEPs measured by Solar Orbiter are produced by the injection of particles along the longer (western) leg of the MC still connected to the Sun at the time of the release of the particles. The determined electron propagation path length inside the MC is around 30% longer than the estimated length of the loop leg of the MC itself (based on the graduated cylindrical shell model), which is consistent with the low number of field line rotations.

Coronal hole picoflare jets are progenitors of both fast and Alfvénic slow solar wind

Solar wind, classified by its bulk speed and the Alfvénic nature of its fluctuations, generates the heliosphere. The elusive physical processes responsible for the generation of the different types of this wind are a topic of active debate. Recent observations reveal intermittent jets, with kinetic energy in the picoflare range, emerging from dark areas of a polar coronal hole threaded by open magnetic field lines. These could substantially contribute to solar wind. However, their ubiquity and direct links to solar wind have not been established. Here, we report a unique set of remote-sensing and in situ observations from the Solar Orbiter spacecraft that establish a unified picture of fast and Alfvénic slow wind, connected to the similar widespread picoflare jet activity in two coronal holes. Radial expansion of coronal holes ultimately regulates the speed of the emerging wind.

High-Speed Target Location Based on Photoelectric Imaging and Laser Ranging with Fast Steering Mirror Deflection

There is an increasing number of spacecrafts in orbit, and the collision impact of high-speed moving targets, such as space debris, can cause fatal damage to these spacecrafts. It has become increasingly important to rapidly and accurately locate high-speed moving targets in space. In this study, we designed a visible-light telephoto camera for observing high-speed moving targets and a laser rangefinder for measuring the precise distance of these targets, and we proposed a method of using fast steering mirror deflection to quickly direct the emitted laser towards such targets and measure the distance. Based on the principle of photographic imaging and the precise distance of targets, a collinear equation and a spatial target location model based on the internal and external orientation elements of the camera and the target distance were established, and the principle of target location and the method for calculating target point coordinates were determined. We analyzed the composition of target point location error and derived an equation for calculating such errors. Based on the actual values of various error components and the error synthesis theory, the accuracy of target location was calculated to be 26.5 m when the target distance is 30 km (the relative velocity is 8 km/s and the velocity component perpendicular to the camera’s optical axis is less than 3.75 km/s). This study provides a theoretical basis and a method for solving the practical needs of quickly locating high-speed moving targets in space and proposes specific measures to improve target location accuracy.

STGLR: A Spacecraft Anomaly Detection Method Based on Spatio-Temporal Graph Learning.

Anomalies frequently occur during the operation of spacecraft in orbit, and studying anomaly detection methods is crucial to ensure the normal operation of spacecraft. Due to the complexity of spacecraft structures, telemetry data possess characteristics such as high dimensionality, complexity, and large scale. Existing methods frequently ignore or fail to explicitly extract the correlation between variables, and due to the lack of prior knowledge, it is difficult to obtain the initial relationship of variables. To address these issues, this paper proposes a new method, namely spatio-temporal graph learning reconstruction (STGLR), for spacecraft anomaly detection. STGLR employs a dynamic graph learning module to infer the initial relationships among telemetry variables. It then constructs a spatio-temporal feature extraction module to capture complex spatio-temporal dependencies among variables, leveraging a graph sample and aggregation network to learn embedded features and incorporating an attention mechanism to adaptively select salient features. Finally, a reconstruction module is used to learn the latent representations of features, capturing the normal patterns in telemetry data and achieving anomaly detection. To validate the effectiveness of the proposed method, experiments were conducted on two public spacecraft datasets, and the results demonstrate that the performance of the STGLR method surpasses existing anomaly detection methods, with an average F1 score exceeding 0.97.

Stereoscopic observations reveal coherent morphology and evolution of solar coronal loops

Coronal loops generally trace magnetic lines of force in the upper solar atmosphere. Understanding the loop morphology and its temporal evolution has implications for coronal heating models that rely on plasma heating due to reconnection at current sheets. Simultaneous observations of coronal loops from multiple vantage points are best suited for this purpose. Here we report a stereoscopic analysis of coronal loops in an active region based on observations from the Extreme Ultraviolet Imager on board the Solar Orbiter Spacecraft and the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory. Our stereoscopic analysis reveals that coronal loops have nearly circular cross-sectional widths and that they exhibit temporally coherent intensity variations along their lengths on timescales of around 30 minutes. The results suggest that coronal loops can be best represented as three-dimensional monolithic or coherent plasma bundles that outline magnetic field lines. Therefore, at least on the scales resolved by Solar Orbiter, it is unlikely that coronal loops are manifestations of emission from the randomly aligned wrinkles in two-dimensional plasma sheets along the line of sight, as proposed in the coronal veil hypothesis.

Modeling of Surface Ablation for Hypersonic Reentry Vehicles Using Direct Simulation Monte Carlo Method

The surface ablation of hypersonic reentry vehicles is modeled at the microscopic level based on direct simulation Monte Carlo method with the open-source SPARTA code. The expression of surface recession rate is derived together with a new ablation rule, which enables a better description of the coupling process between surface ablation and flow. Additionally, the grid cell size independence of the ablation rate is reached, and satisfactory results are obtained for the test cases. The simulation results of the two-dimensional wedge indicate that ablation starts from the stagnation point at the front side while the flow region near the local roughness is highly rarefied. The reentry and ablation of a three-dimensional CubeSat is also simulated to show the effectiveness of the present ablation procedure and, at the same time, may provide practical guidance for end-of-life disposal schemes of in-orbit spacecraft.

Quantifying the Impact of Sustained Acceleration on Critical Care Transport Medical Equipment

ABSTRACT Introduction Military and commercial stakeholders are investing to explore the use of hypersonic aircraft and orbital spacecraft to transport cargo, medical supplies, passengers, and casualties. These vehicle platforms require periods of sustained acceleration, but to date, these dynamic forces have not been comprehensively considered in the environment of critical care patient movement because injured patients and advanced aeromedical evacuation (AE) equipment are rarely subjected to these conditions. While military AE equipment does undergo crash hazard acceleration testing, equipment functionality during or after sustained acceleration remains to be evaluated. This study was performed to fill that knowledge gap. Materials and Methods AE equipment currently used by the U.S. Air Force and Critical Care Air Transport Teams (ZOLL EMV+ 731 ventilator and ZOLL Propaq MD cardiac monitor) was subjected to low (2.5 g), moderate (4.5 g), and variable acceleration (1.5–4.5 g) for 3-minute periods at the KBR Brooks Centrifuge. AE equipment was tested for functionality in 3 different orientations (gX, gY, and gZ). Predetermined variations were made in equipment input settings to ensure each equipment item would function across mission-relevant conditions (differing ventilator tidal volumes, differing cardiac monitor arterial pressure inputs, etc.). AE was evaluated for accuracy compared to controlled inputs, alarm conditions, and equipment failure. Results The EMV+ 731 ventilator and Propaq MD cardiac monitor had no equipment failures during testing. The ventilator had clinically negligible variations in tidal volume, peak pressure, and fraction of inspired oxygen during acceleration. At the highest tidal volume tested (480 mL), the ventilator had elevated peak pressure results. However, we believe this was due to limitations in test-lung resistance and was not related to a ventilator fault. Mild effects of sensor orientation were recorded in the Propaq MD blood pressure results; for example, gX and gY differed by 5.9 ± 1.21 mmHg at 75 mmHg input (P < .01) and 6.45 ± 1.229 mmHg with 150 mmHg input (P < .001). Conclusions The EMV+ 731 ventilator and Propaq MD cardiac monitor had reliable clinical performance despite sustained acceleration. This knowledge will facilitate immediate follow-on experimentation with advanced models of combat injury during simulated medical evacuation in sustained acceleration environments.

Enhanced Space Debris Detection and Monitoring Using a Hybrid Bi-LSTM-CNN and Bayesian Optimization

Space debris detection is important to the integrity of space missions and satellites, especially with the increase in the number of satellites and spacecraft in orbit. This paper addresses this by a new concept innovative approach using hybrid Bi-LSTM-CNN architecture which is optimized using Bayesian Optimization. The study presents an analysis approach based on the whole combination of machine learning and deep learning, a high-quality space debris detector, that can identify both the kind of object and the size of its RCS. The new method goes beyond what we have done so far and shows better results on a wide range of evaluation parameters, such as accuracy, precision, memory, and F1 score. Also, the study takes up the pragmatic issue of training time, thereby ensuring performance in real time. Esthetic trials on real datasets confirm the fit of the hybrid model, sensitivity, and efficacy with 99.16% and 99.98% detection and prediction of space debris types, respectively. In summary, this paper makes space debris tracking much more robust and mitigates threats associated with spaceflight and satellite operations, but they can offer a lot of information on threats and mitigation measures. The findings suggest that this hybrid model could be augmented with current space debris tracking systems, to increase their predictive power and operational effectiveness. Received: 2 July 2024 | Revised: 15 August 2024 | Accepted: 6 September 2024 Conflicts of Interest The author declares that she has no conflicts of interest to this work. Data Availability Statement The datasets cited in this manuscript are publicly available and can be accessed from the original sources referenced in the text. The data that support the findings of this study are openly available in Kaggle at https://www.kaggle.com/datasets/kandhalkhandeka/sate llites-and-debris-in-earths-orbit/data. No additional data were generated or analyzed during the current study Author Contribution Statement Ishaani Priyadarshini: Conceptualization, Methodology, Software, Validation, Formal analysis, Investigation, Resources, Data curation, Writing – original draft, Writing – review & editing, Visualization, Supervision, Project administration, Funding acquisition.

Effects of cold electron emissions on thermal plasma measurements on board Solar Orbiter spacecraft

Emissions of photo and secondary electrons influence thermal electron measurements on board spacecraft, typically below a threshold determined by the spacecraft's potential. We aim to examine and quantify this contamination of the observed low-energy electron fluxes. We seek to provide effective constraints for the correction methods used to accurately estimate unperturbed solar wind plasma parameters in the context of the Solar Orbiter mission. We performed a long-term statistical analysis of electron velocity distribution functions acquired by the Electron Analyser System experiment, which is part of the Solar Orbiter's Solar Wind Analyser suite of instruments. We employed analytical fits of time-averaged phase space density spectra to identify the energy break separating ambient solar wind electron populations from cold electron populations emitted by the spacecraft body. We analysed correlations between the observed energy break and the spacecraft potential, as well as other relevant plasma properties. Our analysis indicates that in contrast to other space missions, emitted electrons from the spacecraft are detected even above the spacecraft potential energy. The derived energy break is found to be uncorrelated with the measured spacecraft potential, but it is correlated strongly with the ambient electron temperature. We attribute this behaviour to the Solar Orbiter's geometric configuration, which can result in the detection of electrons emitted from spacecraft surfaces that are located far from the instrument's detector. We derived a theoretical expression for the energy break, assuming Maxwellian distribution functions for both the ambient and spacecraft electrons. This provides an effective constraint for the observed contamination by spacecraft electrons.

Reliability analysis of space debris mitigation strategies using the Monte Carlo process

In light of growing space exploration, the risk of collisions involving satellites, rockets and the International Space Station has increased significantly due to the significative number of space debris (objects in orbit that are no longer useful). In this scenario, several public and private organizations have developed strategies to mitigate this problem. The CBERS-1 satellite, launched in 1999 in a Brazil-China collaboration, is still in orbit, despite being decommissioned in 2003. This study aims to evaluate the effectiveness and reliability of various mitigation strategies that could have been implemented during the decommissioning of CBERS-1, using the DRAMA (Debris Risk Assessment and Mitigation Analysis) program and the OSCAR (Orbital Spacecraft Active Removal) application, which uses the Monte Carlo method. The objective is to ensure that CBERS-1 re-enters the Earth's atmosphere within a period of 25 years, meeting the ESA (European Space Agency) space debris mitigation requirements. This work contributes to understanding and improving space debris mitigation practices in the context of increasing activity in space.

Enabling efficient satellite mission design with rule-based collision avoidance

The growing number of operational spacecraft in Earth's orbit entails an increasing operational effort for collision avoidance (COLA), particularly regarding the coordination of evasive measures. To reduce the associated workload, COLA operations should already be considered in the early planning phases of space missions. The Mission Analysis Software (MAS) is a web-based application developed within the ESA-funded CASCADE (Collision avoidance, satellite coordination assessment demonstration environment) project by OKAPI:Orbits and TU Darmstadt for this purpose. The software follows a data-driven approach to offer satellite operators, mission designers, service providers, agencies, and authorities two services: conjunction assessment and rule analysis. The conjunction assessment provides an estimation of the number and type of conjunctions to be expected on the targeted orbit and identifies frequently conjuncting parties for the current population of active satellites as well as for conceivable future scenarios. The rule analysis follows a rule-based approach to coordinate COLA between individual operators, allowing users to build custom hierarchical rule sets from pre-defined rule building blocks to achieve a desired split of effort between the conjunction parties. The MAS enables the assessment of the operational consequences for a chosen rule set, empowering users to reach bilateral agreements with identified frequently conjuncting parties to determine the obligation to take evasive measures for future conjunctions. The approach of the MAS allows for the pre-emptive reduction of the expected number of conjunctions enabling operators to optimize orbit parameters within their mission constraints as well as the automatization of COLA coordination during operations. Through this, the MAS optimizes propellant needs, mission time, and required workforce associated with COLA for space missions.This paper presents the MAS, showcasing the key features and use cases that have been developed closely with stakeholders and the European Space Agency. Furthermore, the data-based simulation approach of the MAS will be explained, covering the data sources and design choices for the conjunction detection and propagation module. The paper also presents the results of a preliminary rule analysis conducted for the population of active satellites in low Earth orbit as of April 2023. As an intermediate result of an on-going research activity involving the authoring entities, a major goal of this paper is to engage with satellite operators, mission designers, service providers, agencies, and authorities in order to tailor the results of the activity to their actual needs.

Static and Dynamic Model Calibration for Upper Thermosphere Determination

AbstractThermospheric density, a crucial factor in spacecraft operations, poses a significant challenge in accurate determination due to the intricate coupling of the thermosphere‐ionosphere system. Despite capturing long‐term trends, the widely used empirical models, which are used for low Earth orbit spacecraft operations, often fail to reproduce small‐scale or short‐term variations in the thermosphere. This work presents a novel approach for model improvement. The background model employed is our recently developed empirical model, which blends numerical simulations and satellite measurements. The model residuals are compiled into longitude and latitude bins, and the corresponding basic modes of describing variabilities are subsequently derived via the PCA method. The attendant amplitudes exhibit significant local time and seasonal dependencies, motivating optimized parameterization, that is, static calibration. Moreover, the present study reveals that the most dominant mode correlates to land‐sea contrasts and manifests global synchronicity upon excluding local time and seasonal dependences. This establishes the real‐time model adjustment foundation by exploiting limited calibration observations, which is referred to as dynamic calibration. The results from the dynamic calibration model indicated considerably improved thermospheric representation, especially for small‐scale or short‐term variations, toward a better thermospheric prediction.

Orbital Analysis of a Dual Asteroid System Explorer Based on the Finite Element Method

In the study of dual asteroid systems, a model that can rapidly compute the motion and orientation of these bodies is essential. Traditional modeling techniques, such as the double ellipsoid or polyhedron methods, fail to deliver sufficient accuracy in estimating the interactions between dual asteroids. This inadequacy primarily stems from the non-tidally locked nature of asteroid systems, which necessitates continual adjustments to account for changes in gravitational fields. This study adopts the finite element method to precisely model the dynamic interaction forces within irregular, time-varying dual asteroid systems and, thereby, enhance the planning of spacecraft trajectories. It is possible to derive the detailed characteristics of a spacecraft’s orbital patterns via the real-time monitoring of spacecraft orbits and the relative positions of dual asteroids. Furthermore, this study examines the orbital stability of a spacecraft under various trajectories, revealing that orbital stability is intrinsically linked to the geometric configuration of the orbits. And considering the influence of solar pressure on the orbit of asteroid detectors, a method was proposed to characterize the stability of detector orbits in the time-varying gravitational field of binary asteroids using cloud models. The insights gained from the analysis of orbital characteristics can inform the design of landing trajectories for binary asteroid systems and provide data for deep learning algorithms that are aimed at optimizing such orbits. By introducing the application of the finite element method, detailed analysis of spacecraft orbit characteristics, and a stability characterization method based on a cloud model, this paper systematically explores the logic and structure of spacecraft orbit planning in a dual asteroid system.

Surface Charging Analysis of Ariel Spacecraft in L2-Relevant Space Plasma Environment and GEO Early Transfer Orbit

Ariel (Atmospheric Remote-sensing Infrared Exoplanet Large-survey) is the ESA Cosmic Vision M4 mission, selected in March 2018 and officially adopted in November 2020, whose launch is scheduled by 2029. It aims at characterizing the atmospheres of hundreds of exoplanets orbiting nearby stars by low-resolution primary and secondary transit spectroscopy. The Ariel spacecraft’s operational orbit is baselined as a large-amplitude, eclipse-free halo orbit around the second Lagrangian (L2) point, a virtual point located at about 1.5 million km from the Earth in the anti-Sun direction, as it offers the possibility of long uninterrupted observations in a fairly stable radiative and thermo-mechanical environment. A direct escape injection with a single passage through the Van Allen radiation belts is foreseen. During both the injection trajectory and the final orbit around L2, Ariel will be immersed in and interact with Sun radiation and the plasma environment. These interactions usually result in the accumulation of net electrostatic charge on the external surfaces of the spacecraft, leading to a potentially hazardous configuration for the nominal operation and survivability of the Ariel platform and its payload, as it may induce harmful electrostatic discharges (ESDs). This work presents the latest results collected from surface charging analyses conducted using the SPIS tool of the European SPINE community along the GEO insertion orbit segment and operational orbit.

Time-Optimal Guidance Laws Using a Frequency Domain Approach for Spacecraft Rendezvous

AbstractThis paper proposes a novel approach to solving the time-optimal rendezvous problem for spacecraft in orbit. Initially, the characteristics of the time-optimal rendezvous solution in the in-plane motion of the relative equations of motion are analyzed using the direct collocation method. A time-delay filter is designed in the frequency domain using the analysis results. And then, it transforms the time-optimal control problem into a parameter optimization problem. By solving this optimization problem, the switching times of the bang–bang control profile can be determined. The effectiveness of the proposed method is examined through various simulations, demonstrating its ability to resolve the discontinuities caused by the bang–bang control profile while also being effectively applicable under various boundary conditions. Additionally, the proposed method turns out to be robust against disturbances through real-time application.

Periodic attitude motions of an axisymmetric spacecraft in an elliptical orbit near the hyperbolic precession

This paper deals with the existence and stability of periodic attitude motion near hyperbolic precession (HP) for a dynamically symmetric rigid body (RB) with its center of mass moving along an elliptical orbit. We present the definitions of undisturbed and disturbed periodic attitude motions, and approximate analytical solutions for them are derived using the multiscale method under non-resonance, internal resonance, and combination resonance conditions. Based on the definition of Lyapunov stability, we demonstrate stability in the non-resonant case and establish the conditions require for stability in the internal resonance scenario and a numerical analysis supports the theoretical results. The findings of this study extend classical results on RB dynamics in central gravitational fields. These insights demonstrate that appropriate parameter selection can achieve stable periodic attitude motion for RBs is in elliptical orbits, offering practical implications for spacecraft attitude control and mission reliability.

Assessment of Transitional Orbits from a High Eccentricity LEO to a Circumlunar Orbit

This study presents an evaluation of the achievability and execution of transitional orbits for spacecraft transitioning from a high eccentricity Low Earth Orbit (LEO) to a circumlunar orbit, with the point of distinguishing the foremost proficient and ideal trajectory while considering variables such as velocity and required fuel. Transitional orbits have a role in space exploration, and optimizing their characteristics can enormously advantage mission planning and spacecraft design. A numerical simulation model was developed to attain this objective, A gravity perturbations effect is included in the calculation of the transition. The model utilized progressed numerical integration strategies for exact trajectory analysis. Three cases were examined to investigate the impacts of varying eccentricity and the argument of perigee on the ideal transition, In the first case, eccentricity values of [0.001, 0.01, 0.1] were inspected, whereas the argument of perigee was fixed at 80 degrees. Within the second case, the argument of perigee values of [80, 170, 260] was considered, with the eccentricity fixed at 0.1. The third case included at the same time varying the eccentricity and argument of perigee values. The results showed that the three cases agreed the most favorable transition occurred when eccentricity was set to 0.001 and the argument of perigee was set to 260 degrees. This produced a velocity increase of 2.195694 km/s, which is the lowest increase in ΔV, a metric used to measure fuel efficiency and power required. This finding also demonstrated the lowest change in eccentricity, the lowest change in inclination, and the lowest change in the ascending node, all of which are indicative of increased orbit stability.

Autonomous orbit maintenance takeover control of ultra-low orbit spacecraft with event-triggered mechanism

In this paper, the problem of high-precision autonomous orbit maintenance takeover control of ultra-low orbit (ULO) spacecraft with event-triggered mechanism (ETM) and tangential continuous low thrust is addressed. First, the ETM I is proposed to reduce the communication burden between Global Navigation Satellite System (GNSS) cellular satellite and controller cellular satellite. Second, a fuzzy adaptive controller is proposed to maintain the orbit altitude of the ULO spacecraft. Furthermore, the ETM II is provided to ensure that the control thrust changes infrequently to extend the lifetime of electric thrust cellular satellite. In addition, the ETM II can lighten the communication burden between controller cellular satellite and electric thrust cellular satellite. By combining fuzzy adaptive control method and ETMs, the ETM-based fuzzy adaptive controller is established. Finally, the simulation is provided to verify the effectiveness of the developed control method.

Study on the Feasibility and Performance Evaluation of High-Orbit Spacecraft Orbit Determination Based on GNSS/SLR/VLBI

Deep space exploration utilizing high-orbit vehicles is a vital approach for extending beyond near-Earth space, with orbit information serving as the foundation for all functional capabilities. The performance of orbit determination is primarily influenced by observation types, errors, geometrical structures, and physical perturbations. Currently, research on orbit determination for high-orbit spacecraft predominantly focuses on single observation methods, error characteristics, multi-source fusion techniques, and algorithms. However, these approaches often suffer from low observation accuracy and increased costs. This paper advocates for the comprehensive utilization of existing multi-source observation methods, such as GNSS (Global Navigation Satellite System), SLR (Satellite Laser Ranging), and VLBI (Very Long Baseline Interferometry), in research. The decoupled Kalman filter reveals a positive correlation between measurement positioning accuracy and orbit determination accuracy, and it derives a simple orbit performance evaluation model that considers the influence of observation value types and geometric configurations, without the need to introduce complex dynamic models. Simulations are then employed to verify and analyze antenna gain, observation values, and performance evaluation. The results indicate the following: (1) Under simulated conditions, the optimal strategy involves employing the SLR/VLBI dual system during periods when VLBI orbit determination is feasible, yielding an average Weighted Position Dilution of Precision (WPDOP) of 26.79. (2) For periods when VLBI orbit determination is not feasible, the optimal approach is to utilize the GNSS/SLR/VLBI triple system, resulting in an average WPDOP of 16.32. (3) The orbit determination performance of the triple system is not significantly impacted by the use of global SLR stations compared to using only Chinese SLR stations. However, the global network enables continuous, round-the-clock orbit determination capabilities.

Phase-difference carrier frequency estimation of signal bursts with phase shift keying

Due to the rapid development of communication systems with time division multiple access (TDMA) there is a need to estimate the carrier frequency of signal bursts with phase shift keying. This paper presents the carrier frequency estimation of signal bursts with phase shift keying based on previously developed methods of optimal weighting of the difference-phase statistics without significant computational costs. Algorithms of computationally efficient methods for estimating the carrier frequency of packet signals with Binary Phase Shift Keying (BPSK) and Quadrature Phase Shift Keying (QPSK), as well as with quadrature amplitude digital modulation, using optimal weighting of the difference-phase statistics are presented. A comparative analysis of computationally efficient methods for estimating the carrier frequency of signal bursts with QPSK is performed for various methods using optimal weighting of the difference-phase statistics, based on the results of experimental observations of packet communication signals of an aircraft under various reception conditions. Statistical simulation of estimation algorithms is performed. Estimation results for different signal-to-noise ratios are illustrated. The proposed algorithms for computationally efficient estimation of the carrier frequency of signal bursts with digital modulation using optimal weighting of phase-difference statistics allow to increase the accuracy of measuring the carrier frequency of these signals for different dynamics of the observed aircraft motion, which is of great importance when receiving signals from low earth orbit (LEO) spacecraft. The proposed algorithms for estimating the carrier frequency of signal bursts with phase shift keying are characterized by high computational efficiency and allow to increase the accuracy of estimating the carrier frequency of signal bursts with phase shift keying under different reception conditions at moderate signal-to-noise ratios, which makes it advisable to use the presented algorithms in the equipment of multi-satellite communication systems based on LEO such as Starlink and OneWeb.