Orbit Research Articles

Forming Massive Terrestrial Satellites through Binary-exchange Capture

The number of planetary satellites around solid objects in the inner solar system is small either because they are difficult or unlikely to form or because they do not survive for astronomical timescales. Here we conduct a pilot study on the possibility of satellite capture from the process of collision-less binary exchange and show that massive satellites in the range 0.01–0.1 M ⊕ can be captured by Earth-sized terrestrial planets in a way already demonstrated for larger planets in the solar system and possibly beyond. In this process, one of the binary objects is ejected, leaving the other object as a satellite in orbit around the planet. We specifically consider satellite capture by an “Earth” in an assortment of hypothetical encounters with large terrestrial binaries at 1 au around the Sun. In addition, we examine the tidal evolution of captured objects and show that orbit circularization and long-term stability are possible for cases resembling the Earth–Moon system.

Secular dynamics and the lifetimes of lunar artificial satellites under natural force-driven orbital evolution

In this paper, we study the long-term (time scale of several years) orbital evolution of lunar satellites under the sole action of natural forces. In particular, we focus on secular resonances, caused either by the influence of the multipole moments of the lunar potential and/or by the Earth’s and Sun’s third-body effect on the satellite’s long-term orbital evolution. Our study is based on a simplified secular model obtained in ‘closed form’, i.e., without expansions in the satellite’s orbital eccentricity. Contrary to the case of artificial Earth satellites, in which many secular resonances compete in dynamical impact, we give numerical evidence that for lunar satellites only the 2g−resonance (ω̇=0) affects significantly the orbits at secular timescales. We interpret this as a consequence of the strong effect of lunar mascons. We show that the lifetime of lunar satellites is, in particular, nearly exclusively dictated by the 2g resonance. By deriving a simple analytic model, we propose a theoretical framework which allows for both qualitative and quantitative interpretation of the structures seen in numerically obtained lifetime maps. This involves explaining the main mechanisms driving eccentricity growth in the orbits of lunar satellites. In fact, we argue that the re-entry process for lunar satellites is not necessarily a chaotic process (as is the case for Earth satellites), but rather due to a sequence of bifurcations leading to a dramatic variation in the structure of the separatrices in the 2g resonance’s phase portrait, as we move from the lowest to the highest limit in inclination (at each altitude) where the 2g resonance is manifested.

Fuel-optimal acquisition and control of a cartwheel formation in Earth displaced heliocentric orbit

An optimization approach for cartwheel formation acquisition and maintenance in an Earth Displaced heliocentric orbit is presented. This work considers non-gravitational perturbations such as solar radiation pressure, thus extending the studies previously performed for the mission LISA. The problem is tackled as a Nonlinear Programming problem using a multiple shooting method. The optimization process is performed in two steps: first, the orbital elements of each satellite in heliocentric orbit are optimized to guarantee the stability during the science phase hence easing maintenance of the cartwheel formation in presence of orbital perturbations. Then, the obtained initial states are propagated to obtain a set of target orbital states which become the final target of a second optimization covering the transfer phase from Earth. For the science phase optimization presents two alternative cost functions are introduced, one based on the arm-length evolution and one on the arm-length-rate evolution. The performance of each cost function is analysed for different initial displacement angles: for target arm-lengths below 2.5 million kilometers the arm-length cost function provides the best results while no significant difference between the two optimized solutions is observed above this value. The transfer phase optimization presents two different approaches, one considering an injection on a trajectory more favourable for one of the three spacecraft and one considering an injection on an intermediate trajectory which minimizes the overall acquisition cost of all spacecraft. The proposed optimization approach performance are studied on a set of test cases covering both transfer and science phase, showing that stable configuration conditions can be found even in presence of orbital perturbations and that the multiple injection transfer is capable of providing a more homogeneous fuel consumption among the three spacecraft.

Satellite Onboard Transmitter Design With Spread Spectrum MIMO Antenna for 5G Wireless Networks

AbstractThe 5G new era implements standalone satellite communications that support wireless networking systems for future mobile communications by locating multiple satellites in low Earth orbit to provide global coverage of the entire Earth's surface. In this research, a newly found model of a satellite onboard transmitter using a uniform circular array multiple‐input multiple‐output antenna was designed to operate at a carrier frequency of 12 GHz and derived theoretical equations compared to the real‐time scenario. The integration of spread spectrum with multiple‐input multiple‐output antenna provides an advantage for higher capacity. It has a higher percentage of gain amplification on improving the transmission of electromagnetic power to meet the bandwidth requirement of center operating frequency, and this can transmit over a bandwidth of 1.28 GHz. The proposed satellite onboard transmitter model design aims to minimize the components, increase the speed of operations for higher bandwidth, and transmit large amounts of information to a large group of users. The transmitter can operate for the speed of 1.28 Gbps using pseudo‐random code, direct‐sequence spread spectrum, quadrature phase shift keying modulation, bandwidth separated in bands for 64 symbols using 128 Chebyshev‐type bandpass filter for transmission using 128‐element uniform circular array multiple‐input multiple‐output antenna. The satellite transmitter antenna produces a maximum gain of 14.526 dBi, and a maximum directivity of 17.986 dBi, and the efficiency at 12 GHz is 45.1% for the radiated power at 0.93 mW. This satellite transmitter will interconnect 5G wireless networks for the application of mobile communications complement terrestrial‐dependent networks.

Gamma radiation-induced changes in the structural and optical properties of CsPbBr3 thin films for space applications

Perovskite nanocrystals (NCs) are emerging as a next generation display technology. In this regard, exploring the structural and optical stability when subjected to radiation is crucial for expanding their application in aerospace and radiation detection technologies. In this study, we investigated the effects of gamma radiation on CsPbBr3 heterojunction thin films through a comprehensive analysis of their structural and optical characteristics. The thin films of CsPbBr3 were subjected to varying doses of gamma radiation, ranging from 100 krad to 1 Mrad, followed by thorough examination using X-ray diffraction (XRD) and optical spectroscopy techniques. Our findings unveil significant changes in the crystal structure of CsPbBr3 thin films when exposed to gamma radiation, including shifts in diffraction peak positions from cubic to monoclinic phases, broadening of peaks, and variations in peak intensities due to induced surface defects. The optical properties, such electroluminescence (EL) and photoluminescence (PL) intensity slightly drops at the moderate irradiation dose of 300 krad, while at an irradiation dose of 1 Mrad deteriorated severely. Notably, 300 krad is equivalent to the radiation dose accumulated by satellites in low-Earth orbit over 10 years. The findings in this work suggest the fabricated CsPbBr3 thin film has the potential to be used in space applications.

A High-Accuracy and High-Efficiency Satellite Shadow Function Model for Oblate Earth

To achieve high-accuracy solar radiation pressure analysis, this study proposes a new high-accuracy and high-efficiency (HAHE) shadow function model considering the oblateness of the Earth, for the oblateness of the Earth has much influence in the calculation of the shadow factor. The sphere shadow function model has been improved in this study with an accurate shadow function that considers the Earth’s oblateness. Then, using the accurate shadow function model, a new HAHE shadow function model is proposed to calculate a simulated satellite orbit’s changes of shadow factor, which is analyzed and compared with the existing shadow function model and the accurate shadow function model. The results show that the difference between the HAHE shadow function and the accurate shadow function is tiny. Moreover, the HAHE shadow function is 113 times faster than the accurate shadow function model.

Tailored accelerometer calibration by POD for thermospheric density retrieval with GRACE and GRACE-FO

The density of the upper atmosphere can be determined by orbit and accelerometer data from low Earth orbit satellites as insitu measurements along the orbit. One main challenge therein is the estimation of physical accelerometer calibration parameters, meaning that these parameters should not absorb other effects and model deficiencies in the Precise Orbit Determination (POD) process. The accelerometers of all geodetic satellites like GRACE and GRACE-FO are affected by time dependent bias and scale factors. Therefore a calibration of the data is indispensable.A dynamic POD based physical accelerometer calibration is developed for the complete GRACE and GRACE-FO missions. We investigate different parametrization strategies and utilize different observation data, as the accurate inter-satellite ranging additionally to GPS orbit data. For the estimation parameters we distinguish between offset and scale, furthermore, cross-track and radial directions are significantly less sensitive than along-track and require a different evaluation. For the offset, constant and time dependent parameters are investigated. Furthermore, a continuous offset calibration over arc boundaries is implemented and tested. The sensitivity of the scale factor is lower, although, in contrast to the offset, it increases with higher total accelerations. This means that it needs to be estimated over longer time periods. We investigate periods between three hours and one month as well as results from Gravity Field Recovery (GFR). Monthly scale factors give valuable results, at least for x-axis and when the Solar activity is not very low. Nevertheless, we also estimate weighted constant scale factors from the monthly results and use these in a subsequent POD, giving more realistic offset results for most periods and cross-track and radial directions.From the used background models in the POD, Earth’s gravitational model has a noticeable influence on the estimated calibration parameters, especially the scale factors. We utilized several different models. Results with monthly ITSG solutions are distinctly better than the ones with the time dependent GOCO06s model.We show that the validation with usual metrics, like post-fit POD residuals, is not able to reflect the quality of the different estimated calibration parameters. For a quantitative validation we introduce an approach based on the modeled non-gravitational accelerations. Therefore, the uncertainty of the models is evaluated first. The influence of main error sources in the models is assessed and propagated to the results.We compare our scale parameters to available references and the complete calibration to TU Delft’s latest results. Finally we show the effect of different calibration options on the retrieved density.The estimated calibration parameters and non-gravitational accelerations for the whole GRACE and GRACE-FO missions are available on our data server www.zarm.uni-bremen.de/zarm_daten.

Rapid attitude stabilization of ultra-low orbit satellites using movable masses and reaction wheels

This paper proposes a combination of movable masses and reaction wheels for the attitude control of ultra-low-orbit satellites. During the attitude control of ultra-low-orbit satellites, the satellite’s attitude is significantly influenced by the aerodynamic torque. Therefore, this paper proposes a combined control method using movable masses and reaction wheels. By adjusting the position of the movable masses to modify the relative distance between the center of mass (CM) and the center of pressure (CP), the aerodynamic torque is effectively reduced. Additionally, a finite-time terminal sliding mode extended state observer (TSMESO) is incorporated to estimate the reduced aerodynamic torque. Then, a finite-time non-singular terminal sliding mode control (NTSMC) method is introduced to achieve rapid attitude stabilization. Simulations demonstrate that under the proposed control system, the aerodynamic torque acting on the ultra-low-orbit spacecraft can be significantly reduced in a short time, and the response and high precision attitude stability can be effectively achieved.

Beam Management in Low Earth Orbit Satellite Networks With Random Traffic Arrival and Time-Varying Topology

Beam Management in Low Earth Orbit Satellite Networks With Random Traffic Arrival and Time-Varying Topology

Case study of high waves in the South Pacific generated by Tropical Cyclone Harold in 2020

This study highlighted a high wave case by severe tropical cyclone Harold and conducted a simulation with a newly developed wave forecasting system for the South Pacific based on the Japan Meteorological Agency third generation wave model (JMA MRI-III) using the National Center for Environment Prediction Global Forecast System (GFS) winds. Harold was a very intense tropical cyclone (TC) and very high waves up to 10 m affected parts of Vanuatu and Fiji. The model results were reasonable and verified against observations of orbital satellites and a wave buoy at Komave in Fiji. The statistical verifications were carefully analysed. The Root Mean Squared Error (RSME), Scatter Index (SI), Bias and R2 are all showing very impressive results. The new wave forecasting system is the first high resolution operational model at Fiji Meteorological Service (FMS), which covers the whole Fiji area. The system will provide guidance to FMS in preparing marine alerts and warning better and more confidence in providing the marine forecast accurately.

Detecting changes in anthropogenic light emissions: Limits due to atmospheric variability

Monitoring the evolution of the anthropogenic light emissions is a priority task in light pollution research. Among the complementary approaches that can be adopted to achieve this goal stand out those based on measuring the direct radiance of the sources at ground level or from low Earth orbit satellites, and on measuring the scattered radiance (known as artificial night sky brightness or skyglow) using networks of ground-based sensors. The terrestrial atmosphere is a variable medium interposed between the sources and the measuring instruments, and the fluctuation of its optical parameters sets a lower limit for the actual source emission changes that can be confidently detected. In this paper we analyze the effect of the fluctuations of the molecular and aerosol optical depths. It is shown that for reliably detecting changes in the anthropogenic light emissions of order ∼1 % per year, the inter-annual variability of the annual means of these atmospheric parameters in the measurement datasets must be carefully controlled or efficiently corrected for.

Magnetic Perturbations on Cable-Connected Satellites in Equatorial Orbit: A Review of the Current State of Research

Cable-connected satellites in equatorial orbit offer enhanced capabilities for various space applications, but their stability is susceptible to magnetic perturbations from the Earth's magnetic field. This literature review examines the current state of research on the effects of geomagnetic field on the dynamics of cable-connected satellites in equatorial orbit. We synthesize findings from previous studies on the impact of magnetic field on orbital dynamics, attitude control, and communication. Our review highlights the significance of considering magnetic perturbations in the design and operation of cable-connected satellites, and identifies knowledge gaps for future research. The results of this review can inform the development of strategies to mitigate the effects of magnetic perturbations and ensure the stability of cable-connected satellites in equatorial orbit.

Nonlinear Stability of Cable-Connected Satellites: A Review of the Combined Effects of Solar Radiation Pressure and Earth’s Magnetic Field

The nonlinear stability of cable-connected satellites in equatorial orbit is crucial for maintaining their operational efficiency and extending their mission duration. This literature review aims to investigate the combined effects of solar radiation pressure and Earth’s magnetic field on the nonlinear stability of cable-connected satellites. We examine the current state of research on the dynamics of cable-connected satellites under the influence of solar radiation pressure and Earth’s magnetic field, focusing on nonlinear stability analysis. The review highlights the key findings, methodologies, and challenges in this research area. Our analysis reveals that the combined effects of solar radiation pressure and Earth’s magnetic field can significantly impact the nonlinear stability of cable-connected satellites, leading to complex dynamics and potential instability. The review identifies areas for future research, emphasizing the need for advanced modeling and simulation techniques to accurately predict and mitigate the effects of these environmental factors on cable-connected satellite systems. This comprehensive review provides a valuable resource for researchers and engineers working on the design and operation of cable-connected satellites in equatorial orbit.

Test Method for Single Satellite’s Inter-Satellite Link Pointing and Tracking via Ground Station

An inter-satellite link is a key technology that improves control accuracy, transmission efficiency, and autonomous capability of constellations. A satellite’s pointing and tracking abilities mainly determine the inter-satellite link’s performance, which should be validated through an in-orbit test. However, during the construction of the constellation, the distribution of satellites does not satisfy the constraints of establishing the inter-satellite link. A test method for inter-satellite link pointing and tracking is developed with respect to a single satellite. A practical mission scenario for testing inter-satellite links’ performance is constructed. A virtual satellite is introduced as the target satellite to establish an inter-satellite link with the local satellite. The orbit of the virtual target satellite between two ground stations is characterized based on the Newton–Raphson method. By comparing the predicted and actual time differences between two ground stations receiving the signals from the local satellite, the inter-satellite link pointing and tracking abilities are evaluated independently. Numerical simulations verify the design of the virtual satellite. The single satellite test method for inter-satellite link pointing and tracking abilities is available.

Decadal evolution of GPS, GLONASS, and Galileo mean orbital elements

We examine the decadal evolution of GPS, GLONASS, and Galileo satellite orbital elements, including the semi-major axis, inclination, eccentricity, right ascension of the ascending node, and the argument of perigee. We focus on the long-term changes in Keplerian elements by averaging them over several complete revolutions forming mean orbital elements giving an explanation of the main perturbing forces for each Keplerian parameter. The combined International GNSS Service (IGS) orbits are employed which were derived in the framework of IGS Repro3 for ITRF2020 preparation spanning eight years from 2013 to 2021. The semi-major axis for GPS satellites is affected by a strong resonance with Earth’s gravity field resulting in a long-period perturbation similar to a secular drift. The semi-major axes of Galileo and GLONASS do not show any large-scale rates, however, Galileo satellites are affected by the Y-bias resulting in semi-major axis drifts. A significant perturbations due to solar radiation pressure affect the semi-major axis, eccentricity, and the argument of perigee. Notably, for Galileo satellites in eccentric orbits, the signal with a one-draconitic year is evident in the semi-major axis. The evolution of the mean right ascension of the ascending node and argument of perigee is primarily characterized by nearly linear regression mainly due to even zonal harmonics of the Earth’s gravity field. The long-term evolution of eccentricity and inclination does not follow a linear trend but exhibits clear oscillations dependent on the secular drift of the right ascension of the ascending node (for inclination) or the argument of perigee (for eccentricity). Additionally, the long-term perturbation of inclination reaches its maximum when the absolute value of the Sun’s elevation angle above the orbital plane (\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\beta$$\\end{document} angle) is at its minimum, while the eccentricity reaches its minimum simultaneously with the minimum of the \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\beta$$\\end{document} angle.

New Transient Co-orbital Asteroids of Venus

Venus has no known natural satellites but has 5 known co-orbitals. These are objects trapped in a 1:1 mean-motion resonance with Venus. Co-orbital configurations include retrograde satellite orbits (RS), tadpole orbits (T) around the Lagrangian equilibrium points L4 or L5, and horseshoe orbits around both L4 and L5 (H). At high eccentricity or inclination, co-orbital configurations may also involve compounds of T and RS (T-RS, T-RS-T), H and RS (H-RS) orbits, or transitions between different co-orbital modes. Here we identify asteroids in 2 RS, 1 L4-tadpole, 2 H-RS, and 2 T-RS orbits, as well as 8 additional asteroids in possible temporary co-orbital status. Although the majority of these objects do not yet have well-characterized orbits, 2020 CL1, and 2020 SB do and are very likely to be new co-orbital asteroids. With the new candidates, Venus would have a population of 20 co-orbital asteroids, comparable to those of Mars and Earth.

Real-time uncombined PPP using BDS-3 PPP-B2b products with different multi-frequency integrations and refined stochastic model

BDS-3 geostationary orbit (GEO) satellites broadcast PPP-B2b real-time precise products to support real-time precise point positioning (RT-PPP) without dependence on the ground network communication. Since all BDS-3 satellites can provide multi-frequency signals, we investigate the effect of different multi-frequency integrations and the refinement of multi-frequency stochastic model for PPP-B2b RT-PPP. Given that the retrieval of PPP-B2b real-time precise corrections relies on the B1C and B2b frequencies, this study first investigates the kinematic uncombined (UC) RT-PPP performance of the B1C/B2b integration with a comparison to the conventional B1I/B3I integration. The results indicate that the convergence time (with a convergence threshold of 20 cm) of the RT-PPP with the B1C/B2b integration is shortened by 16 %, 15 %, and 12 % over the B1I/B3I integration in the east, north, and up directions, respectively. Further, this study compares the kinematic UC RT-PPP performance of the B1C/B2b dual-frequency integration, B1C/B2b/B3I triple-frequency integration, and B1C/B2b/B3I/B1I/B2a five-frequency integration. Compared with the dual-frequency integration, the positioning performance of the triple-frequency integration is slightly improved. By contrast, the performance improvement of the five-frequency integration is more significant, which can reach 6 %, 32 %, and 9 % for the convergence time, and 11 %, 9 %, and 6 % for the positioning accuracy in three directions, respectively. To further enhance the multi-frequency PPP performance, a refined stochastic model for the BDS-3 five-frequency integrated PPP-B2b RT-PPP is proposed by taking the inconsistency of signal quality among multi-frequency signals into account. After applying the refined stochastic model, the convergence time of the five-frequency kinematic RT-PPP is shortened by 10 %, 14 %, and 9 % to 32, 7, and 19 min in east, north, and up directions, respectively. The positioning accuracy (the root mean square of all the positioning errors excluding the first two hours) of the five-frequency RT-PPP with the refined stochastic model can reach the optimal level, which is 9.9, 6.5, and 14.0 cm in three directions, respectively.

Integrating terrestrial and non-terrestrial networks via IAB technology: System-level design and evaluation

As the telecommunications industry embarks on the transition to Sixth-Generation (6G) networks, this paper examines the integration of Non-Terrestrial Networks (NTN), and in particular satellite backhauling, in the context of Fifth-Generation (5G) systems. The Integrated Access and Backhaul (IAB) technology, conceived as a wireless terrestrial backhauling system in the Next Generation Radio Access Network (NG-RAN), has been identified as a possible enabler for the integration of satellite nodes. Despite the work already done in this direction, the combination of IAB architectures with satellite nodes operating in both the access and backhaul side requires further evaluations on feasibility and limitations for networks integrating Low Earth Orbit (LEO) and Geostationary Earth Orbit (GEO) satellites. To this end, this work contributes providing insights on background technologies, as well as a detailed analysis of the issues and challenges arising from such integration and a definition of use cases to support narrow-band and broadband services. Furthermore, the design and implementation of a simulation tool is proposed for a performance evaluation in terms of registration time, link capacity, single-hop and end-to-end delay. Results show that the integration turns out to be feasible, even if with strong constraints coming from the satellite system rather than the IAB usage itself. Indeed, the earth-satellite link in LEO systems has a significant impact on the packet delivery time due to the discontinuous coverage. In case of GEO satellite instead, a non-terrestrial backhaul link could limit the performance of the whole system, especially at lower elevation angles.

A new data-driven framework for progressive anomaly event alerts in spacecraft based on reconstruction discrepancy

In the use of deep learning for spacecraft anomaly detection, a key issue arises from the insufficient extraction of temporal dependencies in telemetry data. This can lead to an inability to accurately discern whether distribution changes in the data are caused by substantive anomalies or merely a consequence of model underfitting. To address this issue, we design a Temporal Dependency Extraction Enhanced Autoencoder model for multi-scale learning of telemetry data. Firstly, this model incorporates Multi-Scale Temporal Dependency Extraction blocks, which integrate self-attention, autoregressive, and feed-forward networks, aimed at systematically dissecting the long-term dependencies, historical information, and complex patterns in telemetry data. Building on these blocks, our model can efficiently and accurately reconstruct telemetry data while maintaining computational efficiency. Furthermore, we utilize an anomaly quantification metric based on the smoothed Manhattan distance, combined with the Drift Streaming Peaks-over-Threshold strategy for setting anomaly thresholds, thus establishing a comprehensive and precise anomaly alerts framework. Finally, we validate our approach using a dataset from the Attitude Control System of a Geostationary Earth Orbit satellite. The experimental results show that our method not only detects anomalies earlier than traditional methods but also provides an in-depth quantitative analysis of anomaly characteristics.

Postseismic processes in the region of the july 29, 2021 Chigni earthquake, Alaska. Part I: modeling results

We analyze the postseismic processes in the region of the Mw 8.2 Chignik earthquake, which occurred on July 29, 2021. Using the seismic rupture surface model constructed in our previous paper (Konvisar et al., 2023), we have simulated the viscoelastic relaxation process. The results of the simulation have shown that reducing the viscosity of the asthenosphere to 1018 Pa ‧ s in the calculations gives displacement velocities close to those recorded at the GPS coastal points. However, the displacements on islands close to the earthquake source region differ significantly not only in magnitude but also in direction. At the same time, the constructed model of the postseismic creep is closely consistent with the GPS displacement data and with the LOS (line-of-sight) displacement map derived from radar images acquired from the descending orbit of Sentinel 1A satellite. We also analyze temporal variations of the gravity field in the earthquake region. The obtained coseismic anomaly agrees with the anomaly calculated from the rupture surface model. Due to the insufficiently long series of gravity models after the earthquake, it is not yet possible to isolate the postseismic anomaly. The analysis of the postseismic processes is continued in the second part of this work (Smirnov et al., 2024), where we present the compare the time evolution of the postseismic displacements of various GPS sites with the aftershock activity, which allows us to draw conclusions about the creep nature of the postseismic processes in the source region of the Chignik earthquake.