Large Number Of Satellites Research Articles

High time effective detection strategy for geosynchronous orbital space debris

After the formation of a multi-satellite network in a hypersynchronous orbit, it has the ability to continuously and in real-time observe the GEO band, which is an ideal way to solve blind spots and semi-backlight observations and improve the system’s high time-effective coverage ability. In response to the application limitations of high-orbit real-time monitoring constellations in hypersynchronous orbits, such as the large number of satellites in the network, high requirements for satellite detection capability, large field of view, and high launch and orbit cost, this paper proposes a constellation system efficiency analysis method that comprehensively covers both time and space dimensions. Based on this, optimization analysis of satellite detection capability, detection field of view, number of satellites, and orbit height is carried out. Finally, three constellation optimization schemes are provided, which are a semi-major axis of 60000 km with seven satellites, a semi-major axis of 55000 km with eight satellites, and a semi-major axis of 50000 km with ten satellites. The three constellation optimization schemes can provide a reference for the development of space-based high-orbit situational awareness in the future.

A New Type of Reflective Reconfigurable Electronic Beam Squinting Feed

With the development of highly integrated technology, a large number of satellites have been launched into synchronous orbit, saturating the number of satellites in these orbits. As a result, there has been a substantial increase in demand for near-Earth orbit satellites. However, due to their proximity to Earth, the location of these satellites rapidly drifts in free space. To maintain the received and transmitted signals within range, the ground antenna must track the satellites immediately. Therefore, near-Earth orbit satellite tracking has become a key technology in satellite communication research. In order to further improvement, we propose a new type of electronic beam squinting (EBS) tracking feed. In this paper, we will conduct both theoretical and experimental analyses of this EBS feed.

Scalable architecture for rapid setup and execution of multi-satellite simulations

This work introduces a novel architecture that allows for easy integration of multiple satellites in a single simulation. The new design focuses on modularity, expandability, and easy scriptability while maintaining Basilisk’s high-fidelity and speed features. Modularity is important to make highly specialized simulations, which include parameters related to the environment but also specific to each spacecraft. Expandability and scriptability are also key, as one of the goals is to facilitate the creation of simulations with a large number of satellites. The architecture is implemented in Basilisk, an open-source, flight-proven physics and flight software engine, although the fundamental principles can be applied to any software application. Through an overhauled messaging system, the architecture also allows for easy addition of homogeneous or heterogeneous satellites with reduced overhead for the user. This paper shows code snippets and multithreading simulation performance to discuss how the architecture achieves its underlying objectives of simplicity, accessibility, and performance.

Autonomous semi-major axis adjustment for mega constellation continuous coverage

Mega constellations have larger number of satellites and higher distribution density compared with traditional constellations, that lead to huge tracking, telemetry and command (TT&C) requirement, heavy computation load for configuration design, and frequent configuration control due to low-Earth perturbations, collision avoidance emergencies, etc. This paper proposes a novel constellation control scheme for mega constellations with the same semi-major axis, that is based on the inter-satellite boundary constraints. Satellites do not follow the designed configuration, but keep bounded and stable flight with respect to adjacent satellites. The continuous coverage requirement is considered for priority. The inter-satellite continuous coverage constraint is formulated as right ascension of ascending node constraint and relative distance boundary constraint between every two adjacent coplanar satellites. To reduce control consumption, the boundary constraint is kept by adjusting the semi-major axes of coplanar satellites. To that end, the relationship between relative distance boundary and semi-major axis difference is studied. The semi-major axis adjustment strategy for a single satellite is proposed, and the control rules for coplanar satellites are determined. The proposed control method is verified in GW-2 sub-constellation, and is compared with relative station-keeping control method. Results indicate its effectiveness and good performance in control frequency and consumption.

Land Classification on Satellite Images Using CNN

Abstract: Land cover classification from these images is a difficult task be- cause of very large sized data and high variation types. Satellite based information is presently available as huge sets of high resolution images from a large number of satellites like Sentinel, Landsat8, etc. Land cover classification from these images is a difficult task be- cause of very large sized data and high variation types. The purpose of land use and land cover classification is that monitoring and identifying the various land cover classes exactly. Land-use is the rational and judicious approach of allocating available land resources for different activities (such as settlements, arable fields, pastures, and managed woods) within a city. The use of a particular patch of land and its physical character are linked. However, research that establishes this link is lacking despite the proliferation of geo spatial data.

The enhanced search procedure in a coordinate domain for precise satellite positioning

Recently, there has been an increase in the availability of GNSS satellites for observation, which poses new challenges in the computational process of precise satellite positioning. Ambiguity resolution is a crucial step in achieving accurate relative positioning. In this regard, an improved version of a searching procedure in a three-dimensional coordinate domain has been proposed and tested. The method starts with a float solution, similar to classic methods like the LAMBDA. However, the subsequent step, the search procedure, is conducted in the coordinate space instead of the ambiguity space. This shift to a three-dimensional coordinate space leads to reduced computation time. A computational experiment was performed to validate the proposed method, which demonstrated a significant reduction in processing time. The advantages of this method are particularly prominent when dealing with a large number of satellites.

The impact assessment of accidental explosions of large constellations on low earth orbit environment

Because of its large number of satellites, a large constellation (a LC) greatly affects other objects in LEO. Several studies reveal the impact of a LC in LEO missions in various operational scenarios. This study evaluated the environmental impact of a LC explosion in the short and long-term using the Near-Earth Orbital Debris Environment Evolutionary Model (NEODEEM). Although setting mission scenarios and analysis conditions is important in LC simulations, it is difficult to consider all operational scenarios due to the many combinations. Therefore, this study conducted impact assessments of explosions in a LC, concentrating on the number of explosions, orbital altitude, and scaling factor of the explosions. The results indicated that it is not enough for LC to comply with the current requirement of probability of accidental explosions which is less than 0.001 during the operation. This is because, if the rate is applied directly to a LC with thousands of satellites, continuous explosions (i.e., several satellites explode every year) will occur during the mission duration of LC. The paper also discusses the behavior of fragments from explosions at different altitudes. The explosions at low altitudes have no significant impact in the long term, although it can cause an incremental change in collision risk in the short term. Similarly, the explosions at high altitudes, such as 1,250 km, have only slightly increments of the expected number of collisions, but its impact could last for over 100 years. The probability of explosions of a LC must be carefully determined through a series of simulations based on the number of satellites and the operational orbit of a LC. This paper also discusses what should be considered in future LC design and operations regarding explosion prevention.

An Improved DTN Scheme for Large-Scale LEO Satellite Networks

A large-scale low Earth orbit (LEO) satellite network has the characteristics of a complex link environment, a large number of satellites, and the limited resources of a single satellite. Applying traditional routing algorithms has disadvantages such as high overhead, high end-to-end latency, and low message delivery rate. This paper proposes an improved delay tolerant (DTN) scheme for large-scale LEO satellite networks (LIDTN) to improve transmission efficiency and reduce the resource overhead and end-to-end latency of large-scale satellite networks. This scheme improves the network performance in three aspects: next hop selection, congestion control mechanism, and acknowledgment mechanism. For the next hop selection, we propose an equivalent distance and priori knowledge-based forwarding strategy (EPFS), which has the advantages of low overhead, loop avoidance, and fast convergence. For congestion control, we put forward an emergency function-based bundle drop algorithm (EBDA). For acknowledging, we propose the virtual acknowledgment algorithm (VAA) by combining the characteristics of many path hops and high link disruption rates in large-scale constellations. Finally, we simulate and verify the LIDTN scheme on the OneWeb constellation. The results show that the LIDTN scheme is suitable for large-scale constellations, the EPFS algorithm can reduce the network overhead during data transmission, EBDA can reduce the bundle drop rate, and VAA can reduce the end-to-end latency. LIDTN provides a new solution for large-scale constellation communication.

The Design and Maintenance of Low-Orbit Navigation Constellation for Traffic Control in a Smart City

The traffic control issue in the smart city scenario gives rise to the higher requirements of Global Navigation Satellite System (GNSS) services, especially in terms of navigation accuracy, together with coverage continuity, and multiplicity. The dense urban environment leads to higher elevation angles for navigation in such areas, which requires a lower altitude of the constellation, as well as a larger number of satellites. In the existing literature, the design and maintenance of the Low Earth Orbit (LEO) navigation constellation that fulfills the requirements of the smart city are not provided. Hence, based on the requirements and constraints of the smart city scenario, this article studies the relation between orbital height, user elevation angle, and coverage. It designs the configuration of an LEO navigation constellation that not only achieves global sensing coverage, but also provides a continuous lane-level navigation service with multiple coverages for the key area. In addition, considering the atmospheric drag in low orbits and the constraint of satellite power and attitude control, a method is proposed by rotating solar panels to change the effective frontal area of the satellite to achieve relative configuration maintenance of the LEO constellation. The results show that the LEO navigation constellation has a 0 s revisit time in five chosen smart cities, and each city has more than four-times coverage every second; the Geographic Dilution of Precision (GDOP) values of five cities are smaller than 0.47. The average navigation accuracy of five cities is 2.01. With the conduction of the one-year station-keeping simulation, the phase deviation of two satellites is less than 0.6° and it gradually converges to 0.1°, where the semi-major axis deviation is less than 80 m. With our proposed method, the active station-keeping control is not needed in one year, and the fuel consumption can be reduced. Finally, the continuity of the navigation service can be assured.

The Missing Satellite Problem outside of the Local Group. II. Statistical Properties of Satellites of Milky Way–like Galaxies

We present a new observation of satellite galaxies around seven Milky Way (MW)–like galaxies located outside of the Local Group (LG) using Subaru/Hyper Suprime-Cam imaging data to statistically address the missing satellite problem. We select satellite galaxy candidates using magnitude, surface brightness, Sérsic index, axial ratio, FWHM, and surface brightness fluctuation cuts, followed by visual screening of false positives such as optical ghosts of bright stars. We identify 51 secure dwarf satellite galaxies within the virial radius of nine host galaxies, two of which are drawn from the pilot observation presented in Paper I. We find that the average luminosity function of the satellite galaxies is consistent with that of the MW satellites, although the luminosity function of each host galaxy varies significantly. We observe an indication that more massive hosts tend to have a larger number of satellites. Physical properties of the satellites such as the size–luminosity relation are also consistent with the MW satellites. However, the spatial distribution is different; we find that the satellite galaxies outside of the LG show no sign of concentration or alignment, while that of the MW satellites is more concentrated around the host and exhibits a significant alignment. As we focus on relatively massive satellites with M V < −10, we do not expect that the observational incompleteness can be responsible here. This trend might represent a peculiarity of the MW satellites, and further work is needed to understand its origin.

Uncertainty Theory-Based Resilience Analysis for LEO Satellite Communication Systems

Resilience, the ability of a system to withstand disruptions and quickly return to a normal state, is essential for a low-Earth-orbit satellite communication system (LEO-SCS), as its large number of satellites, may encounter various disturbances. As a developing system with asymmetrical and insufficient data, it is with both aleatory and epistemic uncertainties, which renders existing resilience measures inapplicable. This paper utilizes uncertainty theory to define belief instantaneous availability, based on which a new resilience measure for the LEO-SCS is proposed. As the resilience is mainly determined by the dynamic and uncertain characteristics of an LEO-SCS, an uncertain satellite network evolution model is developed to describe its operating patterns, and an evaluation method is proposed to estimate its resilience. To illustrate our proposed uncertain theory-based resilience evaluation method, an LEO-SCS case with 48 satellites is studied, and its resilience values under different backup strategies are compared to assist in system design decisions.

Analytical simulations of the effect of satellite constellations on optical and near-infrared observations

Context. The number of satellites in low-Earth orbit is increasing rapidly and many tens of thousands of satellites are expected to be launched in the coming years. There is a strong concern among the astronomical community about the contamination of optical and near-infrared observations by satellite trails, what has led to several initial investigations of the impact of large satellite constellations. Aims. We expand the impact analysis of such constellations on ground-based optical and near-infrared astronomical observations in a more rigorous and quantitative way, using updated constellation information and considering imagers and spectrographs and their very different characteristics. Methods. We introduce an analytical method that allows us to rapidly and accurately evaluate the effect of a very large number of satellites, accounting for their magnitudes and the effect of trailing of the satellite image during the exposure. We use this to evaluate the impact on a series of representative instruments, including imagers (traditional narrow field instruments, wide-field survey cameras, and astro-photographic cameras) and spectrographs (long-slit and fibre-fed), taking their limiting magnitude into account. Results. Confirming earlier findings, the effect of satellite trails is more damaging for high-altitude satellites, on wide-field instruments, or essentially during the first and last hours of the night. Thanks to their brighter limiting magnitudes, low- and mid-resolution spectrographs will be less affected, but the contamination will be at about the same level as that of the science signal, introducing additional challenges. High-resolution spectrographs will essentially be immune. We propose a series of mitigating measures, including one that uses the described simulation method to optimise the scheduling of the observations. We conclude that no single mitigation measure will solve the problem of satellite trails for all instruments and all science cases.

Using Super-Resolution Algorithms for Small Satellite Imagery: A Systematic Review

In recent years, we have witnessed significant development in the space sector, in particular regarding Earth imaging. Small satellites, whose size and construction make their production much cheaper, are becoming increasingly popular. As a result, a larger number of satellites may be placed in space, and thus, they may perform more frequent observations of selected spots on Earth. Unfortunately, the construction of these satellites also affects their observation capacity as they have a weaker spatial resolution. Scientists have been dealing with the problem of improving the spatial resolution of satellite imaging for many years. Numerous methods were developed that allow for the best possible representation of high-resolution images based on low-resolution images. However, the application of traditional solutions to improve the resolution of digital images requires an additional high-resolution image. As far as images obtained by small satellites (e.g., nano, micro, or mini) are concerned, the difference between the spatial resolution of panchromatic and multispectral images is small (e.g., for SkySat-3 – SkySat-15 satellites, it is only 0.16 m). The need to increase the spatial resolution of an image that does not have a corresponding higher resolution image (e.g., a panchromatic image or a sequence of images) causes additional problems. This article presents a review of the methods to improve the spatial resolution of small-satellite imaging. The authors analyze the interpolation, pansharpening, and digital image processing methods. Additionally, the article focuses on presenting solutions based on deep learning that enables the enhancement of the spatial resolution of images obtained from small satellites. The methodology of creating databases used for network training is described. Finally, the authors present the main limitations of the analyzed solutions and future development trends that will enable to improve the spatial resolution with the use of a single image.

Hosts and triggers of AGNs in the Local Universe

Based on the spectroscopic and shear catalogs for SDSS galaxies in the local Universe, we compared optically selected active galactic nuclei (AGNs) with control star-forming and quiescent galaxies on galactic and inter-halo scales, and larger. We find that AGNs are preferentially found in two specific stages of galaxy evolution: in the starburst and ‘green valley’ phases. We also find that the stellar population of their host galaxies is quite independent of stellar mass, which is not the case for more typical galaxies. Combining galaxy-galaxy lensing and galaxy clustering on large scales, we measured the mass of AGN host halos. The typical halo mass is about 1012 h−1 M⊙, similar to the characteristic mass in the stellar mass-halo mass relation (SHMR). For a given stellar mass, AGN host galaxies and star-forming galaxies share the same SHMR, while quiescent galaxies have more massive halos. Clustering analyses on halo scales reveals that AGNs are surrounded by a larger number of satellites (with stellar mass down to 1/1000 of the mass of the central galaxy) than star-forming galaxies and that galaxies with a greater stellar velocity dispersion have a greater number of satellites. The number of satellites also increase with halo mass, reaching unity around 1012 h−1 M⊙. Our results suggest a scenario in which the interaction of the central galaxy with the satellites triggers an early episode of starburst and AGN activity, followed by multiple AGN cycles driven by the non-axisymmetric structure produced by the interaction. The feedback from the starburst and AGN reduces the amount of cold gas for fueling the central black hole, producing a characteristic halo mass scale, that is, ∼1012 h−1 M⊙, where the AGN fraction peaks.

How do field-aligned currents influence plasma flows? Laboratory and space plasma experiments

It is known that the electrodynamic coupling of plasma flows with a magnetic field and background plasma leads to the generation of field-aligned currents that cause many effects in the auroral regions of the Earth during magnetic storms and sub-storms. Much less is known about the influence of field-aligned currents on the dynamics and evolution of plasma flows themselves. The study of this effect in space is complicated by the scale of the phenomenon and requires simultaneous measurements in various regions of the magnetosphere and ionosphere using a large number of satellites. In addition, taking into account the non-stationary nature of these processes, an extremely complex and expensive experiment must be carried out over a long time period. At the same time, such studies can be quite effective in controlled laboratory and ionospheric plasma experiments. This review is devoted to exploring how the generation and evolution of field-aligned currents influences the state and dynamics of plasma flows moving in the magnetic field.

GIS approaches to creating maps based on vegetation indices for forest management

The article considers the main approaches to providing information support for improving forest management on the territory, taking into account the most up-to-date experience, modern approaches and implementing sustainable forestry management based on the data of remote sensing and geoinformational modelling. To identify the state of vegetation in the area under analysis, the authors of the article propose to introduce the definition of a normalized differential vegetation index. A characteristic feature of vegetation and its state is spectral reflectivity, which is characterized by substantial differences in reflecting radiation from different wavelengths. To obtain the necessary MODIS packages, we used the LAADS DAAC service supported by NASA. The data of this service are freely accessible, convenient for the user, and they are taken from a large number of satellites and their spectra. The optimal option for solving the tasks of compiling NDVI maps is using the geographic information system QGIS. Among the main advantages of this GIS we can consider user-friendliness and its multi-platform basis. For proper visualization of the NDVI map, a special discrete scale of values is used, the purpose of which is to differentiate between organic and non-organic nature, as well as determine the density of vegetation. The introduction of the proposed technology will significantly increase the mobility and effectiveness of forest management.

Oil Spill Detection from PlanetScope Satellite Image: Application to Oil Spill Accident near Ras Al Zour Area, Kuwait in August 2017

Park, S.-H.; Jung, H.-S.; Lee, M.-J.; Lee, W.-J., and Choi, M.-J., 2019. Oil spill detection from PlanetScope satellite image: Application to oil spill accident near Ras Al Zour area, Kuwait in August 2017. In: Jung, H.-S.; Lee, S.; Ryu, J.-H., and Cui, T. (eds.), Advances in Remote Sensing and Geoscience Information Systems of Coastal Environments. Journal of Coastal Research, Special Issue No. 90, pp. 251-260. Coconut Creek (Florida), ISSN 0749-0208.Oil spill accidents are major marine disasters that can destroy the ocean ecosystem. Satellite images are widely used to respond immediately to oil spill accidents. A miniaturized satellite equipped with an optical sensor has an advantage that the imaging period is very short because a large number of satellites can be operated. In this study, oil slick areas were detected by applying the artificial neural network (ANN) technique to the PlanetScope satellite optical image captured near Ras Al Zour, Kuwait on August 10, 2017. However, the image included sunglint effects owing to ocean waves and yellow dust areas, making it difficult to classify the oil slick area. In addition, the spilled oil had three different spectral information characteristics through interaction with the sea surface of the Persian Gulf. The image processing was divided into the pre-processing step and the oil slick classification step to detect the oil slick area and to mitigate these limitations. In the pre-processing step, a directional median filter was applied to reduce the sunglint effects caused by ocean waves, and the negative effects from the sea surface and dust were mitigated using the differences with the low-pass filtered image. In the oil slick detection step, three types of oil probability maps and one sea surface probability map were produced using the ANN technique. Subsequently, an oil slick classification map was produced by applying the maximum probability choosing method and dust area rejection. Through validation, the overall accuracy of the oil classification map was obtained to be 82.01 % and the kappa coefficient was 72.42 %. The proposed oil detection method can effectively detect different types of oil spill areas in optical images with sunglint and dust handicaps. Moreover, it has high potential to be used in the future because the revisit time of the satellite image used is shorter than that of other optical images.

Исследование напряженно-деформированного состояния щеки водила планетарной передачи

Planetary gears are commonly used in drive technology due to their high load capacity and good weight and size parameters. Among planetary gears, multi-satellite structures with a minimum number of excessive links are most widely used. They have a close to uniform distribution of the load in the engaged gears, which has a positive effect on the strength and bearing capacity of the drive. Such designs include planetary gears, the satellites of which are mounted on spherical bearings, and one of the main links (most often the sun gear) is self-aligning. This provides a theoretically uniform distribution of the load in the engaged gears when the mechanism has three satellites. However, high-loaded drives often use designs with a large number of satellites where the load is distributed unevenly due to gear manufacturing errors. The deformability of individual transmission elements has a significant positive effect on the distribution of the load in the gears, thus compensating for the manufacturing errors. In view of this, the authors propose a multi-satellite planetary gear with a carrier made with grooves in the cheeks, which reduces their rigidity and provides, with a rational choice of the parameters of the mechanism, an increase in the mechanism’s bearing capacity. When determining the carrier cheek’s compliance, two schemes of loading in the coupling zone with the axis of the satellite (uniform and nonuniform) are considered. The solution is obtained using Mohr’s integrals. A numerical analysis of the stressed-strain state of the carrier cheek performed using the finite element method in the SolidWorks environment showed that the results of the analysis were close to the theoretical ones. They corresponded to a uniform load distribution in the coupling zone of the satellite axis and the carrier cheek. The obtained dependences can be used in the design of a mechanical drive to determine the coefficients of the uneven load distribution over the planetary gear satellites and over the individual crowns of the satellite.

The Number of Dwarf Satellites of Disk Galaxies versus their Bulge Mass in the Standard Model of Cosmology

Abstract There is a correlation between the bulge mass of the three main galaxies of the Local Group (LG), i.e., M31, Milky Way (MW), and M33, and the number of their dwarf spheroidal galaxies. A similar correlation has also been reported for spiral galaxies with comparable luminosities outside the LG. These correlations do not appear to be expected in standard hierarchical galaxy formation. In this paper, and for the first time, we present a quantitative investigation of the expectations of the standard model of cosmology for this possible relation using a galaxy catalog based on the Millennium-II simulation. Our main sample consists of disk galaxies at the centers of halos with a range of virial masses similar to M33, MW, and M31. For this sample, we find an average trend (though with very large scatter) similar to that observed in the LG; disk galaxies in heavier halos on average host heavier bulges and a larger number of satellites. In addition, we study sub-samples of disk galaxies with very similar stellar or halo masses (but spanning a range of 2–3 orders of magnitude in bulge mass) and find no obvious trend in the number of satellites versus bulge mass. We conclude that, while for a wide galaxy mass range a relation arises (which seems to be a manifestation of the satellite number–halo mass correlation), for a narrow range there is no relation between number of satellites and bulge mass in the standard model. Further studies are needed to better understand the expectations of the standard model for this possible relation.

Foreword to the Special Issue on Cyclone Global Navigation Satellite System (CYGNSS) Early on Orbit Performance

The papers in this special section examine the orbit performance pf the Cyclone Global Navigation Satellite System (CYGNSS), a constellation of eight satellites that were successfully launched on December 15, 2016 into low earth orbit. Each satellite carries a four-channel bistatic radar receiver that measures GPS signals scattered by the earth surface. Global Navigation Satellite System Reflectometry (GNSS-R) techniques are used to retrieve near surface wind speed over ocean and soil moisture over land. The measurements are unique in several respects, most notably in their ability to penetrate through high levels of precipitation, made possible by the low frequency at which GPS operates, and in the frequent revisit time and complete sampling of the diurnal cycle, made possible by the large number of satellites in a low inclination orbit. Engineering commissioning of the constellation was successfully completed in March 2017. Since then, CYGNSS science data products have been continuously produced.