Satellite Cluster Research Articles

Event-triggered coordinated attitude method for chip satellite cluster

Event-triggered coordinated attitude control problem for chip satellite cluster was investigated in this paper. Considering the constraints of computation, measurement and communication on chip satellites, adaptive attitude tracking controller based on event-triggered strategy was proposed for chip satellite cluster with leader-follower architecture. Triggering function with state tracking error was designed to adjust update period of controller, event was triggered and controller was updated once triggering function value satisfied the condition, while controller in non-triggering time used state information of triggering time. As the state of cluster system gradually tended to be stable, triggering frequency was reduced, which effectively reduced update frequency of controller and reduced resource on board. Cluster system was proved to be globally asymptotical convergence by Lyapunov stability theory. Simulation results showed that the proposed event-triggered adaptive attitude tracking controller could reduce control execution frequency, meet the constraints of resource and ability of chip satellites, as well as ensure control performance of cluster system. The influence of control gain coefficients and triggering parameters on control performance of cluster system were further analyzed, and criterion for parameters design was provided.

Decomposition analysis of spacecraft relative motion with different inter-satellite ranges

With the development of satellite cluster and giant constellations in recent years, the orbit design and long-term maintenance of these systems become more difficult with the restriction of fuel consumption and the influence of orbital perturbations. It's necessary to study the analytical model of relative motion which applicable to different inter-satellite ranges. Then, considering the perturbed evolutions of orbital elements, the decomposed relative motion model was proposed by separating the higher-fidelity relative motion model into two different parts, which reflect the circling motion around chief, and their overall motion relative to chief respectively. Eccentricity expansions had been carried out to provide a time-explicit analytical solution of the decomposed model. Based on this first order time-explicit analytical solution, the bound relative motions with different inter-satellite ranges were studied in Kepler orbit. The initial condition calculation formula for general chief centered circular relative motion was derived at the same time. The accuracy of first order analytical solution of the decomposed model was estimated both theoretically and numerically, to show the effect of inter-satellite range and chief's eccentricity. At last, the first order analytical solution using mean orbital elements was compared with high precision numerical solution under perturbations to validate it's effective in long-term stability analysis.

Source Identification of Episodic Rain Pollutants by New Approach: Combining Satellite Observations and Backward Air Mass Trajectories

ABSTRACT In this study, various source apportionment methods, viz., enrichment factor, relative source contribution, and factor analysis in addition to cluster analysis coupled with satellite observations, were used to investigate the origin of rainwater pollutants in an arid urban area of Saudi Arabia. The rainwater samples were collected by an automatic wet-only sequential rain sampler and analyzed for their pH, electrical conductivity (EC), and major ions (Cl–, NO3–, SO42–, HCO3–, Na+, K+, NH4+, Ca2+, and Mg2+). The results revealed that the chemical composition was dominated by Ca2+, SO42–, Cl–, HCO3–, and Na+, which represented 80% of the total ionic equivalent concentration. Ca2+, the most abundant ion, exhibited a mean concentration of 480 µeq L–1 and accounted for 30% of the total ionic equivalent concentration. The study area received a total ionic wet deposition flux (FWD) of 4.07 tons km–2 y–1, and SO42– and NO3– contributed 76% and 24%, respectively, of the rainwater acidity. Ca2+ was responsible for 80% of the rainwater’s neutralization. The source apportionment indicated that intense local human activity and medium- to long-range transport from Kuwait, Iraq, Qatar, Riyadh, and the Western Province produced the majority of the anthropogenic components (SO42–, NO3–, and NH4+), which represented 47% of the total ionic FWD. However, moderate to high particulate matter loads over the southern part of Saudi Arabia and long-range transport from Iraq and Kuwait contributed the crustal components (Ca2+, HCO3–, K+, and Mg2+), which accounted for 36% of the total ionic FWD, whereas the Arabian Gulf was the primary source of the marine components (Na+ and Cl–). We found combining satellite observations and cluster analysis of backward air mass trajectories to be an effective new approach for assessing the source-receptor relationships for atmospheric air pollutants.

Evolution of the Pattern of Spatial Expansion of Urban Land Use in the Poyang Lake Ecological Economic Zone.

To grasp the evolutionary characteristics and regularity of urban land expansion patterns in the Poyang Lake Ecological Economic Zone, this study, based on nighttime lighting data, uses the Landsat series satellite simultaneous data and cluster analysis to correct the Defense Meteorological Satellite Program–Operational Linescan System (DMSP-OLS) nighttime lighting data and then uses the auxiliary data-based comparison method to determine the threshold for extracting the urban built-up area. Based on this threshold, a total of eight typical landscape pattern indicators, including landscape total area, total patches number, patches density, maximum patches index, and agglomeration index, etc., are selected. Next, the landscape spatial pattern analysis method and standard deviation ellipse method are used. The results show the following: (1) In 1992–2013, urbanization in the Poyang Lake Ecological Economic Zone expanded rapidly. The urban built-up area increased by 8.13 times, the number of plaques increased by 1.5 times, and the shape complexity of landscape plaques gradually increased. There is a large correlation between the changes in the total boundary length, and the average boundary density, the average annual growth rate of the two is 21.33% and 17.45%. (2) The two indicators of maximum plaque index and aggregation index show a downward trend year by year. However, there are some fluctuations and irregularities in the evolution of the total landscape area, total plaque number and plaque density. (3) The long axis and the short axis of the standard deviation ellipse of the Poyang Lake Ecological Economic Zone show small variation during the inspection period and generally have an elliptical shape. The movement of the center of gravity is mainly from the southwest to the northeast, but the migration of the center of gravity is relatively small. Based on this, this paper proposes three countermeasures and suggestions as a guide to promote the optimization and development of the spatial expansion pattern of the Poyang Lake eco-economic zone.

Atoh1 Controls Primary Cilia Formation to Allow for SHH-Triggered Granule Neuron Progenitor Proliferation

During cerebellar development, granule neuron progenitors (GNPs) proliferate by transducing Sonic Hedgehog (SHH) signaling via the primary cilium. Precise regulation of ciliogenesis, thus, ensures proper GNP pool expansion. Here, we report that Atoh1, a transcription factor required for GNPs formation, controls the presence of primary cilia, maintaining GNPs responsiveness to SHH. Loss of primary cilia abolishes the ability of Atoh1 to keep GNPs in a proliferativestate. Mechanistically, Atoh1 promotes ciliogenesis by transcriptionally regulating Cep131, which facilitates centriolar satellite (CS) clustering to thebasal body. Importantly, ectopic expression of Cep131 counteracts the effects of Atoh1 loss in GNPs by restoring proper localization of CS and ciliogenesis. This Atoh1-CS-primary cilium-SHH pro-proliferativepathway is also conserved in SHH-type medulloblastoma, a pediatric brain tumor arising from the GNPs. Together, our data reveal how Atoh1modulates the primary cilium to regulate GNPs development.

Approach to MAI cancellation for micro-satellite clusters

With the development of micro-satellite technology, traditional monolithic satellites can be replaced by micro-satellite clusters to achieve high flexibility and dynamic reconfiguration capability. For satellite clusters based on the frequency division-code division multiple access (FD-CDMA) communication system, the inter-satellite ranging precision is usually constrained due to the influence of multi-address interference (MAI). The multi-user detection (MUD) is a solution to MAI, which can be divided into two categories: the linear detector (LD) and the non-linear detector (NLD). The general idea of the LD is aiming to make a better decision during the symbol decision process by using the information of all channels. However, it is not beneficial for the signal phase tracking precision. Instead, the principle of the NLD is to rebuild the interference signal and cancel it from the original one, which can improve the ranging performance at the expense of considerable delays. In order to enable simultaneous ranging and communication and reduce multi-node ranging performance degradation, this paper proposes an NLD scheme based on a delay locked loop (DLL), which simplifies the receiver structure and introduces no delay in the decision process. This scheme utilizes the information obtained from the interference channel to reconstruct the interference signal and then cancels it from the original delayed signal. Therefore, the DLL input signal-to-interference ratio (SIR) of the desired channel can be significantly improved. The experimental results show that with the proposed scheme, the standard deviation of the tracking steady error is decreased from 5.59 cm to 3.97 cm for SIR = 5 dB, and 13.53 cm to 5.77 cm for SIR = -5 dB, respectively.

Coulomb tether double-pyramid formation, a potential configuration for geostationary satellite collocation

This paper proposes the Coulomb tether double-pyramid satellite formation, which includes a cluster of charged satellites repelling each other by Debye-shielded Coulomb forces and two counterweights connecting to each satellite via elastic massless tethers. The center of mass of the formation is prescribed to move along the geostationary orbit. The equations of motion of the formation are obtained by using Lagrange's equation. Analytical individual satellite charges are derived for the spinning and non-spinning three-satellite configurations, respectively. When the number of satellites is more than three, approximate analytical charges are obtained. Numerical simulations indicate that the proposed formation may be successfully applied to the geostationary satellite collocation in the future.

Self-organizing control for satellite clusters using artificial potential function in terms of relative orbital elements

Self-organizing control for satellite clusters is a challenging and promising problem which has drawn considerable attention in the recent past. The artificial potential function method has been widely used for self-organizing control due to its elegant mathematical analysis and simplicity. This paper proposes a set of self-organizing control rules for satellite clusters described by artificial potential functions, so that the reconfiguration, uniform distribution and collision avoidance operations can be achieved spontaneously. It may work regardless of the failure of satellites, attendance of new members or existence of space debris, and the corresponding communication and control system are completely distributed. Particularly, the artificial potential functions are written in terms of relative orbital elements derived from T–H equations, so that the self-organizing control can reflect relative motion dynamics, and guide the satellite along a fuel-efficient trajectory. The proposed method is especially suitable for highly distributed micro-satellite clusters and large-scale clusters to track moving targets, with few fuel cost and relatively high control accuracy, and it is applicable to clusters in either deep space or near-earth space. The stability of the control was proved by Lyapunov second method, and verified by Monte Carlo simulation. Finally, the comparison between self-organizing control and fuel-optimal control was made to demonstrate the performance properties.

A new multi-satellite autonomous mission allocation and planning method

To overcome the issues of inflexible interactive mode, low negotiation efficiency and poor dynamic response capability of satellite clusters, we propose a new multi-dimensional and multi-Agent clusters collaboration model (MDMA-CCM), including task pre-processing, allocation, scheduling and re-planning under failed conditions. First, the task clustering based pre-processing method is adopted to improve the observation efficiency by combining potential targets. Second, the Contract Net Protocol (CNP) based secondary allocation strategy is developed to effectively increase the observation benefit and reduce the impact of task conflicts through announcement, bidding and awarding. Third, a new Interactively Re-planning Method (IRM) is proposed to effectively reduce the loss by re-inserting tasks in case of failure. Simulation results show that the new planning model not only has obvious advantages in calculation time, but also outperforms the centralized multi-Agent system in terms of benefit value and completion rate.

Heat transfer by satellite cluster of cylinders at subcritical Reynolds number

2D unsteady computations were conducted in Fluent for differently configured cluster of cylinders at constant-heat-flux wall condition subjected to transverse air-flow at subcritical Reynolds number of 3.5 × 104. The investigation aimed to observe the performance of satellite arrangement of nine clustered cylinders for stage-wise heat exchange process in waste-heat-recovery recuperators (WHRR). Nusselt numbers were analyzed while the pressure distributions and flow visualizations were used to interpret the flow and heat transfer phenomenon. The analysis of heat transfer data revealed an improvement in heat transfer ratio of 3.55% by the satellite arrangement over that of cluster of nine single cylinders providing the heat transfer ideally.

Exact and Heuristic Methods for Observing Task-Oriented Satellite Cluster Agent Team Formation

With the development of aerospace science and technology, Earth Observation Satellite cluster which consists of heterogeneous satellites with many kinds of payloads appears gradually. Compared with the traditional satellite systems, satellite cluster has some particular characteristics, such as large-scale, heterogeneous satellite platforms, various payloads, and the capacity of performing all the observation tasks. How to select a subset from satellite cluster to perform all observation tasks effectively with low cost is a new challenge arousing in the field of aerospace resource scheduling. This is the agent team formation problem for observation task-oriented satellite cluster. A mathematical scheduling model is built. Three novel algorithms, i.e., complete search algorithm, heuristic search algorithm, and swarm intelligence optimization algorithm, are proposed to solve the problem in different scales. Finally, some experiments are conducted to validate the effectiveness and practicability of our algorithms.

Capacity reservation optimization for distributed satellite cluster networks

SummaryWe investigate the problem of link capacity reservation in distributed satellite cluster networks. In the optimization problem, the objective is to minimize the link reservation cost under the link capacity constraints. The original optimization problem can be formulated as a set of the linear programs. For the small‐scale networks, the general linear program solvers have the capability to solve the problem within an acceptable time. To solve the problem in the large‐scale network, we propose a heuristic method on the basis of the alternating direction method of multipliers, in which the original problem is decoupled to parallel small problems that can be solved simply. In the heuristic, the upper and lower bounds are computed iteratively. When the upper and lower bounds are close enough, then the optimal value can be obtained approximately. The simulation results show that the proposed method is comparatively exact when the stopping criterion is properly chosen.

Problem A of the 9th China trajectory optimization competition: Results found at Tsinghua University

This paper presents the crucial method for obtaining results of Tsinghua University in the 9th China Trajectory Optimization Competition (CTOC-9). To monitor the usage of the important frequency resources of GEO satellites, CTOC-9 focuses on the orbit design and trajectory optimization of satellite cluster flight for geostationary orbit (GEO) satellite beams monitoring missions. The three cluster satellite orbits and complex constraints cause much difficulties in the design and optimization. The search for the globally optimal mission trajectory with multi-impulse orbit maneuver is performed in two steps. The first step involves a roughly global search in the search space that has been bounded based on the fuel constraints, the monitoring conditions and the formation flying model of three monitoring cluster satellites. To bound the global search space, several legs are patched together to represent the whole trajectory of monitoring mission, and the impulses occurring in the patch points are estimated by the Hohmann transfer. And the particle swarm optimization (PSO) algorithm is modified and then employed to the multi-leg optimization. The second step involves the local optimization of the multi-impulse patched-conic legs which stand out from the roughly global search. The main task of the local optimization is to solve a series of J2 perturbed Lambert problems by the homotopic approach. Based on the impulsive results, some specific subtasks are selected and re-optimized to reduce the number of subtasks. Of the many trajectories found, the optimal trajectory submitted for the competition is reported. A post-competition result is reported, which is with the primary objective of 19.61 days, prior to the winner of 20.43 days.

Problem A of CTOC-9: Results found at Research Center of Flight Dynamics and Control of NUDT

The problem A of the 9 t h China Trajectory Optimization Competition (CTOC-9) requires monitoring 18 geostationary orbit (GEO) satellite beams using a satellite cluster which has three members. This paper summarizes the solution strategies and gives the best results found at Research Center of Flight Dynamics and Control of NUDT. The visibility conditions of the satellite beams are analyzed firstly. A circular configuration is selected for the satellite cluster due to its uniform monitoring performance, and several repeat-groundtrack orbits are chosen as the cluster's working orbits for their revisit feature. Since the satellite beams points to quite different directions in the space, a combination of two or three repeat-groundtrack orbits is adopted to reduce the mission duration. The optimal combination is found out by using exhaustive method. When the satellites transfer between different working orbits, the Particle Swarm Optimization (PSO) and Sequence Quadratic Programming (SQP) algorithms are used to minimize the fuel consumption. An orbit propagation algorithm that can quickly predict the beam visibility to the cluster is introduced to improve the computational efficiency. Two results were found according to two different orbit combinations. Specifically, when the combination of two repeat-groundtrack orbits is adopted, it requires 24.931 days and 244.531 kg fuel to complete the mission. When the combination of three repeat-groundtrack orbits is adopted, it requires 21.408 days and 450.640 kg fuel. The latter is the best result found by our team for the competition.

Satellite Cluster Close Approaches Determination for Collision Avoidance

As the number of space objects in orbit about the Earth increases, it is extremely important to determine the close approaches between them. In this paper the close approaches is determined for the satellite cluster using a simulation tool STK for the following (i) satellites of interest within a cluster (ii) a satellites of interest in a cluster and the space objects as listed in the space catalog and the close approach reports are analyzed. The results have indicated that the details of intruder satellites and the duration of close approaches and their minimum separation distances or the relative distances.

СОЗДАНИЕ АРХИТЕКТУРЫ «РАСПРЕДЕЛЕННОГО СПУТНИКА» ДЛЯ НИЗКООРБИТАЛЬНЫХ ИНФОРМАЦИОННО-ТЕЛЕКОММУНИКАЦИОННЫХ СИСТЕМ НА ОСНОВЕ ГРУППИРОВКИ МИКРО- И НАНОСПУТНИКОВ

Presented are the results of an analysis of the growing interest in the use of low Earth orbits (up to 1500 km high) for the introduction and development of the Internet of things (Internet of Things - IoT). Industrial Internet of things (Industrial Internet of Things-IIoT). Internet of things for remote areas (Remote Internet of Things - RioT, for the purposes of scientific research and economic use of natural resources, control of the development and operation of infrastructure projects, the operation of territorially distributed industrial production, transport infrastructure. Factors significantly limiting the further introduction of micro and nano satellites are given. The authors proposed to resolve this contradiction on the basis of the developed concept of creating the architecture of a "distributed satellite". As an example, the article considers possible applications of the distributed satellite architecture in two segments of the space information systems market: remote sensing of the Earth and telecommunication systems. The application of the "distributed satellite" in radar systems with synthesized aperture (SAR-system) was considered taking into account the requirements of the operators of satellite SAR-systems and consumers of their information. It is shown. that the use of the "distributed satellite" architecture in SAR-systems also makes it possible to realize the technology of multi-static radar with a "soft" interference base (from 200 m to 1 km). The scheme of organization and interaction of the "distributed satellite" in the satellite-transmitter on the platform of the micro satellite, which is the core of the satellite cluster, and several satellites-receivers on the cube-sat platform is presented. The functions performed by the satellite-transmitter, the inter-satellite radio link and the satellite-receiver are considered in detail. The work of the "distributed satellite" is illustrated by the presented structural diagram of the SAR-system for remote sensing of the Earth, a version of the architecture of the low-orbit satellite communication system and the scheme for constructing a satellite system for the provision of IoT services. In conclusion, it is noted that the architecture of the "distributed satellite" makes it possible to effectively use satellites of the class of micro/nano satellite (cube-sat) to create complex space-based information and telecommunication systems

Canyons pride and prejudice: Exploring the submarine canyon research landscape, a history of geographic and thematic bias

We mapped submarine canyon research using a scientometric approach to define and characterize its scientific landscape based on a comprehensive bibliographic dataset. The abundance of studies covering structural and functional aspects of submarine canyons allowed us to identify the existing knowledge clusters, historical trends, and emergent topics in canyon research. Our analysis documented a network of knowledge clusters of which four were particularly relevant: a strong cluster on “Geology & Geophysics”, well established since the beginnings of canyon research; a cluster on “Biology & Ecology” that gained strength primarily over the past two to three decades; a cluster on “Oceanographic Processes” which occupied a central position in the network and connected strongly to almost all the other clusters and especially to the fourth main cluster on “Modelling”. A smaller, but also well connected, cluster on “Biogeochemistry” related closely to “Biology & Ecology”, and three other small clusters (“Sedimentology”, “Sediments & Tidal Currents”, “Canyon Sampling”) bridged the main clusters. Finally, we identified three small, but specific satellite clusters (“Oil & Gas”, “Chemosynthetic Communities”, “Molecular & Symbionts”). The high-level structure of the knowledge network reflects a latent interdisciplinarity in canyon research. However, the evolution of the research lines over the past nine decades suggests that this pattern arose mostly in the new millennium. Emergent research topics in the last decade also reveal a concern regarding anthropogenic impacts and climate-driven processes. Our results also show a well implemented and international collaboration network, although research efforts have been mainly directed towards only a few canyon systems. A geographical and thematic bias also characterizes canyon research, with specific topics addressed preferentially in particular canyons by different leading research institutions. This spatial and thematic bias, together with the paucity of truly inter-disciplinary studies, may be the most important limitation to integrated knowledge and development in canyon research and hinders a global, more comprehensive understanding of canyon patterns and processes. The scientific landscape mapping and the complementary results are made available as an open and interactive platform that canyon stakeholders can use as a tool to identify knowledge gaps, to find key players in the global collaboration network and to facilitate planning of future research in submarine canyons.

Mineral exploration by decision tree classification using multi temporal cluster images in Jharkhand region

India, being an abundant source of minerals, Mineral exploration, on a large scale, is promising to provide good impact for the future of the country. India has a rich source of coal, bauxite, limestone etc. With the advent of remote sensing technologies capturing broader area, exploration of minerals has now become an appreciable problem. Satellite Cluster Images spanning over wider areas can effectively serve as a tool for mapping minerals, qualitatively and quantitatively. In this paper, an algorithm, based on decision tree classification, is developed to map minerals, specifically, coal and limestone for a specific region. Multi-temporal cluster images are employed to map dynamic change detection resulting in greater accuracy. In this paper, multi-temporal cluster images (Landsat 8 OLI/TIRS) are analyzed to map coal, limestone and ‘no-mineral’ regions with the help of the algorithm developed using decision tree classification. Classification results are compared with ground truth data for assessing its accuracy.

ZOMG - III. The effect of halo assembly on the satellite population

We use zoom hydrodynamical simulations to investigate the properties of satellites within galaxy-sized dark-matter haloes with different assembly histories. We consider two classes of haloes at redshift $z=0$: `stalled' haloes that assembled at $z>1$ and `accreting' ones that are still forming nowadays. Previously, we showed that the stalled haloes are embedded within thick filaments of the cosmic web while the accreting ones lie where multiple thin filaments converge. We find that satellites in the two classes have both similar and different properties. Their mass spectra, radial count profiles, baryonic and stellar content, and the amount of material they shed are indistinguishable. However, the mass fraction locked in satellites is substantially larger for the accreting haloes as they experience more mergers at late times. The largest difference is found in the satellite kinematics. Substructures fall towards the accreting haloes along quasi-radial trajectories whereas an important tangential velocity component is developed, before accretion, while orbiting the filament that surrounds the stalled haloes. Thus, the velocity anisotropy parameter of the satellites ($\beta$) is positive for the accreting haloes and negative for the stalled ones. This signature enables us to tentatively categorize the Milky Way halo as stalled based on a recent measurement of $\beta$. Half of our haloes contain clusters of satellites with aligned orbital angular momenta corresponding to flattened structures in space. These features are not driven by baryonic physics and are only found in haloes hosting grand-design spiral galaxies, independently of their assembly history.

Concept design and cluster control of advanced space connectable intelligent microsatellite

In this note, a new type of advanced space connectable intelligent microsatellite is presented to extend the range of potential application of microsatellite and improve the efficiency of cooperation. First, the overall concept of the micro satellite cluster is described, which is characterized by autonomously connecting with each other and being able to realize relative rotation through the external interfaces. Second, the multi-satellite autonomous assembly algorithm and control algorithm of the cluster motion are developed to make the cluster system combine into a variety of configurations in order to achieve different types of functionality. Finally, the design of the satellite cluster system is proposed, and the possible applications are discussed.