Satellite Cluster Research Articles

Ordered Arrangement and Optical Properties of Silica-Stabilized Gold Nanoparticle-PNIPAM Core-Satellite Clusters for Sensitive Raman Detection.

Gold-polymer hybrid nanoparticles attract wide interest as building blocks for the engineering of photonic materials and plasmonic (active) metamaterials with unique optical properties. In particular, the coupling of the localized surface plasmon resonances of individual metal nanostructures in the presence of nanometric gaps can generate highly enhanced and confined electromagnetic fields, which are frequently exploited for metal-enhanced light-matter interactions. The optical properties of plasmonic structures can be tuned over a wide range of properties by means of their geometry and the size of the inserted nanoparticles as well as by the degree of order upon assembly into 1D, 2D, or 3D structures. Here, the synthesis of silica-stabilized gold-poly(N-isopropylacrylamide) (SiO2 -Au-PNIPAM) core-satellite superclusters with a narrow size distribution and their incorporation into ordered self-organized 3D assemblies are reported. Significant alterations of the plasmon resonance are found for different assembled structures as well as strongly enhanced Raman signatures are observed. In a series of experiments, the origin of the highly enhanced signals can be assigned to the interlock areas of adjacent SiO2 -Au-PNIPAM core-satellite clusters and their application for highly sensitive nanoparticle-enhanced Raman spectroscopy is demonstrated.

Spacecraft Recognition in Co-Located Satellites Cluster Through Optical Measures

The optical orbit determination is one of the most important ways for noncooperative object tracking. One of the main problems with noncooperative object tracking is its recognition through different nights. In this study, the conditions that ensure the recognition of a geostationary satellite inside a cluster were assessed through a hard real case study. This study was developed through a three-phase approach. The first phase was the observation campaign for the images acquisition. The second phase was the image's astrometric reduction for the data collection and the third phase was the orbit determination and data analyses. To evaluate the recognition ability, the residuals between the celestial coordinates obtained from the propagated orbit, which was carried out from the fitting between first night data and the environment gravity model through a least squares approach, and the measures collected during the second night were assessed. This approach, which is totally independent from the satellite cooperation actions, can be extended to the space debris recognition during different nights.

Consensus of satellite cluster flight using an energy-matching optimal control method

This paper presents an optimal control method for consensus of satellite cluster flight under a kind of energy matching condition. Firstly, the relation between energy matching and satellite periodically bounded relative motion is analyzed, and the satellite energy matching principle is applied to configure the initial conditions. Then, period-delayed errors are adopted as state variables to establish the period-delayed errors dynamics models of a single satellite and the cluster. Next a novel satellite cluster feedback control protocol with coupling gain is designed, so that the satellite cluster periodically bounded relative motion consensus problem (period-delayed errors state consensus problem) is transformed to the stability of a set of matrices with the same low dimension. Based on the consensus region theory in the research of multi-agent system consensus issues, the coupling gain can be obtained to satisfy the requirement of consensus region and decouple the satellite cluster information topology and the feedback control gain matrix, which can be determined by Linear quadratic regulator (LQR) optimal method. This method can realize the consensus of satellite cluster period-delayed errors, leading to the consistency of semi-major axes (SMA) and the energy-matching of satellite cluster. Then satellites can emerge the global coordinative cluster behavior. Finally the feasibility and effectiveness of the present energy-matching optimal consensus for satellite cluster flight is verified through numerical simulations.

Small-scale Intensity Mapping: Extended Lyα, Hα, and Continuum Emission as a Probe of Halo Star Formation in High-redshift Galaxies

Abstract Lyα halos are observed ubiquitously around star-forming galaxies at high redshift, but their origin is still a matter of debate. We demonstrate that the emission from faint unresolved satellite sources, , clustered around the central galaxies may play a major role in generating spatially extended Lyα, continuum (UV + VIS), and Hα halos. We apply the analytic formalism developed in Mas-Ribas & Dijkstra to model the halos around Lyman Alpha Emitters (LAEs) at z = 3.1, for several different satellite clustering prescriptions. In general, our UV and Lyα surface brightness profiles match the observations well at physical kpc from the centers of LAEs. We discuss how our profiles depend on various model assumptions and how these can be tested and constrained with future Hα observations by the James Webb Space Telescope (JWST). Our analysis shows how spatially extended halos constrain (i) the presence of otherwise undetectable satellite sources, (ii) the integrated, volumetric production rates of Lyα and LyC photons, and (iii) their population-averaged escape fractions. These quantities are all directly relevant for understanding galaxy formation and evolution and, for high enough redshifts, cosmic reionization.

High-sensitive bioorthogonal SERS tag for live cancer cell imaging by self-assembling core-satellites structure gold-silver nanocomposite

A novel, high–sensitivity, biocompatible SERS tag with core-shell structure based on gold nanoparticles containing alkynyl molecule core -silver nanoparticle satellites shell was fabricated for the first time to be used for live cancer cells Surface enhanced Raman scattering (SERS) imaging. (E)-2-((4-(phenylethynyl)benzylidene) amino) ethanethiol (PBAT) synthesized facilely in our lab is the Raman-silence region reporter which is advantage for bioorthogonal SERS cell imaging. In order to enhance the intensity of the Raman tags for live cancer cell imaging, a series of news measures have been adopted. Firstly, reporter molecules of the PBAT were added twice, which is embedded in the gold core with the reduction of tetrachloroaurate and then PBAT is conjugated again on disperse gold nanoparticles (PBAT-Au). Furthermore, numerous Ag nanoparticles self-assembly were densely arranged around PBAT-Au core surface (PBAT- Au@Ag), just like a circle of satellites cluster, which produce obvious “hot spots” effects enhancing the signal of the Raman tags enormously. Finally, Bovine serum albumin (BSA) and polydopamine (PDA) coated on the PBAT- Au@Ag successively, defined as (PBAT-Au@Ag@BSA@PDA), which make as-synthesized nanocomposites own features of bio-compatibility and facilitates antibody modification. Compared with Au@PBAT@PDA, PBAT-Au@Ag@BSA@PDA with core-shell satellites structure showed 10-fold increase in the Raman signals intensity. Moreover, PBAT-Au@Ag@BSA@PDA nanocomposites were successfully applied in the Raman imaging of human glioma cells (U251) by the recognition of the anti-epidermal growth factor receptor (EGFR). All experimental results demonstrated that the nanocomposites have high value and huge potential application in the live cancer cells imaging and biomedical diagnostics in the near future.

Analysis of Nanosatellite Formation Establishment and Maintenance Using Electric Propulsion

Nanosatellite clusters are one of the current and future trends in space technology. To maintain a satellite cluster over a long period of time, the nanosatellites need to mitigate the alongtrack drift created by the initial orbit injection. In the mass range of 1–10 kg, CubeSats have strict constraints on allowed mass, volume, and electrical power; and they are equipped with only limited sensor and actuator capabilities. A state-of-the-art miniaturized electric propulsion system is one option to realize the required orbit control capability. Due to the low thrust provided by an electric propulsion system, long orbit control maneuvers are required. Therefore, mission design is highly affected by long-term attitude and power constraints. Assuming a cyclic thrust controller, four methods are developed to allocate the satellite power and attitude resources for orbit control. Two time division methods are presented that allocate dedicated time slots for each of the satellite’s main tasks. Alternatively, two cosine methods are presented that use an error cone, around the required attitude, as a criterion for selecting when to operate the thruster. It is demonstrated that the proposed methods are capable of maintaining a realistic CubeSat formation-flying mission using low-power electric propulsion. For a CubeSat with deployable solar panels, the double cosine method shows the best performance.

Orbit design and control method for satellite clusters and its applications to NetSat project

In this paper, an optimal orbit design and control method for satellite clusters is presented and the method is applied to the four pico/nano-satellite system NetSat. Firstly, the relative motion based on relative eccentricity/inclination vectors is reviewed. Then, an optimal orbit design method for the cluster flight is developed, and the initial states of satellites in the cluster are derived using a graphical representation of the relative eccentricity/inclination vectors combined with a constrained nonlinear programming method. Next, a novel satellite cluster feedback control method is designed, and an optimal three-maneuver strategy is proposed, which could maintain the satellites in a bounded relative motion, satisfying the tight fuel consumption constraints and fuel balance for a long operational lifetime. Finally, the feasibility and effectiveness of the optimal orbit design and control for satellites cluster and its application to NetSat project are verified through numerical simulations.

Debris Avoidance Maneuvers for Spacecraft in a Cluster

Spacecraft formation flying and satellite cluster flight have seen growing interest in the last decade. However, the problem of finding the optimal debris collision avoidance maneuver for a satellite in a cluster has received little attention. This paper develops a method for choosing the timing for conducting minimum-fuel avoidance maneuvers without violating the cluster intersatellite maximal distance limits. The mean semimajor axis difference between the maneuvering satellite and the other satellites is monitored for the assessment of a maneuver possibility. In addition, three techniques for finding optimal maneuvers under the constraints of cluster keeping are developed. The first is an execution of an additional cluster-keeping maneuver at the debris time of closest approach, the second is a global all-cluster maneuver, and the third is a fuel-optimal maneuver, which incorporates the cluster-keeping constraints into the calculation of the evasive maneuver. The methods are demonstrated and compared. The first methodology proves to be the most fuel-efficient. The global maneuver guarantees boundedness of the intersatellite distances as well as fuel and mass balance. However, it is rather fuel-expensive. The last method proves to be useful at certain timings and is a compromise between fuel consumption and the number of maneuvers.

A Topology Control Strategy with Reliability Assurance for Satellite Cluster Networks in Earth Observation.

This article investigates the dynamic topology control problem of satellite cluster networks (SCNs) in Earth observation (EO) missions by applying a novel metric of stability for inter-satellite links (ISLs). The properties of the periodicity and predictability of satellites’ relative position are involved in the link cost metric which is to give a selection criterion for choosing the most reliable data routing paths. Also, a cooperative work model with reliability is proposed for the situation of emergency EO missions. Based on the link cost metric and the proposed reliability model, a reliability assurance topology control algorithm and its corresponding dynamic topology control (RAT) strategy are established to maximize the stability of data transmission in the SCNs. The SCNs scenario is tested through some numeric simulations of the topology stability of average topology lifetime and average packet loss rate. Simulation results show that the proposed reliable strategy applied in SCNs significantly improves the data transmission performance and prolongs the average topology lifetime.

A Comprehensive Evaluation Approach Based on AHP-BP Neural Network for Resource Allocation in Distributed Satellite Cluster Network

The distributed satellite cluster network (DSCN) is a novel concept in satellite communication field. Considering the dynamism and heterogeneity of the DSCN, the resource allocation algorithm must make adjustments dynamically according to the requirements of users as well as the utility and availability of the resource. This paper investigates the evaluation problem of the resource allocation utility in DSCN. Considering the heterogeneity of DSCN and the multi-dimensional of the resource, a distributed evaluation architecture and a multi-index evaluation system are constructed. To solve the multi-index evaluation problem, a comprehensive evaluation approach based on analytic hierarchy process and back-propagation (AHP-BP) neural network is proposed. Via several simulation results, we verify the effectiveness of the proposed approach.

Joint Downlink Power and Time-Slot Allocation for Distributed Satellite Cluster Network Based on Pareto Optimization

In this paper, we design a novel architecture of distributed satellite cluster network (DSCN). In order to achieve a good trade-off between the energy consumption and the total capacity, we investigate the joint downlink power and time-slot allocation problem, taking into account the limitation of resource, collaborative coverage of multi-satellite, and dynamism, which is proved to be a Pareto optimization and NP-hard problem. Different from the existing 1-D multi-objective optimization algorithm (1D-MOA) based on meta-heuristics, such as immune clonal algorithm (ICA), we propose an improved 2-D dynamic immune clonal algorithm (TDICA) to search the solution space for approaching the Pareto front. From simulation results, several important concluding remarks are obtained as follows: 1) the proposed TDICA can obtain more non-dominated solutions in each iteration with better accuracy than existing algorithms; 2) with inter-satellite resource optimization, the total capacity can be improved; 3) compared with 1D-MOAs, the 2D-MOA can save more energy and achieve higher total capacity; d) MOAs can be transferred into multiple single-objective optimization algorithms (SOAs) under certain conditions.

A performance analysis of multi-satellite joint geolocation

Determining the position of an emitter on Earth by using a satellite cluster has many important applications, such as in navigation, surveillance, and remote sensing. However, in realistic situations, a number of factors, such as errors in the measurement of signal parameters, uncertainties regarding the position of satellites, and errors in the location of calibration sources, are known to degrade the accuracy of target localization in satellite geolocation systems. We systematically analyze the performance of multi-satellite joint geolocation based on time difference of arrival (TDOA) measurements. The theoretical analysis starts with Cramer–Rao bound (CRB) derivations for four localization scenarios under an altitude constraint and Gaussian noise assumption. In scenario 1, only the TDOA measurement errors of the emitting source are considered and the satellite positions are assumed to be perfectly estimated. In scenario 2, both the TDOA measurement errors and satellite position uncertainties are taken into account. Scenario 3 assumes that some calibration sources with accurate position information are used to mitigate the influence of satellite position perturbations. In scenario 4, several calibration sources at inaccurate locations are used to alleviate satellite position errors in target localization. Through comparing the CRBs of the four localization scenarios, some valuable’s insights are gained into the effects of various error sources on the estimation performance. Two kinds of location mean-square errors (MSE) expressions under the altitude constraint are derived through first-order perturbation analysis and the Lagrange method. The first location MSE provides the theoretical prediction when an estimator assumes that the satellite locations are accurate but in fact have errors. The second location MSE provides the localization accuracy if an estimator assumes that the known calibration source locations are precise while in fact erroneous. Simulation results are included to verify the theoretical analysis.

In Memorium: Thomas Hilker

Dr. Thomas Hilker left us on 4 September 2016 following a sudden cardiac arrest. Thomas was adevoted husband to Yhasmin, and a brother and son to his family in Germany to whom we expressour deepest sympathies. Friends and colleagues of Thomas in the remote sensing and ecologicalcommunities lament this tragic loss. During his short but stellar science career, Thomas becamea world leader in the field of carbon, water and energy exchange from the land. He pioneeredstudies in the Amazonian forests, using anisotropy information acquired from satellites to describethree-dimensional structures that linked these ecosystems functionally to climatic variation.Thomas had an extreme range of interests—from the engineering of advanced spectrometers toproviding new theories and innovative methods to process remotely sensed data. Dr. Piers Sellers,Acting Director of the Earth Sciences Division at NASA/GSFC, and Deputy Director of the Sciences andExploration Directorate wrote: “Thomas Hilker was something of a renaissance man in Earth Science.He could climb towers, measure tall trees, and calculate spectral indices in his head. Working with himwas like collaborating with two or three normal people. He had some of the best and most originalideas in remote sensing that I’ve come across, but unlike most of us, he could go get the data to provehis point. And he was always the best fun. I remember him coming to a couple of parties of ours—hewas always relaxed, humorous, charming. He could make people laugh and everyone felt so goodaround him.”Thomas obtained a Bachelor of Science degree in Forestry from the University of Applied Sciences,in Goettingen, Germany in 2000, a Master in Photogrammetry and Geoinformatics from the Universityof Applied Sciences in Stuttgart in 2002 and a PhD from the University of British Columbia (UBC) inForestry in 2008. After a three year postdoctoral position at UBC (2008–2011), he worked as a ResearchAssociate at NASA’s Goddard Space Flight Center (2011–2012). From 2012 to 2016, Thomas held aposition as Assistant Professor at Oregon State University’s College of Forestry, leading the RemoteSensing Laboratory and teaching classes in Remote Sensing and Spatial Data Analysis. In 2015 and2016 he was a visiting researcher at the National Institute for Space Studies in Brazil (Instituto Nacionalde Pesquisas Espaciais, INPE). He looked forward to starting a position as an Associate Professor ofEarth System Science and Remote Sensing at the University of Southampton, UK.Thomas became fascinated by the global carbon cycle following receipt of his Master’s degree andwas keen to utilize his geospatial skills to unlock the details of the cycle. Inspired by the linksbetween canopy reflectance and photosynthesis, Thomas designed an Automated MultiangularSpectroradiometer for Estimation of Canopy reflectance [1] and improved it in subsequentiterations [2,3] to be able to continuously monitor subtle changes in the reflected spectra from

Bottlenose dolphin Tursiops truncatus group dynamics, site fidelity, residency and movement patterns in the Madeira Archipelago (North-East Atlantic)

The bottlenose dolphin Tursiops truncatus is one of the most frequently sighted cetacean species in the Madeira Archipelago (North-East Atlantic); however, little is known about its population ecology in these waters. Photo-identification undertaken during systematic, non-systematic and opportunistic surveys conducted between 2001 and 2012 was used to assess group dynamics, site fidelity, residency and movement patterns of bottlenose dolphins in the archipelago. Three different patterns of residency were assigned, based on individual sighting histories. Group size ranged between 2 and 90 individuals (median 12), with no significant monthly difference in group size. All resident dolphins formed a core, complex network with migrant and transient dolphins. In contrast, satellite clusters were formed exclusively by transient individuals. The lagged identification rate (LIR) model indicated that a dolphin remained in the area for an average of 90 days, whereas the average time an individual spent outside the study area was approximately 313 days. The Madeira Archipelago appears to be only a section of a much larger home range for this population, with the dolphins exhibiting three different patterns of occurrence that associate with each other. The information gained about this poorly studied population contributes to the overall knowledge of bottlenose dolphins in insular oceanic habitats.

Joint cooperative spectrum sensing and spectrum opportunity for satellite cluster communication networks

Satellite communication networks composed of various satellites with different heights can be regarded as cooperative primary users in the space segment. Cooperative spectrum sensing as the key techniques of cognitive radio has been paid more attention to the application of satellite communications. To fully explore the potentials of the mobile satellite communication networks based on the concept of satellite cluster in supporting of heterogeneous applications, a trust-weighted cooperative spectrum sensing to primary satellite system is proposed in this paper. And the proposed algorithm allows the fusion center to combine all the 1-bit local decisions from all the secondary satellite systems through trust weights, in order to obtain a final decision on the presence of the primary satellite system. Moreover, according to the spectrum dynamics and node mobility, we propose a spectrum opportunity-based routing protocol (SORP) in which the nodes can exploit the local information and find local available channel to provide reliable routing in cluster-based satellite networks. Specifically, a novel metric which is aware of the unique properties is introduced to select the cluster head of each cluster. Simulation results show the comparison of the efficiency of proposed cooperative spectrum sensing and protocol with a few other related works.

A satellite cluster as a gravitational-wave detector

The detection of gravitational waves by a cluster of satellites is considered. The detector is an optical interferometer formed of several satellites. The calculations for three spacecraft are given. The complete detector response to the monochromatic gravitational wave generated by a binary star is computed.

Using multi-agent technology for the distributed management of a cluster of remote sensing satellites

In recent years, the interest for space missions involving multiple satellites has been rapidly growing. This trend is responsible for an increasing need for management strategies able to coordinate the different satellites and to allocate tasks among them. In most existing systems, the management of a cluster of satellites is organized centrally and statically, which significantly reduces the responsiveness to changes in the target environment. Our research aims at designing a distributed dynamic management system where tasks are assigned to a whole constellation of satellites and their performers can adaptively change depending on emerging events. In this paper, we explore the potentiality of multi-agent technology and ontology to develop an intelligent space system. We describe our software prototype and how it can be applied to the planning problem of remote sensing satellites. In this solution, each satellite has been represented as an agent enabling communication, coordination, and negotiation among the other agents to achieve intended business goals. Moreover, we present the results of experiments showing the advantages of the proposed approach.

Virtual multi-beamforming for distributed satellite clusters in space information networks

This article introduces some basic theories of space information networking (SIN), which is a novel research field. A SIN is a network that is able to achieve real-time acquisition, transmission, and processing of space information. The article first investigates the basic satellite-terrestrial architecture of SINs, and then three key technologies of SINs are presented, specifically more details on the high data rate transmission theory. The DSC is the foundation of high data rate transmission; thus, the core technology of DSC, which is beam/beamforming theory, is discussed in detail. Compared to the traditional spot beam theory, this article proposes a novel VBF concept, which is capable of increasing the channel capacity. Some key technologies are also investigated for VBF; they are channel capacity theoretical analysis, opportunistic beamforming, virtual multi-beamforming, and resource management.

Templated growth of gold satellites on dimpled silica cores.

We synthesize robust clusters of gold satellites positioned with tetrahedral symmetry on the surface of a patchy silica core by adsorption and growth of gold on the patches. First we conduct emulsion polymerization of styrene in the presence of 52 nm silica seeds whose surface has been modified with methacryloxymethyltriethoxysilane (MMS). We derive four-dimple particles from the resulting silica/polystyrene tetrapods. Polystyrene chains are covalently bound to the silica surface within the dimples due to the MMS grafts and they may be thiolated to induce adsorption of 12 nm gold particles. Using chloroauric acid, ascorbic acid and sodium citrate at room temperature, we grow gold from these 12 nm seeds without detachment from or deformation of the dimpled silica surface. We obtain gold satellites of tunable diameter up to 140 nm.

A planning approach to monitor and control the satellite cluster

There are many satellites in space that revolve round the Earth. Increase in the number of satellites leads to the importance of monitoring satellites for collision detection and avoidance. Collision of satellites can occur if their orbits intersect each other. In order to detect collision and to avoid the collision of satellites, the relative distance between any two satellites needs to be calculated as they revolve. As an objective to calculate the distance between any two satellites, parallel computation is required in order to detect collision. Our paper shows the prediction of collision possibilities between any two satellites and proposes at parallelizing the relative distance and position computation for a satellite of interest and its neighboring satellites.