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To fully harness the burgeoning array of in-orbit satellite resources and augment the efficacy of dynamic surveillance of densely clustered terrestrial targets, this paper delineates the following methodologies. Initially, we leverage the Density-Based Spatial Clustering of Applications with Noise (DBSCAN) clustering algorithm to aggregate the concentrated terrestrial targets, taking into account the field-of-view peculiarities of agile staring satellites. Subsequently, we architect a model for a synergistic multiple angle earth observation satellites (AEOSs) mission planning with the optimization objectives of observational revenue, minimal energy expenditure, and load balancing, factoring in constraints such as target visibility time window, AEOSs maneuverability, and satellite storage. To tackle this predicament, we propose an improved heuristic ant colony optimization (ACO) algorithm, utilizing the task interval, task priority, and the length of time a task can start observation as heuristic information. Furthermore, we incorporate the notion of the max–min ant system to regulate the magnitude of pheromone concentration, and we amalgamate global and local pheromone update strategies to expedite the convergence rate of the algorithm. We also introduce the Lévy flight improved pheromone evaporation coefficient to bolster the algorithm's capacity to evade local optima. Ultimately, through a series of simulation experiments, we substantiate the significant performance improvements achieved by the improved heuristic ant colony algorithm compared to the standard ant colony algorithm. We furnish proof of its efficacy in resolving the planning of multiple AEOS staring observation missions. [ABSTRACT FROM AUTHOR]

With the rapid development of agile Earth observation satellites (AEOSs), these satellites are able to conduct more high-quality observation missions. Nevertheless, while completing these missions takes up more data transmission and electrical energy resources, it also increases the coupling within each satellite subsystem. To address this problem, we propose a reasoning-based scheduling method for an AEOS under multiple subsystem constraints. First, we defined the AEOS mission scheduling model with multi-subsystem constraints. Second, we put forward a state variable prediction method that reflects the different coupling states of a satellite after analyzing the coupling relationships between various subsystems and identifying the primary limiting coupling states for each subsystem. Third, we established the reasoning rules corresponding to the planning strategies of different coupling states of the satellite by adding two planning strategies based on the planning strategies of existing planning methods. By comparing the proposed method to three heuristic scheduling methods and a meta-heuristic scheduling method, the results show that our method has better performance in terms of scheduling results and efficiency. [ABSTRACT FROM AUTHOR]

Very High Resolution Passive Scan Agile Earth Observation Satellites are able to maneuver around all their three body axes and scan the target area in different directions, simultaneously. The most stringent mid-level requirements which dominate their attitude determination and control subsystem performance are applied in detumbling and fine pointing modes. These performance requirements are maneuverability, agility, accuracy and stability. In this research, first, we derive the analytical and statistical relationships between quantitative criteria of mid-level requirements and spatial resolution as a high-level mission requirement, next the design drivers of reaction wheels are extracted consequently. Then the size, mass and consuming power of an operational satellite and the reaction wheels torque authority and momentum capacity is guesstimated based on its imaging payload size and specifications.

In recent earth observing missions, agile satellites enable various imaging modes beyond the traditional along-track strip imaging. However, it requires maneuvering with boundary conditions of considerable angular velocity, i.e., spin-to-spin maneuvering. This paper proposes an attitude command generation method for spin-to-spin maneuvering that can provide feedforward commands for the attitude control loop. A general solution for arbitrary flight time is provided which steers a satellite to the given final attitude and angular velocity at the prescribed time. In addition, an alternative method is proposed that further improves the maneuvering speed, which is applicable to small-angle maneuvering cases. The proposed solutions are both closed-form which are more intuitive and easier to comprehend than numerical solutions. It also has a great advantage in computational efficiency, which could enable its use on-board in real time. Numerical examples demonstrate the performance of the proposed methods in a single maneuvering case as well as in a consecutive maneuvering case integrated with a realistic earth observing scenario. [ABSTRACT FROM AUTHOR]

When the targets are distributed irregularly, it is of great significance to quickly acquire color images with a wide field by agile satellite. Attributed to the changing of the three-axis attitude and Earth’s rotation, there are misalignment and distortion during the processing of imaging by agile satellite. It makes the fusion of interband images slower and the stitching of interdetector images poorer. In this article, a rigorous velocity vector field (VVF) model is established through tracing rays between the image and the object. It calculates the misalignment among the images of bands in each detector to align and fuse multispectral images. Based on the reference image selected by VVF, the fused images are stitched with the method of leveraging line-point consistency. Finally, both field and in-orbit experiments are conducted. The time of calculating misalignment in image fusion with VVF is 13.19% of the minimum time of the traditional registration algorithm. In image stitching, our RMSE values are 1.15, which is the smallest among the RMSE values of SIFT, SURF, and SPW. In preserving linear structure, compared with SPW, the values of ${E_{\text {dis}}}$ , ${E_{\text {err}}}$ , and ${E_{\text {cross}}}$ , respectively, reduce 60%, 50%, and 50%. The results show that images of the agile satellite can be fast fused and precisely stitched using VVF while correcting distortion. The compensation strategy of the VVF provides a theoretical basis for the agile satellite in image fusion and stitching. [ABSTRACT FROM AUTHOR]

The past decade has seen an increase in the number of satellites in orbit and in highly dynamic satellite requests, making the control by ground stations inefficient. The traditional management composed of ground planning with separate onboard execution is seriously lagging in response to dynamically incoming tasks. To meet the demand for the real-time response to emergent events, a multi-autonomous-satellite system with a central-distributed collaborative architecture was formulated by an integer programming model. Based on the structure, evolutionary rules were proposed to solve this problem by the use of sequence solution construction and a constructed heuristic method based on gene expression programming evolution. First, the features of the problem are extracted based on domain knowledge, then, the problem-solving rules are evolved by gene expression programming. The simulation results reflect that the evolutionary rule completely surpasses the three types of heuristic rules with adaptive mechanisms and achieves a solution effect close to meta-heuristic algorithms with a reasonably fast solving speed. [ABSTRACT FROM AUTHOR]

This paper presents a new anti-saturation strategy to avoid external singularity, improve reliability, and fast maneuvers of a satellite by combining the novel three-dimensional magnetically suspended wheel (3-D MSW) actuator and magnetorquer. The MSW is the preferred actuator for agile maneuvering compared to the traditional control moment gyro due to frictionlessness, low vibration, and long lifetime. The anti-saturation strategy includes 3-D MSW arrangement with pyramid configuration and three orthogonal magnetorquers. A steering law is designed to distribute control torque between actuators by calculating command tilt angles of the 3-D MSW and magnetic dipoles of the magnetorquer. A nonlinear disturbance observer backstepping sliding mode controller is designed to control the rotor shaft of 3-D MSW for agile maneuvers and desaturate it with the magnetorquer despite high-frequency disturbances. Finally, simulation results of attitude control based on anti-saturation hybrid actuators demonstrate the effectiveness and accuracy of agile maneuvers. Compared with usual steering laws, simulation outcomes confirm the proposed method and desaturate the 3-D MSW system when it experiences a maximum workspace and does not have extra angular momentum. [ABSTRACT FROM AUTHOR]

The agile Earth observation satellite (AEOS) is rapidly becoming the leading platform in Earth observation missions, as it implements attitude maneuvers and remote sensing simultaneously. However, present methods limit not only its remote sensing coverage to a small area during attitude maneuvering but also its operation to only certain orbit shapes. This paper proposes a new method, namely envelope curves hierarchical overlapping (ECHO), for the target area coverage analysis of an AEOS that implements attitude maneuvers during its mission. This method involves two stages. In the preparation stage, the satellite's instantaneous access area (IAA) is defined and analytically determined by solving the spatial equations of an oblate Earth and the sensor's view field. Then, the coverage belt of an AEOS is delineated by the envelope curves of a set of IAAs. In the manipulation stage, the coverage problem of a target area is solved by iteratively using the polygon clipping technique and hierarchically taking the intersection parts between the coverage belt and the target area. Numerical simulations demonstrate the practicability and high accuracy of the proposed method. • The coverage belt method is proposed to avoid traditional grid-point technique for area coverage. • Suitable for arbitrarily shaped target areas, all orbital types, multiple types of fields of view (FOV). • Attitude maneuver paths and WGS84 oblate Earth model are considered. • The multiple-time coverage problem is investigated and the polygon clipping technique is introduced to solve the problem. [ABSTRACT FROM AUTHOR]

The overall problem of scheduling and planning in space-borne observations has always been a focused research to enhance the efficiency of agile optical satellites. However, few studies have been conducted on specific problems about time delay integration (TDI) imaging missions. In this article, a novel framework is proposed to solve the coupling scheduling and planning problems of a TDI imaging mission with multiple target strips, in which the primary objective is the average imaging resolution, and the secondary objective is the energy consumption evaluated by torque integrals. The directional reversals in push-scan imaging and TDI accumulating are considered for the first time. With the combined efforts of geometric approximations, dynamic estimations, and neural network fitting, the original problem, which is a mixed-integer nonlinear programming, is split into a series of parameter optimization problems and solved by conventional methods. Thus, details of both the scheduling and planning are studied independently without the loss of the information provided by each other. Extensive numerical simulations, including extreme scenarios with high density and large-scale clusters, indicate that the decoupled framework is reliable in generating optimized profiles for arbitrary TDI imaging missions. [ABSTRACT FROM AUTHOR]

We present a comparison study of state-of-the-art classical optimization methods to a D-Wave 2000Q quantum annealer for the scheduling of agile Earth observation satellites. The problem is to acquire high-value images while obeying the attitude maneuvering constraint of the satellite. In order to investigate close to real-world problems, we created benchmark problems by simulating realistic scenarios. Our results show that a tuned quantum annealing approach can run faster when used to find the optimal solution than a classical exact solver for some of the problem instances. Moreover, we find that the solution quality of the quantum annealer is comparable to the heuristic method used operationally for small problem instances, but degrades rapidly due to the limited precision of the quantum annealer. [ABSTRACT FROM AUTHOR]

In recent years, on-orbit constellations providing global communication and observation services have attracted widespread attention for economic and military interests. Thus, the design of satellite constellations has become a popular topic, which is mainly approached using different optimization methods. However, there are still some drawbacks to traditional methods, such as poor convergence and long computation time, which usually limit engineering applications. In this paper, a novel optimization method, the hybrid-resampling particle swarm optimization (HRPSO) algorithm, is proposed that provide higher efficiency for constellation design. The simulation results showed that the HRPSO algorithm is more efficient than the standard particle swarm optimization (PSO) algorithm and other improved resampling particle swarm optimization (RPSO) algorithms. Therefore, the HRPSO algorithm is expected to be a practical choice for constellation design. • Different types of sensors are considered, including complex cone and rectangular fields. • The attitude maneuver of the sensor is considered. • Different coverage performance indices are considered, including single- or double-fold coverage. • A novel and efficient HRPSO algorithm is proposed. [ABSTRACT FROM AUTHOR]

We present in this work the third catalog of terrestrial gamma‐ray flashes (TGFs) by the AGILE mission and the new search algorithm that was developed to produce it. We firstly introduce the new selection criteria, designed from the characteristics of WWLLN‐identified TGFs, and then applied on all data from March 2015 to September 2018. Association with sferics was performed by an independent search, described in a companion paper by Lindanger et al. (2020, https://doi.org/10.1029/2019JD031985). This search showed that many TGFs were not recognized by the existing selection algorithm, hence the need for this work. Several new selection criteria were tested and are compared in this paper. We then present the chosen selection criteria and the obtained sample, which includes 2,780 events and represents the most extensive TGF catalog available for the equatorial regions. Finally, we discuss the characteristics of this sample, including geographic distribution, intensity and duration, and seasonal variations. Key Points: A new set of selection criteria for AGILE TGFs is designed based on a lightning‐associated TGF sampleA sample of 2,780 events detected by AGILE over a 3‐year period is presented, the largest sample to date across the equatorGeographical, local time, and seasonal variability of the sample is discussed [ABSTRACT FROM AUTHOR]

We present a complete and systematic search for terrestrial gamma‐ray flashes (TGFs), detected by AGILE, that are associated with radio sferics detected by the World Wide Lightning Location Network (WWLLN) in the period February 2009 to September 2018. The search algorithms and characteristics of these new TGFs will be presented and discussed. The number of WWLLN identified (WI) TGFs shows that previous TGF selection criteria needs to be reviewed as they do not identify all the WI TGFs in the data set. In this analysis we confirm with an independent data set that WI TGFs tend to have shorter time duration than TGFs without a WWLLN match. TGFs occurs more often on coastal and ocean regions compared to the distribution of lightning activity. Several multipulse TGFs were identified and their WWLLN match are always associated with the last gamma‐ray pulse. We also present the first Terrestrial Electron Beam detected by AGILE. This data set together with the TGF sample identified by selection criteria (companion paper Maiorana et al., 2020) constitute the 3rd AGILE TGF catalog. Key Points: A sample of 592 AGILE detected TGFs associated to lightning sferics is presentedTGF duration, geographic dependence of the TGF/lightning ratio, and multipulse TGFs are discussedThe first Terrestrial Electron Beam detected by AGILE is presented [ABSTRACT FROM AUTHOR]

In the work reported in this paper, a lost-in-space star pattern identification algorithm for agile spacecraft was studied. Generally, the operation of a star tracker is known to exhibit serious degradation or even failure during fast attitude maneuvers. While tracking methods are widely used solutions to handle the dynamic conditions, they require prior information about the initial orientation. Therefore, the tracking methods may not be adequate for autonomy of attitude and control systems. In this paper a novel autonomous identification method for dynamic conditions is proposed. Additional constraints are taken into account that can significantly decrease the number of stars imaged and the centroid accuracy. A strategy combining two existing classes for star pattern identification is proposed. The new approach is intended to provide a unique way to determine the identity of stars that promises robustness against noise and rapid identification. Moreover, representative algorithms implemented in actual space applications were utilized as counterparts to analyze the performance of the proposed method in various scenarios. Numerical simulations show that the proposed method is not only highly robust against positional noise and false stars, but also guarantees fast run-time, which is appropriate for high-speed applications. [ABSTRACT FROM AUTHOR]

Satellite observation schedule is investigated in this paper. A mission planning algorithm of task clustering is proposed to improve the observation efficiency of agile satellite. The newly developed method can make the satellite observe more targets and therefore save observation resources. First, for the densely distributed target points, a preprocessing scheme based on task clustering is proposed. The target points are clustered according to the distance condition. Second, the local observation path is generated by Tabu algorithm in the inner layer of cluster regions. Third, considering the scatter and cluster sets, the global observation path is obtained by adopting Tabu algorithm in the outer layer. Simulation results show that the algorithm can effectively reduce the task planning time of large-scale point targets while ensuring the optimal solution quality. [ABSTRACT FROM AUTHOR]

Terrestrial gamma ray flashes (TGFs) are very short bursts of gamma radiation associated to thunderstorm activity and are the manifestation of the highest‐energy natural particle acceleration phenomena occurring on Earth. Photon energies up to several tens of megaelectronvolts are expected, but the actual upper limit and high‐energy spectral shape are still open questions. Results published in 2011 by the AGILE team proposed a high‐energy component in TGF spectra extended up to ≈100 MeV, which is difficult to reconcile with the predictions from the Relativistic Runaway Electron Avalanche (RREA) mechanism at the basis of many TGF production models. Here we present a new set of TGFs detected by the AGILE satellite and associated to lightning measurements capable to solve this controversy. Detailed end‐to‐end Monte Carlo simulations and an improved understanding of the instrument performance under high‐flux conditions show that it is possible to explain the observed high‐energy counts by a standard RREA spectrum at the source, provided that the TGF is sufficiently bright and short. We investigate the possibility that single high‐energy counts may be the signature of a fine‐pulsed time structure of TGFs on time scales ≈4 μs, but we find no clear evidence for this. The presented data set and modeling results allow also for explaining the observed TGF distribution in the (Fluence × duration) parameter space and suggest that the AGILE TGF detection rate can almost be doubled. Key Points: TGFs detected by AGILE with counts energy larger than 40 MeV are compatible with RREAData show no evidence of a fine time structure of TGFs on microsecond time scale.TGFs simultaneous to lightning suggest that the AGILE TGF sample can be significantly increased [ABSTRACT FROM AUTHOR]

This paper investigates the mission planning problem of an agile satellite equipped with a two-dimensional antenna pointing mechanism. Multiple relay satellites and ground stations are included into the scenario to ensure the real-time data downlink. Therefore, to achieve the optimal real-time data transmission performance, two optimization modes are proposed in this paper to generate the slew path for both the satellite base and the antenna pointing mechanism. First, a baseline attitude coordinate system is introduced to efficiently handle the constraint of the problem. Second, the decoupled method is presented based on the two-level optimization strategy, which combines the genetic algorithm and the artificial potential method. Third, the dynamic programming concept is introduced to generate the optimal slew path by multi-body control approach. Simulation results show that the proposed algorithms can properly circumvent the complex mission planning problem, and that the maximum real-time data downlink can be established while ensuring the complete coverage of the target area. [ABSTRACT FROM AUTHOR]

Highlights • We study the problem of agile satellite scheduling with real-time cloud coverage. • A hierarchical scheduling model is established. • A hierarchical scheduling algorithm based on the ant colony algorithm is proposed. • The influence of environmental changes is well-mitigated by the proposed method. • The proposed method can greatly reduce the CPU time and increase the total profit. Abstract The imaging processes of optical satellites can be easily affected by unexpected environmental changes, such as changes in cloud coverage. Given the difficulty to predict environmental uncertainties, traditional offline scheduling methods need a follow-up re-scheduling process that responds to real-time environmental information. This repetitive scheduling processes make the offline fine scheduling process a waste of computational resources. Additionally, the offline scheduling method is quite complex owing to its lack of a hierarchy mechanism. To solve these problems, we propose a hierarchical scheduling method for the real-time scheduling problem. This method divides the scheduling process into three steps: pre-assignment, rough scheduling, and fine scheduling. A hierarchical scheduling algorithm based on ant colony algorithm is proposed. Tests with 36 scenarios show that the calculation time is efficiently reduced with this new mechanism. With this consideration of the dynamic environment, the re-scheduling process becomes unnecessary, meaning the wasting of computational resources is avoided and the solution profit is improved. [ABSTRACT FROM AUTHOR]

Abstract In recent years, the application of imaging satellites has entered a completely new stage, with the new demands such as rapid response to emergency events, observation of large-scale regional targets and multivariate data fusion, the multi-autonomous satellite constellation has been proposed. This paper first designs the structure of multi-autonomous satellite constellation, and a centralized-distributed structure is proposed. This structure could improve the dynamic response capacity of the whole constellation. Then, this paper adds adapted filtering mechanism to single autonomous satellite online scheduling algorithm to enhance its performance. This article also pays more attention on task allocation strategies of the master satellite in constellation, and ten different task allocation strategies based on five dimensions are analyzed by simulation experiments. At last, this paper extracts several characteristic features of the regular observation targets and designs a selector based on support vector machine (SVM). This selector could select an appropriate strategy according to the features of each experiment scenario. [ABSTRACT FROM AUTHOR]

Highlights • A realistic repeating ground track orbit of agile satellite is investigated. • The variation of all feasible solutions over orbital parameters is analyzed. • A multi-objective optimization technique for optimal orbit design is proposed. • Results demonstrate the validity and effectiveness of the proposed technique. Abstract Satellite orbit design is a fundamental and important task during the mission analysis and the agile satellite design. In this paper we first investigate the design of a more realistic repeating ground track orbit in an accurate geopotential model of Earth. Furthermore, by considering the view field of the resource equipped on an agile satellite, we calculate the variation of the orbital altitude, the tilt angle, and the off-nadir resolution with the desired revisit time. Additionally, we analyze the distribution of all feasible solutions. In considering the spatial resolution and temporal resolution simultaneously, we propose a multi-objective optimization technique for optimal feasible orbits generation. Finally, through various case studies, the application of multi-objective optimization in orbit design of agile satellite is successfully demonstrated. Results also illustrate the validity and effectiveness of the proposed technique. [ABSTRACT FROM AUTHOR]

The Agile Satellite Attitude Control System Simulator (ASACSS) is a laboratory system designed for the purpose of developing and testing attitude control algorithms in a low-risk, low-cost environment. In this paper, the design and development of the ASACSS is described, including hardware and software. There are many papers that present a new mathematical technique or prove a new theory, but this study presents the design and development of a new experimental system. This simulator consists of four main components: 1) power supply system 2) on-board control system 3) supporting equipments and 4) monitoring computer. On-board control system includes a industrial computer, four single gimbal control moment gyros and a sensor for attitude determination. Supporting equipments include a platform for installing simulator subsystems, a semi-spherical air bearing and a pedestal. A high-speed wireless LAN connection enables remote command initiation, monitoring and data collection for post-experimental analysis. In this paper, The design and construction process of the simulator are described. More over some experimental results presented from the application of a simple PID attitude controller on the spacecraft simulator. Finally, experimental results are compared with those obtained from simulation.

This paper investigates a new Agile Earth Observation Satellite (AEOS) mission planning algorithm. This new developed algorithm is based on Modified Mixed-Integer Linear Programming (MILP) approach, which takes the minimum slew angle and highest priority criterion. The key point of the paper lies in that the planning process is treated as a Dynamical Combinatorial Optimization (DCO) problem due to the time-varying constraint and the requirement of the problem. The design of the new algorithm is also to meet the real-time requirement of onboard mission planning. The mathematical formulation of the problem is modified to satisfy the demand of the LP solver, and a newly developed dynamic database is used to simulate the constantly changing satellite-target relative position with limited observation windows. The new mission planning model is solved by the LP method to test its reliability. Another solution with Generic Algorithm (GA) is also given to check the result. The calculation time of these two methods is compared to show that the LP approach has a better compatibility with the onboard mission planning requirement. [ABSTRACT FROM AUTHOR]

Copyright of Acta Automatica Sinica is the property of Chinese Academy of Sciences, Institute of Automation and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Telecommunication Engineering is the property of Telecommunication Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Telecommunication Engineering is the property of Telecommunication Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This paper investigates the integrated attitude control algorithm and steering law for agile small satellites configured with control moment gyroscope (CMG). Firstly, considering the deterioration over time of the typical pyramid-shaped CMG cluster with 4 single-gimbal CMGs, the CMG dynamic model was built. Then, based on the adaptive control theory, the integrated attitude control algorithm and steering law were designed, and the asymptotic stability of the closed-loop system was proved via Lyapunov analysis. Finally, mathematical simulation has validated the solution in a satellite closed-loop attitude control system, and the simulation shows that the solution is simple and effective for attitude maneuver control of agile small satellites. [ABSTRACT FROM AUTHOR]

The problem of managing an Agile Earth Observing Satellite consists of selecting and scheduling a subset of photographs among a set of candidate ones that satisfy imperative constraints and maximize a gain function. We propose a tabu search algorithm to solve this NP-hard problem. This one is formulated as a constrained optimization problem and involves stereoscopic and time window visibility constraints; and a convex evaluation function that increases its hardness. To obtain a wide-ranging and an efficient exploration of the search space, we sample it by consistent and saturated configurations. Our algorithm is also hybridized with a systematic search that uses partial enumerations. To increase the solution quality, we introduce and solve a secondary problem; the minimization of the sum of the transition durations between the acquisitions. Upper bounds are also calculated by a dynamic programming algorithm on a relaxed problem. The obtained results show the efficiency of our approach. [ABSTRACT FROM AUTHOR]

• A control scheme of the camera's vibration isolator with time-varying stiffness is proposed. • A systematic methodology to optimize the vibration isolator stiffness control is presented. • Reinforcement learning optimization can learn a general variable stiffness policy. • This policy can satisfy the conflictive requirements on both image quality and efficiency. With the increasing demand for high-resolution remote sensing images, both the image quality and the image acquisition efficiency should be concerned for an agile remote sensing satellite. Effective vibration isolation is essential to ensure image quality since the attitude vibration could cause line-of-sight jitter and image blur. To improve the image acquisition efficiency, the capability of performing agile attitude maneuvers is another indispensable requirement of the satellite. These requirements mean an extreme level of attitude stability and vibration isolation from onboard disturbances. However, they have conflicting demands on the connection stiffness between the camera and the satellite bus, i.e., high on the former but low on the latter. By varying its stiffness, this paper develops a dynamic stiffness control scheme for the camera's vibration isolator, whose variable stiffness policies are learned from a reinforcement learning methodology with a feature of low online complexity. The proposed policy optimization algorithm for stiffness control has such merits as simultaneously optimizing both vibration isolation and attitude stabilization. Furthermore, it possesses an adaptive ability to deal with pervasive onboard disturbances. Simulation experiments demonstrate that the learned variable stiffness policies could strike a favorable balance between the agility and the image quality. [ABSTRACT FROM AUTHOR]

This article concerns the problem of managing the new generation of Agile Earth Observing Satellites (AEOS). This kind of satellites is presently studied by the French Centre National d'E´tudes Spatiales (PLEIADES project). The mission of an Earth Observing Satellite is to acquire images of specified areas on the Earth surface, in response to observation requests from customers. Whereas non-agile satellites such as SPOT5 have only one degree of freedom for acquiring images, the new generation satellites have three, giving opportunities for a more efficient use of the satellite imaging capabilities. Counterwise to this advantage, the selection and scheduling of observations becomes significantly more difficult, due to the larger search space for potential solutions. Hence, selecting and scheduling observations of agile satellites is a highly combinatorial problem. This article sets out the overall problem and analyses its difficulties. Then it presents different methods which have been investigated in order to solve a simplified version of the complete problem: a greedy algorithm, a dynamic programming algorithm, a constraint programming approach and a local search method. [Copyright &y& Elsevier]

Drift angle is a major factor which limits the quality of remote sensing images. This paper presents an attitude scheduling algorithm aimed to eliminate drift angle and its verification for dynamic imaging of agile satellites. First, the attitude scheduling algorithm was derived intuitively based on two dynamic imaging criterions. Then a drift angle model based on differentiation was described for empirical verification of the proposed algorithm. For dynamic imaging mode, satellite manoeuvre velocity was taken into consideration in drift angle model. Finally, dynamic imaging simulation along a inclined target intersecting with sub-satellite track was performed based on ellipsoid model of globe. Comparison was carried out between the proposed approach and conventional compensatory approach, the results of which demonstrated the effectiveness and accuracy of the proposed approach in eliminating the drift angle. [ABSTRACT FROM AUTHOR]