C. Karlgaard, M. Schoenenberger, John W. Van Norman
{"title":"Base Drag Model Derived from Mars 2020 Backshell Pressure Measurements","authors":"C. Karlgaard, M. Schoenenberger, John W. Van Norman","doi":"10.2514/1.a35774","DOIUrl":"https://doi.org/10.2514/1.a35774","url":null,"abstract":"","PeriodicalId":50048,"journal":{"name":"Journal of Spacecraft and Rockets","volume":"1 1","pages":""},"PeriodicalIF":1.6,"publicationDate":"2023-08-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"69273065","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Contactless space debris transportation systems based on the use of an ion beam are a promising direction among active space debris removal systems. The magnitude of the force generated by the ion beam depends on the orientation of the space debris object in the ion beam created by an active spacecraft. During the ion transport process, the space debris object can oscillate or rotate, which leads to a change in the generated force. The aim of this study is to develop an algorithm for determining the attitude motion mode of space debris, which is most favorable for its contactless transportation. The time-averaged generated ion force is used as the performance index. A simplified system of equations describing the spatial motion of a cylindrical axisymmetric object in a circular orbit is obtained. A generalized energy integral is found. An algorithm for determining the most favorable angular motion mode of a space debris object is developed. A numerical study of a cylindrical space debris object attitude motion under the action of an ion torque is carried out. The favorable attitude motion mode is determined, and the average forces in the most favorable and unfavorable modes are compared.
{"title":"Determining the Effective Space Debris Attitude Motion Modes for Ion-Beam-Assisted Transportation","authors":"A. Ledkov","doi":"10.2514/1.a35735","DOIUrl":"https://doi.org/10.2514/1.a35735","url":null,"abstract":"Contactless space debris transportation systems based on the use of an ion beam are a promising direction among active space debris removal systems. The magnitude of the force generated by the ion beam depends on the orientation of the space debris object in the ion beam created by an active spacecraft. During the ion transport process, the space debris object can oscillate or rotate, which leads to a change in the generated force. The aim of this study is to develop an algorithm for determining the attitude motion mode of space debris, which is most favorable for its contactless transportation. The time-averaged generated ion force is used as the performance index. A simplified system of equations describing the spatial motion of a cylindrical axisymmetric object in a circular orbit is obtained. A generalized energy integral is found. An algorithm for determining the most favorable angular motion mode of a space debris object is developed. A numerical study of a cylindrical space debris object attitude motion under the action of an ion torque is carried out. The favorable attitude motion mode is determined, and the average forces in the most favorable and unfavorable modes are compared.","PeriodicalId":50048,"journal":{"name":"Journal of Spacecraft and Rockets","volume":" ","pages":""},"PeriodicalIF":1.6,"publicationDate":"2023-08-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41501685","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A direct adaptive scheme is presented as an alternative approach for minimum-fuel low-thrust trajectory design in non-coplanar orbit transfers using fitness landscape analysis (FLA). The spacecraft dynamics is modeled with respect to modified equinoctial elements by considering [Formula: see text] orbital perturbations. Taking into account the timings of thrust arcs, the discretization nodes for thrust profile, and the solution of multi-impulse orbit transfer, a constrained continuous optimization problem is formed for low-thrust orbital maneuvers. An adaptive method within the framework of the estimation of distribution algorithms (EDA) is proposed, which aims at conserving the feasibility of the solutions within the search process. Several problem identifiers for low-thrust trajectory optimization are introduced, and the complexity of the solution domain is analyzed by evaluating the landscape feature of the search space via FLA. Two adaptive operators are proposed, which control the search process based on the need for exploration and exploitation of the search domain to achieve optimal transfers. The adaptive operators are implemented in the presented EDA and several perturbed and nonperturbed orbit transfer problems are solved. The results confirm the effectiveness and reliability of the proposed approach in finding optimal low-thrust transfer trajectories.
{"title":"Adaptive Estimation of Distribution Algorithms for Low-Thrust Trajectory Optimization","authors":"A. Shirazi","doi":"10.2514/1.a35570","DOIUrl":"https://doi.org/10.2514/1.a35570","url":null,"abstract":"A direct adaptive scheme is presented as an alternative approach for minimum-fuel low-thrust trajectory design in non-coplanar orbit transfers using fitness landscape analysis (FLA). The spacecraft dynamics is modeled with respect to modified equinoctial elements by considering [Formula: see text] orbital perturbations. Taking into account the timings of thrust arcs, the discretization nodes for thrust profile, and the solution of multi-impulse orbit transfer, a constrained continuous optimization problem is formed for low-thrust orbital maneuvers. An adaptive method within the framework of the estimation of distribution algorithms (EDA) is proposed, which aims at conserving the feasibility of the solutions within the search process. Several problem identifiers for low-thrust trajectory optimization are introduced, and the complexity of the solution domain is analyzed by evaluating the landscape feature of the search space via FLA. Two adaptive operators are proposed, which control the search process based on the need for exploration and exploitation of the search domain to achieve optimal transfers. The adaptive operators are implemented in the presented EDA and several perturbed and nonperturbed orbit transfer problems are solved. The results confirm the effectiveness and reliability of the proposed approach in finding optimal low-thrust transfer trajectories.","PeriodicalId":50048,"journal":{"name":"Journal of Spacecraft and Rockets","volume":" ","pages":""},"PeriodicalIF":1.6,"publicationDate":"2023-08-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44656118","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The focus of this research is the optimization of impulsive transfer trajectories in the presence of stochastic effects. A trajectory design method is introduced that accounts for a normally distributed initial state dispersion and minimizes the sum of nominal impulsive [Formula: see text] plus [Formula: see text] trajectory correction maneuver (TCM) magnitude. Four main problems are presented. First, a deterministic optimal trajectory is developed; in the coplanar cases, the optimal solution is Hohmann transfer. For the second problem, an initial state dispersion and a target position dispersion constraint are introduced. It is shown to be possible to modify the nominal two-impulse trajectory to satisfy the dispersion constraint. In the third problem, a TCM is performed at the optimal point along the deterministic optimal trajectory, resulting in a more efficient method to influence the target position dispersion. Problem 4 is the development of a robust trajectory, where the nominal impulsive maneuvers and [Formula: see text] TCM [Formula: see text] are simultaneously optimized. The result is a different nominal trajectory and TCM that is less expensive than the total cost of problem 3. The optimal TCM is rapidly computed along each nominal trajectory using the numerically propagated state transition matrix history as a step inside the optimization algorithm.
{"title":"Optimal Robust Two-Body Trajectory Design with Corrective Maneuvers","authors":"Scott Kelly, D. Geller","doi":"10.2514/1.a35725","DOIUrl":"https://doi.org/10.2514/1.a35725","url":null,"abstract":"The focus of this research is the optimization of impulsive transfer trajectories in the presence of stochastic effects. A trajectory design method is introduced that accounts for a normally distributed initial state dispersion and minimizes the sum of nominal impulsive [Formula: see text] plus [Formula: see text] trajectory correction maneuver (TCM) magnitude. Four main problems are presented. First, a deterministic optimal trajectory is developed; in the coplanar cases, the optimal solution is Hohmann transfer. For the second problem, an initial state dispersion and a target position dispersion constraint are introduced. It is shown to be possible to modify the nominal two-impulse trajectory to satisfy the dispersion constraint. In the third problem, a TCM is performed at the optimal point along the deterministic optimal trajectory, resulting in a more efficient method to influence the target position dispersion. Problem 4 is the development of a robust trajectory, where the nominal impulsive maneuvers and [Formula: see text] TCM [Formula: see text] are simultaneously optimized. The result is a different nominal trajectory and TCM that is less expensive than the total cost of problem 3. The optimal TCM is rapidly computed along each nominal trajectory using the numerically propagated state transition matrix history as a step inside the optimization algorithm.","PeriodicalId":50048,"journal":{"name":"Journal of Spacecraft and Rockets","volume":" ","pages":""},"PeriodicalIF":1.6,"publicationDate":"2023-08-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42154579","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Srujan K. Naspoori, A. Appar, Rakesh Kumar, Kishore K. Kammara
In the present work, nonreactive gas–surface interactions between nitrogen molecules and a [Formula: see text]-cristobalite surface are analyzed using the molecular dynamics framework. A sampling method is employed to perform trajectory calculations, and the tangential momentum accommodation coefficient is computed. The credibility of the reactive force field potential to model [Formula: see text] cristobalite is investigated, and the effect of the surface and gas temperatures on the tangential momentum accommodation coefficient is studied in detail. The obtained value of the tangential momentum accommodation coefficient (from molecular dynamics analysis) is used as an input parameter in the Maxwell gas–surface interaction model using the direct simulation Monte Carlo method to investigate the surface heat flux on the nose region of a model reentry vehicle. The computed heat-flux results obtained using a molecular-dynamics-derived accommodation coefficient are found to be in excellent agreement with the experimental data.
{"title":"Molecular Dynamics Study of Gas–Surface Interactions on β-Cristobalite Surface","authors":"Srujan K. Naspoori, A. Appar, Rakesh Kumar, Kishore K. Kammara","doi":"10.2514/1.a35596","DOIUrl":"https://doi.org/10.2514/1.a35596","url":null,"abstract":"In the present work, nonreactive gas–surface interactions between nitrogen molecules and a [Formula: see text]-cristobalite surface are analyzed using the molecular dynamics framework. A sampling method is employed to perform trajectory calculations, and the tangential momentum accommodation coefficient is computed. The credibility of the reactive force field potential to model [Formula: see text] cristobalite is investigated, and the effect of the surface and gas temperatures on the tangential momentum accommodation coefficient is studied in detail. The obtained value of the tangential momentum accommodation coefficient (from molecular dynamics analysis) is used as an input parameter in the Maxwell gas–surface interaction model using the direct simulation Monte Carlo method to investigate the surface heat flux on the nose region of a model reentry vehicle. The computed heat-flux results obtained using a molecular-dynamics-derived accommodation coefficient are found to be in excellent agreement with the experimental data.","PeriodicalId":50048,"journal":{"name":"Journal of Spacecraft and Rockets","volume":" ","pages":""},"PeriodicalIF":1.6,"publicationDate":"2023-08-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44152063","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Sabin V. Anton, Claudio Rapisarda, Oliver J. Ross, E. Mooij
Parachute/flow interaction is dominant in evaluating a decelerator’s performance. Such interaction is characterized by nonlinear deformations and complex flow phenomena. While testing methods are available to investigate parachute performance, these are often costly and nonrepresentative of the desired flight conditions. To address the need for an accessible technique capable of modeling parachutes at the early design stages, this paper proposes a robust fluid/structure interaction methodology for three-dimensional subsonic simulations. This is attained by replacing the linear springs in Provot’s equation with polynomial expressions whose coefficients are fitted to tensile test data. The nonlinear cloth algorithm is coupled with the rhoPorousSimpleFoam solver in the open-source OpenFOAM toolbox, thereby establishing an iterative process that reaches steady-state convergence in at most six iterations. The transient response is obtained from the average distributed load of the steady-state pressure field and an inertial damping contribution. The simulations are performed for two disk-gap-band parachutes and a ringsail parachute over a velocity range of ring sail 5–30 m/s. The results are compared to the experimental data measured in the Open Jet Facility of Delft University of Technology, yielding errors below 5% for the steady-state cases and overestimations in peak loads of 4.4–12.4% for the transient simulations.
{"title":"Development and Validation of a Nonlinear Fabric Model for Subsonic Parachute Aerodynamics","authors":"Sabin V. Anton, Claudio Rapisarda, Oliver J. Ross, E. Mooij","doi":"10.2514/1.a35583","DOIUrl":"https://doi.org/10.2514/1.a35583","url":null,"abstract":"Parachute/flow interaction is dominant in evaluating a decelerator’s performance. Such interaction is characterized by nonlinear deformations and complex flow phenomena. While testing methods are available to investigate parachute performance, these are often costly and nonrepresentative of the desired flight conditions. To address the need for an accessible technique capable of modeling parachutes at the early design stages, this paper proposes a robust fluid/structure interaction methodology for three-dimensional subsonic simulations. This is attained by replacing the linear springs in Provot’s equation with polynomial expressions whose coefficients are fitted to tensile test data. The nonlinear cloth algorithm is coupled with the rhoPorousSimpleFoam solver in the open-source OpenFOAM toolbox, thereby establishing an iterative process that reaches steady-state convergence in at most six iterations. The transient response is obtained from the average distributed load of the steady-state pressure field and an inertial damping contribution. The simulations are performed for two disk-gap-band parachutes and a ringsail parachute over a velocity range of ring sail 5–30 m/s. The results are compared to the experimental data measured in the Open Jet Facility of Delft University of Technology, yielding errors below 5% for the steady-state cases and overestimations in peak loads of 4.4–12.4% for the transient simulations.","PeriodicalId":50048,"journal":{"name":"Journal of Spacecraft and Rockets","volume":" ","pages":""},"PeriodicalIF":1.6,"publicationDate":"2023-07-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45633762","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A group of satellites, with either homogeneous or heterogeneous orbital characteristics and/or hardware specifications, can undertake a reconfiguration process due to variations in operations pertaining to Earth observation missions. This paper investigates the problem of optimizing a satellite constellation reconfiguration process against two competing mission objectives: 1) the maximization of the total coverage reward, and 2) the minimization of the total cost of the transfer. The decision variables for the reconfiguration process include the design of the new configuration and the assignment of satellites from one configuration to another. We present a novel biobjective integer linear programming formulation that combines constellation design and transfer problems. The formulation lends itself to the use of generic mixed-integer linear programming (MILP) methods such as the branch-and-bound algorithm for the computation of provably optimal solutions; however, these approaches become computationally prohibitive even for moderately sized instances. In response to this challenge, this paper proposes a Lagrangian relaxation-based heuristic method that leverages the assignment problem structure embedded in the problem. The results from the computational experiments attest to the near-optimality of the Lagrangian heuristic solutions and a significant improvement in the computational runtime as compared to a commercial MILP solver.
{"title":"Regional Constellation Reconfiguration Problem: Integer Linear Programming Formulation and Lagrangian Heuristic Method","authors":"Hang Woon Lee, Koki Ho","doi":"10.2514/1.a35685","DOIUrl":"https://doi.org/10.2514/1.a35685","url":null,"abstract":"A group of satellites, with either homogeneous or heterogeneous orbital characteristics and/or hardware specifications, can undertake a reconfiguration process due to variations in operations pertaining to Earth observation missions. This paper investigates the problem of optimizing a satellite constellation reconfiguration process against two competing mission objectives: 1) the maximization of the total coverage reward, and 2) the minimization of the total cost of the transfer. The decision variables for the reconfiguration process include the design of the new configuration and the assignment of satellites from one configuration to another. We present a novel biobjective integer linear programming formulation that combines constellation design and transfer problems. The formulation lends itself to the use of generic mixed-integer linear programming (MILP) methods such as the branch-and-bound algorithm for the computation of provably optimal solutions; however, these approaches become computationally prohibitive even for moderately sized instances. In response to this challenge, this paper proposes a Lagrangian relaxation-based heuristic method that leverages the assignment problem structure embedded in the problem. The results from the computational experiments attest to the near-optimality of the Lagrangian heuristic solutions and a significant improvement in the computational runtime as compared to a commercial MILP solver.","PeriodicalId":50048,"journal":{"name":"Journal of Spacecraft and Rockets","volume":"7 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-07-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135359402","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Vicente Lafarga, Rasa Jamshidi, G. Rodrigues, R. Seiler, C. Collette
Reaction wheels are widely used in the attitude control of spacecraft due to their capability of applying control torques, greatly reducing the propellant requirements and limiting its use to reaction wheel desaturation. However, the presence of unavoidable mechanical imperfections results in significant mechanical disturbances, being applied to the spacecraft, which can severely impact the operation of sensitive payloads. These microvibrations are broadband in nature, and therefore the effective mitigation of their effects requires a high isolation factor throughout a wide frequency range. This paper presents the development and experimental verification of a six-degree-of-freedom active isolation platform for a reaction wheel, integrating a soft suspension and active control using self-sensing actuators. A reduction in the transmitted forces of 65 dB at 270 Hz was experimentally demonstrated, while exhibiting negligible amplifications by its suspension resonance, which constitute very attractive performances.
{"title":"Multi-Degree-of-Freedom Active Isolation Platform for Microvibrations","authors":"Vicente Lafarga, Rasa Jamshidi, G. Rodrigues, R. Seiler, C. Collette","doi":"10.2514/1.a35550","DOIUrl":"https://doi.org/10.2514/1.a35550","url":null,"abstract":"Reaction wheels are widely used in the attitude control of spacecraft due to their capability of applying control torques, greatly reducing the propellant requirements and limiting its use to reaction wheel desaturation. However, the presence of unavoidable mechanical imperfections results in significant mechanical disturbances, being applied to the spacecraft, which can severely impact the operation of sensitive payloads. These microvibrations are broadband in nature, and therefore the effective mitigation of their effects requires a high isolation factor throughout a wide frequency range. This paper presents the development and experimental verification of a six-degree-of-freedom active isolation platform for a reaction wheel, integrating a soft suspension and active control using self-sensing actuators. A reduction in the transmitted forces of 65 dB at 270 Hz was experimentally demonstrated, while exhibiting negligible amplifications by its suspension resonance, which constitute very attractive performances.","PeriodicalId":50048,"journal":{"name":"Journal of Spacecraft and Rockets","volume":" ","pages":""},"PeriodicalIF":1.6,"publicationDate":"2023-07-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48926599","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Conventional hypersonic transition prediction relies upon the highly empirical [Formula: see text] method, which is predicated on theoretical approximations of relative disturbance growth. This does not account for the receptivity mechanism and the high degree of variability present in experimental wind-tunnel conditions, which itself leads to high degrees of variability in transition [Formula: see text] factors. The amplitude method, which better approximates the broadband nature of boundary-layer disturbances, was previously proposed to account for the effects of receptivity. In this study, high-fidelity simulated second-mode receptivity data for two blunt cones at Mach 10 to broadband disturbances are applied to an iterative approximation of the amplitude method tuned for second-mode dominated flows. The studied geometries consist of 9.525- and 5.080-mm-nose-radius 7 deg half-angle straight cones based on experimental cases from Arnold Engineering Development Center’s wind tunnel 9. Amplitude method predictions show improvement over the accuracy of [Formula: see text] estimates using standard threshold [Formula: see text] factors. In particular, the less blunt 5.080 mm cone demonstrates the best agreement due to its stronger second-mode response. The results of this work provide a preliminary framework for applying high-fidelity receptivity simulations to the amplitude method for transition prediction in hypersonic flows.
{"title":"Application of Broadband Receptivity Data to the Amplitude Method for Transition Prediction","authors":"Simon He, X. Zhong","doi":"10.2514/1.a35742","DOIUrl":"https://doi.org/10.2514/1.a35742","url":null,"abstract":"Conventional hypersonic transition prediction relies upon the highly empirical [Formula: see text] method, which is predicated on theoretical approximations of relative disturbance growth. This does not account for the receptivity mechanism and the high degree of variability present in experimental wind-tunnel conditions, which itself leads to high degrees of variability in transition [Formula: see text] factors. The amplitude method, which better approximates the broadband nature of boundary-layer disturbances, was previously proposed to account for the effects of receptivity. In this study, high-fidelity simulated second-mode receptivity data for two blunt cones at Mach 10 to broadband disturbances are applied to an iterative approximation of the amplitude method tuned for second-mode dominated flows. The studied geometries consist of 9.525- and 5.080-mm-nose-radius 7 deg half-angle straight cones based on experimental cases from Arnold Engineering Development Center’s wind tunnel 9. Amplitude method predictions show improvement over the accuracy of [Formula: see text] estimates using standard threshold [Formula: see text] factors. In particular, the less blunt 5.080 mm cone demonstrates the best agreement due to its stronger second-mode response. The results of this work provide a preliminary framework for applying high-fidelity receptivity simulations to the amplitude method for transition prediction in hypersonic flows.","PeriodicalId":50048,"journal":{"name":"Journal of Spacecraft and Rockets","volume":" ","pages":""},"PeriodicalIF":1.6,"publicationDate":"2023-07-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46382623","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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