1,720,998 research outputs found
Attitude control and tra jectory planning of a space manipulator system using Kane's formulation
No full textOn-orbit servicing is one of the most challenging tasks of the recent space era. Space Manipulator Systems (SMS) can represent viable technological solutions for several space operations, such as in situ refueling, repairing of operating spacecraft, or debris grappling. Regardless of the specific task, SMS must approach the target object and then establish a physical connection with it using a single or more robotic arms. This work considers a space vehicle equipped with a pair of two-link robotic arms, for the purpose of efficiently designing and simulating the overall spacecraft dynamics until contact takes place. The links that compose each arm are modeled as rigid bodies, assuming a relatively slow dynamic. Instead, flexibility is introduced in the dynamical modeling of the rotary joints. The overall dynamics is investigated using Kane's methodology, which is general, highly systematic, and joins the advantages of both the Newton/Euler and the Lagrangian formulation. Both SMS and the target, assumed as noncooperative, are placed in low Earth orbit, in close proximity. Trajectory planning of the robotic arm is investigated, while considering the effect of the arm motion on the overall attitude dynamics. Precise attitude maneuvering is mandatory in order that grappling be successfully completed. To do this, a quaternion-based, globally stable attitude feedback law is designed, implemented, and tested. Actuation is demanded to an arrangement of control momentum gyroscopes. These devices are modeled with the inclusion of gyroscopic coupling effects, and are driven by means of suitable steering laws, for the purpose of pursuing the desired attitude control action. Accurate modeling of SMS, with also the inclusion of disturbances due to joint flexibility, in conjunction with the use of suitable feedback attitude control and steering laws for both the robotic arms and the actuation devices, allows obtaining the desired outputs, i.e. (i) the motor torques (for steering both the joints and the attitude devices) and (ii) the constraint actions (forces and torques). Monte Carlo analysis points out effectiveness of the control architecture proposed in this study in the challenging mission scenario of interest
Design, realization and characterization of a free-floating platform for flexible satellite control experiments
No full textExperimental verification of numerical models is a key aspect in all scientific and technological disciplines, yet space systems can be particularly hard to test on ground: in fact, a terrestrial mock-up replicating the orbital dynamics should be in a gravity-free environment. One of the most common approaches to (at least partially) realize this condition, consists in free-floating systems, in which the friction between an experimental platform and the working surface is almost completely removed. The vertical axis is still subject to gravity, and only 3 degrees of freedom (two horizontal translations and one rotation about the vertical axis) are available to replicate the orbital behavior. Our research group had been developing since 2012 a free-floating platform named PINOCCHIO (Platform Integrating Navigation and Orbital Control Capabilities Hosting Intelligent Onboard). The need to investigate with higher accuracy the attitude control problem for flexible satellites called for the design, realization and characterization of a new platform with enhanced performance. This paper describes the main components of the system, including the pressure air system, the navigation and communication system, the GNC architecture and relevant hardware. The attention is specifically on the characterization of the subsystems' performance. The physical (mass, moment of inertia), control (thrusters' torque and force) and IMU characteristics are experimentally measured with the associated uncertainty level. The accuracy of the VICON system in static and dynamic conditions is also characterized, obtaining a 100 micrometers-level resolution for external measurement of rigid and elastic displacements; this information is fundamental for performing tests of fine pointing control algorithms for flexible and agile satellites. The proposed characterization methodology and associated results could be of interest for university and industry laboratories intended to develop new free-floating platforms
ATTITUDE MANEUVERS OF A FLEXIBLE SPACECRAFT FOR SPACE DEBRIS DETECTION AND COLLISION AVOIDANCE
No full textThis work addresses the problem of trajectory and attitude maneuvering of a spacecraft equipped with two flexible solar panels, in response to an alert in two distinct operational scenarios: (a) detection of an approaching debris, and (b) collision avoidance of an impacting debris. In scenario (a) the approaching debris is assumed to be off a collision course with the satellite. As a result, the latter can track the debris, to provide supplementary observations (in addition to those given by ground stations) that allow improving the estimation of its trajectory. Instead, in scenario (b) an impact is predicted, therefore the satellite shall perform a collision avoidance maneuver. This is designed with the objective of minimizing propellant consumption, while ensuring a miss distance greater than a specified threshold value. This research considers the overall dynamics by modeling the spacecraft as a multibody structure, with the use of the Kane's method, which simplifies the process of deriving all the governing equations, while identifying their minimum number. Flexibility is introduced using a modal decomposition technique, under the assumption of small amplitude oscillations. In the two scenarios of interest, efficient strategies are introduced to rotate the solar panels, for the purpose of either maximizing their irradiation or minimizing their oscillations. Attitude maneuvers are driven by two distinct feedback control laws that enjoy quasi-global stability properties. Actuation is modeled as well, by assuming the use of a pyramidal array of four single-gimbal control momentum gyroscopes. Their steering law includes singularity avoidance, based on the singular value decomposition of the actuation matrix. Numerical simulations demonstrate that the agile attitude maneuvering strategies proposed in this study allow achieving the operational objectives in the two scenarios of interest, with limited elastic oscillations
Optimal design of a net of adaptive structures for micro-vibration control in large space mesh reflectors
No full textLarge deployable antennas are required for the advancement of space communications, Earth observation, radio astronomy and deep space exploration. The core requirements of a space antenna are high gain, high directivity and persistent accuracy, which are mainly dependent on the size of the reflector. Most contemporary space antennas have exceeded the size of launching vehicles, leading to the necessity of stowed concepts to overcome the limitation. Many structural models have been investigated by different organizations. Generally, mesh deployable reflectors are currently more mature compared to other foldable solutions and will be the topic of this paper. In-orbit disturbances affecting the deployed configuration can deteriorate the accuracy of the communications system. Perturbations originated by on board sources can be transmitted from the satellite platform to the supporting frame of the antenna. Furthermore, the structure accuracy is affected by thermal deformation and elastic vibration due to thrusters jetting. Undesired dynamic behaviour of structural components have to be predicted and counteracted. Therefore, vibration control is a key technology to correct the distortions altering the proper functioning of the system. An intelligent adaptive structure is introduced as a structure configured with distributed actuators and sensors and guided by a controller to modify the dynamic response of the system. In this paper, the supporting structure of a very large mesh reflector is described. The antenna reflector foldable membrane is supported by a deployable adaptive truss structure. A FEM formulation is adopted to assemble the frame and it is validated by comparing it with commercial codes. According to the presented model, the active elements can be embedded in the middle of the truss elements. Of course, active control of all the devices at the same time requires a cost from the power consumption point of view which could be not affordable in space applications. However, the effectiveness is not the same for all the actuators. In this study, an optimization procedure is performed to assess the best authority of the actuators that must be controlled for a variety of disturbances. The objective function is set as a weighted sum of power consumption of the actuators. As a study case, a feedback strategy is implemented to coordinate the simultaneous action of the devices to ensure the damping performance of the system is enhanced
GNC architecture solutions for robust operations of a free-floating space manipulator via image based visual servoing
No full textOn-orbit servicing often requires the use of robotic arms, and a key asset in this kind of operations is autonomy. In this framework, the use of optical devices is a solution, already analyzed in many researches both for autonomous rendezvous and docking and for the evaluation of the control of the manipulator. In the present paper, simulations for assessing the controller performance are realized in a high-fidelity purposely developed software architecture, in which not only the selected 6 DOF space manipulator is modeled, but also a virtual camera, acquiring in the loop images of the target CAD model imported, is included in the GNC loop. This approach allows to emphasis several problems that would not emerge in simulations with ideal images. At the scope, a specific GNC architecture is developed, based on finite-state machine logic. According to this approach, two different IBVS strategies are alternatively performed, commanding only linear or angular velocity of the camera, switching between the two control techniques when the “stack” or “divergence” condition is triggered. In this way a stable and robust accomplishment of the tasks is achieved for many configurations and for different target models
Data-driven deep neural network for structural damage detection in composite solar arrays on flexible spacecraft
Full text linkA data-driven approach based on Deep Neural Network (DNN) techniques is here proposed for Structural Health Monitoring of large in-orbit flexible systems. Damage scenarios are generated via a Finite Element commercial code to train and test the machine learning model, by considering equivalent properties of the composite material of the solar panels. The fully coupled 3D equations for the flexible spacecraft are integrated to test typical profiles of attitude manoeuvres in case of different damages. The DNN model is trained using sensor-measured time series responses, with each response associated with the label of the corresponding damage scenario, and tested via k-folding approach. This methodology offers a promising approach to detect structural damage in solar arrays on spacecraft using machine learning techniques
A model predictive control for attitude stabilization and spin control of a spacecraft with a flexible rotating payload
No full textMany Earth Observation missions, implementing space-based microwave sensing techniques for collecting surface information, employ spinning sensors to cover large swaths of terrestrial areas, thus improving the rate at which global maps of those measured data are generated. These spacecraft (as Soil Moisture Active Passive (SMAP) developed by NASA or Copernicus Imaging Microwave Radiometer (CIMR) currently under development by Thales Alenia Space) consist of a main non-spun platform and a rotating part composed of an antenna boom, a deployable reflector and a rotation mechanism. As the reflector is designated to rotate about the nadir axis producing conically scanned antenna beams with precise surface incidence angle, the payload pointing accuracy needs to be addressed at both spin subsystem and platform level. In this work, a representative model of the dynamic behaviour of SMAP satellite is developed as a study case to design the proposed control strategies; in particular, a SMAP-like payload structural model is built using FEM commercial codes. The spacecraft is equipped with a Reaction Wheels Assembly (RWA) to accomplish both momentum compensation for the spun element and three-axis attitude control and a motor for the spin mechanism. The objective of the study is to develop the spacecraft control architecture in the frame of Model Predictive Control (MPC) theory. MPC refers to a class of algorithms in which the control action is obtained by computing an open-loop optimal sequence of control moves over a predefined time horizon; moreover, the ability to set constraints on process inputs and outputs directly in the problem formulation allows to account for actuators’ limits. In the study two operative phases of the satellite are addressed: the Spin-up, in which the 6-meter diameter antenna is spun-up to the operative condition of 14.6 RPM, and the Science Phase, in which precise nadir pointing and stability of the flexible system must be kept for acquiring high-resolution measurements. To this purpose, control–structure interaction between attitude/spin control system and flexible dynamics, as well as system's imbalances, are carefully addressed by the proposed control architecture. The nonlinear in-orbit dynamics of the flexible spacecraft is then used to evaluate the performance of the MPC controller in terms of pointing accuracy and robustness to uncertainties
A general Control/Structure Co-design framework to optimize attitude/flexible dynamics of Earth Observation (EO) satellites
No full textModern space missions for Earth Observation (EO) purposes often rely on satellites equipped with very large flexible appendages, such as antennas and solar panels, which are demanded to perform agile slew manoeuvres. In most cases, the elasticity of such systems cannot be neglected in the design of the attitude controller, as excessive elastic displacements of the structural elements may compromise their stability and pointing performance. Therefore, the integration of GNC laws in flexible space systems still represents an open challenging task, whose best solution often depends on the specific type of application. In this scenario, the most widely adopted techniques in control design are the classical but yet labour intensive tuned feedback controllers, generally integrated with low pass/notch filters to suppress the resonant peaks of the spacecraft flexible modes. Alternatively, in the early phases of spacecraft design, structure and control disciplines perform separate and time-consuming iterative sequences to avoid interactions between the flexible and rigid dynamics. In this context, as opposed to the latter approach, this paper aims at proposing an automated nested optimization framework to simultaneously optimize spacecraft structural and control dynamics, to be applicable to a wide range of flexible spacecraft. The objective of such a co-design architecture is to modify design parameters, at both structural and control levels, to minimize the mass of the spacecraft while maximizing its agility and satisfying imposed requirements. Moreover, as robust multivariable techniques have become more and more applied to ensure satisfactory robust performance margins, this paper's goal is to pose a multi-channel structured H∞ control architecture in the co-design problem. To guarantee the generality of implementation, a structural design tool (MSC Nastran) is interfaced with a coding environment (Matlab/Simulink) to set-up an autonomous exchange of information between structural and control domains. Starting from an initial definition of the spacecraft material, geometry and control requirements (in terms of loop-shaping transfer functions), relevant parameters are extracted from the structural tool and a linearized dynamic model assembled. Then, a controller is synthetized based on the provided requirements, followed by a V&V phase on the nonlinear plant of the satellite. The procedure is repeated until the stop criteria (based on tolerance and max iterations) is satisfied. Finally, the output of the proposed architecture is obtained as an optimized structural model and robust controller tailored for the satellite dynamics
GNC architecture solutions for robust operations of a free-floating space manipulator via image based visual servoing
Full text linkOn-orbit servicing often requires the use of robotic arms, and a key asset in this kind of operations is autonomy. In this framework, the use of optical devices is a solution, already analyzed in many researches both for autonomous rendezvous and docking and for the evaluation of the control of the manipulator. In the present paper, simulations for assessing the controller performance are realized in a high-fidelity purposely developed software architecture, in which not only the selected 6 DOF space manipulator is modeled, but also a virtual camera, acquiring in the loop images of the target CAD model imported, is included in the GNC loop. This approach allows to emphasis several problems that would not emerge in simulations with images characterized by easily-identifiable, purposely-created markers. At the scope, a specific GNC architecture is developed, based on finite-state machine logic. According to this approach, two different Image Based Visual Servoing strategies are alternatively performed, commanding only linear or angular velocity of the camera, switching between the two control techniques when the “stack” or “divergence” condition is triggered. In this way a stable and robust accomplishment of the tasks is achieved for many configurations and for different target models
On-line center of mass and inertia determination of a space debris during a deorbiting mission
No full textThe problem of removing debris from LEO or GEO is broadly recognized as one of the most pressing in the near future and passive mitigation obtained by reducing the de-orbiting time after the operational satellite lifetime is demonstrated to be an insufficient remedy. Active debris removal by means of a chaser satellite is therefore being intensively studied. In particular, space manipulators appear to be a promising solution, due to their long operational history in the space environment. According to this approach, the chaser, clamped to the target debris, changes its orbital altitude by applying a pushing thrust, which is an unstable configuration from the attitude control point of view: a misalignment between the force vector and the chaser+target system center of mass (CoM) leads to a torque that must be continuously compensated, which could be an unacceptable cost in terms of attitude control. Unfortunately, this misalignment must be expected, since the target inertia characteristics are only known with a limited degree of confidence. In this framework, the determination of the characteristics of the chaser+target system is studied by means of a Kalman filtering approach, in a simulation environment in which both the multibody dynamics and the orbital dynamics are taken into account. The estimate variables are the components of the inertia tensor and (above all) the coordinates of the system's CoM, while the measurements are limited to the angular velocity coming from the gyro sensors. It is fundamental for the success of the inertia determination to excite the system dynamics, and this could be done by using the robotic connection between chaser and target, which however brings good results only if the mass of the target is not much larger than the mass of the chaser. Alternatively, the chaser could apply small controlled forces to the system, using the resulting attitude dynamic as input for the filter: this paper investigates the accuracy obtained performing different kinds of maneuvers. Interestingly, this algorithm for center of mass determination can be run even during the deorbiting push: the algorithm is included in closed loop with a thrust vector control, continuously analyzing the attitude motion and improving the knowledge of the CoM position (which by the way will vary due to the fuel consumption). In this way the direction of the thrust is corrected and the attitude control is relieved by the heavy task of compensating the thrust misalignment
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