1,721,046 research outputs found
Inverse-dynamics particle swarm optimization for real time optimal control: Challenges and opportunities
No full textThe paper described the most recent advances in the development of the Inverse-dynamics Particle Swarm Optimization technique for determining approximate solutions to constrained optimal control problems. Near-optimal solutions are searched for using a differential flatness approach such that the kinematic of the problem is directly approximated whereas the dynamics is given by a generic non-linear combination of successive time-derivatives of the state. Numerical results are presented evaluating the proposed technique with a constrained reorientation maneuver of a spacecraft already considered in literature. A rest-to-rest slew maneuver is considered where an optical sensor cannot be exposed to sources of bright light such as the Earth, the Sun and the Moon. It is established that the computation of minimum time, minimum fuel and minimum energy maneuvers with the proposed technique leads to near optimal solutions, which fully satisfy all the boundary and path constraints. The rapid convergence characterizes the proposed technique as a feasible future on-board path-planner for terrestrial and space applications
Experimental assessment of node crosstalk limitations enhanced by nonlinear effects in all optical transport networks
No full textA geometrical approach for the angular velocity determination using a star sensor
No full textIn this paper, a geometrical investigation of the star sensor image is performed under dynamic conditions where the angular velocity effects are non-negligible. It is shown that, when the spacecraft is rotating, the streaks left by the stars’ signal onto the star sensor detector belong to portions of conic sections which features depend on the angles between the instantaneous rotation axis, the sensor line of sight and the stars’ direction. The geometrical properties discussed in the first part of the paper can be used to develop new numerical methods for the evaluation of the angular velocity. Hence, the chord method is proposed and discussed. This approach needs at least two stars in two successive images and, despite its simplicity, is quite effective to get a preliminary estimation of the spacecraft angular velocity in terms of direction and magnitude. Using the stars’ centroids from two successive images, the chord method evaluates the angular velocity direction as the intersection of the normals to the streaks. The proposed method is firstly presented by means of simple examples using some reference geometries, and then it is applied to real scenarios by using a high fidelity star sensor simulator. The pre-processing and processing of simulated images are discussed, presenting the geometrical techniques used to cluster the streaks and compute the centroids. Results are presented and discussed, validating the reported theoretical speculations
Augmented gyro-stellar model in the presence of measurements delay
No full textIn recent years, the tendency to decrease satellites’ size and costs has turned into more stringent requirements for lesser-performing sensors. The study of attitude estimation for micro-sat under measurements’ date errors in a gyro-stellar configuration is here presented. An augmented model is studied in which both the star tracker's and gyro's data are used as update measurements for the feed of the multiplicative extended Kalman filter. The analyzed configuration presents high-levels of gyro's noises. The augmented model successfully reduced the angular rate's estimation error compared to the well-established "Replacement mode" model of Farrenkopf’s equations. The filter is then modified to compensate the date error between the rate and attitude measurements by means of different algorithms, which capabilities are analyzed in a parametric study of the performances under variation of sampling time and measurements' delay. The compensation algorithms proved to be successful, but the performances are strictly dependent on the gyro's capabilities. The results are then exploited for the design of a filter that combines the two aspects and is applied with a star tracker and a rate-gyro readily available in the marke
Sub-optimal thrust modulation algorithm for autonomous soft lunar landing
No full textThis work presents an algorithm for the 6-DoF guidance and control for the final descent of a Lunar lander with a non-throttleable engine. At first, the 3-DoF landing problem, defined by the initial state of the lander, the desired landing site and the time of flight needed to complete the manoeuvre, is set and solved using a quadratic programming approach. The resulting control sequence is, then, converted to a series of pulses by a Pulse Width Modulation (PWM) algorithm that considers the variation of mass of the lander during the descent. The attitude dynamics is included at this stage and a suitable sequence of rotations, needed to orient the lander before each ignition, is determined. The final control sequence is obtained modifying the results of the PWM in order to fulfil the time constraints of the attitude variations and to achieve a safe landing. The proposed guidance and control algorithm is tested to evaluate its performances and also its capabilities of handling one or multiple retargeting are assessed
Optimization criteria of band-pass matching networks for optical receivers in microwave optical links
No full textInverse dynamics particle swarm optimization applied to constrained minimum-time maneuvers using reaction wheels
No full textThe paper deals with the problem of time-optimal spacecraft reorientation maneuvers by means of reaction wheels, with boundary and path constraints. When searching for solutions to optimal attitude-control problems, spacecraft can be easily modeled as controlled by external torques. However, when using actuators such as reaction wheels, conservation of the total angular momentum must be taken into account and the wheel dynamics must be included. A rest-to-rest slew maneuver is considered where an optical sensor cannot be exposed to sources of bright light such as the Earth, the Sun and the Moon. The motion must be constrained to prevent the sensor axis from entering into established keep-out cones. The minimum-time solution is proposed using the Inverse Dynamics Particle Swarm Optimization technique. The attitude and the kinematics of the satellite evolve, leading to the successive attainment of the wheel control input via fixed-step numerical integration. Numerical results are evaluated over different scenarios. It is established that the computation of minimum time maneuvers with the proposed technique leads to near optimal solutions, which fully satisfy all the boundary and path constraints. The ability to converge in a variety of different scenarios always requiring the same computational effort characterizes the proposed technique as a feasible future on-board path-planner
Riflessioni nella conferenza. Lettura critica in: P. Properzi (a cura di), Conferenza nazionale del territorio. Genova 8-9 febbraio 2001. Riflessioni e prospettive.
No full textImproved magnetic charged system search optimization algorithm with application to satellite formation flying
Full text linkThis paper is devoted to the implementation and application of an improved version of the metaheuristic algorithm called magnetic charged system search. Some modifications and novelties are introduced and tested. Firstly, the authors’ attempt is to develop a self-adaptive and user-friendly algorithm which can automatically set all the preliminary parameters (such as the numbers of particles, the maximum iterations number) and the internal coefficients. Indeed, some mathematical laws are proposed to set the parameters and many coefficients can dynamically change during the optimization process based on the verification of internal conditions. Secondly, some strategies are suggested to enhance the performances of the proposed algorithm. A chaotic local search is introduced to improve the global best particle of each iteration by exploiting the features of ergodicity and randomness. Moreover, a novel technique is proposed to handle bad-defined boundaries; in fact, the possibility to self-enlarge the boundaries of the optimization variables is considered, allowing to achieve the global optimum even if it is located on the boundaries or outside. The algorithm is tested through some benchmark functions and engineering design problems, showing good results, followed by an application regarding the problem of time-suboptimal manoeuvres for satellite formation flying, where the inverse dynamics technique, together with the B-splines, is employed. This analysis proves the ability of the proposed algorithm to optimize control problems related to space engineering, obtaining better results with respect to more common and used algorithms in literature
Time suboptimal formation flying manoeuvres through improved magnetic charged system search
Full text linkThe development of fast and reliable optimization algorithms is required in order to obtain real-time optimal trajectory on-board spacecraft. In addition, the wide spread of small satellites, due to their low costs, is leading to a greater number of satellite formations in space. This paper presents an Improved version of the Magnetic Charged System Search (IMCSS) metaheuristic algorithm to compute time-suboptimal manoeuvres for satellite formation flying. The proposed algorithm exploits some strategies aimed at improving the convergence to the optimum, such as the chaotic local search and the boundary handling technique, and it is able to self-tune its internal parameters and coefficients. Moreover, the inverse dynamics technique and the differential flatness approach, through the B-splines curves, are used to approximate the trajectory. The optimization procedure is applied to the circular J2 relative model developed by Schweighart and Sedwick and to the elliptical relative motion model developed by Yamanaka and Ankersen. The results of this paper show that the convergence is better achieved by using the proposed tools, thus proving the efficiency and reliability of the algorithm in solving some space engineering problems
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