Model Predictive Control for Spacecraft Rendezvous in Elliptical Orbits with On/Off Thrusters

IFAC Workshop on Advanced Control and Navigation for Autonomous Aerospace Vehicles. 08/06/2015. SevillaIn previous works, the authors have developed a trajectory planning algorithm for spacecraft rendezvous which computed optimal Pulse-Width Modulated (PWM) control signals, for circular and eccentric Keplerian orbits. The algorithm is initialized by solving the impulsive problem first and then, using explicit linearization and linear programming, the solution is refined until a (possibly local) optimal value is reached. However, trajectory planning cannot take into account orbital perturbations, disturbances or model errors. To overcome these issues, in this paper we develop a Model Predictive Control (MPC) algorithm based on the open-loop PWM planner and test it for elliptical target orbits with arbitrary eccentricity (using the linear time-varying Tschauner-Hempel model). The MPC is initialized by first solving the open-loop problem with the PWM trajectory planning algorithm. After that, at each time step, our MPC saves time recomputing the trajectory by applying the iterative linearization scheme of the trajectory planning algorithm to the solution obtained in the previous time step. The efficacy of the method is shown in a simulation study where it is compared to MPC computed used an impulsive-only approach

Trajectory Planning for Spacecraft Rendezvous in Elliptical Orbits with On / Off Thrusters

The 19th World Congress of the International Federation of Automatic Control 2014 Cape Town, SudáfricaIn a previous work, the authors developed a trajectory planning algorithm for spacecraft rendezvous which computed optimal Pulse-Width Modulated (PWM) control signals, assuming that the target was moving in a circular Keplerian orbit. In this paper we extend the algorithm to the case of an elliptical target orbit with arbitrary eccentricity. Since the orbit is elliptical, the linear time-varying Tschauner-Hempel model is used, whose exact solution is possible by using true (or eccentric) anomaly instead of time (which is directly related to both via Kepler's equation). Unlike in the circular case, computing the PWM solution itself requires numerical integration. However, explicit linearization around the computed solution turns out to be possible and is exploited for rapidly improving the solution using linear programming (LP) techniques. The algorithm is initialized by solving the impulsive problem first; the impulses are converted to PWM signals, which are used as an initial guess. Using the explicit linearization and LP, the solution is refined until a (possibly local) optimal value is reached. The efficacy of the method is shown in a simulation study where it is compared to the impulsive-only approach

Robust Model Predictive Control for Spacecraft Rendezvous with Online Prediction of Disturbance Bounds

IFAC Workshop Aerospace Guidance, Navigation and Flight Control Systems (AGNFCS' 09) Samara, RUSSIA June 30 - July 2, 2009A Model Predictive Controller is introduced to solve the problem of rendezvous of spacecraft, using the HCW model and including additive disturbances and line-of-sight constraints. It is shown that a standard MPC is not able to cope with disturbances. Then a robust Model Predictive Control that introduces the concepts of robust satisfaction of constraints is proposed. The formulation also includes a predictor of the disturbance properties which are needed in the robust algorithm. In simulations it is shown that the robust MPC scheme is able to handle not only additive disturbances (which are the ones used in the formulation) but also large multiplicative disturbances and unmodelled dynamics (due to eccentricity of the orbit of the target spacecraft)

Trajectory Planning for Spacecraft Rendezvous with On / Off Thrusters

18th World CongressThe International Federation of Automatic ControlMilano (Italy) August 28 - September 2The objective of this work is to present a trajectory planning algorithm for spacecraft rendezvous that is able to incorporate Pulse-Width Modulated (PWM) control signals. The algorithm is based on linearization around a previously computed solution. To initialize the algorithm, a first solution needs to be obtained. To do so, the trajectory planning problem is solved using Pulse-Amplitude Modulated (PAM) control signals; these are then converted to PWM signals, which are used as an initial guess. Iterating, the solution is refined until an optimal value is reached. Simulations show that this method converges after a few iterations. The algorithm is simple and fast, hence it could be implemented online or used together with a Model Predictive Controller

Pulse-width predictive control for LTV systems with application to spacecraft rendezvous

This work presents a Model Predictive Controller (MPC) that is able to handle Linear Time-Varying (LTV) plants with Pulse-Width Modulated (PWM) control. The MPC is based on a planner that employs a Pulse-Amplitude Modulated (PAM) or impulsive approximation as a hot-start and then uses explicit linearization around successive PWM solutions for rapidly improving the solution by means of quadratic programming. As an example, the problem of rendezvous of spacecraft for eccentric target orbits is considered. The problem is modeled by the LTV Tschauner–Hempel equations, whose state transition matrix is explicit; this is exploited by the algorithm for rapid convergence. The efficacy of the method is shown in a simulation study.Ministerio de Economía y Competitividad DPI2008–05818Ministerio de Economía y Competitividad MTM2015-65608-

Feedback linearization control for a distributed solar collector field

This article describes the application of a feedback linearization technique for control of a distributed solar collector field using the energy from solar radiation to heat a fluid. The control target is to track an outlet temperature reference by manipulating the fluid flow rate through the solar field, while attenuating the effect of disturbances (mainly radiation and inlet temperature). The proposed control scheme is very easy to implement, as it uses a numerical approximation of the transport delay and a modification of the classical control scheme to improve startup in such a way that results compared with other control structures under similar conditions are improved while preserving short commissioning times. Experiments in the real plant are also described, demonstrating how operation can be started up efficiently.Ministerio de Ciencia y Tecnología DPI2004-07444-C04-04Ministerio de Ciencia y Tecnología DPI2005-0286

HONGOS COMESTIBLES SILVESTRES COLECTADOS EN LA X REGION DE CHILE

Se reportan 30 especies de hongos silvestres comestibles (autóctonos y alóctonos), Basidiomycota y Ascomycota que fructifican en restos vegetales, bosques nativos, plantaciones forestales, parques, jardines ypraderas de la X Región de Chile. Se entrega una descripción macro-microscópica de ellos, se comentan sus aspectos ecológicos y distribución. Además, se da una lista de los Basidiomycota silvestres comestibles que fructifican en otras Regiones del país. En Chile existiríanaproximadamente 53 especies de hongos silvestres comestibles. En la zona de Valdivia es posible recolectar unas 30 especies distintas de éstos, destacando entre los apetecidos por la población local: Agaricuscampestris (champigñon de campo), A. macrosporus (champiñon), Armillariella montagnei (pique), Boletus loyo (loyo), Grifola gargal (gargal), Ramaria flava var. subtilis (changle), Gyromytra cf esculenta (chicharrón de campo) y varias especies de Cyttaria (dihueñe,pinatra, llaullau). De los hongos silvestres presentes en Chile, por su excelente sapidez y demanda en el mercado internacional, destacan: Agaricus arvensis, Lactarius deliciosus, Macrolepiota bonaerense, Suillusluteus, Volvariella especiosa, Xerocomus chrysenteron y varias especies de Morchella.

CARACTERIZACIÓN MOLECULAR Y FISIOLÓGICAS DE LEVADURAS DE SUELO TRUMAO

Las levaduras juegan un importante rol en la naturaleza siendo el mayor reservorio de ellas  el suelo. Mediante el método de las diluciones seriadas y posterior siembra en agar Sabouraud se aislaron en cultivo puro 77 cepas de levaduras desde un mismo suelo trumao del sur de Chile, usado como pradera permanente (30 cepas), pradera en rotación (30 cepas) y como control bosque nativo (17 cepas), estas cepas se identificaron molecularmente por PCR-RFLP en conjunto con secuenciación del rDNA de ITS-5.8S, además se realizo una caracterización fisiológica (asimilación fuente de carbono, de nitrógeno y fermentación de azucares) a cada cepa. Mediante las técnicas moleculares las 77 cepas se  reunieron  en 10 grupos, de estos solamente tres grupos se pudieron identificar a nivel de especie y uno hasta género: Devariomyces hansenii. Pichia fermentan. Kazachstania exigua., Candida sp

Trajectory Planning for Spacecraft Rendezvous with On / Off Thrusters

Proceedings of the 18th World CongressThe International Federation of Automatic ControlMilano (Italy) August 28 - September 2The objective of this work is to present a trajectory planning algorithm for spacecraft rendezvous that is able to incorporate Pulse-Width Modulated (PWM) control signals. The algorithm is based on linearization around a previously computed solution. To initialize the algorithm, a first solution needs to be obtained. To do so, the trajectory planning problem is solved using Pulse-Amplitude Modulated (PAM) control signals; these are then converted to PWM signals, which are used as an initial guess. Iterating, the solution is refined until an optimal value is reached. Simulations show that this method converges after a few iterations. The algorithm is simple and fast, hence it could be implemented online or used together with a Model Predictive Controller

Estructura de regulación con generación automática de consignas y control por adelanto para un campo de colectores solares

En este artículo se muestran los resultados de operación de un Campo de Colectores Solares del tipo Cilindro Parabólico de forma automática por una estructura de control por adelanto en paralelo con un controlador tipo I-PD con generación automática de consignas. El objetivo de control para este sistema es mantener la temperatura de salida del fluido que circula por las tuberías del campo a un valor establecido, a pesar de las perturbaciones a las que está sometida la planta. Dichas perturbaciones se producen en la temperatura del fluido que entra al campo, procedente de un tanque de almacenamiento térmico, en la temperatura ambiente o en la radiación solar. Esta última constituye la fuente primaria de energía del sistema. Las dificultades para operar la planta son debidas a las perturbaciones citadas anteriormente y que no son manipulables, a las no linealidades y a su dinámica compleja. Para ello se ha diseñado una estructura de control que mantiene la temperatura de salida de los lazos a un nivel que se determina automáticamente mediante un generador de consignas que tiene en cuenta las condiciones en las que se encuentra la planta (radiación, temperatura a la entrada y temperatura ambiente) y ciertos parámetros necesarios para la operación segura de la planta. La variable manipulada es la velocidad a la que una bomba de alimentación envía al campo solar el aceite procedente del tanque de almacenamiento. La energía térmica almacenada se utiliza para producir agua desalinizada o energía eléctrica.Ministerio de Ciencia y Tecnología DPI2001- 2380-C02Ministerio de Ciencia y Tecnología DPI2002-04375-C0