1,720,963 research outputs found
Time-Optimal Control of a Multidimensional Integrator Chain with Applications
No full textThis letter studies the time-optimal control problem for a chain of multidimensional integrators subject to convex state and input constraints. It is shown that, by performing a suitable change of variables, this problem can be cast as a single convex program for certain realizations of the boundary conditions. For general realizations, the problem is nonconvex. A constructive procedure based on the solution of a sequence of convex problems is proposed in order to approach asymptotically a global optimum. The proposed approach is demonstrated on three applications involving aerial and space vehicle systems
Sum-of-Norms Model Predictive Control for Spacecraft Maneuvering
No full textThis letter tackles spacecraft optimal control problems in which the cost function is defined by a sum of vector norms, in order to optimize fuel consumption while achieving sparse actuation. A model predictive control (MPC) strategy is devised for such type of problems, accounting for different spacecraft maneuvering modes. Closed-loop stability is guaranteed by a conic Lyapunov function, which is employed as a terminal cost in the formulation. A systematic method to construct such function is presented. The proposed design is compared to a standard quadratic MPC scheme on a long-range rendez-vous mission
Sum-of-Norms Periodic Model Predictive Control for Space Rendezvous
No full textModel predictive control (MPC) is receiving increasing attention in space applications, as a key technology for enhancing autonomy of the flight control system. Sum-of-norms formulations are specifically suited to this context, because they allow to optimize meaningful performance figures and to promote control sparsity. This brief presents a sum-of-norms MPC scheme for linear periodically time-varying systems. Closed-loop stability is proven by suitably defining periodic sequences of terminal weights and terminal sets. The proposed solution is applied to a rendezvous case study involving periodic dynamics due to geopotential effects and solar eclipses
Autonomous station keeping for LEO missions with a hybrid continuous/impulsive electric propulsion system
No full textSpacecraft localization via angle measurements for autonomous navigation in deep space missions
No full textThis paper addresses the problem of spacecraft localization based on angular measurements, for deep space missions. The dynamic model of the spacecraft accounts for several perturbing effects, such as Earth and Moon gravitational field asymmetry and errors associated with the Moon ephemerides. The measurement process is based on elevation and azimuth of Moon and Earth with respect to the spacecraft reference system. Distance measurements are not employed. Position and velocity of the spacecraft are estimated by using both the Extended Kalman Filter (EKF) and the Unscented Kalman Filter (UKF). The performance of the filters are evaluated on an example of Earth-to-Moon transfer mission. Copyright © 2007 IFAC
An MPC-based attitude control system for all-electric spacecraft with on/off actuators
No full textPointing accuracy is a key requirement in communication satellites and Earth observation missions. Attitude control systems must guarantee tracking of the reference attitude and angular rate, while accounting for mission performance indexes such as fuel consumption and actuator wear. In this paper, an MPC-based attitude control scheme is proposed for an all-electric spacecraft using cold gas and resistojet thrusters as on/off actuators for attitude control. This technology imposes restrictions on the number of thruster firings, which are explicitly taken into account in the MPC formulation and suitably traded-off with fuel consumption. The performance of the proposed attitude control system is demonstrated on a GEO mission and compared with other control schemes involving on/off actuators
Minimum switching control for spacecraft precision pointing with on/off actuators
No full textMaintaining the spacecraft attitude precisely aligned to a given orientation, while rejecting a persistent disturbance, using on/off actuators, is crucial for missions involving electric propulsion spacecraft. The objective is to enforce an oscillating attitude motion about the setpoint, so as to simultaneously minimize both the propellant consumption and the switching frequency of the control system. This paper evaluates the feasibility of a recently proposed feedback control law for this problem. This techniques is able to track both the period and the phase of periodic oscillations along the rotational axes, which is instrumental to minimize the switching frequency in the presence of input coupling. Two simulation case studies of a low Earth orbit missions are considered, showing that the proposed approach can effectively deal with both constant and time-varying disturbance torques
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
- …
