274 research outputs found
Nonlinear Adaptive State Estimator Approach to Attitude and Orbit Determination Using Only a Magnetometer
No full text
F. Finotti, Retorica della diffrazione. Bembo, Aretino, Giulio Romano e Tasso: letteratura e scena cortigiana, Firenze, Olschki, 2004
No full textLa recensione analizza i diversi capitoli del volume di Fabio Finotti dedicato ad alcune figure centrali della letteratura di età rinascimentale e tardo rinascimentale
A genetic algorithm for Initial Orbit Determination from a too short arc optical observation
No full textOptical observations constitute a source of angular measurements of a satellite pass. Commonly, these observations have short durations
with respect to the satellite orbit period. As a consequence, the use of classical orbit determination algorithms, as Laplace, Gauss or Escobal methods, give very poor results. The present work faces with the problem of estimating the orbital parameters of an orbiting object using its optical streak acquired by a telescope or a high accuracy camera. In the paper a new technique is developed for the Initial
Orbit Determination from optical data by exploiting the genetic algorithms. The algorithm works without restrictions on the observer
location. A recent challenging problem is the Initial Orbit Determination with space-based observations. This work focuses on the problem of determinating the orbital parameters of a satellite from an orbiting observer in LEO, using short time observations. We present the results based on a simulation with the observer on a sun-synchronous orbit with a single observation of just 60 s. Monte Carlo simulations are presented with different levels of sensor accuracy to show the reliability of the algorithm. The algorithm is able to yield a
candidate solution for each observation. The coplanar case is analyzed and discussed as well
TETHER LENGTH CONTROL FOR ORBITAL MANEUVRES
No full textIt is well known that the cable elongation or retraction in a tether system causes pitch oscillations, whose amplitude depends on the radial velocity vector of the tip masses. The Coriolis forces, responsible for such deviations from the local vertical, can be exploited to control the pitch angle. Hereby, we propose a strategy to progressively increase such angle by forcing the system to leave the potential hole where it is trapped by the stabilizing gravity gradient torque. As a result, the tether will start to rotate around the center of mass of the system. Such a strategy is based on a suitable continuous control that, upon measuring the angular velocity of the pitch angle, shortens and lengthens the tether during oscillations. Once the dumbbell is spinning, the mass of interest can be released where, for instance, its absolute tangential velocity attains the maximum or the minimum value in order to modify the orbital parameters or in order to begin a re-entry phase. In the spinning mode, the tether length control can increase the pitch angular velocity by decreasing the length of the cable. This allows for the possibility of tuning the tangential velocity of the mass of interest and, as a consequence, of selecting the parameters of the new trajectory of the mass. The possible applications are, however, manifold and for some of them it is important to explore the influence of the aerodynamic drag acting on the mass, which, for low orbits, plunges periodically into the upper layer of the atmosphere. During the orbital motion, the aerodynamic forces pump rotational energy into the tether system, thus, increasing its spin and assisting in the attainment of the desired tangential velocity. By exploiting the interaction with the upper atmosphere, it is then possible to minimize the power budget necessary to put the system into rotation. In fact, once the minimum excess of pitch velocity sufficient to escape the gravity gradient torque has been achieved, the residual energy will be provided by the activity the aerodynamic forces carry out. Copyright ©2010 by the International Astronautical Federation. All rights reserved
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