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1,227 results on '"*ASTRONOMICAL unit"'

2. Astronomical Unit

Author

Gargaud, Muriel, editor, Irvine, William M., editor, Amils, Ricardo, editor, Claeys, Philippe, editor, Cleaves, Henderson James, editor, Gerin, Maryvonne, editor, Rouan, Daniel, editor, Spohn, Tilman, editor, Tirard, Stéphane, editor, and Viso, Michel, editor

Published
2023
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3. Physics-Informed Neural Networks for Optimal Planar Orbit Transfers.

Author

Schiassi, Enrico, D'Ambrosio, Andrea, Drozd, Kristofer, Curti, Fabio, and Furfaro, Roberto

Abstract

This paper presents a novel framework, combining the indirect method and Physics-Informed Neural Networks (PINNs), to learn optimal control actions for a series of optimal planar orbit transfer problems. According to the indirect method, the optimal control is retrieved by directly applying the Pontryagin minimum principle, which provides the first-order necessary optimality conditions. The necessary conditions result in a two-point boundary value problem (TPBVP) in the state-costate pair, constituting a system of ordinary differential equations, representing the physics constraints of the problem. More precisely, the goal is to model a neural network (NN) representation of the state-costate pair for which the residuals of the TPVBP are as close to zero as possible. This is done using PINNs, which are particular NNs where the training is driven by the problem's physics constraints. A particular PINN method will be used, named Extreme Theory of Functional Connections (X-TFC), which is a synergy of the classic PINN and the Theory of Functional Connections. With X-TFC, the TPBVP's boundary conditions are analytically satisfied. This avoids having unbalanced gradients during the network training. The results show the feasibility of employing PINNs to tackle this class of optimal control problems for space applications. [ABSTRACT FROM AUTHOR]

Published
2022
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4. Introduction to the Sun

Author

Severino, Giuseppe, Ashby, Neil, Series editor, Brantley, William, Series editor, Deady, Matthew, Series editor, Fowler, Michael, Series editor, Hjorth-Jensen, Morten, Series editor, Inglis, Michael, Series editor, and Severino, Giuseppe

Published
2017
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5. The Presentation of Numerical Results

Author

Christodoulides, Costas, Christodoulides, George, Ashby, Neil, Series editor, Brantley, William, Series editor, Deady, Matthew, Series editor, Fowler, Michael, Series editor, Hjorth-Jensen, Morten, Series editor, Inglis, Michael, Series editor, Klose, Heinz, Series editor, Sherif, Helmy, Series editor, Christodoulides, Costas, and Christodoulides, George

Published
2017
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10. Introduction

Author

Gallaway, Mark, Ashby, Neil, Series editor, Brantley, William, Series editor, Deady, Matthew, Series editor, Fowler, Michael, Series editor, Hjorth-Jensen, Morten, Series editor, Inglis, Michael, Series editor, Klose, Heinz, Series editor, Sherif, Helmy, Series editor, and Gallaway, Mark

Published
2016
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19. A Man from Planet Earth

Author

Genta, Giancarlo, Alpert, Mark, Series editor, Ball, Philip, Series editor, Benford, Gregory, Series editor, Brotherton, Michael, Series editor, Callaghan, Victor, Series editor, Eden, Amnon H, Series editor, Kanas, Nick, Series editor, Landis, Geoffrey, Series editor, Rucker, Rudi, Series editor, Schulze-Makuch, Dirk, Series editor, Vaas, Rüdiger, Series editor, Walter, Ulrich, Series editor, Webb, Stephen, Series editor, and Genta, Giancarlo

Published
2016
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22. The Solar System

Author

Valtonen, Mauri, Anosova, Joanna, Kholshevnikov, Konstantin, Mylläri, Aleksandr, Orlov, Victor, Tanikawa, Kiyotaka, Valtonen, Mauri, Anosova, Joanna, Kholshevnikov, Konstantin, Mylläri, Aleksandr, Orlov, Victor, and Tanikawa, Kiyotaka

Published
2016
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23. From Comets to Chaos

Author

Valtonen, Mauri, Anosova, Joanna, Kholshevnikov, Konstantin, Mylläri, Aleksandr, Orlov, Victor, Tanikawa, Kiyotaka, Valtonen, Mauri, Anosova, Joanna, Kholshevnikov, Konstantin, Mylläri, Aleksandr, Orlov, Victor, and Tanikawa, Kiyotaka

Published
2016
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39. Astronomical distance scales.

Author

Mignard, François

Subjects
*COSMOLOGICAL distances, *EXTRAGALACTIC distances, *SOLAR system, *ASTROMETRY, *STELLAR parallax
Abstract

This article is an overview of the determination of astronomical distances from a metrological standpoint. Distances are considered from the Solar System (planetary distances) to extragalactic distances, with a special emphasis on the fundamental step of the trigonometric stellar distances and the giant leap recently experienced in this field thanks to the ESA space astrometry missions Hipparcos and Gaia. [ABSTRACT FROM AUTHOR]

Published
2019
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40. Experimental Investigation of Total Photoemission Yield from New Satellite Surface Materials.

Author

Diaz-Aguado, Millan F., Bonnell, John W., Bale, Stuart D., Rezvani, S. J., Koshmak, Konstantin, Giglia, Angelo, Nannarone, Stefano, and Gruntman, Mike

Abstract

Electron photoemission influences spacecraft surface potentials and the surrounding plasma, and many modern spacecraft use new uncharacterized materials. The angle-dependent photoemission properties were measured for niobium C103 alloy, molybdenum TZM alloy, tantalum tungsten alloy, Elgiloy, graphite lubricant epoxy (DAG213) and titanium nitride at the Bending for Emission Absorption and Reflectivity beam line. The properties of tungsten were also studied to verify the method with past data. The materials were prepared similarly to flight materials. The properties were measured from 0 (normal) to 80 deg (grazing) incidence preannealed and postannealed conditioning of the samples. The yield was measured in all cases for both p and s polarization at each angle of incidence. Results are presented for the photoelectric threshold and photoelectron yield for photon energies up to 30 eV. The work function was also found for each material tested. An analytical equation was then used to fit the normal photoelectron yield for each material to help obtain photocurrents, which were calculated assuming solar illumination at 1 astronomical unit (AU) at normal incidence. [ABSTRACT FROM AUTHOR]

Published
2019
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41. Resonance-Averaged Solar Torque Dynamics for Tumbling Satellites

Author

Conor J. Benson and Daniel J. Scheeres

Subjects
Physics, Spin states, Applied Mathematics, Astronomical unit, Aerospace Engineering, Astronomy, Resonance (particle physics), Euler angles, symbols.namesake, Space and Planetary Science, Control and Systems Engineering, Physics::Space Physics, symbols, Torque, Condensed Matter::Strongly Correlated Electrons, Satellite, Geostationary Operational Environmental Satellite, Electrical and Electronic Engineering, Heliocentric orbit, Computer Science::Databases, Physics::Atmospheric and Oceanic Physics
Abstract

Observations indicate that the spin states of retired and otherwise defunct satellites are diverse and can change significantly over time. Understanding defunct satellite spin state evolution is im...

Published
2021

42. Trajectory approximation of a passively actuated solar balloon in near-Earth mission scenarios

Author

Marco Bassetto, Giovanni Mengali, and Alessandro A. Quarta

Subjects
Physics, Spacecraft, Passively actuated solar balloon, business.industry, Astronomical unit, Aerospace Engineering, Solar sail, Solar balloon, Trajectory approximation, Near-Earth orbits, Osculating orbit, Physics::Space Physics, Orbit (dynamics), Trajectory, Astrophysics::Solar and Stellar Astrophysics, Astrophysics::Earth and Planetary Astrophysics, Aerospace engineering, business, Apse line
Abstract

The aim of this paper is to investigate the heliocentric motion of a passively actuated solar balloon placed at a distance of about one astronomical unit from the Sun. The analysis exploits a recent thrust model, according to which a solar balloon undergoes a passive control of its lightness number (that is, the ratio of the generated thrust to the local weight of the entire spacecraft) in the form a proportional feedback controller of constant gain. The spacecraft trajectory is obtained with a regularization of the equations of motion, in such a way that the heliocentric dynamics of the passively actuated solar balloon becomes equivalent to that of a nonlinear oscillator with a single degree of freedom. The approximate solution available for this type of nonlinear oscillator is then used to accurately describe the heliocentric motion of the passively actuated solar balloon and to analyze a couple of mission scenarios, that is, the execution of a phasing maneuver on an elliptical working orbit and the rotation of the apse line of the osculating orbit.

Published
2021

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