Using Upgraded Versions Of Close Approach Maneuvers As Transportation Solutions For Deep Space Missions

Gravity-Assisted maneuvers have been used as a technique to reduce fuel consumption in deep space missions for several decades now. It opened the doors of the exterior solar system. The literature shows those results, as well as new versions of this maneuver, which includes: the use of propulsion combined with the close approach, both high or low thrust; the passage by the atmosphere of a planet to help to change the trajectory of the spacecraft; the use of tethers to increase the changes in the velocity of the spacecraft. All those new versions have the goal of increasing the variations of energy given by the maneuver, making possible missions that would not be possible without this technique

Low-Thrust Out-of-Plane Orbital Station-Keeping Maneuvers for Satellites

This paper considers the problem of out of plane orbital maneuvers for station keeping of satellites. The main idea is to consider that a satellite is in an orbit around the Earth and that it has its orbit is disturbed by one or more forces. Then, it is necessary to perform a small amplitude orbital correction to return the satellite to its original orbit, to keep it performing its mission. A low thrust propulsion is used to complete this task. It is important to search for solutions that minimize the fuel consumption to increase the lifetime of the satellite. To solve this problem a hybrid optimal control approach is used. The accuracy of the satisfaction of the constraints is considered, in order to try to decrease the fuel expenditure by taking advantage of this freedom. This type of problem presents numerical difficulties and it is necessary to adjust parameters, as well as details of the algorithm, to get convergence. In this versions of the algorithm that works well for planar maneuvers are usually not adequate for the out of plane orbital corrections. In order to illustrate the method, some numerical results are presented

Suppression of Chaotic Motion of Tethered Satellite Systems Using Tether Length Control

This study focuses on attitude and control motion of two bodies (a base-satellite and a sub-satellite) connected by an inextensible and massless tether in a circular orbit under the influence of the Earths gravitational force. The base-satellite is assumed to be far more heavier than the sub-satellite. In such cases, the base-satellite is regarded as the reference spacecraft. Because of the complexity of the problem, no thrusters on the sub-satellite are considered, and the effect of atmospheric drag, Earths oblateness, and electrodynamic force on the spacecraft are neglected

The dynamical environment of asteroid 21 Lutetia according to different internal models

One of the most accurate models currently used to represent the gravity field of irregular bodies is the polyhedral approach. In this model, the mass of the body is assumed to be homogeneous, which may not be true for a real object. The main goal of the present paper is to study the dynamical effects induced by three different internal structures (uniform, three- and four-layers) of asteroid (21) Lutetia, an object that recent results from space probe suggest being at least partially differentiated. The Mascon gravity approach used in the present work, consists of dividing each tetrahedron into eight parts to calculate the gravitational field around the asteroid. The zero-velocity curves show that the greatest displacement of the equilibrium points occurs in the position of the E4 point for the four-layers structure and the smallest one occurs in the position of the E3 point for the three-layers structure. Moreover, stability against impact shows that the planar limit gets slightly closer to the body with the four-layered structure. We then investigated the stability of orbital motion in the equatorial plane of (21) Lutetia and propose numerical stability criteria to map the region of stable motions. Layered structures could stabilize orbits that were unstable in the homogeneous model.Comment: 10 pages, 7 figures, and 4 Tables. Accepted for publication in MNRA

A Study on Binary Asteriod System Deflection

The study of asteroids, its composition and trajectories, has been a persistent interest in the space exploration community. In addition, they are also perceived as a great threat to life on Earth, considering the possibility of an impact with our planet. A considerable portion, around 15%, of the asteroid population are believed to be part of a double or triple asteroid system

Using the “U-Multirank” to Compare the Performances of Brazilian Universities with Latin American Countries in Academic and Industry Products

The present research makes comparisons of the performances of Brazilian Universities in terms of academic and industry related production, based in the “U-Multirank”, in the years 2017 to 2020. These comparisons are made with other Latin American countries listed in this ranking. Academic production is measured by indicators related to the number of papers published and citations received by Brazilian Universities, while Industry related products performance is based in the number of patents obtained and citations that Brazilian publications received in patents. This analysis is made for the average performances of all Brazilian universities listed in the “U-Multirank”, which is an academic multidimensional ranking implemented in Europe in 2014. It is based in five Dimensions, which are composed by 35 Indicators, with some of them related to pure academic productions and some others related to researches that are applied to industry. The results show that the performances of Brazilian universities are better in terms of academic products and below average in industry related products, such as the number of patents. It is also noted improvements in those numbers, a tendency that needs to be verified in the future. In Latin America, Chile has the best performances in all the Indicators related to Industrial products

Low Thrust Propelled Close Approach Maneuvers

The study of orbital maneuvers in space missions is a very important problem in astrodynamics. One of the options is the use of a “gravity assisted” maneuver, which is a technique where a spacecraft passes close to a celestial body and uses the gravity of this body to change its trajectory. This approach trajectory has symmetry with respect to the periapsis line when observed from a reference frame fixed in the approached body. There is also a more complex maneuver, when the passage by the celestial body is combined with the application of propulsion, either to give extra energy to the spacecraft or to help to satisfy other constraints required by the mission, like passing by a giving point or region in space. The main object of this study is to measure the efficiency of the application of a continuous thrust combined with the “gravity assisted” maneuver. The effect of this combination is analyzed using maps that give the energy variation of the spacecraft as function of the parameters related to the maneuver. This analysis is made from the point of view of the variation of energy of the spacecraft with respect to the main body of the system. The continuous thrust is applied in the different regions of the trajectory to evaluate the effects of the locations of the thrusting arcs in the variations of energy. The effects of the variations of the direction of the thrust are also studied. This type of combined maneuver may be used to give extra energy to the spacecraft and keeping control of the trajectory during the close approach to better position the spacecraft to complete the mission

Measurement of {\eta} meson production in {\gamma}{\gamma} interactions and {\Gamma}({\eta}-->{\gamma}{\gamma}) with the KLOE detector

We present a measurement of {\eta} meson production in photon-photon interactions produced by electron-positron beams colliding with \sqrt{s}=1 GeV. The measurement is done with the KLOE detector at the \phi-factory DA{\Phi}NE with an integrated luminosity of 0.24 fb^{-1}. The e^+e^- --> e^+e^-{\eta} cross section is measured without detecting the outgoing electron and positron, selecting the decays {\eta}-->{\pi}^+{\pi}^-{\pi}^0 and {\eta}-->{\pi}^0{\pi}^0{\pi}^0. The most relevant background is due to e^+e^- --> {\eta}{\gamma} when the monochromatic photon escapes detection. The cross section for this process is measured as {\sigma}(e^+e^- -->{\eta}{\gamma}) = (856 \pm 8_{stat} \pm 16_{syst}) pb. The combined result for the e^+e^- -->e^+e^-{\eta} cross section is {\sigma}(e^+e^- -->e^+e^-{\eta}) = (32.72 \pm 1.27_{stat} \pm 0.70_{syst}) pb. From this we derive the partial width {\Gamma}({\eta}-->{\gamma}{\gamma}) = (520 \pm 20_{stat} \pm 13_{syst}) eV. This is in agreement with the world average and is the most precise measurement to date.Comment: Version accepted by JHE

Theory of Functional Connections and Nelder-Mead optimization methods applied in satellite characterization

The growing population of man-made objects with the build up of mega-constellations not only increases the potential danger to all space vehicles and in-space infrastructures (including space observatories), but above all poses a serious threat to astronomy and dark skies. Monitoring of this population requires precise satellite characterization, which is is a challenging task that involves analyzing observational data such as position, velocity, and light curves using optimization methods. In this study, we propose and analyze the application of two optimization procedures to determine the parameters associated with the dynamics of a satellite: one based on the Theory of Functional Connections (TFC) and another one based on the Nelder-Mead heuristic optimization algorithm. The TFC performs linear functional interpolation to embed the constraints of the problem into a functional. In this paper, we propose to use this functional to analytically embed the observational data of a satellite into its equations of dynamics. After that, any solution will always satisfy the observational data. The second procedure proposed in this research takes advantage of the Nealder-Mead algorithm, that does not require the gradient of the objective function, as alternative solution. The accuracy, efficiency, and dependency on the initial guess of each method is investigated, analyzed, and compared for several dynamical models. These methods can be used to obtain the physical parameters of a satellite from available observational data and for space debris characterization contributing to follow-up monitoring activities in space and astronomical observatories.Comment: Submitted to Acta Astronautic

Measurement of \Gamma(\eta -> \pi^+\pi^-\gamma)/\Gamma(\eta -> \pi^+\pi^-\pi^0) with the KLOE Detector

The ratio R_{\eta}=\Gamma(\eta -> \pi^+\pi^-\gamma)/\Gamma(\eta -> \pi^+\pi^-\pi^0) has been measured by analyzing 22 million \phi \to \eta \gamma decays collected by the KLOE experiment at DA\PhiNE, corresponding to an integrated luminosity of 558 pb^{-1}. The \eta \to \pi^+\pi^-\gamma proceeds both via the \rho resonant contribution, and possibly a non-resonant direct term, connected to the box anomaly. Our result, R_{\eta}= 0.1856\pm 0.0005_{stat} \pm 0.0028_{syst}, points out a sizable contribution of the direct term to the total width. The di-pion invariant mass for the \eta -> \pi^+\pi^-\gamma decay could be described in a model-independent approach in terms of a single free parameter, \alpha. The determined value of the parameter \alpha is \alpha = (1.32 \pm 0.08_{stat} +0.10/-0.09_{syst}\pm 0.02_{theo}) GeV^{-2}Comment: Paper in press, accepted by PL