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

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

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

Competencia e incentivos a la cooperación en la interacción de grupos de interés que pretenden aumentar su influencia política directa: ¿cuál es la importancia de la presión política?

This study is about the interactions between GDI and government under political pressure, in a context with an agency relationship and the existence of relevant information. In particular, interactions are studied when the agency relationship is with symmetric information and it is build a research model of the GDI-government interactions in a context with an agency relationship and asymmetric information, where groups can operate in a competitive or cooperative manner. The model highlights that government expectations of utility are higher when the GDI works together, and the benefit when the GDI makes pressure in an independent way is limited to the reserve. Cooperation establishes a type of relations based on credibility that benefit to the government and the GIDI, and this will help to strengthen those linksGroups with Direct Influence (GDI), Political Pressure, Lobby (-ing), Agency Relationship, Symmetric and Asymmetric information

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

Orbit transfer using Theory of Functional Connections via change of variables

This work shows that a class of astrodynamics problems subject to mission constraints can be efficiently solved using the Theory of Functional Connections (TFC) mathematical framework by a specific change of coordinates. In these problems, the constraints are initially written in non-linear and coupled mathematical forms using classical rectangular coordinates. The symmetries of the constrained problem are used to select a new system of coordinates that transforms the non-linear constraints into linear. This change of coordinates is also used to isolate the components of the constraints. This way the TFC technique can be used to solve the ordinary differential equations governing orbit transfer problems subject to mission constraints. Specifically, this paper shows how to apply the change of coordinates method to the perturbed Hohmann-type and the one-tangent burn transfer problems.Comment: Paper submitted to The European Physical Journal Special Topic

Analysis of the orbital evolution of space debris using a solar sail and natural forces

In this work, the orbital evolution of these objects that are located in the geostationary orbit (GEO) is analyzed. Knowing this, the possibility of using a solar sail is considered to help to clean the space environment. The main natural environmental perturbations that act in the orbit of the debris are considered in the dynamics. Such forces acting in the solar sail can force the growth of the eccentricity of these objects in the GEO orbit. Several authors have presented models of the solar radiation pressure considering the single-averaged model. But, doing a literature research, we found that the authors consider the Earth around the Sun in a circular and inclined orbit. Our contribution to the SRP model is in developing a different approach from other authors, where we consider the Sun in an elliptical and inclined orbit, which is valid for other bodies in the solar system when the eccentricity cannot be neglected. The expression of the SRP is developed up to the second order. We found that the first-order term is much superior to the second-order term, so the quadrupole term can be neglected. Another contribution is the approach to identify the initial conditions of the perigee argument (g) and the longitude of the ascending node (h), where some values of the (g, h) plane contribute to amplify the eccentricity growth. In the numerical simulations we consider real data from space debris removed from the site Stuff in Space. The solar sail helps to clean up the space environment using a propulsion system that uses the Sun itself, a clean and abundant energy source, unlike chemical propellants, to contribute to the sustainability of space exploration

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

Study of the nanometric grain size distribution in iron compacts obtained by mechanical milling

A study has been carried out on the grain size distribution of cylindrical compacts obtained by consolidation of iron powder severely deformed by mechanical milling. Consolidation has been performed in two consecutive steps: cold and hot conditions. The hot one was done at two temperatures, namely 425 and 475ºC. After milling, the iron powder has a grain size of 8 nm (± 4 nm) with an average hardness of 800 HV. After hot compaction the grain size increases up to 50 nm, especially at 475ºC where a small fraction of grains reach larger values than the average. The grain size was evaluated by two different techniques, X-Ray Diffraction and Transmission Electron Microscopy. Results showed some differences between both methods. The advantage of using TEM is that grain size distribution, and not only the average size, can be obtained. Small discs were also obtained from the compacted specimen in order to fracture them on a “ball on three balls” equipment. The fracture behaviour of the samples was then studied by SEM.Postprint (published version