arXiv subjects

Elisa Maria Alessi

Publications and source records attributed to Elisa Maria Alessi.

26 records · Page 2Linked to original sources

arXiv2018

A frequency portrait of Low Earth Orbits

In this work we deepen and complement the analysis on the dynamics of Low Earth Orbits (LEO), carried out by the authors within the H2020 ReDSHIFT project, by characterising the evolution of the eccentricity of a large set of orbits in terms of the main frequency components. Decomposing the quasi-periodic time series of eccentricity of a given orbit by means of a numerical computation of Fourier transform, we link each frequency signature to the dynamical perturbation which originated it in order to build a frequency chart of the LEO region. We analyse and compare the effects on the eccentricity due to solar radiation pressure, lunisolar perturbations and high degree zonal harmonics of the geopotential both in the time and frequency domains. In particular, we identify the frequency signatures due to the dynamical resonances found in LEO and we discuss the opportunity to exploit the corresponding growth of eccentricity in order to outline decommissioning strategies.

physics.space-ph↗

arXiv2018

Natural highways for end-of-life solutions in the LEO region

We present the main findings of a dynamical mapping performed in the Low Earth Orbit region. The results were obtained by propagating an extended grid of initial conditions, considering two different epochs and area-to-mass ratios, by means of a singly averaged numerical propagator. It turns out that dynamical resonances associated with high-degree geopotential harmonics, lunisolar perturbations and solar radiation pressure can open natural deorbiting highways. For area-to-mass ratios typical of the orbiting intact objects, these corridors can be exploited only in combination with the action exerted by the atmospheric drag. For satellites equipped with an area augmentation device, we show the boundary of application of the drag, and where the solar radiation pressure can be exploited.

astro-ph.EP↗

arXiv2018

Exploiting dynamical perturbations for the end-of-life disposal of spacecraft in LEO

As part of the dynamical analysis carried out within the Horizon 2020 ReDSHIFT project, this work analyzes the possible strategies to guide low altitude satellites towards an atmospheric reentry through an impulsive maneuver. We consider a fine grid of initial conditions in semi-major axis, eccentricity and inclination and we identify the orbits that can be compliant with the 25-year rule as the target of a single-burn strategy. Besides the atmospheric drag, we look for the aid provided by other dynamical perturbations - mainly solar radiation pressure - to facilitate a reentry. Indeed, in the case of typical area-to-mass ratios for objects in LEO, we observed that dynamical resonances can be considered only in combination with the atmospheric drag and for a very limited set of initial orbits. Instead, if an area augmentation device, as a solar sail, is available on-board the spacecraft, we verified that a wider range of disposal solutions become available. This information is exploited to design an improved mitigation scheme, that can be applied to any satellite in LEO.

physics.space-ph↗

arXiv2015

Galileo disposal strategy: stability, chaos and predictability

Recent studies have shown that the medium-Earth orbit (MEO) region of the Global Navigation Satellite Systems is permeated by a devious network of lunisolar secular resonances, which can interact to produce chaotic and diffusive motions. The precarious state of the four navigation constellations, perched on the threshold of instability, makes it understandable why all past efforts to define stable graveyard orbits, especially in the case of Galileo, were bound to fail; the region is far too complex to allow of an adoption of the simple geosynchronous disposal strategy. We retrace one such recent attempt, funded by ESA's General Studies Programme in the frame of the GreenOPS initiative, that uses a systematic parametric approach and the straightforward maximum-eccentricity method to identify long-term stable regions, suitable for graveyards, as well as large-scale excursions in eccentricity, which can be used for post-mission deorbiting of constellation satellites. We then apply our new results on the stunningly rich dynamical structure of the MEO region toward the analysis of these disposal strategies for Galileo, and discuss the practical implications of resonances and chaos in this regime. We outline how the identification of the hyperbolic and elliptic fixed points of the resonances near Galileo can lead to explicit criteria for defining optimal disposal strategies.

astro-ph.EP↗

arXiv2015

The dynamical structure of the MEO region: long-term stability, chaos, and transport

It has long been suspected that the Global Navigation Satellite Systems exist in a background of complex resonances and chaotic motion; yet, the precise dynamical character of these phenomena remains elusive. Recent studies have shown that the occurrence and nature of the resonances driving these dynamics depend chiefly on the frequencies of nodal and apsidal precession and the rate of regression of the Moon's nodes. Woven throughout the inclination and eccentricity phase space is an exceedingly complicated web-like structure of lunisolar secular resonances, which become particularly dense near the inclinations of the navigation satellite orbits. A clear picture of the physical significance of these resonances is of considerable practical interest for the design of disposal strategies for the four constellations. Here we present analytical and semi-analytical models that accurately reflect the true nature of the resonant interactions, and trace the topological organization of the manifolds on which the chaotic motions take place. We present an atlas of FLI stability maps, showing the extent of the chaotic regions of the phase space, computed through a hierarchy of more realistic, and more complicated, models, and compare the chaotic zones in these charts with the analytical estimation of the width of the chaotic layers from the heuristic Chirikov resonance-overlap criterion. As the semi-major axis of the satellite is receding, we observe a transition from stable Nekhoroshev-like structures at three Earth radii, where regular orbits dominate, to a Chirikov regime where resonances overlap at five Earth radii. From a numerical estimation of the Lyapunov times, we find that many of the inclined, nearly circular orbits of the navigation satellites are strongly chaotic and that their dynamics are unpredictable on decadal timescales.

astro-ph.EP↗

arXiv2015

Chaos in navigation satellite orbits caused by the perturbed motion of the Moon

Numerical simulations carried out over the past decade suggest that the orbits of the Global Navigation Satellite Systems are unstable, resulting in an apparent chaotic growth of the eccentricity. Here we show that the irregular and haphazard character of these orbits reflects a similar irregularity in the orbits of many celestial bodies in our Solar System. We find that secular resonances, involving linear combinations of the frequencies of nodal and apsidal precession and the rate of regression of lunar nodes, occur in profusion so that the phase space is threaded by a devious stochastic web. As in all cases in the Solar System, chaos ensues where resonances overlap. These results may be significant for the analysis of disposal strategies for the four constellations in this precarious region of space.

astro-ph.EP↗

arXiv2012

Desaturation Maneuvers and Precise Orbit Determination for the BepiColombo Mission

The purpose of this work is the analysis of the consequences that desaturation maneuvers can have in the precise orbit determination corresponding to the Radio Science Experiment (MORE) of the BepiColombo mission to Mercury. This mission is an ESA/JAXA joint project with very challenging objectives regarding geodesy, geophysics and fundamental physics. In the neighborhood of Mercury, the s/c will experience strong solar radiation pressure torques; the s/c attitude is controlled by inertial wheels that after some time reach their maximum rotation state. Then they have to be slowed down by means of thruster pulses, inducing a residual acceleration on the s/c, with a desaturation (or off-loading) maneuver. In this paper, we will show how such maneuvers affect the orbit of the s/c and the radio science measurements and, also, how to include them in the orbit determination and parameter estimation procedure. The non linear least squares fit we consider is applied on a set of observational arcs separated by intervals of time where the probe is not visible. With the current baseline of two ground stations, two maneuvers are performed per day, one during the observing session, the other in the dark. To reach the scientific goals of the mission, they have to be treated as "solve for quantities". We have developed a specific methodology based on the deterministic propagation of the orbit, which is able to deal with these variables, by connecting subsequent observational arcs in a smooth way. The numerical simulations we will show demonstrate that this constrained multi-arc strategy is able to determine the maneuvers, including the ones in the dark, together with the other parameters of interest at a high level of accuracy. The future development consists in including accelerometer readings and calibrations in the method.

physics.space-ph↗

arXiv2010

A Motivating Exploration on Lunar Craters and Low-Energy Dynamics in the Earth -- Moon System

It is known that most of the craters on the surface of the Moon were created by the collision of minor bodies of the Solar System. Main Belt Asteroids, which can approach the terrestrial planets as a consequence of different types of resonance, are actually the main responsible for this phenomenon. Our aim is to investigate the impact distributions on the lunar surface that low-energy dynamics can provide. As a first approximation, we exploit the hyberbolic invariant manifolds associated with the central invariant manifold around the equilibrium point L_2 of the Earth - Moon system within the framework of the Circular Restricted Three - Body Problem. Taking transit trajectories at several energy levels, we look for orbits intersecting the surface of the Moon and we attempt to define a relationship between longitude and latitude of arrival and lunar craters density. Then, we add the gravitational effect of the Sun by considering the Bicircular Restricted Four - Body Problem. As further exploration, we assume an uniform density of impact on the lunar surface, looking for the regions in the Earth - Moon neighbourhood these colliding trajectories have to come from. It turns out that low-energy ejecta originated from high-energy impacts are also responsible of the phenomenon we are considering.

astro-ph.EP↗