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Orbital resonances can drive a growth of the eccentricity of Low Earth Orbits. This growth can be exploited to facilitate the end-of-life reentry of LEO satellites.

A numerical and analytical study of the web of resonances in Low Earth Orbits is shown.

The orbital perturbations (resonances) il Low Earth orbit can be exploited to enhance the end-of-life disposal of satellites.

The orbital resonances in LEO can be exploited to facilitate the end-of-life disposal of satellites.

The growth of the number of space objects in the Low Earth Orbit (LEO) region requires both the implementation of prevention strategies and the outline of advanced re-entry solutions. By means of a dedicated orbit propagator, we studied the dynamics of sample objects over 120 years, in a dense grid of orbital elements covering the whole LEO phase space, considering two initial epochs. Beyond the standard area-to-mass ratio of typical payloads in LEO, we also assumed the use of area augmentation devices. The final goal of this analysis is to take advantage of the dynamical instabilities induced by orbital perturbations to reduce the residual lifetime of disposed spacecraft. The output of the simulations highlighted that the orbital perturbations due to geopotential, lunisolar perturbations and solar radiation pressure can significantly change the eccentricity of the orbit at selected inclinations bands. A Fourier transform analysis confirmed the role of given resonances in the eccentricity evolution as a function of the initial orbital elements. An impulsive strategy to move the spacecraft at end-of-life towards the unstable zones is also sketched.

The main focus of this work is to highlight the main parameters driving the future evolution of the debris environment, in presence of the planned LEO mega constellation of satellites. The goal is to define the best management practices, able to minimize the debris production in the future. First, in order to identify the most important parameters that are actually driving the evolution of the environment and in an effort to discrimiate between possibly equivalent scenarios, we applied tools from the statistical sciences, namely the Wilcoxon signed rank test, i.e., a nonparametric test which, without assuming normality in the data, allows us, given two samples, to assess whether their population mean ranks differ. Then, building on the index described in [6] and [3] and on the analysis of the simulations performed in the aforementioned studies, by means of a simplified model of the constellation building and managing, we define an index able to quantify the environmental impact of the mega constellations. The index takes into account the physical and orbital characteristics of the constellation satellites, along with the mitigation practices adopted for each constellation. Based on the expected collision risk and the capability of avoiding impacts, the operational and non-operational satellites and the related upper stages, present in each constellation, enter the index computation with different relative weights to properly account for the global constellation effects on the environment. An averaged, time evolving, index computed on altitude shells can give quantitative and visually effective indication of the effectivenes of the mitigation practices applied by a constellation operator. The model and the associated index, along with other metrics described in [6] and [4], allows us not only to highlight the prominence of some of the parameters entering in the definition of a satellite constellation but also to "predict" the influence that a change in that particular parameter is going to produce on the long term evolution of the environment. The metrics and the index are applied to the results of a sub-sample of the long term simulations, showing the relative importance of different design parameters and allowing a better ranking of possible mitigation measured. In the simulated scenarios, the parameters playing a major role in the effect that a mega-constellation cause on the environment are: the mass and the area of the satellites, the failure rate in the operational orbit and the collision avoidance success rate.

Natural perturbation and orbital resonances can be exploited to achieve passive dynamical de-orbiting for satellites at the end-of-life from LEO to GEO.

Within the definition of the scientific program of the Sardinian Radio telescope (under construction), our team has proposed to use this facility as radar system for the study of near-Earth objects (NEOs) and space debris.

Earth Moon and Planets, 95, pp. 5-10; International audience

O¨pik's analytical expressions relate in a simple way the semimajor axis, eccentricity and inclination of the projectile orbit to the magnitude and direction of the relative velocity vector at impact on a given target on circular orbit. These interesting quantities, along with the impact probability of any given projectile, can be all represented on a suitable projection giving a comprehensive picture of the impact risk on the selected target. By means of this theory a complete analysis of the impact risk on the International Space Station (ISS) is performed. It is found that the large majority of the debris population is on orbits such that a correlation exists between their impact velocity on the ISS and the angle between the velocity vector of the impactor and that of the ISS. The impactor population also is separated in terms of nature of the projectiles, with most of the low-medium velocity ones being particles related to solid rocket motor slag condensates. On the other hand, the highest velocity projectiles are composed mainly by fragments of past in-orbit explosions. The flux of projectiles on the ISS has been calculated for the planned operative lifetime of the Station, by assuming a realistic scenario of the future debris environment evolution and the actual planned altitude profile for the ISS mission. There is a factor 2-3 variation of the flux due to the changing ISS altitude. The most dangerous part of the mission appears to be the central one, when the ISS will orbit at about 450 km above the Earth.

The authors here propose a mission scenario, aimed at close exploration of a NearEarth Asteroid, exploiting low- V resonant trajectories. These trajectories allow repeated fly-bys of a chosen target. A selection procedure, which has been used to find some interesting mission opportunities in the 2005­2015 time frame, is described and the corresponding detailed mission profiles are derived, using an indirect optimization method.

We consider a small sample of known Near Earth Objects (NEOs), both asteroids and comets, with low Minimum Orbital Intersection Distance (MOID). Through a simple numerical procedure we generate slightly different orbits from this sample in such a way that these bodies will collide with the Earth at a specific epoch. Then we study the required change in orbital velocity (along track) in order to deflect these NEOs at different epochs before the impact event. The orbital evolution of these NEOs is performed through a full N-body numerical integrator. A comparison with analytical estimates is also performed in selected cases. Interesting features in the DeltaV Vs Time before impact plots are found; as a prominent result, we find that close approaches to the Earth before the epoch of the impact can make the overall deflection easier.

An abstract is not available.

The effect, on the growth of the space debris population, of the mitigation measures proposed at the international level, is investigated. We consider scenarios involving only the de-orbiting of satellites at the end-of-life and mixed scenarios involving both the de-orbiting and the re-orbiting in different super-LEO graveyard zones(above 1700, 2000 or 2500 km). Then the mitigation measures are analyzed in terms of the Delta V required to accomplish the de-orbiting or re-orbiting maneuvers, in a realistic traffic scenario. The use of delayed reentry disposal orbits, e.g. with 25-years residual lifetime, allows, on average, a saving of ~30 % on the amount of propellant. The use of the graveyard regions further reduces the propellant needs, while introducing possible problems due to the accumulation of a large number of objects in restricted regions of space. In particular, a collision risk analysis shows that the use of the lowest proposed graveyard zone, above 1700 km, gives way to a dramatic increase in the number of catastrophic collisions in the graveyard region, in the next decades. On the other hand, it has been shown that the de-orbiting of old spacecraft on elliptical disposal orbits with residual lifetime around 25 -- 50 years significantly increase the collision risk for the International Space Station. A mixed strategy, involving de-orbiting to 25-year residual lifetime disposal orbits and re-orbiting to a storage zone above 2000 km, appears to be the best compromise between the debris mitigation problem and the practical operational issues (i.e. in terms of Delta V required to accomplish the maneuvers).

An abstract is not available.

We use Opik's analytical expressions that relate in a simple way the semimajor axis, eccentricity and inclination of the projectile orbit to the magnitude and direction of the relative velocity vector at impact on a given target on circular orbit, and the CODRM-94 model of debris population, to find that the large majority of the debris population is on orbits such that a correlation exists between their impact velocity on the ISS and the angle between the velocity vector of the impactor and that of the ISS.

Two new missions to Near Earth Asteroids have been recently proposed to ESA. In this paper we present a selection of possible targets for these missions on the basis of the attainable Delta V and of the scientific interest of the asteroids.