Exploiting orbital resonances for the disposal of objects from Low Earth Orbit

The steadily growing exploitation of the circumterrestrial space with the significant increase in the traffic launch, mostly related to private sector and associated to the forthcoming advent of the mega-constellations of satellites, calls for a renewed and increased effort towards efficient and effective mitigation measures. The de-orbiting of the spacecraft at the end-of-life, within a given residual orbital lifetime, currently represents a fundamental part of a space mission and an essential step to guarantee the future exploitation of the Earth orbit. In this respect an accurate dynamical characterization of the circumterrestrial region can identify the natural orbital mechanisms that can be exploited to improve the current end-of-life measures. The goal is to identify stable and unstable regions in the phase space where the objects could be moved to exploit either long term "graveyards" or, possibly and preferentially, faster escape routes. To this purpose, the most accurate dynamical mapping of the circumterrestrial space, from the Low Earth Orbit to the Geostationary Orbit, ever performed at this date was realized within the Horizon 2020 project ReDSHIFT (Revolutionary Design of Spacecraft through Holistic Integration of Future Technologies). The underlying idea stems from the asteroid dynamics where small Main Belt bodies are driven towards the inner Solar System by powerful resonances (and non-gravitational forces) which increase their eccentricity leading them to gravitationally interact with the terrestrial planets. Similarly, in the Earth orbit we identified the main resonances, involving the rate of precession of Right Ascension of the Ascending Node, the argument of perigee and the apparent mean motion of the Sun with respect to the ecliptic plane. The long-term effects associated with these resonances that can be used to de-orbiting is indeed a variation in eccentricity, that can become quasi-secular when the effects of the solar radiation pressure is coupled with the planetary oblateness. From the theoretical point of view, the effect was explained by computing the equilibrium points and the corresponding stability of the dynamical system associated with solar radiation pressure and Earth's oblateness. In particular, it turns out that the natural de-orbiting can occur in two situations, either by following the hyperbolic invariant curves stemming from a saddle equilibrium point or by following a wide enough libration curve in the neighborhood of an elliptic equilibrium point. A thorough characterization of these resonances by means of a frequency analysis was performed too. Finally, by means of long term simulations of the evolution of a sample traffic launch we showed how these resonances can sometimes be exploited as natural reentry corridors (the so-called "de-orbiting highways") to improve the disposal of the spacecraft at the end-of-life and help in stabilizing the space debris population.