Mitigation

No guidelines currently exist for the end-of-life of Libration Point Orbits (LPOs) and Highly Elliptical Orbit missions; however, as current and future missions are planned to be placed on these orbits, it is a critical aspect to clear these regions at the end of operations. Methodologies for the design of optimal transfers to end-of-life disposal were studied. The definition of stable and unstable orbit conditions developed in Task 1 suggested a novel way of active spacecraft disposal at the end-of mission by identifying natural long-term stable graveyard orbits, or fast eccentricity grow trajectories which lead to Earth re-entry. The effect of natural perturbations such as luni-solar perturbation or solar radiation pressure and artificial low-thrust propulsion or impulsive manoeuvres were exploited for the disposal design. In this phase the research was focused on the disposal of Highly Elliptical Orbits, Libration Point Orbits and Medium Earth Orbits. The options analysed are Earth re-entry, or injection into a graveyard orbit for HEOs, while spacecraft on LPOs can be disposed through an Earth re-entry, or towards the inner or the outer solar system, by means of delta-v manoeuvres or the enhancement of solar radiation pressure with some deployable light reflective surfaces. In order to perform a parametric study, different starting dates and conditions for the mission disposal were considered, while the manoeuvre was optimised considering the constraints on the available fuel at the end-of-life. Five European Space Agency missions were selected as scenarios: Herschel, GAIA, SOHO as LPOs, and INTEGRAL (see Fig. 2) and XMM-Newton as HEOs. The robustness of the end-of-life strategies was evaluated by analysing the risk of an uncontrolled re-entry into the Earth’s atmosphere or the planetary protection compliance for mission at the Libration Point Orbits.

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