Compliance of disposal orbits with the French Space Operations Act: The Good Practices and the STELA tool☆

Abstract Space debris mitigation is one objective of the French Space Operations Act (FSOA), in line with Inter-Agency Space Debris Coordination Committee (IADC) recommendations, through the removal of non-operational objects from populated regions. At the end of their mission, space objects are to be placed on orbits that will minimize future hazards to space objects orbiting in the same region. The FSOA, which came into force in 2010, ensures that technical risks associated with space activities are properly mitigated. The Act confers CNES a central support role in providing technical expertise to government on regulations dealing with space operations. In order to address the compliance of disposal orbits with the law technical requirements, CNES draws up Good Practices as well as a dedicated tool, Semi-analytic Tool for End of Life Analysis (STELA). The verification of the criteria of the French Space Operations Act requires long term orbit propagation to evaluate the evolution of the orbital elements over long time scales (up to more than 100 years). The Good Practices define the minimum dynamical model required to compute the orbital evolution with sufficient accuracy, and detail key computation hypotheses such as drag and reflecting areas, drag coefficient, reflectivity coefficient, solar activity, atmospheric density model and so on. They also recommend a methodology adapted to each orbit type (LEO, GEO, GTO) to assess the criteria of the French Space Operations Act. The most recent works have concerned GTO, for which some couplings occur between dynamic perturbations. A small change in the initial conditions or in the estimation of the drag effect will significantly change the entrance conditions in resonance areas and thus the orbital evolution. To cope with this difficulty, a statistical method has been developed. This paper gives an overview of the Good Practices for orbit propagation in LEO, GEO and GTO as well as a brief description of the STELA tool. It explains the specificities of GTO and the need for a statistical approach, through a Monte-Carlo campaign of orbital propagations. Then, it raises the question of the statistical convergence and proposes a methodology to estimate a confidence interval for the results. Finally, special cases consisting of typical GTO are treated.