A comparative assessment of object-based index formulations through long-term simulations of the space debris environment in Earth orbit

As the number of space missions in orbit is increasing, the amount of space debris in orbit is set to rise, even if with a stricter adherence to space debris mitigation rules are advocated for. The dynamic change in the space object environment is calling an international effort in defining indicators that can be used to assess the severity of the current space debris environment and to characterise its future possible evolutions. It is important to define what those indicators should measure, what their input are and how a shared methodology can be achieved to push for an international consensus around the concept of the space carrying capacity. In this paper, two approaches are followed, an object-based approach and environmental-based approach. For the object-based approach, a comparative analysis of the different formulations of a space debris index present in literature is performed, with the aim of identifying common underlying input parameters, dependencies from space debris populations characteristics, and assumptions among the different proposed formulations. Then, some of these formulations are selected to compute the space debris index on all the objects present in a long-term simulation of the space debris environment, under a specific future traffic and mitigation scenario to understand whether, by properly normalising the indicators, different space debris formulations can give a consistent picture of how the global space debris environment is evolving. On the other side, an environment-based approach is also followed where a single parameter summarises the overall status of the debris environment. We target at linking an environment-based metric to an object-based space debris metric, aggregated on all the space missions to have a unique evaluation on how a given evolution scenario is performing.