Evaluating the environmental sustainability of large satellite constellations in Low Earth Orbit

The current plans envisaging the deployment of very large constellations in low Earth orbit (LEO), some consisting of thousands of spacecraft, raised a growing concern regarding the long-term sustainability of the near-Earth space environment with the present-day guidelines recommended by the Inter-Agency Space Debris Coordination Committee (IADC). Assessing the impact of the proliferation of small satellites and large constellations has therefore been identified as a priority, in order to evaluate if additional, and more stringent, mitigation measures might be needed to preserve the long-term access and utilization of the LEO protected region. With this goal in mind, several analytical expressions, based on reasonable simplifying assumptions, were developed for the assessment of the environment criticality of large constellations and huge numbers of small satellites in LEO. They can provide preliminary quantitative answers to difficult questions, with no need of complex models and computations, suggesting clues and insights useful for steering further refinements with more complex and time expensive tools and approaches. Moreover, a specific figure of merit was introduced for gauging the environment criticality of new large constellations: the collision rate percentage increase. Of course, the applicable alert threshold may be open to discussion, but due to the fact that several constellations might be operated at the same time, assuming a tolerability limit of no more than 10% per single constellation seemed a sensible recommendation. Finally, several quantitative examples and the associated results are presented and discussed.