The low LEO protected region: new challenges from large satellite constellations

Since the definition of a Low Earth Orbit (LEO) protected region, up to the altitude of 2000 km, at the beginning of the 2000s, most of the attention of the space debris mitigation community was focused on heights greater than 600 km. In such orbital regimes, in fact, the average residual lifetimes of inert satellites and rocket bodies are typically greater than 20 years and the highest concentrations of functional satellites and space debris were historically found. The low LEO region, below 600 km, is however extremely important for space applications. In fact, since the last Apollo mission to the Moon, in December 1972, all human spaceflight was carried out there, the International Space Station, the planned large Chinese space station, the Indian crewed program and possible human tended private havens are making or will make use of this region of space, and also absolutely critical missions, like the Hubble Space Telescope, are orbiting below 600 km. In recent years there was a dramatic increase in the launch rate of small satellites and cubesats in low LEO, boosting the number of potentially risky objects to be tracked and monitored. But the most dramatic development currently going on is the deployment of large satellite constellations, with almost 10,000 spacecraft planned only in low LEO in the coming years. Even though any failed satellite of the planned mega-constellations will decay from orbit in less than 25 years, therefore formally complying with current international space debris mitigation guidelines, it is realistic to expect a relatively high number of failures, considering the experimental nature of spacecraft tested in space, and in great numbers, for the first time. The short- and medium-term consequences for the satellite operations in low LEO might therefore be far from negligible. The aim of this paper is therefore to present a preliminary review of the new challenges to be faced by spacecraft and space operations below 600 km, in the coming years, due to the deployment of large constellations of small satellites.