Orbital debris in low earth orbit: how the situation has changed since the advent of mega-constellations

Despite the crude impression from looking superficially only at the total numbers, the situation in low Earth orbit has not deteriorated appreciably from late 2009 to early 2025, as far as orbital debris proper is concerned, even though satellite mega-constellations have appeared in the meantime, and the number of active spacecraft has increased tenfold. This is because mega-constellations have so far been handled appropriately, putting effective debris prevention and mitigation measures in place. But luck also played its part, as no serious accidents occurred, nor any catastrophic accidental collisions, which would have had more than a 50% chance of happening. The sensitivity of the low Earth orbit environment to sporadic single catastrophic events, as collisions involving abandoned spacecraft and upper stages, especially above 650 km, remains a pending threat that cannot be ignored. Therefore, a combination of adequate mitigation and remediation measures is needed to ensure smooth short-term operations in low Earth orbit and the long-term sustainability of space activities.