The evolution of cataloged orbital debris in low Earth orbit (LEO) over the last quarter of century was analyzed in detail, to gather insights on the development of space activities, on the effectiveness of the debris mitigation measures recommended in the meantime, and on the environmental impact of fragmentations, in particular collisions, both intentional and accidental. The main conclusion was that the observed evolution matched on the whole the predictions of the unmitigated business-as-usual scenarios simulated twenty years ago, and that the benefits caused by the progressive worldwide adoption of mitigation measures were unfortunately offset by a couple of catastrophic collisions and prolonged weak solar activity. Concerning the recorded growth of cataloged fragmentation debris, nowhere have the signs of an exponential increase been revealed so far. Nevertheless, the overall picture has worsened during the last quarter of a century and extreme care is required in planning and conducting new space activities from now on, especially in a phase of increased and ever more rapid exploitation. In order to assess the sustainability of space activities, especially over the next 10–30 years, several environmental criticality indexes have been introduced and discussed, estimating their current values in LEO, as well as their magnitudes associated with specific scenarios of debris growth. They could provide simple tools for evaluating the relative and absolute impact on the debris environment, either in LEO as a whole or in specific altitude shells, of new spacecraft deployments and operations, as in the case of mega-constellations of satellites. The main result of this preliminary analysis was that all indexes were consistent in indicating that from one third to one half of the LEO capacity to sustain long-term space activities – as they are currently conceived – has already been saturated. The 2020s, with their many planned launches, will therefore be crucial years for enforcing more effective debris mitigation and remediation measures.

详细分析了近四分之一世纪以来编目轨道碎片在低地球轨道（LEO）中的演变，以收集有关空间活动发展，同时建议的减缓碎片措施的有效性以及关于地球活动的见解。碎片的环境影响，尤其是故意和偶然的碰撞。主要结论是，观察到的演变总体上与20年前模拟的未缓和的照常使用情景的预测相符，不幸的是，两次灾难性的碰撞抵消了全球范围内逐步采用缓解措施所带来的收益。并延长了弱太阳活动。关于记录的碎片碎片的增长记录，到目前为止，还没有发现指数级增长的迹象。然而，整个情况在过去的25年中恶化了，从现在开始，在规划和开展新的太空活动时需要格外小心，尤其是在越来越多和越来越快的开发阶段。为了评估空间活动的可持续性，尤其是在未来10-30年内，已经引入和讨论了几个环境关键性指标，以估计它们在LEO中的当前值以及与碎片增长的特定场景相关的大小。它们可以提供简单的工具来评估新航天器的部署和运行对整个LEO或特定高度壳中碎片环境的相对和绝对影响，就像巨型卫星一样。这项初步分析的主要结果是，所有指标均保持一致，表明当前设想的维持长期空间活动的LEO能力的三分之一至一半已经饱和。因此，2020年及其计划中的许多次发射，对于执行更有效的减缓碎片和补救措施至关重要。