Airspace closures due to reentering space objects.

Uncontrolled reentries of space objects create a collision risk with aircraft in flight. While the probability of a strike is low, the consequences could be catastrophic. Moreover, the risk is rising due to increases in both reentries and flights. In response, national authorities may choose to preemptively close airspace during reentry events; some have already done so. We determine the probability for a rocket body reentry within airspace over a range of air traffic densities. The highest-density regions, around major airports, have a 0.8% chance per year of being affected by an uncontrolled reentry. This rate rises to 26% for larger but still busy areas of airspace, such as that found in the northeastern United States, northern Europe, or around major cities in the Asia-Pacific region. For a given reentry, the collision risk in the underlying airspace increases with the air traffic density. However, the economic consequences of flight delays also increase should that airspace be closed. This situation puts national authorities in a dilemma-to close airspace or not-with safety and economic implications either way. The collision risk could be mitigated if controlled reentries into the ocean were required for all missions. However, over 2300 rocket bodies are already in orbit and will eventually reenter in an uncontrolled manner. Airspace authorities will face the challenge of uncontrolled reentries for decades to come.