CRASH Clock (June 2025): 5.5 days
NOTE: The CRASH Clock is still under development, and we are currently refining its value. Check back soon for updates.
The CRASH Clock is an environmental indicator for assessing the collision risk in low Earth orbit (LEO). Details can be found in this preprint (revised based on community feedback): https://arxiv.org/abs/2512.09643.
The CRASH Clock asks what is the expected time for a collision in LEO between tracked artificial objects, which includes satellites, debris, and abandoned rocket bodies — if all manoeuvres were to stop. While this is a hypothetical situation, it reflects the degree to which humanity is dependent on errorless operations in orbit. The CRASH Clock also does not consider non-trackable objects. Thus, its value is conservative.
As of June 2025, the CRASH Clock is 5.5 days. In January 2018, it was 164 days.
Another way to think of the CRASH Clock is the reaction time needed to respond to a serious loss of space situational awareness. As an example, consider the probability of a collision within 24 hr (for no manoeuvres) as a function of CRASH Clock value. The “Danger Zone” is given as the CRASH Clock for which there is more than a 50% probability of having a collision, while the green represents CRASH Clock values for which there is less than a 10% probability.
