Safety of multi-impulse kinetic deflection below fragmentation thresholds

Determine whether performing deflection of near-Earth asteroid 2024 YR4 by applying multiple smaller kinetic-impactor strikes, each imparting a change in velocity ΔV less than 10% of the asteroid’s surface escape velocity (the fragmentation-avoidance heuristic used in this study), will avoid unwanted fragmentation of the asteroid.

Background

The paper adopts a heuristic to minimize fragmentation risk during deflection: limiting the imparted ΔV to no more than 10% of the asteroid’s surface escape velocity. For 2024 YR4, some deflection scenarios—especially for smaller mass realizations or when larger deflection distances are needed—would require multiple kinetic impactors launched on different dates to cumulatively achieve the necessary deflection while keeping each single impulse below the fragmentation threshold.

However, the authors note it is currently unknown whether splitting a deflection into multiple impulses actually avoids fragmentation. This uncertainty directly affects the feasibility and safety of multi-impactor deflection strategies, where generating debris could endanger astronauts or spacecraft in the Earth–Moon system.

References

In fact, the question of whether splitting a deflection up into multiple impulses to keep each under the fragmentation threshold will actually avoid unwanted fragmentation remains unanswered. Further modeling and simulation work is needed to properly address that question.

— Space Mission Options for Reconnaissance and Mitigation of Asteroid 2024 YR4  (2509.12351 - Barbee et al., 15 Sep 2025) in Subsection ‘Kinetic Impactor Deflection Mission Analysis’ (within Section ‘Mission Trajectory Options’)