This paper evaluates how effectively the Vera C. Rubin Observatory’s LSST can detect asteroids on a direct collision course with Earth and how much warning time those detections provide. LSST performs well for large, hazardous asteroids but struggles to give long advance warning for smaller impactors, which are often discovered only days to weeks before impact. The authors show that cadence and linking limitations, not sky coverage, are the main bottlenecks, and argue that LSST must be paired with high-cadence surveys to achieve robust planetary defense.