In the quiet arithmetic of orbital mechanics, a five-story remnant of human ambition is set to meet the moon at over 5,000 miles per hour — not by design, but by the indifferent logic of physics. A defunct Falcon 9 upper stage, left adrift after carrying lunar landers in January 2025, will strike the moon's northwestern region near Einstein Crater on Wednesday at 2:35 a.m. Eastern time. What began as a mission of exploration becomes, in its aftermath, an unplanned experiment — one that NASA intends to study as a rare window into how the lunar surface responds to collision.