About 24 hours prior to its collision, NASA’s Double Asteroid Redirect Test (DART) probe performed its last course correction based on commands sent by ground controllers. “It’s pointed to within a football field of the central body,” said Bobby Braun of the Johns Hopkins Applied Physics Lab (APL). “That last maneuver was spot-on.”

Even at this late stage, DART’s onboard camera couldn’t resolve its ultimate target, the small asteroid Dimorphos, so the central body it was targeting is the partner Dimorphos orbits, called Didymos. DART’s onboard navigation couldn’t start navigating toward its target until it could see it, which was only expected to occur about 90 minutes before impact. At that point, the navigation started adjusting DART’s course to get it heading straight at Dimorphos. Ground controllers, separated by about a minute of communications time, could only watch.

“Space is full of moments, and we’re going to have a moment tonight, hopefully,” said Braun.