Engineers started preparing the Artemis 1 Space Launch System moon rocket for launch on Monday for a long-overdue test flight to send an unmanned Orion capsule on a 42-day journey around the moon.
This preparation came after months of tests, troubleshooting, and repairs.
After midnight, lightning and rain showers moved within five nautical miles of launch pad 39B, causing Launch Director Charlie Blackwell-Thompson to postpone the beginning of propellant loading by 55 minutes.
Then, as the fueling was proceeding, a hydrogen leak was found.
Finding the root of a brief communications hiccup in one of the channels carrying commands and information to and from the Orion spacecraft.
One such probable concern was a potential sign of a leak of some kind, a thermal insulation crack, or some other malfunction seen on the exterior of the rocket's core stage.
What effect, if any, the problems may have on the scheduled 8:33 a.m. launch time was not immediately apparent.
During a two-hour launch window, engineers had intended to send the most potent rocket NASA has ever constructed out on its eagerly anticipated first flight.