The countdown for the launch of NASA’s Space Launch System (SLS) moon rocket officially began just over 48 hours before the six massive engines on the 32-story rocket at last lit at 1:47 a.m. ET this morning, muscling the 2.6 million kg (5.75 million lb.) machine off of launch Pad 39B at the Kennedy Space Center in Florida, and hurling it moon-ward. With the successful liftoff, NASA’s Artemis program—which aims to have Americans back on the moon by as early as late 2025—at last got underway.

In some respects, however, the true countdown for this morning’s launch began on Jan. 15, 2004, when then President George W. Bush announced that the U.S. would be returning astronauts to the moon and called for the construction of a new heavy-lift rocket to make …