Artemis II hit a key milestone Thursday when Orion ignited its engine, propelling the crew on a trip that will reach deeper into space than any human has traveled.

A key engine burn Thursday is expected to put NASA's Artemis II astronauts on an irreversible path around the moon.

The Artemis II astronauts, after saying goodbye to family and friends, were strapped into their seats aboard the Orion spacecraft by early afternoon, hours before the launch window opened at 6:24 p.m. Eastern time. As the astronauts sat, NASA continued with checks to ensure the safety of the crew before liftoff.

Track the progress of the Artemis II mission with the latest updates and news from the historic mission to the moon's orbit.

A NASA crew of four astronauts are preparing for a critical stage of their journey that will set them on course for the moon, a step that will ultimately bring them closer to the lunar surface than anyone has been in more than 50 years.

Victor Glover, Jeremy Hansen, Reid Wiseman and Christina Koch's mission is partly intended to pave the way for a future lunar landing in the coming years.