March 30 (Reuters) - NASA's Artemis program is the U.S. effort to return astronauts to the moon for the first time since the Apollo era and eventually establish a sustained human presence there, a goal Washington has framed as central to maintaining space leadership amid growing competition from China.

The Artemis II mission will not land on the moon but will instead circle it to test NASA's Orion capsule.

NASA hopes its gigantic Space Launch System (SLS) rocket will launch the Orion capsule containing its four-person crew during a two-hour window that opens at 6:24 p.m. EDT today.