Closing out a 25-day voyage around the moon, NASA's Artemis 1 spacecraft closed in on Earth Saturday, on track for a 25,000-mph re-entry Sunday that will subject the unpiloted capsule to a hellish 5,000-degree inferno before splashdown off Baja California. In an unexpected but richly-symbolic coincidence, the end of the Artemis 1 mission, expected at 12:39 p.m., will come 50 years to the day after the final Apollo moon landing in 1972. Testing the Orion capsule's 16.5-foot-wide Apollo-derived Avcoat heat shield is the top priority of the Artemis 1 mission, "and it is our priority-one objective for a reason," said mission manager Mike Sarafin. "There is no arc jet or aerothermal facility here on Earth capable of replicating hypersonic reentry with a heat shield of this size," he said. "And it is a brand new heat shield design, and it is a safety-critical piece of equipment. It is designed to protect the spacecraft and (future astronauts) ... so the heat shield needs to work." Launched N