What critical preparations and systems testing do astronauts perform during the Artemis II mission's high Earth orbit phase?

During the Artemis II mission's high Earth orbit phase, astronauts conduct a comprehensive 24-hour systems check while remaining relatively close to Earth, allowing them to familiarize themselves with the Orion spacecraft that serves as their home for the mission duration. A key component involves the Proximity Operations Demonstration, where crew members practice manual handling tests using the expended upper stage and adapter as targets. This exercise prepares future crews for essential rendezvous, docking, and undocking maneuvers with other spacecraft, representing crucial training for lunar missions and deep space operations.