As Artemis II races home from the moon, its crew is preparing for its “riding a fireball through the atmosphere” moment, the most dangerous phase of the mission as the Orion spacecraft plunges back to Earth for a high-speed re-entry on Friday.The capsule is expected to endure extreme heat and pressure during its descent, putting renewed focus on Orion’s heat shield, the critical system designed to protect the astronauts as they return from deep space.Artemis II is scheduled to begin its entry interface at 7.53 pm ET, with splashdown expected in the Pacific Ocean at 8.07 pm ET.As Orion heads home, Nasa says the spacecraft is still gaining speed. Artemis II entry flight director Rick Henfling said it is expected to reach a maximum speed of 38,366 km/h before re-entry.“We’re continuing to speed up as we speak,” he said.The capsule will plunge through the atmosphere at 25,000 mph and face temperatures of about 5,000 degrees Fahrenheit- roughly half as hot as the sun’s surface. The crew’s survival will depend on Orion’s 16.5-foot-wide heat shield, a dome on the bottom of the spacecraft designed to slough away at controlled rates during descent.But the heat shield remains under close watch after problems seen during the uncrewed Artemis I mission in 2022.That mission’s shield returned with more than 100 cracks and abrasions. Photos from the re-entry showed pockmarks across the surface where chunks of protective material appeared to have broken away.“The unexpected behavior of the [shield material] creates a risk that the heat shield may not sufficiently protect the capsule’s systems and crew from the extreme heat of reentry on future missions,” a 2024 Nasa assessment of the Artemis I heat shield read, according to Spacenews.com.Nasa later determined the issue was caused by the way the shield’s protective material, called Avcoat, had been applied. According to Space.com, the material had been packed too densely, preventing hot gases from escaping and causing the cracking.Orion capsule manufacturer Lockheed Martin adjusted the Avcoat application for Artemis II, and Nasa gave the spacecraft clearance to fly. The agency said cabin temperatures during Artemis I would still have remained safe for astronauts despite the damage.“We just slightly modified the density to allow gases in the [Avcoat] to escape during high heating and cool down,” said Blaine Brown, the Lockheed Martin systems director who helped direct construction of the Artemis Orion capsules.“We support Nasa’s decision to fly the Artemis II mission with its current heat shield and are committed to seeing Orion safely launch and return on its historic mission to the moon with crew onboard,” he told Space.com.Avcoat was also used on Apollo heat shields, though it was applied by hand to a honeycomb-like framework. Artemis heat shields, by contrast, are assembled from about 200 Avcoat blocks.Even with Nasa’s confidence in the updated design, Friday’s return will be the first full test of the revised shield during a crewed mission.The concerns have revived memories of the 2003 Columbia disaster, when the space shuttle broke apart during re-entry after a piece of debris damaged its heat shield during launch. All seven astronauts on board were killed.Columbia remains the only crewed spacecraft lost because of re-entry heat. Russian cosmonaut Vladimir Komarov also died during the return of Soyuz 1 in 1967, but that was caused by an electrical failure that prevented his parachutes from deploying.Nasa officials say Orion appears to be in excellent condition for re-entry and that weather conditions are looking favourable, even as they stress that the final phase of the mission remains one of its highest-risk moments.“We’re down to the wire now,” said Lakiesha Hawkins, acting deputy associate administrator for Nasa’s Exploration Systems Development Mission Directorate.“Obviously getting the crew back home and getting them landed safely is a significant part of the risk that’s still in front of us.”Nasa officials said the USS John P Murtha has left port and is heading toward the recovery area in the Pacific Ocean. Nasa and U.S. military personnel aboard the ship are preparing to assist with splashdown and recovery.Artemis II landing and recovery director Liliana Villarreal said divers will open Orion’s hatch after splashdown and help the astronauts from their seats onto an inflatable raft known as the front porch.From there, two Navy helicopters will rotate to pick up the four astronauts and bring them back to the recovery ship “within a few minutes of each other,” Villareal said.The astronauts will then undergo routine post-flight medical checks aboard the ship.While teams on the ground and at sea prepare for landing, the crew has spent its final days in space getting ready for the return.Commander Reid Wiseman, pilot Victor Glover and mission specialists Christina Koch and Jeremy Hansen woke up Wednesday 322,316 kilometres from Earth and 134,459 kilometres from the moon to the sound of Queen and David Bowie’s Under Pressure.During an evening news conference, the crew reflected on the mission and what lies ahead. Glover said he has been thinking about splashdown “since April 3, 2023, when we got assigned to this mission.”“We’ve still got two more days, and riding a fireball through the atmosphere is profound as well,” he said. “I’m gonna be thinking about and talking about all of these things for the rest of my life.”Wiseman described watching the eclipse of the Earth from the spacecraft.“It is amazing to watch your home planet disappear behind the moon,” he said. “It was just an unbelievable sight, and then it was gone.”The mission has already made history. Artemis II broke the distance record Monday as the farthest humans have flown from Earth, reaching 406,771 kilometres on the far side of the moon and surpassing the previous record of 400,171 kilometres set by Apollo 13 in 1970.The astronauts spent several hours capturing images and describing the sights as they looped around the moon before beginning the trip back toward Earth.
