The 10-day Artemis II mission will send four astronauts to the Moon, including Christina Koch, Reid Wiseman, Victor Glover, and Canadian Jeremy Hansen. The mission won’t include a landing, but it will be the first time astronauts launch aboard NASA’s Space Launch System rocket inside the Orion crew capsule that will orbit the Moon before returning to Earth with a planned splashdown in the Pacific Ocean.

It will follow the uncrewed Artemis I mission that finally launched in November 2022 after years of delays due to technical difficulties and even a few hurricanes. Although Artemis I was a success, investigations into unexpected charring on the Orion capsule’s heat shield, critical to protecting astronauts when re-entering the Earth’s atmosphere, have contributed to the additional delays.

Following extensive analysis, NASA says it has determined that the Orion capsule’s heat shield “did not allow for enough of the gases generated inside a material called Avcoat to escape,” causing some of it to unexpectedly crack and break off during the Artemis I mission, instead of wearing away gradually as it heats up. Despite the charring, temperature sensors indicated the interior of the Orion capsule remained comfortable and safe for astronauts.

For Artemis II, NASA engineers have decided the capsule “can keep the crew safe during the planned mission with changes to Orion’s trajectory as it enters Earth’s atmosphere” and are preparing the capsule using the heat shield already attached. “The updates to our mission plans are a positive step toward ensuring we can safely accomplish our objectives at the Moon and develop the technologies and capabilities needed for crewed Mars missions,” said Catherine Koerner, associate administrator Exploration Systems Development Mission Directorate.

However, for the more ambitious Artemis III mission, the agency says it is “implementing enhancements to how heat shields for crewed returns from lunar landing missions are manufactured” based on what it learned from Artemis I.