NASA astronaut Don Pettit, accompanied by two Russian cosmonauts, arrived at the International Space Station on Sept. 11. The trio joined the crew of Expedition 71, which is exploring neuro-degenerative diseases and therapies, space botany, space-caused fluid shifts, and algae-based life support systems. He will spend approximately six months aboard the orbital outpost advancing scientific research before returning to Earth in the spring of 2025.

Pettit, a flight engineer who earned a University of Arizona chemical engineering PhD in 1983, will join the crew of Expedition 72 during his stay when Expedition 71 is complete. His research will help prepare crew for future space missions.

This is Pettit’s fourth NASA mission. During his previous stints, Pettit logged 370 days in space and conducted two spacewalks totaling 13 hours and 17 minutes and made “integral advancements in technology and demonstrations for human exploration,” according to NASA. Since his first mission aboard the ISS in 2002, he’s taken hundreds of thousands of photos, some of which are published in the book Spaceborne.

Pettit was selected by NASA in 1996. Prior to becoming an astronaut, he worked as a staff scientist at the Los Alamos National Laboratory in New Mexico.

Pettit has learned to laugh when changes are called for during a mission, he said.

“Change happens all the time,” he said. “It’s just the way of life when you’re dealing with the frontier. Space station is in a frontier. It’s a place where mistakes can cost you dearly. It’s a place that’s rich in discovery.”