Expedition 4 was a mission to the International Space Station (ISS) that took place from December 2001 to June 2002. It was part of the continuous human presence in space and involved a crew of three astronauts: Yuri Onufrienko, Daniel Bursch, and Carl Walz. The mission focused on scientific research and technology demonstrations in microgravity. During their time aboard the ISS, the crew conducted various experiments in fields such as biology, physics, and materials science. They also performed maintenance tasks and contributed to the ongoing construction of the ISS, helping to expand its capabilities for future missions.