Their return caps a protracted space mission that was fraught with uncertainty and technical troubles and turned a rare instance of NASA's contingency planning - and the latest failures of Boeing's Starliner - into a global spectacle.

NASA astronauts are returning to Earth after nine months in space. Experts have said a prolonged period in space can come with changes to human physiology and psychology.

NASA astronauts Butch Wilmore and Suni Williams have returned to Earth after being stuck in space for more than nine months.