It would be the first US splashdown in darkness since Apollo 8‘s crew returned from the moon in 1968.
NASA’s Mike Hopkins, Victor Glover and Shannon Walker, and Japan’s Soichi Noguchi, headed home in the same Dragon capsule that delivered them to the space station last November.
The ride back was expected to take just 6 1/2 hours.
“Thanks for your hospitality,” Hopkins radioed as the capsule undocked 260 miles (420 kilometers) above Mali.
SpaceX targeted a splashdown around 3 am Sunday in the Gulf of Mexico off the coast of Panama City, Florida.
Despite the early hour, the Coast Guard deployed extra patrols — and spotlights — to keep any night-owl sightseers away.
The capsule of the first SpaceX crew was surrounded by pleasure boaters last summer, posing a safety risk.
Hopkins, the spacecraft commander, rocketed into orbit with his crew on November 15 from NASA‘s Kennedy Space Center.
Their replacements arrived a week ago aboard their own Dragon capsule — the same one that launched SpaceX’s first crew last spring.
The four should have been back by now, but high offshore wind kept them at the space station a few extra days.
SpaceX and NASA determined the best weather would be before dawn.
The delays allowed Glover to celebrate his 45th birthday in space Friday.
“Gratitude, wonder, connection. I’m full of and motivated by these feelings on my birthday, as my first mission to space comes to an end,” Glover tweeted.
Saturday night’s undocking left seven astronauts at the space station: three Americans, two Russians, one Japanese and one French.