A Russian Progress M-10M freighter left the International Space Station for a return flight to Earth Saturday, officials said.

The unmanned spacecraft, which brought 2.5 tons of supplies to the space station six months ago, was scheduled to land in the Pacific Ocean a few hours after undocking from the ISS.

The next launch is set for Sunday from the Baikonur Space Center in Kazakhstan.

That launch is a critical one, Space.com reported. Another unmanned Progress freighter crashed after launch in August because of the failure of its Soyuz rocket.

If Sunday's launch is unsuccessful, plans to send three new crew members to the station Nov. 14 are expected to be scrubbed. Russia's manned and unmanned space vehicles use similar Soyuz rockets for launching.

The three crew members now on the space station are scheduled for departure Nov. 22, so a decision to delay sending replacements would leave the station with no one on board.

With the end of the U.S. space shuttle program, the station is dependent on Russian spacecraft.