Russia's Progress M-50, which had been docked at the International Space Station (ISS) for some time,disengaged late Wednesday night and sank in the Pacific Ocean early Thursday morning.

According to the Russian Mission Control Center, the disengagement was to prepare for the Progress M-51, which was set for launch early Friday morning from the Baikonur launch pad, to deliver food supplies and other cargo to the space station.

The new cargo space ship was expected to arrive on Saturday, Christmas Day, with replenishments.

Such maneuvers were "a routine thing." The returning pod contained trash that were incinerated upon reentry to Earth's atmosphere.

The Progress M-50 was launched into space in August, bringing 2.5 tons of supplies to the two astronauts, who have been aboard the ISS for two months on a six-month mission.

ISS Expedition 10 commander Leroy Chiao and flight engineer Salizhan Sharipov have had to cut calorie intake by 10 percent to make sure the food onboard the ISS would last until the delivery.

The calorie cutbacks began earlier this month when Earth bound officials realized the two men had begun digging into a 45-day food reserve earlier than planned.

A Soyuz vehicle remains docked at the ISS at all times for an emergency evacuation in case something goes wrong with the Baikonur launch.

Supply problems have persisted at the space station since the larger-capacity US space shuttles were grounded in 2003 after the crash of the Columbia shuttle. Russian spacecraft have carried the heavy load of delivering crews and cargoes to the ISS for nearly two years.