Corrections to the space station's orbit are conducted periodically before launches of Russian cargo ships and U.S. shuttles to compensate for the Earth's gravity and to ensure successful dockings.
"Mission Control Wednesday test-fired two Zvezda module engines [on board the ISS] to check their operation before the scheduled ISS orbit correction April 28," a mission control spokesman said.
"The maneuver is required to create optimal conditions for a Progress M-60 cargo ship docking with the ISS," the official said, adding that the launch of the spacecraft has been scheduled for May 12 from the Baikonur space center in Kazakhstan.
The current ISS crew consists of Commander Fyodor Yurchikhin and Flight Engineer Oleg Kotov, both from Russia, who will spend 189 days at the station and will conduct three spacewalks, one in U.S.-made spacesuits and the other two in Russian-made outfits.
The third crewmember, U.S. astronaut Sunita Williams, who replaced the European Space Agency's German astronaut Thomas Reiter in December 2006, will stay on board the ISS for a further several months.
They will later be joined by astronaut Clayton Anderson, who will arrive on board the space shuttle Endeavor June 28, and Daniel Tani, who will be carried to the ISS by the space shuttle Discovery, scheduled for lift off September 7.
