The Discovery crew began their long journey back to Earth Saturday as the shuttle cast off from the International Space Station (ISS) after eight days of orbital work. Discovery pulled away from its berth at the end of the station's Destiny laboratory at about 6:08 a.m. EDT (1008 GMT) to begin its planned two-day trip back to Earth.

The STS-121 astronaut took some final parting snapshots before hatches linking their spacecraft to the ISS were closed at about 4:00 a.m. EDT (0800 GMT). “We have physical separation,” Discovery’s commander Steven Lindsey said as the 100-ton orbiter pulled away from the 200-ton space station 223 miles above and off the coast of New Zealand.

Meanwhile, the three astronauts aboard the ISS watched their departing comrades after a busy week of restocking the space station's supply, testing an orbital inspection boom for use as a repair platform and evaluating a heat shield crack repair method. “This moment came so fast,” ISS Expedition 13 commander Pavel Vinogradov. “Have a safe trip, soft landings, and we’ll see you on the ground in a few months,” was ISS Expedition 13 flight engineer Jeffrey Williams' message as the shuttle pulled away.

Discovery will hover about 40 nautical miles (74 kilometers) from the ISS today while STS-121 mission specialists Lisa Nowak and Stephanie Wilson complete a final check of the orbiter’s nose cap and starboard wing leading edge. Back on earth, engineers continue to study a potential hydrazine fuel leak in one of Discovery’s three auxiliary power units. Flight controllers will test the small leak on Sunday to determine if the APU should remain in operation during Monday’s planned landing. Discovery is set to to land in Cape Canaveral, Florida at NASA’s Kennedy Space Center on July 17 at about 9:14 a.m. EDT (1314 GMT)