The space shuttle Discovery touches down on the runway at the Kennedy Space Center in Cape Canaveral on July 17, 2006. (Photo: John Raoux/AP Wide World)

The space shuttle Discovery safely returned to Earth on Monday, wrapping up a successful 13-day mission. The shuttle landed at Kennedy Space Center in Cape Canaveral, Florida, at 9:14 a.m.—right on schedule.

"Welcome back, Discovery," said NASA astronaut Stephen N. Frick from Houston's Mission Control to the six-member crew aboard the shuttle.

Earlier Monday morning, nearby storm clouds threatened to postpone Discovery's landing plans, but officials gave the go-ahead when conditions were considered safe.

According to NASA officials, re-entry into the Earth's atmosphere is one of the most dangerous parts of a space mission. As the shuttle re-enters the atmosphere, a gas called "plasma" heats its surface, causing temperatures to shoot up to nearly 3000° F. This led to the 2003 Columbia disaster: A damaged left wing allowed heat to seep into the craft, causing it to disintegrate.

Discovery began its descent high above the Indian Ocean. Meanwhile, astronauts' relatives, NASA staff, and onlookers gazed at the sky, listening closely for the sound that signals approaching shuttles. Sure enough, a double sonic boom filled the air as the shuttle made its final approach.

"It was a great mission," said Discovery shuttle commander Colonel Steven W. Lindsey. "A really great mission."

Next Up for NASA

Discovery successfully transported German astronaut Thomas Reiter to the International Space Station, where he became the third member of the crew. During its mission, the Discovery crew focused on the space station, making necessary inspections and repairs, delivering supplies, and bringing back trash and used equipment.

Following the success of the mission, NASA turns its attention to the future. Atlantis is the next shuttle on the calendar, with a launch that might take place as early as August.