Space shuttle Discovery and its crew of six returned to Earth through thick clouds Monday, ending an impressive mission that put NASA's space program back on a solid, safer course. Discovery landed at Kennedy Space Center at 9:14 a.m. (1314 GMT) in only the second shuttle flight since the 2003 Columbia disaster. "Welcome back, Discovery, and congratulations on a great mission," Mission Control told shuttle commander Steven Lindsey after Discovery rolled to a stop. "It was a great mission, a really great mission, and enjoyed the entry and the landing," Lindsey replied. The smooth landing was sure to leave NASA officials jubilant, after conquering the chronic threat of foam chunks that break off the external fuel tank during launch - still a problem, but not a serious one in this mission.