The Atlas V rocket carrying the Mars Science Laboratory lifted off right on time from Cape Canaveral, Fla., shortly after 10 a.m. After achieving Earth orbit a second burst from the upper stage pushed it out of orbit and onto its 352-million-mile trajectory to Mars.
It will take the spacecraft nine months to reach Mars and if all goes well, the car-sized Curiosity rover will be parachuted to the planet's surface next August.
NASA has been struggling to keep its budget and define its relevance with the end of the space shuttle program this past summer. It escaped big cuts in the latest round of appropriations in Congress but is under pressure to perform.
The space agency is relying on public-private partnerships such as this one, with United Launch Alliance.
Curiosity is much larger than the spectacularly successful rovers Spirit and Opportunity, which crept around the surface of Mars for years longer than planned. Spirit was declared dead in May after lasting six years.
"It will go longer. It will discover more than we could ever possibly imagine," Colleen Hartman, assistant associate administrator, NASA Science Mission Directorate, told a news conference earlier this week.
"Mars really is the Bermuda triangle of the solar system. It is the death planet. And the United States is the only nation in the world that has landed and driven robot explorers on the surface of Mars."
The one-ton rover has a robotic arm, a drill, video cameras and other equipment for collecting and analyzing rocks and soil in search of evidence of past or present life.