NASA's Mars Reconnaissance Orbiter has been launched on an Atlas V rocket, bound for a 25-month mission to survey Mars.
The rocket took off at 11.43am Irish time from the Kennedy Space Centre at Cape Canaveral, Florida.
The Orbiter is being sent to step up the search for signs of water on the Red Planet and help pick sites for possible landings on Mars in the future.
A technical problem with the rocket, which is being used for the first time by NASA, had been blamed for postponing the planned launch on Wednesday.
Yesterday, space officials blamed a faulty sensor on a fuel pump and related computer software, and deferred the launch until today.
The MRO is to start circling Mars in a low orbit from next March, taking close up images of the planet to help scientists understand what happened to the planet's water.
