The six-wheeled robot, named Opportunity, is set for launch Thursday at 12:27 a.m. EDT from Cape Canaveral, Fla. If delayed further, NASA has through July 15 to launch the 400-pound rover to ensure its Jan. 25 arrival at Mars.
Its launch was delayed a day by setbacks to the earlier liftoff of the first rover, Spirit. NASA launched Spirit on June 10.
On Thursday, NASA was preparing to fine-tune for the first time the path Spirit is following to Mars. The first of as many as six rocket-firings was expected Friday.
Spirit is scheduled to reach Mars on Jan. 4.
The $800 million double mission aims to send the robots roaming across the surface of Mars to prospect for minerals that would indicate whether the planet could have harbored life.