Storms and high wind Sunday forced NASA to reschedule the flight for Monday afternoon, and a prediction Monday of afternoon thunderstorms over Cape Canaveral Air Force Station again delayed the launch.
The weather was expected to improve by Tuesday, and the lift-off was rescheduled for 1:58:47 p.m. EDT Tuesday with a backup opportunity available at 2:36:49 p.m. The forecast for Tuesday and Wednesday calls for a 70 percent chance of acceptable weather.
The second rover is scheduled for launch later this month, and both vehicles are to arrive on Mars in January.
"We sincerely hope it will be the successful beginning to one of the first great 21st century voyages of exploration," NASA Administrator Sean O'Keefe said Sunday.
The rovers were officially named on Sunday. Third-grader Sofi Collis, 9, of Scottsdale, Arizona, chose the name Spirit for the first rover and Opportunity for the second in a nationwide contest that drew 10,000 entries.
"I used to live in an orphanage. It was dark and cold and lonely," said Sofi, who was adopted from Siberia at age 2. "In America, I can make all my dreams come true. Thank you for the spirit and the opportunity."
The rovers act as robotic geologists, moving on six wheels. Each is equipped with a pair of panoramic cameras, a camera for close-ups and a drill to sample rocks.
Previous missions have shown Mars had water in the past, but scientists want to find out how long the water was there and in what amounts. Scientists believe the water may show that Mars once was able to support life.
The rovers' landing sites, on opposite sides of the planet, were chosen for their likelihood of holding evidence of water. Studying the minerals in rocks can tell scientists how the rocks were formed, whether they were ever submerged in water, and whether hot water ever ran over them.
The rovers are expected to travel up to 132 feet each Martian day, which is 24 hours and 39½ minutes long.
The rovers' missions are expected to last three months but could run longer. They eventually will shut down as dust builds up on their solar panels.
Only 12 out of 30 previous attempts have reached Mars, and only three out of nine attempts have succeeded in landing on the planet. The current rovers cost $800 million.