A last-minute computer problem delayed NASA’s planned launch early today of a Mars spacecraft carrying the first-ever interplanetary rover.

The weather was near-perfect for the early-morning flight of Mars Pathfinder, but a computer on the ground failed with just a little over a minute remaining in the countdown. A backup computer also would not work, leading officials to suspect a software problem.

It was the second day in a row that the launch was scrubbed. On Monday, rain, clouds and strong winds kept the rocket grounded.

The launch was rescheduled tentatively for early Wednesday, pending quick resolution of the problem.

Pathfinder will be the second U.S. spacecraft to be sent to Mars this year.

NASA’s Global Surveyor was launched in early November and is already on its way to the Red Planet. A Mars spacecraft launched one week later by the Russians plummeted from orbit.