CAPE CANAVERAL, Fla. – NASA postponed the launch of a spacecraft to Mars yesterday after a glitch popped up in the computer software used for monitoring the fueling of the rocket used for liftoff.

The problem with sensors and software that measure the amount of fuel being loaded into the rocket appeared with just minutes left until liftoff. The launch was rescheduled for Friday morning, three days after the shuttle Discovery returned to Earth.

Before the glitch, the only problem NASA faced was with an early morning thunderstorm that had delayed fueling. But NASA officials couldn’t explain why sensors were reading “dry” when other data showed that the rocket was being filled with propellant.

“We weren’t quite sure what the cause was and we felt we didn’t have enough time left … to pursue it any further,” said Charles Dovale, NASA launch director.

The Mars Reconnaissance Orbiter, equipped with the largest telescopic camera ever sent to another planet, was expected to spend at least four years circling Mars, collecting information that will help NASA plan where to land two robotic explorers later this decade.

The two-ton orbiter will collect information on Mars’s weather, climate, and geology. The $720 million mission is also expected to build knowledge of the history of the planet’s ice.

The information will aid possible future human exploration of the Red Planet. The craft is to join three other orbiting spacecraft when it arrives at the planet next March. Two NASA rovers launched in 2003, Spirit and Opportunity, also continue to roam the planet.