They were supposed to stop at a half-mile. They were supposed to poop out after 90 days.

But seven months and a couple of dusty miles later, NASA’s twin Mars rovers, Spirit and Opportunity, are still tooling around the Red Planet.

And while these interplanetary Energizer bunnies continue to hum, the National Aeronautics and Space Administration is looking forward to its next chance to land a rover there.

Rongxing Li, an Ohio State University mapping expert who has helped NASA point Opportunity and Spirit in the right directions, is on board to do the same in 2009.

He and his colleagues were recently awarded a three-year, $900,000 NASA contract to develop navigation equipment for a minivan-size roving laboratory scheduled for launch in five years.

The goal is for the new rover to travel at least 3 miles.

Armed with microscopes, chemical spectrometers and cameras, the rovers have probed rocks, dug holes and photographed rock formations that indicate Mars had a watery past.

Under the new contract, Li and coworkers at the Jet Propulsion Laboratory in Pasadena, Calif., and Washington University in St. Louis, will develop an idea to use satellites orbiting Mars to identify mountains, hills, large rocks and other landmarks.

A satellite has a much larger field of view and can relate the landmarks to the rover’s eventual destination. In essence, the satellite can tell whether the new rover should turn left or right at a landmark.

This information can then be relayed to the rover, which will look for those landmarks and use them as navigation points.

The goal, Li said, is to reduce navigation error to no more than about 1 yard for every 1,000 yards traveled, a rate at least 10 times better than the accuracy of the current rovers.

After the team tests the technology in the Mojave Desert in 2006, the results will be compared with those from other teams.

mlafferty@dispatch.com