Engineers have uncovered a potential problem with the two identical Mars Exploration Rovers that will be launched to the Red Planet in the coming months, prompting NASA to delay liftoff of the first rover by one week.

One of the Mars Exploration Rovers during testing at Kennedy Space Center. Photo: NASA

"The concern regards cabling that connects the spacecraft's main computer, which is inside the rover, to peripherals in the cruise stage, lander and small deep space transponder. The connection to the cruise stage is severed during approach to Mars and the connection to the lander is severed before the rover drives off," NASA said in a statement Monday.

"Pre-launch testing revealed a potential problem in how the spacecraft interprets signals sent when the cables are severed. The problem will require fixing on both rovers."

The repair will require some disassembly of the spacecraft, which are located at Kennedy Space Center.

The extra work cannot be completed within the schedule of preparations for the original May 30 launch date for the first rover, forcing a postponement to no sooner than June 6 at 2:12:44 p.m. EDT. The mission will have two launch opportunities each day during the planetary alignment window, which is scheduled to close on June 19.

Arrival at Mars is set for January 4, 2004, regardless of launch date within that period.

Repairs are not expected to effect the planned 12:38:16 a.m. EDT liftoff June 25 of the second rover. That launch period extends through July 15, setting up a landing on January 25, 2004.

Both rovers will fly atop Boeing Delta 2 rockets launched from Complex 17 at Cape Canaveral Air Force Station, Florida. Ten days will be needed between launches.

Fitted with a suite of science instruments, the rovers will look for geological evidence of past liquid water on Mars and conditions that could have supported life.

Just last week NASA announced the two landing sites for the rovers. The first will be targeted to land at Gusev Crater, 15 degrees south of Mars' equator. The second will head to Meridiani Planum, an area with deposits of an iron oxide mineral (gray hematite) about two degrees south of the equator and halfway around the planet from Gusev.

"Meridiani and Gusev both show powerful evidence of past liquid water, but in very different ways," said Steve Squyres, principal investigator for the rovers from Cornell University.

"Meridiani has a chemical signature of past water. Gray hematite is usually, but not always, produced in an environment where there is liquid water. At Gusev, you've got a big hole in the ground with a dry riverbed going right into it. There had to have been a lake in Gusev Crater at some point. They are fabulous sites, and they complement each other because they're so different."

"Landing on Mars is very difficult, and it's harder on some parts of the planet than others," added Ed Weiler, NASA's associate administrator for space science. "In choosing where to go, we need to balance science value with engineering safety considerations at the landing sites. The sites we have chosen provide such balance."