NASA scientists got control of the ailing Mars Spirit rover by putting it in "cripple mode," they said on Saturday as the second spacecraft, Opportunity, closed in on the Red Planet for an on-time landing hours away.

The mission control team said it expected to be able to get good scientific work out of Spirit, which suffered a communications breakdown on Wednesday, less than a week after successfully rolling off its landing platform to begin searching for signs of life-supporting water.

Sean O'Keefe, NASA administrator, addresses the risks of the space program, as he discusses the upcoming landing of the Mars Rover Opportunity during a news conference, Saturday, Jan. 24, 2004. [AP]

The control team was beginning to rule out the worst case scenarios for the three-month mission, Mars Exploration Rover Project Manager Pete Theisinger told reporters at Jet Propulsion Laboratory, the mission's command center.

"They think they are going to get more of the vehicle back than they may have thought 48 hours ago," Theisinger said. "We got control of the vehicle back; we got power, good comm.(communications); we can deal with it," he added. "This is very good news."

The Jet Propulsion Laboratory upgraded Spirit's status to serious from critical after apparently isolating the problem in the spacecraft's flash memory chips, the same storage medium used by digital cameras on earth, or software that works with the flash.

The flash memory on Spirit also holds pictures and scientific data.

Once they found the probable source of the spacecraft's confusion, scientists told Spirit to ignore the flash memory and go into "cripple mode." That allowed Spirit to shut down, ending the cycle of computer resets -- around 130 since it began to malfunction -- which drained the batteries of the lander.

The sun's rays will power up Spirit's solar array and wake up the rover after sunrise on Gusev Crater, where the lander is stranded. Scientists will then tell it to go back into cripple mode and try to establish a better communications link.

"I think we are probably three weeks away from driving," Theisinger said.

OPPORTUNITY FEELS MARS GRAVITY

A few hours before Spirit wakes up, its sister craft is scheduled to join it on Mars, on the other side of the planet. Landing is scheduled for 12:06 a.m. EST Sunday, and Theisinger said mission control would not slow down Opportunity's mission because of the problems with Spirit.

Opportunity is headed toward Meridiani Planum, a smooth plain near Mars' equator, which is believed to be full of iron-bearing hematite, a mineral that on Earth usually forms in the presence of liquid water.

Opportunity may immediately send news of its landing, if all goes well, although the spacecraft may not phone home for as many as 22 hours, scientists cautioned.

Opportunity has begun speeding up as Mars gravity begins to pull it in, said Rob Manning, the entry, descent and landing manager at Jet Propulsion Laboratory.

"We just started to feel the gravity well a few hours ago," he said.

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