PASADENA, Calif. - NASA engineers got a half-hour of transmissions Friday morning from the Spirit rover and planned further communications to try to diagnose and possibly patch up their ailing robotic patient on Mars.

NASA heard from the six-wheeled rover for 10 minutes at about 4:30 a.m. and received data for 20 minutes about an hour later.

"The spacecraft sent limited data in a proper response to a ground command, and we're planning for commanding further communication sessions later today," Pete Theisinger, rover project manager at NASA's Jet Propulsion Laboratory, said in a statement early Friday.

Officials did not immediately elaborate on the signals. If they contain significant data, the transmissions would mark the first such signals in two days - a period of anxious waiting for scientists after normal communications halted Wednesday.

Engineers hope Spirit will manage to send some engineering data, which can be used to assess the health of the spacecraft, pinpoint any problems and allow NASA to begin working on a potential fix or fixes.

Scientists and spokesmen at the Jet Propulsion Laboratory did not immediately return calls seeking comment on Friday. The statement said Friday's signal was received by NASA's Deep Space Network antenna complex near Madrid, Spain.

Since Wednesday, its 19th day on Mars, the Spirit had sent back to Earth only meaningless radio noise or simple beeps acknowledging receipt of commands.

Among the possible causes: a corruption of its software or computer memory. If the software is awry, NASA can fix it from Earth by beaming patches across more than 100 million miles of space or by rebooting the rover's computer. But if the problem lies with the rover's hardware, the situation would be far more grave - perhaps beyond repair.

Baffled scientists have struggled to pinpoint the trouble.

"It is precisely like trying to diagnose a patient with different symptoms that don't corroborate," said Firouz Naderi, manager of NASA's Jet Propulsion Laboratory Mars exploration program.

Spirit is one-half of an $820 million mission. Its twin, Opportunity, is expected to land on Mars late today. The twin rovers are supposed to examine the Red Planet's dry rocks and soil for evidence that it was once wetter and more hospitable to life.

Until Wednesday, Spirit had functioned almost flawlessly and NASA scientists and engineers had been jubilant.

Steven Squyres of Cornell University, the mission's main scientist, cautioned that communications problems are common on spacecraft.

The problem surfaced while Spirit was preparing to resume analysis of its first rock, just a few yards from where it landed.

Early Thursday, NASA initially heard nothing from Spirit that would indicate it was in "fault mode," a state that the rover enters by itself when it has experienced a problem. Later, NASA sent a command to Spirit as if it were in fault mode, anyway. Spirit acknowledged with a beep that it received the command, indicating an onboard problem. That puzzled engineers.

Preliminary indications suggested the rover's radio was working, and it continued to generate power from the sun with its solar panels. Spirit's internal clock also was running and had roused the rover several times on cue.

Engineers hoped to receive engineering data from Spirit by early Friday, JPL director Charles Elachi said.

"We can do a diagnostic and understand what happened, what are the corrective actions that need to be done and how do we bring it carefully and thoughtfully to its normal operation mode," Elachi said.

Initially, engineers believed bad weather on Earth - a thunderstorm near a Deep Space Network antenna in Australia - had caused the communications glitch. But weather was later discounted as the source.

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