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Mars Polar Lander Tweaked

The Mars Polar Lander successfully performed a 12-second thruster firing Saturday to fine-tune its flight path to arrive on the Red Planet's south pole on Dec. 3.

Preliminary data showed that the adjustment, which began at 10:28 a.m. PDT, achieved the desired change in trajectory, said Mary Beth Murrill, spokeswoman for NASA's Jet Propulsion Laboratory in Pasadena, Calif.

Scientists and engineers had checked -- and double-checked -- the thruster firing process in order to avoid a repeat of the problem that doomed NASA's Mars Climate Orbiter.

Trajectory correction maneuvers are routine in solar system flights spanning millions of miles, but the procedure for Mars Polar Lander has come under greater scrutiny since the loss of its companion mission in September.

Lockheed Martin Astronautics, which was participating in the Climate Orbiter mission, sent files of data in English units of measurement to JPL navigators who were expecting metric units. The undetected problem led the craft too close to Mars on Sept. 23.

The Polar Lander's course correction maneuver, originally set for Oct. 20, was pushed back 10 days so that mission officials could evaluate the spacecraft's systems and operational procedures.

More checks were in place, mission engineer Phil Knocke said Friday.

"There's been more emphasis on peer reviews of what's going on, bringing in other independent assessors to double-check our work and make sure there's nothing that we've overlooked," he said. "In a sense we now have many more eyes looking at our processes."

File transfers between teams involved in the mission were under continuing watch, he said, but no significant issues have appeared.

"We haven't found anything in our processes that would have presented a real problem," Knocke said.

The thruster firing was designed to change the spacecraft's speed by six-tenths of a meter per second.

The spacecraft was expected to be out of contact for about 15 minutes because its orientation must be changed for the burn. It will then return to its original attitude to send data back to controllers for analysis.

Another trajectory correction maneuver is scheduled for Nov. 30, three days before the lander enters the atmosphere and sets down on rolling plains near the Martian south pole.

Knocke said there was a provision for yet another maneuver seven or eight hours before the Dec. 3 entry if needed.

"I'd say the mood is good," Knocke said. "We're all working very hard to make sure that all these maneuvers and do exactly what they're supposed to do."

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