NASA will start its plan to free its Mars exploration rover Spirit from its Martian sand trap, it was announced here Thursday. Spirit has been lodged on Mars at a site scientists call 'Troy' since April 23 this year. NASA announced that it will begin to transmit commands to Spirit on Monday to save the rover. But researchers expect the extraction process to be long and the outcome uncertain based on tests here on Earth this spring that simulated conditions at the Martian site. Scientists found Spirit is straddling the edge of a 26-foot- wide crater that had been filled long ago with sulfate-bearing sands produced in a hot water or steam environment. Spirit's wheels broke through the soil on Mars. The buried crater lies mainly to Spirit's left. Engineers have plotted an escape route from Troy that heads up a mild slope away from the crater. JPL rover driver and Spirit extraction testing coordinator Ashley Stroupe said they will start by steering the wheels straight and driving, though they may have to steer the wheels to the right to counter any downhill slip to the left. Spirit has six wheels to rove the planet. The first command will tell the rover to rotate its five working wheels forward approximately six turns. Since 2006, Spirit's right-front wheel has been inoperable, possibly because of wear and tear on a motor as a result of the rover's longevity. Spirit is expected to return data the next day from its first drive attempt. The results will be assessed before engineers develop and send commands for a second attempt. Using results from previous commands, engineers plan to continue escape efforts until early 2010, according to NASA. NASA said Spirit has provided outstanding scientific discoveries and shown astounding vistas during its long life on Mars, which is more than 22 times longer than its designed life. Spirit and its twin rover landed on Mars in January 2004. They have explored Mars for five years, far surpassing their original 90-day mission. JPL in Pasadena, California, manages the rovers for NASA's Science Mission Directorate in Washington. 