The Spirit rover's wheels have rolled for the first time on Mars, the mission team said Tuesday, and scientists have mapped out what the rover will do and most likely where it will die.
Overnight, the golfcart-sized rover cut the final cord tying it to the landing platform that it came in on 10 days ago, then backed up about 10 inches (25 centimeters) and turned 45 degrees. These were the first maneuvers planned in preparation for having Spirit roll 10 feet (3 meters) down a ramp onto the Martian surface on Wednesday night or early Thursday morning.
"The engineering team is just elated that we're driving, finally," flight director Chris Lewicki told journalists at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "We cut our ties loose and we're ready to rove."
Scientists had hoped that the six-wheeled rover would be rolling on the surface by now, but its primary path off the landing platform was blocked by a couple of the airbags that cushioned the spacecraft's Jan. 3 descent. When the landing platform unfolded, those airbags failed to retract as fully as engineers had hoped. Thus, the engineering team is having to turn the rover 120 degrees on its platform to go down a secondary ramp. The turn is being done in three stages, and the final two stages are to come late Tuesday and early Wednesday.
Where it is, where it's going
In the interim, Spirit has been sending back high-resolution pictures of its surroundings in Mars' Gusev Crater, and scientists have matched up the landmarks with overhead imagery from other Mars probes to figure out where the landing site is to an accuracy of about 100 feet, or 30 meters. (For cartography geeks, the coordinates are latitude -14.5718, longitude 175.4785.)
"The biggest uncertainty for us is in the maps now," said Joe Guinn, a member of the navigation team. Gusev Crater, with a diameter of 90 miles (145 kilometers), is so wide and flat that the location had to be calculated by looking for hills and smaller craters within the plain.
The mission team determined that the spacecraft, surrounded by airbags, bounced 28 times over a distance of about two-tenths of a mile (250-300 meters), settling to a stop 57 seconds after the first impact.
A 650-foot-wide (200-meter-wide) impact crater lies just about 850 feet (260 meters) northeast of the landing site, and principal scientific investigator Steve Squyres said that would be Spirit's first major destination. The material ejected from the crater could tell much about the geological history of Mars.
Spirit might even be able to mount the estimated 15-foot (5-meter) incline to peer into the crater and perhaps even stick its robotic toe inside.
"It will provide a window into the subsurface of Mars," Squyres said.
Based on past Mars missions, scientists have come to believe that Mars was warmer and wetter billions of years ago. A more detailed analysis of Mars' geological layers could shed light on the mission's key question: Could liquid water have persisted on Mars long enough to allow for the development of life?
Spirit won't make a beeline to the crater: Along the way, it will use its cameras and scientific instruments to take pictures and analyze the Martian soil and rocks. It could take days to reach the crater, and weeks more for the rover to finish its work there.
Squyres said the mission team then would set a course for the eastern hills, which are about 2 miles (3 kilometers) away. But he couldn't promise that the rover could complete the trip. The rover was built for a 90-day primary mission, with the expectation that it would have a range of half a mile (600 meters).
"These hills are five times that far away," Squyres said, "so don't sit here and think, 'Oh, we're going to go to the hills.' We're going to go toward the hills."
In the end, the scientists may be willing, but the Spirit may be too weak. There could be a mechanical breakdown along the way, and eventually there won't be enough sunlight to keep the solar-powered rover going in the Martian winter.
Nevertheless, Squyres said the trip itself would yield valuable science: As the terrain gets higher, Spirit will get a better overall view of Gusev Crater, which scientists believe may have been a lakebed many millions of years ago. The rover also could sample rocks that may have been pushed down from the eastern hills by erosion or by impacts.
Squyres said the journey would offer "a shared adventure that I think is going to be unprecedented in human history."
Spirit represents one-half of an $820 million, "two-for-one" mission to Mars: Its twin, the Opportunity rover, is due to touch down on Jan. 24 in Meridiani Planum, a hematite-rich region on the other side of Mars. Spirit was launched last June, and Opportunity in July. Spirit followed a roughly 300-million-mile (500-million-kilometer) arc to the Red Planet, which is currently about 110 million miles (175 million kilometers) from Earth.