The battered Opportunity rover has finally reached its ultimate destination after the most severe dust storm it has ever encountered, but further progress is still uncertain.

Yesterday Opportunity finally descended into the famous Victoria Crater, which has been its main target for more than two years. According to NASA, the very resistive explorer transmitted the first information about its Victoria endeavor through a link established with NASA's Mars Odyssey orbiter, reporting its activities for the day.

Scientists here on Earth have assessed the best possible route for Opportunity in order to ensure the rover’s return to the “surface”. This September marks the end of one of the most difficult missions for the tiny robot, during which Opportunity had to face not only the most severe dust storm since its landing in January 2004, but also some serious mechanical problems that keep draining its energy even while you read these lines (a heater switch that has been stuck in the "on" position since landing day).

"We chose a point that gives us a straight path down, instead of driving cross-slope from our current location," said Paolo Bellutta, a JPL rover driver plotting the route. "The rock surface on which Opportunity will be driving will provide good traction and control of its path into the crater."

For the descent inside the crater, Opportunity needed some preparations, which have been coordinated from Earth. It first needed to get its six wheels in and then back out a bit to assess slippage on the inner slope.

NASA said that the rover descended on September 11 for about 4 meters (13 feet), before backing uphill for about 3 meters (10 feet). The driving commands for the day included a precaution for the rover to stop driving if its wheels were slipping more than 40 percent. Slippage exceeded that amount on the last step of the drive, so Opportunity stopped with its front pair of wheels still inside the crater.

"We will do a full assessment of what we learned from the drive today and use that information to plan Opportunity's descent into the crater," said John Callas, rover project manager at NASA's Jet Propulsion Laboratory, Pasadena, Calif.

"For almost two years now, we've felt that Victoria Crater was the most compelling science for Opportunity," Callas said.

"Opportunity might be ready for that first 'toe dip' into the crater as early as next week," said JPL's John Callas, rover project manager. "In addition to the drives to get to the entry point, we still need to conduct checkouts of two of Opportunity's instruments before sending the rover into the crater."

One of the problems that need to be solved in the following period is related to the proper functioning of the microscopic imager, which seems to have been damaged. If it still works, it should help NASA’s engineers figure out whether another tool, called miniature thermal emission spectrometer (Mini-TES) is indeed displaying pictures of the Martian soil or images from rover's camera mast.

"If the dust cover or mirror is no longer moving properly, we may have lost the ability to use that instrument on Opportunity," said Steve Squyres of Cornell University, Ithaca, N.Y., principal investigator for the rovers' science instruments. "It would be the first permanent loss of an instrument on either rover. But we'll see."

"Mini-TES has told us a lot about the rocks and soils at Meridiani, but we've learned that the differences among Meridiani rocks are often too subtle for it to distinguish," Squyres said. "The same instrument on Spirit, at Gusev Crater, has a much more crucial role for us at this point in the mission because there is such diversity at Gusev."

Opportunity had reached Victoria Crater’s edge in June and was programmed for descent on June 27, when the massive dust storm had formed. The descent was further delayed by the need to find a suitable sliding place, and for that the rover had to circle around Victoria. That crater is so important because it contains an exposed layer of bright rocks that may preserve evidence of interaction between the Martian atmosphere and surface from millions of years ago, when the atmosphere might have been different from today's.

Victoria is the biggest crater the rover has visited in its 43-month-old mission.