NASA's Mars Curiosity rover is three-quarters of the way through a major software upgrade NASA has dubbed a "brain transplant."

The four-day software upgrade started Saturday and, if all goes as planned, should wrap up by Tuesday afternoon. So far all has gone exactly as planned, said Guy Webster, a spokesman for NASA's Jet Propulsion Laboratory (JPL).

There are two computers onboard Curiosity, which has been on the surface of Mars for a little more than a week. The main computer was upgraded over the weekend and the backup computer is halfway through its own upgrade.

The software upgrade, dubbed R10, is focused on running the rover's surface mission. It was uploaded to the rover during its 350-million-mile trek to Mars but sat waiting to be activated.

Instead, software focused on getting the spacecraft through the Martian atmosphere and safely landed inside the Gale Crater ran operations.

Now that the rover is on the ground and ready to begins its surface mission, it was time to transition to the new software.

"The surface mission is quite complicated and needs a lot of smarts," Ben Cichy, a senior software and systems engineer at JPL, said late last week. "Curiosity was born to drive. We're giving her the capability to get out and stretch her wheels on the surface of Mars."

The surface software holds advanced controls to drive Curiosity, as well as to operate its 7-foot robotic arm, its ability to scoop up soil samples and its ability to spot hazards in its path.

Curiosity is tasked with a two-year mission designed to gather evidence that Mars is, or has been, capable of supporting life, probably in microbial form.

The SUV-sized, nuclear-powered robotic rover is equipped with 10 scientific instruments. Curiosity has the most advanced payload of scientific gear ever used on the surface of Mars, including chemistry instruments, environmental sensors and radiation monitors.

The payload is more than 10 times as large as those of earlier Mars rovers.

Curiosity isn't working alone on Mars. Along with a few Mars orbiters, NASA also has one other working rover on the Red Planet.

NASA's Spirit and Opportunity rovers have been two of the agency's most successful robotic projects. While Spirit was given up for dead last year, both rovers worked on the Martian surface for more than six years -- far longer than the three months that NASA initially expected them to last.

However, the rover Opportunity continues its work. It has been upgraded with artificial intelligence software to enable the robot to make some of its own decisions about what rocks or geological formations it should stop and analyze.

Sharon Gaudin covers the Internet and Web 2.0, emerging technologies, and desktop and laptop chips for Computerworld. Follow Sharon on Twitter at @sgaudin, on Google+ or subscribe to Sharon's RSS feed . Her email address is sgaudin@computerworld.com.

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