NASA’s Curiosity Mars rover is a day away from finishing its thoroughgoing checkout period, and soon will begin driving in search of a good rock to touch with its robotic arm and analyze.

Performance of the rover’s Canadian-built alpha particle X-ray spectrometer (APXS) has checked out on a sample target of polished basalt from Earth that is mounted on the rover’s deck. Plans call for Curiosity to set off Friday in search of a piece of Mars basalt to reach out and touch with the APXS sensor on the end of the rover’s robotic arm.

“Starting on Friday evening, the plan is to drive, drive, drive until the science team finds a desired rock, where we want to perform the first contact science observations with Mahli (the Mars Hand Lens Imager] and the APXS instrument,” said Jennifer Trosper of the Jet Propulsion Laboratory, a Curiosity mission manager.

Also on the agenda is an attempt to collect video images of the Martian moon Phobos passing in front of the Sun, and a final day of control tests of the arm, Trosper said. As the checkout draws to a close after 37 Martian days – or sols – since Curiosity landed on the floor of Gale Crater Aug. 6, the JPL rover engineering team is “just about ready to turn over the keys” to the mission’s science team, she said.

After that, scientists will play the principal role in deciding where Curiosity drives and what scientific work it does along the way. Mission engineers and scientists will work together during the Martian nights to analyze data coming down from Curiosity through two NASA spacecraft orbiting Mars, decide what the best scientific strategy will be for the next sol, generate the necessary commands and send them for the rover to execute autonomously.

The APXS, a version of similar instruments that flew on the Mars Pathfinder Sojourner rover and the two Mars Exploration Rovers – Spirit and Opportunity – queries samples with a small dose of radiation and then reads the X-rays emitted as a result. Those X-rays have unique signatures signifying the chemical elements that produced them, which tells scientists the composition of the sample touched with the cupcake-sized sensor head.

The sensor on Curiosity performed very well in its measurement of the sample on the rover’s deck, according to Ralf Gellert of the University of Guelph in Ontario, the APXS principal investigator. In addition to the known sample values, the test picked up sulfur and chlorine in a thin coating of Martian dust on the sample, as well as atmospheric elements, he said.

“These are our first Martin solid data, and it emphasizes how sensitive this instrument is to sulfur and chorine salt forming very important elements,” he said in a telephone status update with reporters on Wednesday afternoon.

The Mahli camera is designed to give scientists on Earth very close-up imagery of samples, much as a geologist’s hand lens does on Earth. Testing against a 1909 Lincoln penny showed remarkable detail, including a couple of sand grains at a resolution of 20 microns per pixel.

That resolution could go up to 14 microns/pixel with the camera closer to the subject, according to Ken Edgett of Malin Space Science Systems, the Mahli principal investigator. The close-up camera also collected wide-angle imagery of the rover’s wheels on the planet’s surface, and sample inlets on the rover deck leading to the portable chemistry lab inside the rover body that will allow wet analysis of samples scooped from the surface.