Mars rover ramps up for its first test drive

NASA's Mars rover Curiosity has zapped a rock, is playing Hokey Pokey at the pace of a drawn-out cricket match, and continues to pass virtually all of its checkouts with flying colors – and tomorrow takes its first test drive.

That's the word from scientists and mission managers in summing up the rover's last few days on Mars.

The one exception to the string of good news is the loss of one of two wind sensors that form part of the rover's weather station. While not a showstopper, it could compromise the quality of some wind speed and direction measurements the station gathers, the team notes.

Despite the hitch, Curiosity and the operations team "continue to hit home runs here," said Michael Watkins, manager for the Mars Science Laboratory mission, of which Curiosity is the robotic star.

The rover is on a quest to help scientists determine if its landing site – Gale Crater and the foothills of its central summit, Mt. Sharp – might have once contained environments where life might have thrived.

Over the past few days, the rover has given its steerable corner wheels a twist to the left and a twist to the right to ensure that they function. It has extended its 7-foot-long arm out and back in, twisting its joints to make sure they all flex – especially at the business end, where a small turret full of rock-sampling tools sits. And tomorrow it takes its first test drive – all of about 10 feet – where it will pivot in place and drive backward part of the way. From an engineering standpoint, that's what it's all about.

Images of the robotic arm's test taken by the rover's navigation camera atop its 7-foot-high mast are driving home that the rover isn't operating on a Jet Propulsion Laboratory test bed, Mr. Watkins says.

"We have looked at images like this so many thousands of times in our test environment," he says. Now, Mars is in the background of the images, rather than test-bed walls.

"It's really a great feeling," he said during a briefing Tuesday.

The rock-zapping ChemCam, also at Curiosity's masthead, conducted its first test on Sunday, revealing a 3-inch-wide target rock to be volcanic basalts, as the research team had anticipated. On Monday, they turned ChemCam's laser on a patch of Martian turf the team has named Goulburn.

It's one of four locations around Curiosity where the rocket motors from the rover's descent stage altered the surface. Goulburn is of special interest because the blast from the descent stage wiped the surface clean, exposing bedrock – a tempting target for the mission's geologists.

Indeed, yesterday they followed up Sunday's highly successful ChemCam test with its first science assignment – using its laser, mini-telescope, and spectrometers to analyze the chemical composition of the exposed bedrock. The results are pending.

The rocket motors that cleared the bedrock may also have triggered a chain of events that rendered useless one set of wind sensors on Curiosity's weather station, sensors that worked as advertised during Curiosity's trip to Mars.

Researchers in Spain and Finland supplied the weather station, whose instruments are housed in two small, offset booms that jut from Curiosity's mast. The wind sensors are built on small circuit boards that must be exposed to the elements in order to take the readings. One of those booms was located near the outside edge of Curiosity's deck as the arm sat folded against the deck for the launch and cruise phases of the mission.

The team noted something unexpected after Curiosity landed. Its deck was strewn with small pebbles. The team suspects that just before Curiosity was cut loose from the rocket-powered sky crane that lowered it to the surface, exhaust from the rocket motors kicked up the pebbles and deposited some of them on Curiosity's deck. Some of those flying pebbles may have struck this outward-facing circuit board, severing some of its fragile connections.

"We may never know what caused this damage," says Ashwin Vasavada, Curiosity's deputy project scientist.

Whatever is responsible for the wind sensor's failure, "the damage is permanent," he adds.

The team is now trying to figure out how to exploit the remaining wind sensor to best gather data on wind speed and direction both as science measurements and to support the operation of other instruments.

If Curiosity's weather wizards had a disappointing day or two, the same can't be said for the researchers using an instrument that will hunt for evidence of water under the surface as Curiosity ambles across the Martian surface.

The instrument, a neutron spectrometer dubbed DAN, was built in Russia and so far has checked out perfectly, says Igor Mitrofanov, a scientist with the Space Research Institute in Moscow and the instrument's lead scientist. The device bombards the surface beneath it with neutrons to a depth of a bit more than three feet, then measures how they are scattered. This scattering reveals the elements present in the layer of soil the neutrons penetrate.

The device is most sensitive to scattering in the top 20 inches or so. The water the team plans to hunt is tied up in hydrated minerals, rather than in ice, which would have a hard time persisting in Gale Crater, which is in Mars' equatorial region.

They should find plenty of hydrated minerals near the surface – evidence that the crater once held water. Data from a similar instrument aboard the Mars Odyssey orbiter, which is still circling the Red Planet, shows Gale Crater as a big patch of watery blue in a broader blue region where hydrated minerals abound. The blue is a false color the researchers added to help them analyze the surface composition. But there's nothing false about their expectations of finding evidence that deep in its past, Gale Crater once was host to a liquid deemed indispensable for organic life.