This engineering model of the Mars Science Laboratory’s chassis, dubbed “Scarecrow” because it does not have a brain of its own, makes its way down a hill in JPL’s Mars Yard. MSL will be about twice as long and four times as heavy as the current Mars rovers, Spirit and Opportunity.

Mars Rovers: The Next Generation

NASA scientists are seeking big pieces of an even bigger puzzle to help answer the biggest question about Mars—was it ever, is it, or could it possibly be a place for life to exist?

The size of a Mini Cooper and having more instruments than any previous Mars rover, the one-ton Mars Science Laboratory (MSL) will find some of those pieces. Expected to launch in September 2009, it will land in the summer of 2010. During the planned mission, which should last one Martian year (almost two Earth years) it will travel 20 miles.

“We’re hoping that the Mars Science Lab will be able to go much further and last much longer than we anticipate, as the rovers Spirit and Opportunity have,” says project scientist John Grotzinger, who came to Caltech in 2005, after years at the Massachusetts Institute of Technology. Those two rovers are still roaming Mars after landing in 2004; they were originally expected to last 90 Martian days.

MSL will be fueled by nuclear power, so it will not be as restricted in its operations as the previous solar-powered rovers have been. The MSL can reach higher latitudes that get less sunlight each day. Previous rovers had to land within 20 degrees of the equator, but MSL should be able to get 10 degrees closer to the poles. At a conference in late October, the original 36 proposed landing sites were narrowed down to six sites and four alternates, all of which are ±30 degrees of Mars’ equator. The farthest poleward proposed site is Terby Crater, at about 27.5 degrees south latitude.

MSL will pioneer a technique called “steered landing” that will get it as close as possible to its selected site. The previous rovers bounced and rolled in their protective airbags, giving little control over where they landed within their 50- to 100-kilometer target ellipse.

“It’s still not perfect, but now we can land within the range of a city rather than an entire county,” says Deputy Project Scientist Ashwin Vasavada.

MSL is equipped with small rockets that fire downward for a few seconds at a time to control landing speed. The shape of the craft also allows the entry, descent, and landing team to control the angle of attack, which determines the lander’s lift and forward velocity. MSL knows its desired trajectory, and sensitive gyroscopes allow it to correct itself, should something push it off course. These tools will shrink the landing ellipse to a mere 10 kilometers or so.

“Mars is now a place for sedimentologists,” says Grotzinger, the Jones Professor of Geology. “Using the same techniques to see what the early earth was like, we can find out what Mars was, and is, like.” On a table in his office sits a large rock from Australia, whose surface bears ripples that look just like the wave patterns that form in sand at the beach, where the tide ebbs and flows. Scientists have already seen ripples like these on Mars, implying that water once flowed there.

But now scientists are going beyond water, seeking compounds containing carbon, hydrogen, nitrogen, phosphorous, and sulfur, all essential ingredients for life, as well as various minerals that may indicate organisms that metabolized these compounds. A suite of instruments named Sample Analysis at Mars (SAM), provided by NASA Goddard, will analyze samples of material collected by MSL’s robotic arm. SAM includes a gas chromatograph and mass spectrometer that will analyze rock and soil samples. A tunable laser spectrometer will determine the ratios of key isotopes in the air, providing clues to the history of Mars’ atmosphere and water.

An X-ray diffraction instrument called CheMin, built by JPL, will identify and analyze minerals in rocks and soil. Previous Mars rovers have used spectroscopy to identify elements, but X-ray diffraction is far less ambiguous. “For understanding geologic history, this is especially important,” says Vasavada. “The same chemical elements will take the form of different minerals depending on the environment in which they were formed.”

These minerals arrange the same atoms into different crystal structures, meaning that the atoms have different three-dimensional spacings. A beam of X rays shot into each different structure will thus be diffracted at a different set of angles. Due to its bulk and weight, an X-ray diffractometer has never been put on a spacecraft before, but CheMin is about the size of a laptop computer bag.

MSL will be the first rover ever equipped with its own light sources. An ultraviolet light will be used to make minerals fluoresce, like the glow-in-the-dark geology displays at many science museums. This isn’t being done to make trippy pictures—the fluorescence spectrum will help identify the minerals in the rocks.

Mounted on the rover’s arm, the lights are part of the Mars Hand Lens Imager (MAHLI), which will take extreme close-up pictures of rocks, soil, and perhaps ice, revealing details smaller than the width of a human hair. MAHLI’s color pictures will have a higher resolution than the Microscopic Imagers on Spirit and Opportunity, which only take pictures in black and white. Using its zoom lens, MAHLI can also focus on objects that the arm cannot reach.

Like Spirit and Opportunity, MSL’s Mast Camera will see the rover’s surroundings in high-resolution color, and its multispectral capability allows rock and mineral types to be identified in the landscape from afar. What’s new is the capability to take and store high-def video—in stereo, no less! Now we’ll be able to watch dust devils form and whip by in 3-D. MastCam has its own internal image storage, processing, and compression, taking this computationally intensive burden off the rover’s main brain.

Another camera, called the Mars Descent Imager (MARDI), will take pictures as the MSL lands.
MAHLI, MastCam, and MARDI are being built by Malin Space Science Systems of San Diego, headed by Michael Malin (PhD ’76).

The ChemCam, a collaboration between France and the U.S., will use laser pulses to vaporize thin layers of material from Martian rocks or soil from up to 10 meters away. A spectrometer will then identify the newly liberated atoms, and a telescope will capture detailed images of the area illuminated by the beam. ChemCam and MastCam will both sit on the rover’s head-high mast, helping researchers decide which objects they should investigate next.

The rover’s Radiation Assessment Detector, provided by the Southwest Research Institute, will provide crucial information for planning human exploration of Mars, and for assessing the planet’s ability to harbor life.
Canadian researchers are also getting in on the action. The Canadian Space Agency will be providing the Alpha Particle X-ray Spectrometer, which will be located on the arm, and will determine the relative abundances of different elements in rocks and soils.

Russia’s Federal Space Agency is providing the Dynamic Albedo of Neutrons instrument to measure subsurface hydrogen up to one meter below the surface. This method has been used on JPL’s Mars Odyssey to map subsurface water from orbit, but this is the first time a neutron spectrometer will land on the surface for a close-up look.

Finally, Spain and Finland are taking part with the Rover Environmental Monitoring Station to measure atmospheric pressure, temperature, humidity, winds, and ultraviolet radiation levels.

Like any other project, this mission has faced challenges. “We’re in the sausage-making stage of it right now,” said Project Manager Richard Cook, referring to the aphorism attributed to Otto von Bismarck, “Laws are like sausages. It’s better not to see them being made.”

Grotzinger was faced with the first of these challenges about six months ago when he took over Edward Stolper’s position as project scientist. (Stolper, the Leonhard Professor of Geology, had been appointed Caltech’s provost, and was unable to give MSL the time it deserved.) In the same week Grotzinger joined MSL, he was told that the project was $75 million over its original budget of $1.7 billion.

Grotzinger needed to cut costs but keep the science program strong. None of the rover’s instruments have been removed from the payload, but some engineering changes have been made. These include reductions in design complexity—for example, a rock-grinding tool has been changed to a rock-brushing tool, and MastCam’s zoom capability got scrapped. There will also be fewer spare parts, simplified flight software, and some ground-test program changes.

MSL will address the puzzle of life on Mars, but the answers won’t come easily, Grotzinger says. “Like most things in science, there’s not a silver bullet.” —JS