NASA's newest, six-wheeled prototype Martian rover - nicknamed Rocky 7 - has successfully passed its most rigorous field test yet, traveling 1,058 meters (six-tenths of a mile) over rugged, Mars-like terrain, while conducting science experiments and snapping 580 photographs along the way.
The week-long series of field tests, carried out May 23-30 at Lavic Lake, an ancient lake bed about 275 kilometers (175 miles) east of Los Angeles, was designed to simulate several weeks of a real Mars rover mission and to test the rover's ability to drive much greater distances than current rovers. In addition, Rocky 7 conducted five simulated science experiments in real-time and collected samples of soil and rocks that would be retrieved and returned to Earth by a later Mars mission.
"One of the chief objectives of these tests was to test Rocky 7's ability to traverse farther over a wide variety of terrain with more Mars-like characteristics than we did in the last set of tests in December 1996," said Dr. Samad Hayati, Rocky 7 task manager at NASA's Jet Propulsion Laboratory (JPL), Pasadena, CA. "The rover actually traveled about 80 percent farther than it traveled in the last set of tests, over three distinct terrains, using a minimum of instructions from us to guide its way."
The Rocky 7 rover represents the newest model of rovers that may be sent to Mars in the years 2001 and 2003. However, it looks very similar to its predecessor, Sojourner, which will land on Mars on July 4. Rocky 7 weighs slightly more than Sojourner at 15 kilograms (33 pounds) and has about the same dimensions -- measuring 48 centimeters (19 inches) wide by 64 centimeters (25 inches) long by 32 centimeters (12.5) inches tall. Rocky 7 also sports the same six-wheeled chassis and spring-less "rocker- bogie" mobility system, which allows the vehicle to conform to the contours of the surface and scale objects almost as tall as itself without tipping over.
Continued robotic exploration of Mars in the next century will focus on the search for water and evidence to confirm hints that life may have existed once in Mars' early history. Successive Mars missions will be designed not only to examine the planet's composition, atmosphere and weather, but also to identify natural resources that could be mined and used for eventual human expeditions to the red planet.
The southern side of Lavic Lake, located in the Twenty-Nine Palms Marine Corps Base near Palm Springs, CA, was chosen for the field tests because it is a playa, analogous to some regions of Mars, with areas of lava flow, cracked mud, terrain strewn with basalt rocks and an alluvial fan.
Rocky's travels began on a basalt flow covered with cobblestones resting in a layer of wind-blown silt, which offered a variety of obstacles for the robot to hurdle. Engineers tested some of the rover's new features, such as a 32-centimeter (12.5- inch) manipulator arm with four degrees of freedom. Mounted on the front of the vehicle, the arm carried a "point reflectance" spectrometer that could be extended 10 centimeters (4 inches) in any direction to study the color of various surfaces. In future rover missions on Mars, science instruments on the rover arm will help researchers determine the composition of surface soils and rocks.
Engineers also tested a 1.4-meter (4.5-foot), antenna-like mast, which would be deployed once the future rover was out and about on Mars. The mast has three degrees of freedom and can be used in much the same way as an arm to deploy science instruments against rocks or align them in the nadir, or down-pointing, position. Two science instruments - a Moessbauer spectrometer and a nuclear magnetic resonance spectrometer - were mounted on the mast to study surface rocks with different types of coatings, such as red iron oxide and desert varnish, which might be found on Mars. To carry out the variety of science experiments performed during the week, Rocky 7 had to raise its mast 85 times.
Rocky 7 carried a pair of stereo imagers on the front and back of the vehicle, which acted as its "eyes." The rover was furnished with simulated descent imaging to recreate landing, then asked to deploy its mast and begin each traverse and sequence of imaging and science experiments.
"Images and science measurements were obtained in several regions of the basalt flow," said Dr. Richard Volpe, chief engineer on the rover development team at JPL. "This pavement of basalt boulders and outcrops offered many terrain obstacles for rover navigation and numerous targets for the rover to measure cobbles and the underlying dust."
In the second journey, the rover set out over the playa, strewn with craters and ejecta fields, and traveled into a crater. Using its mast and arm, the vehicle was able to measure properties of the mud-cracked floor. Rocky 7 also took images of its own tire tracks to help scientists update its location.
"The rover conducted several long traverses across the playa floor, taking images of the tracks left by its wheels so that we could trace its path," said Dr. Raymond Arvidson, science team lead and chairman of the Earth and Planetary Sciences Department at Washington University, St. Louis, MO. "The tracks are used to update positional information, after the observations are completed, and help us map out the vehicle's next route."
The last excursion was the most challenging - an obstacle course taking the rover over an alluvial fan extending from the nearby mountains. There, Rocky 7 was asked to use its science instruments to look for evidence that water had been transported to the sediment and to explore the region for cobbles and boulders that had come from volcanic rocks, just as it will do on Mars some day.
"Imaging and spectroscopy data were acquired for the fan rocks and fine-grained sediment, and samples of the sediment were collected," Arvidson said. "The data are currently being analyzed and will be used to fine-tune rover designs and operations and to evaluate what can be learned about ancient lake environments and desert pavement formation."
By the end of the week, the rover had returned 580 images to remote operators in the field and those stationed at JPL. The field test simulated 32 days of a real Mars rover mission.
Classrooms across the country and as far away as Finland participated in a remote driving test on the last day of the field work. The demonstration was designed to determine how well the vehicle could be controlled remotely using a World Wide Web operator interface called the Web Interface for Telescience (WITS). Six schools in California, Oregon, Georgia, Idaho, Texas and Finland participated in the exercise to command the rover from their classrooms, as scientists will do one day from their home institutions.
Additional information about the field tests are available on the World Wide Web at: http://wundow.wustl.edu/rocky7. More information about rover development for future Mars missions is also available at: http://robotics.jpl.nasa.gov/tasks/scirover.
The Rocky 7 rover development and field testing was supported by JPL's Robotics and Mars Exploration Technology Program Office for NASA's Office of Space Science, Washington, DC.