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       A task force of NASA's Advisory Council has called for an aggressive unmanned exploration of Mars as precurser to manned exploration of the planet in the next century.

       The Space Goals Task Force focused heavily on recommendations of the earlier National Commission on Space which also highlighted Mars exploration.

       Jet Propulsion Laboratory has been studying ways of returning Martian soil and rock samples to earth by means of robotic rover that could explore parts of the Martian surface.

       A recent study bringing the Apollo Lunar rover technology to state-of-the-art has resulted in recommendations for Mars Rover 1996 Mission Concept. The study, prepared by JPL group led by James Randolph, defined design concept for Mars rover vehicle which would explore the face of Mars for five years or more.

       The current rover technology includes stereo camera vision system, sensors, computer brain, controlled manipulators and drill system for acquiring samples.

       The proposed vehicle would have mass of no more than 700 kilograms (1,540 pounds), be six meters long and two meters across.

       It would have mobility, guidance and control system that could be expected to traverse safely at least one kilometer (0.62 of mile) per day for five years over Martian equatorial terrain, climb vertical steps one meter high and cross crevasses one meter wide. The vehicle also could climb smooth grades of 60 degrees and 35 degree grades on loose sand.

       The rover would provide volume of 1.2 cubic meters for science payload of 100 kg (220 pounds). There would be an average of 50 watts of electrical power for the science package during data acquisition -- not while moving -- and 25 watts of standby power for the science package. Power would be provided by radioisotope thermoelectric generator.

       The study results state that the robot would probably require stereo imaging, but some novel laser ranging or designation technique may also be considered.

       Two guidance systems were considered in the study. One is Computer-Aided Remote Driving (CARD), which allows human operator to designate an extended path for vehicle based on stereo images. laser range finder would measure the distances between the rover and any obstacles not previously considered and planned for. Images of the local terrain around the rover would be taken by the stereo cameras and sent to earth. After analyses by earth-based operators, the data would be returned to the rover's on-board computer and would instruct it to travel over the safest course toward given destination.

       An alternative is semi-autonomous control using an orbiter to map and relay to earth so operators could plan traversals of perhaps 10 km for the rover to execute at time. The use of orbiter support images to help plan where the orbiter could go could increase daily traverse distances as much as ten times.

       The orbiter also would be radio relay that would allow communications with the vehicle when it otherwise would be beyond the view of earth.

       The proposed rover configuration includes three cabs, each with two independently powered wheels, connected by flexible ties which permit pitch, yaw and roll motions. The rover is steered by counter rotation of the two end cabs. The vehicle's wheels are one meter in diameter and its axle spacing is 1.6 meters to allow climbing l.5 meter obstacle.

       Brian Wilcox, supervisor of Robotics and Teleoperators Research Group at JPL, said rover could be sent to Mars using single launch of the space shuttle. The mission would employ soft lander similar to the Viking landers.

       "The possibility of Martian rover makes sense," he said, "because it will take substantial effort to land men on Mars. One can expect delay of perhaps 10 years or more between the landing of rover for unmanned exploration and the time when the first manned expedition arrives."

       A mission scenario now under consideration calls for five-year rover mission, or longer. After the first year it would return rock and soil specimens to sample return vehicle which would then be launched to earth.

       Wilcox stressed the value of another Mars mission. "The Viking experience was that we found planet which, far from being an essentially dead hulk as is the moon, has rich geologic history. It has volcanoes; it has river valleys; apparently at one time it had flowing water; it has sand dunes; it has lava beds; it has all the structures and tectonic richness that planet like earth would have.