NASA FACTS/Planetary Rovers 1992
National Aeronautics and
Planetary rovers - wheeled or multi-legged robots that cross rugged terrain - can act both as independent explorers and as pathfinders for human missions. NASA is vigorously developing technologies for these mobile robots and testing them in ground situations that correspond to planenetary surfaces. The research will boost the operational capabilities of NASA missions, make them safer and more cost-effective and increase the chances of success.
The concepts that NASA is studying differ in size, shape and the way they move. AMBLER, for example, ia a six-legged, 12-foot-tall walking robot developed for NASA by Carnegie Mellon University, Pittsburgh. It has two sets of stacked legs, with three legs in each stack. The legs separately lift, advance and theo return to their original positions, much like an egg beater. AMBLER can cross a rough landscape simply by stepping over large bouIders and crevices.
AMBLER's computerized "brain" lets it decide where to go and what to do based on a set of general preprogrammed instructions. With input from its vision system, the robot creates 3-D maps of the area to cross and any interesting objects it might want to explore. After studying the maps, AMBLER figures out which way to move and where to place its feet.
NASA's Jet Propulsion Laboratory (JPL), Pasadena, Calif., has come up with a very different rover testbed. JPL's 13-foot long "Robby" travels on six 35-inch-diameter wheels and its three-part body lets it go over obstacles about 3 feet high. The rover is also equipped with a battery of four video cameras and a robotic arm that can be used for sampling experiments.
Robby is testing two advanced navigation methods. Computer-Aided Remote Driving lets human operators plan an extended travel path (several hundred feet) using stereo images from the onboard cameras, then send that route to the rover for execution. Using the other technique, Semi-Autonomous Navigation, humana plot a much longer path (tens of miles) for the vehicle, then the rover automatically moves around obstacles using data from its sensors and its stored data base.
Some "autonomous" capability is critical for rovers that will explore planetary surfaces because they cannot be controlled in real-time from Earh. On Mars, sending a signal to a rover and confirming that it has carried out the order via a return signal would take up to 4O minutes depending on the distance between Earth and the Red Planet. That is much too long for effective Earth-based direction of a rover's activities - and the situation gets worse the farther out in the Solar System a robot goes because travel time for communications increases.
Not all NASA's rovers are large machines. The agency also is testing prototypes of mini- rovers (up to 220 pounds) and micro-rovers (under 22 pounds) that could give NASA mission planners a new class of low-cost planetary exploration options.
These rover concepts - two testbeds have been dubbed "Rocky" and "Tooth" by JPL engineers - would carry tiny cameras for close-up views of rocks and soil and for horizon scans. They also would have micro-sensors to test the atmosphere and soil, spectrometers to get geological data and aeismometers to detect crustal motions. The latest design, Rocky IV, even has a behavioraI control system that permits limited autonomous functions.
"Go-For," a somewhat different concept, is designed to be hosted by a simulated planetary lander that provides computing and communications services to the micro-rover; the testbed Robby is being used for evaluations. In the initial tests, Go-For navigates using stereo images from the cameras on Robby's moveable "head." Eventually the micro-rover will have its own video camera.
Go-For can move around very large obstacles and over rough terrain using a novel suspension design having four wheels mounted on "forks" (pairs of struts that rotate together at the end of an axle). A control system adjusts the fork positions so that 80 percent of Go-For's weight is always over the rear wheels, which gives tbem the traction to push and lift the front wheels over objects in its path.
Into The Caldera
NASA and Carnegie Mellon are planning a unique field evaluation of a rover in late 1992. The goal: Send an 8-legged, 422-pound robot called "Dante" into the crater of an active Antarctic volcano, Mt. Erebus.
Parts of Antarctica come as close to imitating conditions on Mars as we can get on Earth. The tests with Dante (and its transporter-robot,"Virgil") will give scientists and engineers invaluable insight into building and controlling a rover using technology similar to what real rovers will use on planetary surfaces. As a bonus, Dante will collect actual science data on the volcano for the National Science Foundation.
Current mission plans call for Virgil to carry the rapeller robot Dante up the slope of Mt. Erebus to the 12,447-foot summit, where the wheeled transporter will park and anchor itself near the crater rim. Dante, attached to Virgil by a quarter-inch-wide tether that provides power and communications, will slowly walk off the transporter and start to descend into the crater.
Because the crater wall is a steep vertical drop, Dante will "rappel" down the sheer rock face, unwinding the tether using its tension to support itself. The robot will sense obstacles by groping with its lead legs. It will chart its own course with a small computer in the middIe of its body.
When Dante reaches the crater floor, it will crawl into the inner crater of Mt. Erebus to obtain rock specimens, take samples of the gases being released from the lava lake and get samples of the lava itself. The rover wilI then retrace its steps across the crater floor, pull itself up the crater wall with the tether and redock with Virgil.
SmaIl missions are likely to be the focus of NASA's planetary exploration plans for the rest of the 1990s. The first of these low-cost (no more than $150 million) efforts may carry a micro-rover as part of its payload.
The Pathfinder mission for the Mars Environmental Survey (MESUR-pronounced "measure") is slated for a 1996 launch. NASA is studying whether the flight could deploy a micro-rover from the lander that will touch down on the Martian surface. The rover would have a camera and one or two science instruments.
The Pathfinder flight will blaze a trail for the full-blown MESUR missions that are planned for 1999 and beyond as vital precursors to human exploration of Mars.