NASA researchers are developing new prototype robots
that can drive up steep hills and descend almost-vertical
cliffs. Working alone or as a team, these autonomous robotic
explorers may go where no rover has gone before — the cliffs
of Mars.

Recent Mars Global Surveyor images suggest water outflows
near cliff edges and the possibility of rich water-borne
mineral deposits that extend all the way to the cliff base.

"We know that some of the most exciting Mars science and
history will be in very rough, currently inaccessible
terrain. Getting to those hard-to-reach spots — navigating
and exploring them — will require altogether new types of
robotic vehicles," said Paul Schenker, supervisor of the
Mechanical and Robotics Technologies Group at NASA’s Jet
Propulsion Laboratory (JPL), Pasadena, Calif., and principal
investigator for the All-Terrain Explorer.

"These include rover systems that can surmount the hilly base
of cliffs, even descend from cliff edges to study cliff
stratigraphy. Some years from now, rovers may literally be
hanging out on Mars," he said.

In a demonstration near JPL, a new mobility system navigates
a cliff face. Two "tether-bot" rovers station themselves at
the cliff’s edge, assisting a third steerable "cliff-bot" as
it actively descends and ascends the steep terrain.

"They’re a true team, tightly coordinating their behaviors,
sharing what they sense," Schenker said. "They communicate
instantaneously, make mutually informed decisions and jointly
implement their control actions. We can think of them as a
climber with two good friends. We’re not yet at the point of
human competence, where one robot can go it all alone."

The rovers can cooperate in a number of ways: controlling
tension to avoid slackness in the tethers, matching velocity
of tether payouts to cliff-bot navigation, maintaining
stability to prevent cliff-bot tip-over and hauling actions
to initiate the "climber’s" uphill driving when the going
gets really rough.

Over the past year, the JPL researchers also successfully
developed and demonstrated a single rover that can traverse
sandy natural terrain on slopes of 40 to 50 degrees. Similar
to an agile animal, this mechanically reconfigurable All-
Terrain Explorer behaviorally adapts its stance and balance,
reacting to visually perceived changes in the terrain ahead
and motion cues from onboard accelerometers.

"These technology advances should enable broader robotic
exploration of planetary surfaces, letting rovers truly
follow the water, thus giving us a better look at
possibilities of past or present life on Mars," Schenker
said. "Similarly, there are potentially important terrestrial
applications, including urban and rural search-and-rescue

Basic research on the All-Terrain Explorer rovers continues,
and engineers envision that their work may well be part of a
future Mars mission to explore the steep hills and gullies,
nooks and crannies of the Red Planet.

More information on this work is available at:

NASA’s Cross Enterprise Technology Development Program
provided funding for this work.

The California Institute of Technology in Pasadena manages
JPL for NASA. JPL is the lead NASA center for robotic
exploration of the solar system.