ESA’s Seeker rover during its May 2012 test campaign in Chile’s Atacama Desert, coasting along one of the rare flat loam deposits. The autonomous rover was built and tested through ESA’s StarTiger program, gathering together a specialized team working in a fixed timescale to achieve technology breakthroughs. The ROBOVOLC platform, which served as the basis for the locomotion system, was not specifically designed for Mars-like conditions, nevertheless it proved very trustworthy. Image: ESA |
The
European Space Agency (ESA) assembled a top engineering team then challenged
them to devise a way for rovers to navigate on alien planets. Six months later,
a fully autonomous vehicle was charting its own course through Chile’s Mars-like Atacama
Desert.
The recent test of the Seeker full-scale rover was the
outcome of gathering a multidisciplinary team at a single site, working against
the clock to achieve a breakthrough.
“Their challenge was to demonstrate how a planetary rover—programmed
with state-of-the-art software for autonomous navigation and making decisions—could
traverse 6 km in a Mars-like environment and come back where it started,”
explained ESA’s Gianfranco Visentin.
Long-range rovers risk getting lost
Mars rovers cannot be ‘driven’ from Earth—it takes radio signals up to 40 min
to make the trip to Mars and back. Instead, they are given instructions to
carry out autonomously.
“ESA’s ExoMars rover, due to land on Mars in 2018, will have
state-of-the-art autonomy,” added Gianfranco.
“However, it will not travel more than 150 m each martian
day and not much more than 3 km throughout its mission.
“The difficulty comes with follow-on missions, which will
require daily traverses of five to ten times longer.
“With longer journeys, the rover progressively loses sense
of where it is.
“Lacking GPS on Mars, the rover can only determine how far
it has moved relative to its starting point, but the errors in ‘dead reckoning’
build up into risky uncertainties.”
The team aimed at fixing their position on a map to 1 m
accuracy. Seeker used its stereo vision to map its surroundings, assess how far
it had moved and plan its route, making sure to avoid obstacles.
Desert testing
First, prototypes were tested indoors and outdoors. Then, in May, the Seeker
team took their rover to the Atacama Desert, one
of the driest places in the world—selected for its similarities to martian
conditions.
“The
European Southern Observatory’s nearby Very Large Telescope was an additional
advantage,” Gianfranco added. “The observatory kindly provided refuge for the cold
and windy desert nights.”
For two weeks the team put the rover into action within a
particularly Mars-like zone. Like anxious parents, they watched the rover
wander out of sight, maintaining only radio surveillance.
Their daily efforts culminated in the final trial, when
Seeker was programmed to perform a 6 km loop.
“It
took a whole day because the rover moves at a maximum 0.9 km/h,” Gianfranco
recalled.
“But this was an unusual day. The usual desert winds
counteracting the fierce heat of the Sun died away.
“The rover grew dangerously warm, and had to be stopped
around midday. Then, when the wind finally picked up there wasn’t enough time
to complete the loop before sundown.
“We
managed 5.1 km, somewhat short of our 6 km goal, but an excellent result
considering the variety of terrain crossed, changes in lighting conditions
experienced and most of all this was ESA’s first large-scale rover test—though
definitely not our last.”
Source: European Space Agency
