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pressed ahead with two Mars
Exploration Rovers (MERs). In June
2003, MER A, named Spirit, and
MER B, Opportunity, were ready for
launch. They were about the same
size as a Lunokhod rover, but were
much lighter, at around 400 lb
(180 kg). By the end of January the
following year, both were traveling
across the Martian deserts, hills,
and plains, photographing surface
features and chemically analyzing
rock samples and atmosphere. They
sent back the most glorious vistas
of the Martian landscape ever seen,
enabling geologists to examine the
large-scale structures of the planet.
Spirit and Opportunity had
landed using the same airbag-
and-tether system as Sojourner.
Like Sojourner, both relied on
solar panels, but the new rovers
were built as self-contained units,
able to wander far from their
landers. Each vehicle’s six wheels
were attached to a rocking
mechanism, which made it
possible for the rovers to keep at
least two wheels on the ground
as they crossed rugged terrain.
The software offered a degree of
autonomy so that the rovers could
respond to unpredictable events,
such as a sudden dust storm,
without needing to wait for
instructions from Earth.
Low expectations
Nevertheless, expectations
for these rovers were low. JPL
expected that they would cover
about 2,000 ft (600 m) and last
for 90 Martian sols (equivalent
to about 90 Earth days). During
the Martian winter, however, the
team did not know whether the
solar-powered rovers would retain
adequate power to keep working.
Of all the solar system’s rocky
planets, the seasons of Mars are the
most Earth-like, due to the similar
tilts of the planets’ rotational axes.
Martin winters are dark and bitterly
cold, with surface temperatures
falling to as low as –225°F (–143°C)
near the polar ice caps.
As predicted, Martian winds
blew fine dust onto the solar arrays,
cutting their generating power; but
the wind also blew the panels clean
from time to time. As winter drew
nearer, the JPL team searched for
suitable locations in which the
rovers could safely hibernate. To
do this, they used a 3-D viewer
built from the images taken from
the rover’s stereoscopic cameras.
They chose steep slopes that facedTHE TRIUMPH OF TECHNOLOGY
the rising sun in order to maximize
electricity generation and to top
off the batteries. All nonessential
equipment was shut down so
that power could be diverted
to heaters that kept the rovers’
internal temperature above
–40°F (–40°C).Continuing mission
The hibernation worked, and
incredibly, JPL has managed to
extend the rover missions from
a few days to several years. More
than five years into its mission,
however, Spirit became bogged
down in soft soil; all attempts
to free it by remote control from
Earth failed, and unable to move
to a winter refuge, Spirit finally
lost power 10 months later. It
had traveled 4.8 miles (7.73 km).
Opportunity, meanwhile, has ❯❯An artist’s impression portrays a
NASA Mars Exploration Rover. Rovers
Opportunity and Spirit were launched
a few weeks apart in 2003 and landed
in January 2004 at two sites on Mars.