Mars Rovers To Last Longer Than Expected
It took more than a
month for NASA's Spirit Mars rover to finish the drive to its
destination, a crater called "Bonneville," but mission planners are
already looking toward more distant pastures, confident that their
robust robot -- and its twin, Opportunity -- will last twice as
long as originally expected. Spirit was scheduled to travel the
last few feet to the rim of Bonneville Tuesday, then look around
with its panoramic camera for anything interesting enough to nuzzle
its science instruments against.
"We have arrived," said Jennifer Trosper, Spirit mission
manager, of the rover's long journey during a press briefing
Thursday at NASA's Jet Propulsion Laboratory (JPL). "Once we've
finished with 'Bonneville,' we'll head on over to the East
JPL scientists had hoped that "Bonneville" crater, the remains
of an ancient Martian impact, would give them a deeper look into
the subsurface geology of Mars. An initial inspection shows the
crater composed of the same regolith material Spirit found
elsewhere in its Gusev crater landing site.
Though there are no signs of rocky outcrops like that studied by
Opportunity, the rover is still identifying science targets. The
East Hills, which lie a mile and a half (2.5 kilometers) from
Spirit, may prove more interesting fare. According to JPL
scientists, Spirit still has enough life to reach them despite the
fact that it is about two-thirds through its planned 90-day mission
lifetime. This week, Spirit also surpassed its minimum mission
success driving distance of 984 feet (300 meters).
"Spirit is kind of post-retirement here and getting ready for
her longest drive yet," Trosper said, adding that Opportunity has
reached middle age. "Neither rover is showing their age and we
believe they will both last 200 plus sols." A sol is one Martian
day, which is 24 hours and 37 minutes long.
Spirit, now in Sol 67 of its Mars mission, was able to catch a
clear view of its heat shield in a navigation camera mosaic taken
from the rim of "Bonneville." The shield, which protected Spirit
during its fiery entry through the Martian atmosphere, apparently
landed near the crater's lip. The landing site of Spirit's
parachute and backshell were also seen far behind the rover. Just
reaching the crater vista was a task for Spirit, which encountered
tougher terrain the closer it crept toward "Bonneville."
"If you tried to drive your car up this slope you'd probably get
a flat tire and a busted oil pan," explained Chris Leger, the
rover's driver. "So it was really a tricky drive."
Leger likened rover navigation to orienteering, and said
Spirit's journey was a combination of constant image studies, blind
driving, the autonomous control of the rover itself and stutter
steps of just a meter or so to make sure the path was safe. But
overall the experience seems enjoyable.
"I still can't believe they're paying me to do this," Leger
On the other side of Mars at Meridiani Planum, Opportunity is
still sitting in the same crater it landed in 46 mission days ago,
but only because there are still more experiments for it to
perform. The rover has driven 239 feet (73 meters) around its
landing site so far.
Phil Christensen, lead
scientist for the rover's miniature thermal emission spectrometer
(Mini-TES), said Opportunity could leave its crater in the next 10
to 12 days, at which time he's hopeful to study the hematite
content of the Martian plains. Hematite is a mineral that can form
in the presence of water, and its wide presence at Meridiani Planum
from orbit was a main reason for choosing to land there in the
first place. However, though Opportunity has found conclusive
evidence that water existed at the site, primary through sulfates
in the crater's outcrop, the hematite levels there are low.
"If the sulfate minerals formed in water, and the hematite
formed in water, we really need to learn what changed," Christensen
said. One possible solution is that the object that caused
Opportunity's crater punched through a thin layer of hematite and
hit a deeper basalt floor, he added.
Meanwhile, Opportunity did offer scientists a chance to collect
a comprehensive temperature profile of Mars' atmosphere during an
overhead flyby of the Mars Global Surveyor (MGS). By combining the
data from the rover's Mini-TES as it was looking up and MGS's
larger thermal emission spectrometer looking down, scientists were
able to compile a ground-up view of the planet's atmosphere.
The rover had a small glitch with its rock abrasion tool (RAT),
which started to stick due to colder than expected Martian
temperatures. Rover engineers increased the voltage setting to
compensate for the lower temperature and the RAT is once again
chewing into Martian rocks.