[meteorite-list] Mars Rover Mission Could Last 1, 000 Days if NASA Agrees

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Mon Apr 4 20:36:42 2005
Message-ID: <200504050023.j350NIp15145_at_zagami.jpl.nasa.gov>

http://sfgate.com/cgi-bin/article.cgi?f=/c/a/2005/04/04/MNGBNC2S9B1.DTL

Scientists push to keep scouting Mars Rovers' 90-day mission, now in its
15th month, could last 1,000 days if NASA agrees

David Perlman
San Francisco Chronicle
April 4, 2005

Fifteen eventful months after the start of their scheduled three- month
mission, the twin Mars rovers are still hard at it, functioning superbly
as they wheel across the sands and past the rocks of a Martian landscape
where evidence of ancient water seems undeniable.

Now the Earthbound leaders of the robotic expedition -- using radio and
sophisticated software to control every maneuver of the six-wheeled
explorers and every deployment of their onboard instruments, and
confronted from time to time with technical problems that could have
spelled the mission's end -- are asking NASA to keep Spirit and
Opportunity working for at least 18 more months, a request likely to be
approved.

"We were good to go for 90 sols when we landed," said Jacob Matijevic,
the mission's team chief for engineering, "but at this stage it looks
like 1, 000 sols -- that's our goal. Engineering-wise, we're in terrific
shape."

A sol is a full Martian day, somewhat longer than an Earth day at
precisely 24 hours, 39 minutes and 35 seconds -- a difference that
forces scientists and engineers at the Jet Propulsion Laboratory in
Pasadena to endure some awkward sleeping times trying to keep up with
sunny days and dark nights on Mars.

These days, the rovers are on the move every day. Spirit is climbing
high in the Columbia Hills, and Opportunity is heading for a mysterious
patch of "etched terrain."

But it's not always clear sailing. From the beginning, the mission's
engineering teams have performed extraordinary feats whenever
emergencies threatened -- and nature even stepped in recently to
accomplish one repair job without human intervention.

Spirit faced that newest crisis only a few weeks ago, when electric
current from its solar panels dropped dangerously low. The panels on
each rover normally provide 900 watt-hours of electricity to keep the
vehicle moving and its instruments performing, but on sol 416 -- March 5
-- Matijevic and his team saw that Spirit's power levels had dropped by
nearly two-thirds, down to 350 watt-hours.

Its panoramic camera, focused on a calibration target aboard the
vehicle, revealed that Martian dust had coated the target, and the
engineers deduced that fine dust from abraded sand grains was also
obscuring the solar panels. With so little power, Spirit and its
instruments would soon be crippled.

At that time, Spirit was driving up the slopes of the Columbia Hills, a
major feature of the broad Gusev Crater where the rover landed in
January 2004.

"It's a gusty place up there where we're climbing," said Steven W.
Squyres, the Cornell astronomer who is the mission's science chief, "and
then our cameras detected several dust devils crossing over -- they were
wind cleaning events, and the gusts apparently swept the dust off the
panels, because a few mornings later the power levels jumped up to 800
watt-hours, and now we're safely back to 830."

Last summer, Spirit challenged the engineers with a really tough and
long- lasting problem when its right-front wheel began binding, as if
something were obstructing its gear box. Each of the six wheels on the
rovers operates independently, and each can be run individually by the
engineers at Mission Control.

"We found the wheel was drawing more current than its limit," Matijevic
said, "and that it could possibly burn out the motor as well."

The engineers turned then to the full-size model rover standing ready to
move in the sand-covered test bed at the laboratory -- "the hangar
queen," as the team calls it -- where even the smallest part of the Mars
rovers is duplicated. There they took the same wheel and the same gear
box apart again and again, and tested them under every conceivable
condition.

"Believe me, we did some very hard thinking and selective heating and
ran that wheel in the test bed back and forth over and over again, and
finally decided to have Spirit itself drive on only five wheels for a
time and then drive backward some of the time," Matijevic said.

"It took months, but we finally found that lubricant wasn't flowing into
the gear box properly. After giving the wheel on Mars some rest time,
and taking time out between drives, and using that balky wheel only once
a week and driving half the time forward and half the time backward --
we've now finally got the lubricant to flow properly again."

Since then, he said, all they've needed to do is pay continued close
attention to driving conditions, "and the wheel is fully back in the
family."

But the engineers can't fix all the problems. One of the instruments on
Spirit is in trouble now -- the Rock Abrasion Tool, better known as the
RAT. The RAT is used to grind away the surface of rocks encountered by a
rover, so the rover's spectrometers can identify the minerals and
analyze their subsurface chemistry for evidence that they might have
once been in contact with water, or perhaps altered or formed by saltwater.

The RAT's head is made of a phenolic resin with layers of tiny diamonds
embedded in it, and when one layer of diamonds wears away, the head
exposes another layer, Squyres said.

And he described the current problem: "Our recent grinds were going very
well, but when we were part way through one very soft rock surface, the
RAT was dancing around if we pressed very hard."

It was hardly the RAT's fault, Squyres said.

"The RAT on each rover was designed to work for only three grindings,
and on Spirit we've used it for 15 grinds already, so no wonder it's
balky," he said. "It's hard to tell whether all the diamonds are worn
away, or whether some are left, so we're keeping it for only the next
high-priority targets.

"But each RAT also has a brush to sweep away rock dust, and Spirit's is
working fine, so we can brush rock surfaces whenever we want, and we're
doing it all the time." Brushing rock surfaces -- even without grinding
the material -- often reveals unsuspected clues to a Martian rock's
structure.

Spirit itself is still climbing up the Columbia Hills, aiming toward a
high spot named Husband Hill, which is about 400 feet above the plain
below.

"There's a bewildering variety of rocks up there, and an interesting set
of terraces on the south side of Husband Hill, and every rock so far has
shown evidence of water -- but no conclusive evidence of surface water
in the past. Yet some of the rocks are 60 percent salt, which is a
pretty powerful sign that saltwater once evaporated on Mars -- perhaps
many millions of years ago, " Squyres said.

As for Opportunity, it has provided the most spectacular discovery of
the entire mission so far, Squyres said.

The second rover landed inside a tiny crater on the far side of Mars
near the equator on a broad plain called Meridiani Planum, and that,
Squyres said, is where "the best evidence for surface water in the far
distant past is -- the best evidence for a habitable environment, and
we've found it."

Now, Opportunity is rolling on full power, heading toward two craters
named Viking and Voyager and covering an area that Squyres calls
"topographically flat and scientifically barren."

"But with so much power," he said, "we're trying to push the rover
really hard. We're covering 220 meters (722 feet) in a single day, and
that's really ripping!"

The rover is approaching what the scientist calls an "etched terrain,"
marked by parallel grooves something like corduroy cloth.

"We don't really know what that etched terrain is," Squyres said, "but
we think it's some kind of sulfate-rich rock. Up to now, all the rocks
we've seen have been exposed by ancient impacts -- and that's like
putting the rocks in a blender." After millions of years of violent
sandblasting, they're hard to read.

In contrast, he said, "the etched terrain looks absolutely flat, and we
might be seeing something completely new, something really important --
or it could possibly turn out to be an impenetrable barrier.

"But if it isn't a barrier, then within the next week we're aiming for
an old eroded crater called Erebus, and after that a huge crater called
Victoria that's 900 kilometers (560 miles) across with 40 meters of
exposed sedimentary rock on the walls. There's a target to look for water!"
Received on Mon 04 Apr 2005 08:23:18 PM PDT