Date: 25 Sep 2006 21:30:19
From: Joe S.
Subject: After 18 months, Mars rovers still humming along
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Mars Rovers Near Key Site
By Marc Kaufman
Washington Post Staff Writer
Tuesday, September 26, 2006; Page A01
When the Mars rovers Opportunity and Spirit reached their distant
destination in early 2004, NASA scientists hoped the vehicles would probe
the planet's frigid landscape for 90 days before they pooped out or were
undone by the harsh Martian environment.
More than 900 days later, however, both robotic explorers are going strong--
and Opportunity is on the cusp of what is likely to be its greatest
accomplishment.
After enduring an 18-month trek through rugged terrain, dust devils and
daily temperature swings approaching 200 degrees, the rover is scheduled to
arrive today within easy lens view of a deep and geologically revealing
crater. By tomorrow, if all goes well, the little robot that could will be
right at Victoria Crater's edge and in position to peer inside and send back
images like none seen before.
"Exploring Victoria is something we joked and fantasized about but never
really thought we could realistically get to it," said Steven Squyres of
Cornell University, principal investigator for the rovers' science
instruments. "This is the absolutely highest-priority destination we could
have reached."
The reason is that Victoria is an impact crater about 200 feet deep and half
a mile wide, with sheer cliffs and layers upon layers of exposed rock.
Before Victoria, the deepest crater the rover visited was Endurance, which
is a mere 23 feet deep.
The scientists think Victoria Crater is the kind of geological formation
that can tell them a great deal about Mars's history, and especially about
whether and when water may have covered parts of the planet. Water is
essential for life as we know it.
"Reaching Victoria Crater is like finding a Martian history book," said John
Callas, rover project manager at the Jet Propulsion Laboratory in Pasadena,
Calif., where the rovers were designed and built. "There are so many more
exposed layers than we've seen before on Mars, and geologists are very
excited about what we might be soon seeing."
The rover, which has found some evidence that liquid water once existed on
the surface of Mars, is now headed for a small notch at the edge of the
crater. From there, Squyres said, Opportunity will be commanded to take
pictures of two promontories that project into the crater. Whichever looks
most appealing will become the rover's destination.
"We want to get Opportunity right to the edge and then take panorama
pictures of the whole crater," Squyres said. "Then we do our fundamental
planning for the attack on the rest of the crater."
Mars is sometimes as close as 36 million miles from Earth, but right now it
is 250 million miles away, making the upcoming push by Opportunity perhaps
even more remarkable. Across that distance, scientists led by Squyres will
send radio commands to the rover tonight to roll forward, and then tomorrow
night they hope to send it to the lip of the crater.
"We want to get as close as we possibly can, but we obviously don't want the
rover to go crashing down into the crater," Squyres said. "Every inch here
matters, so we have to be cautious. But we also have to push forward as far
as we possibly can."
Callas explained that the rovers have built-in defense systems -- an ability
to, in effect, determine that a move is too risky and to avoid it.
"The rovers are very smart," he said. "Eight of their nine cameras are for
their own observing and navigation, and they have a depth perception that
allows them to anticipate danger.
"Her first priority is always to keep herself safe," said Callas, who said
the team refers to the two robots as female, just as earlier explorers did
with their ships. "We will pick a cautious path, but the final arbiter is
always the rover."
While that programmed instinct for self-preservation has helped keep the
rovers going, unexpected winds and warmer-than-expected weather have allowed
them to operate for so long.
The rovers get their power from solar panels, which the scientists thought
would become covered with Martian dust fairly quickly and stop producing
electricity. But strong winds have regularly blown the dust off the panels.
Electricity not only powers the rovers' six wheels but also keeps them warm
during the long and cold (as in 150 degrees below zero Fahrenheit) Martian
nights. Without heating, the rovers would quickly freeze up and expire.
The rover Spirit, which has explored some hilly areas on the other side of
Mars from Opportunity, almost suffered that fate earlier this year. With the
sun very low in the sky, the panels were not getting enough sunlight. But
the team maneuvered the rover onto an incline that allowed it to point its
solar panels more directly toward the sun. With the additional power, Spirit
is alive -- but hibernating through the depths of the Martian winter.
The rovers, each about the size of a riding lawn mower, weigh 380 pounds on
Earth, but 140 pounds in lesser Martian gravity. While they have shown a
remarkable ability to keep moving, they are hardly speedy. Opportunity has
traveled a total of about six miles on Mars and Spirit about four miles.
Squyres said a science and engineering team of about 40 people convenes
every day -- in person, through videoconference and electronically -- to
study pictures from the night before and a record of where the rover has
gone and what it has done. The team spends about eight hours formulating a
plan for the next day, and by evening it transmits the signals that the
rover's computers read and respond to.
The conception, development and operation of the rover program have cost
about $900 million since it began in earnest in 2000, considered a bargain
for a major space program. While the rovers could grind to a halt any day,
it is also possible that they will continue their missions for months.
Over the weekend, Squyres said, NASA radioed new software that will make
Opportunity even more capable. The rover will now, for instance, be better
able to assess which of the thousands of images it takes show swirling dust
devils, which are of considerable interest to scientists. With that
improvement, less precious communication time will be spent sending images
that contain nothing of particular interest.
The rover also got some new software to control its motions in a more
sophisticated and smooth manner. Squyres said the team spent the weekend
sending commands to Opportunity to make it roll back and forth, ensuring
that the new commands were being understood.
"We're about to send Opportunity to the edge of a cliff, and we wanted to be
sure she's working the way she should," he said.
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