[meteorite-list] Opportunity: Longest-Running Mars Rover

[Ron Baalke]

http://www.space.com/18289-opportunity-rover.html?

Opportunity: Longest-Running Mars Rover
Elizabeth Howell
space.com
October 30, 2012

Opportunity passed its warranty date long ago, but the rover is still healthy 
and changing our perceptions of Mars after years of work on the Red Planet.

Initially intended to last 90 Martian days or "sols," Opportunity has now 
driven more than 20 miles and explored two large craters: Victoria and 
Endeavour. Along the way, the rover has found multiple signs of water - while 
surviving a sand trap and bad dust storm.

 Opportunity and its twin rover, Spirit, received their names from 9-year-old 
Sofi Collis. She was the winner of a naming contest NASA held (with assistance 
from the Planetary Society and sponsorship from Lego) to find monikers for the 
Mars Exploration Rovers. Siberian-born Collis was adopted at age two and came 
to live with her new family in Scottsdale, Arizona.

"I used to live in an orphanage," Collis wrote in her winning essay. "It was 
dark and cold and lonely. At night, I looked up at the sparkly sky and felt 
better. I dreamed I could fly there. In America, I can make all my dreams come 
true. Thank you for the 'Spirit' and the 'Opportunity.'"

The Mars Exploration Rovers launched in 2003 on a 283-million-mile (455.4 million 
km) journey to hunt for water on Mars. The $800-million cost for the two of them 
covered a suite of science instruments. Site survey tools included a panoramic 
camera, as well as a mini-thermal emission spectrometer that was supposed to 
search for signs of heat. Each rover also had a small arm with tools such as 
spectrometers and a microscopic imager.

Cruise to Mars

Opportunity left Earth July 7, 2003, aboard a Delta II rocket en route to a landing 
site at the Martian equator called Meridiani Planum. NASA was intrigued by a layer 
of hematite that the orbiting Mars Global Surveyor spotted from above. As hematite 
(an iron oxide) often forms in a spot that had liquid water, NASA was 
curious about how the water got there in the first place and where the 
water went.
 
The 384-pound rover made its final approach to Mars on January 25, 2004. It plowed 
through the Martian atmosphere, popped out a parachute and then vaulted to the 
surface in a cocoon of airbags.

Opportunity rolled to a stop inside a shallow crater just 66 feet (20 meters) across, 
delighting scientists as the first pictures beamed back from the Red Planet. 
"We have scored a 300-million mile interplanetary hole-in-one," quipped 
Cornell University's Steve Squyres, principal investigator for the rover's 
science instruments, in a press release in the days after the landing.

Early sols of science

Opportunity and Spirit (which had landed successfully three weeks earlier, on Jan. 3, 
2004) had a primary goal to "follow the water" during their time on Mars. They would 
hunt for any environments that showed evidence of water activity, particularly looking 
for minerals that may have been left behind after water came through.

Both rovers met that goal quickly. In early March, just six weeks after landing, 
Opportunity identified a rock crop that showed evidence of a liquid past. The rocks 
at "Guadalupe" had sulfates as well as crystals inside of niches, which 
are both signs of water. Spirit found water evidence of its own that same 
week.

Two weeks later, Opportunity found hematite inside some small spheres 
that NASA dubbed "blueberries" because of their size and shape. Using 
a spectrometer, Opportunity found evidence of iron inside a group of berries 
when comparing it to the bare, underlying rock.

The month wasn't yet over when Opportunity found more evidence of water, this time 
from images of a rock outcrop that probably formed from a deposit of saltwater in 
the ancient past. Chlorine and bromine found in the rocks helped solidify 
the theory.

All in all, it was a positive start to Opportunity's mission 
- and it hadn't even left the crater where it had landed yet. Before Opportunity's 
90-day prime mission was over, the golf-cart size rover clambered out 
of Eagle Crater and ventured to its next science target about half a mile 
away: Endurance Crater. It spotted more water signs there in October.


Stuck in the sand

One of Opportunity's most dangerous moments came in 2005, 
when the rover was mired in the sand for five weeks. NASA had put the 
rover into a "blind drive" on April 26, 2005, meaning the rover was not 
checking for obstacles as it went. Opportunity then plowed into a 12-inch-high 
(30 cm) sand dune, where the six-wheeled rover initially had trouble getting 
out.

To save the stranded rover, NASA ran tests on a model of the rover 
in a simulated Martian "sandbox" at the Jet Propulsion Laboratory. Based 
on what they learned in the sandbox, the rover drivers then sent a series 
of commands to Opportunity. It took the rover about 629 feet (191 meters) 
of wheel rotations before it was able to move forward three feet, but 
it cut itself free in early June 2005.

NASA chose to move the rover forward in more careful increments, which was 
especially important because Opportunity lost the full use of its right-front 
wheel (because of a seized steering motor) just days before it got stuck in the 
sand. The rover could still move around just fine with its other three steerable 
wheels, NASA said.

Opportunity's experience in the sand came in handy in October 2005, when NASA 
detected unusual traction problems on Sol 603. Just 16 feet into a planned 148-foot 
drive, a slip check system on board automatically stopped the rover when 
it went past a programmed limit. Two Martian days later, Opportunity backed 
itself out of the problem and kept on going.

A marathon on Mars

In late September 2006, Opportunity wheeled up to Victoria Crater after 21 months 
on the road. It circled the rim for a few months snapping pictures and 
getting a close look at some layered rocks surrounding the crater. NASA 
then made a gutsy decision in June 2007 to take Opportunity inside the 
crater. It was a risk to the rover as it might not have been able to climb 
up again, but NASA said the science was worth it.

"The scientific allure is the chance to examine and investigate the compositions and 
textures of exposed materials in the crater's depths for clues about ancient, wet 
environments," NASA stated in a press release. "As the rover travels farther 
down the slope, it will be able to examine increasingly older rocks in 
the exposed walls of the crater."

The trek down was interrupted by a severe dust storm in July 2007. Opportunity's 
power-generating capabilities dropped by 80 percent in only one week as its solar 
panels became covered in dust. Late in the month, Opportunity's power dipped to 
critical levels. NASA worried the rover would stop working, but Opportunity pulled 
through.

It wasn't until late August that the skies cleared enough for Opportunity 
to resume work and head into the crater. Opportunity spent about a year 
wandering through Victoria Crater, getting an up-close look at the layers 
on the bottom and figuring that these were likely shaped by water.

Opportunity climbed out successfully in August 2008 and began a gradual journey to 
Endeavour, an incredible 13 miles (21 km) away. It took about three years 
to get there, as the rover was stopping to look at interesting science 
targets on the way. But Opportunity successfully arrived in August 2011.

Opportunity is still doing science there today, beaming back findings such as a 
mineral vein deposited by water. The little rover has completed nearly a marathon's 
worth of mileage on Mars.