The Mars Exploration Rovers Begin Their Mission

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On 3 January 2004, the spacecraft holding Spirit entered the Martian atmosphere and began its EDL phase. The spacecraft signals received by JPL confirmed that every critical phase of EDL was occurring precisely on time. When it was announced that they had received the signal that the airbag-protected rover and lander were bouncing on the Martian surface at Gusev Crater, the mission control room erupted in cheers and applause. Over the next several hours the airbags were deflated, the lander petals opened and locked and the rover's PMA deployed in preparation for sending the first images from Spirit back to Earth. When the first images were placed up on the displays, the room was once again filled with cheers and applause. This was a moment of excitement and wonder for all those present. Spirit would soon start its scientific mission of exploration.

The JPL team took its time getting Spirit ready for its mission. Each of the rover's scientific instruments and systems was carefully checked over the next several sols until, on 15 January, the commands were sent for Spirit to egress the lander. Twenty minutes later, JPL received the data that the rover had completed this successfully and was on the surface of Mars. Another mission milestone had been reached. The following sol, the robotic arm, formally known as the Instrument Deployment Device, was activated and extended and the first images with the microscopic imager were taken. The other instruments on the arm were checked in preparation for a close-up examination of a nearby rock. On 19 January, the rover approached a football-sized rock, named Adirondack. This was the first target of examination to employ the rock abrasion tool and the other instruments. As the rover was about to use the rock abrasion tool on the rock, the station in Canberra, Australia reported to JPL that it had not received confirmation from the rover to begin. Communication

On sol 175 (30 June 2004) Sprit took this image, with its front hazard avoidance camera, of the instrument deployment device inspecting a rock target named "Bread Basket''. The close-up image of the rock was captured by its microscopic imager. (NASA/JPL)

with Spirit had been lost. JPL worked around the clock over the next several days to determine the problem and work a solution to reestablish contact with the ailing rover.

As the Spirit mission team dealt with the rover's communication blackout, the Opportunity team prepared for EDL on 25 January. The spacecraft successfully landed at Meridiani Planum and that same day, Opportunity returned breath-taking color images of its landing site, showing dark reddish-brown soil and rock outcroppings. The spacecraft had landed in a small impact crater, which JPL named Eagle Crater. The rover's Pancam returned startling images of its amazing surroundings during the next several sols. Opportunity rolled off its lander in the early morning hours of 31 January. By 6 February, the Spirit mission team had also succeeded in restoring the rover to health, having stopped the rover's constant system rebooting, cleared its flash file memory of thousands of files by reformatting, and uploaded critical software to restore full functionality. The same software was sent to Opportunity to prevent a similar occurrence. The two rovers were now ready for their missions of unknown duration. It was hoped that they would operate for their full 90-sol mission plan. JPL and the world would be pleasantly surprised.

Spirit explores Gusev Crater

Spirit resumed its mission in the first week of February and put the RAT to work grinding a portion of the rock Adirondack, which was examined by the microscopic imager on sol 34. Over the next twenty sols it would use its suite of instruments and cameras as it examined soils and rocks while driving in the direction of Bonneville Crater. On its trek toward the crater, Spirit took the first image of its home planet, Earth. After it reached Bonneville Crater on sol 66, scientists estimated that the shallow crater measured roughly 200 meters in diameter. From the rover's cameras and instruments, scientists discovered no identifiable layering in the walls of the crater, but Spirit spent several more sols moving along the rim of the crater in an

The MER rovers were fitted with a rock abrasion tool capable of a 5 cm-diameter cut. Close-up images were taken on 7 March 2004 by the microscopic imager and four frames were assembled to produce this final image. The specimen was a rock dubbed "Humphrey". (NASA/JPL)

effort to discover more intriguing surface features. As the rover passed sol 80, it looked like both Spirit and Opportunity would meet their mission length requirement and go into the extended portion of the mission that had been planned for. On 8 April 2004, NASA announced that it was extending the MER missions by an additional five months.

This would permit JPL to set Spirit off toward the Columbia Hills more than two kilometers away. The rover's rocker-bogie suspension system and individual wheel drives continued to perform perfectly, the solar panels were providing the needed electrical power as there was very little dust on them, and the scientific instruments continued to perform to specifications. Spirit helped scientists to ascertain sedimentary rocks that had evidence of water action upon them. The ground the rover had been traveling over in its quest for Columbia Hills was relatively flat but was strewn with rocks of all sizes over most of the surface. However, the rover was slowly approaching an area of the plain with fewer rocks. It would be slow going, but the rover had much exploring and scientific investigation to do before it would get there. Spirit was driven in virtually a straight line toward Columbia Hills and took two months to approach the base of the hills.

"This is the first time we've had a close look at hills on Mars,'' Dr. James Rice, one of the rover's science team members from Arizona State University, Tempe, said in a JPL news release. "We could only observe Twin Peaks from a distance and wonder about them,'' Dr. Rice stated of the hills visible from the Pathfinder lander, "but with a more capable rover we can get to Columbia Hills.''

Spirit began its climb into Columbia Hills after more than 150 sols on the Martian surface. Scientists examining images from the rover saw one rock having unique formations and took the rover in for a closer look. Using the microscopic imager, they believed they were looking at a rock containing hematite - in many cases this is formed in the presence of water on Earth. They dubbed the rock Pot of Gold. However, Spirit had developed problems with its right front wheel and JPL chose to turn the rover around and essentially drive it backwards. This was another contingency JPL had considered and planned for. The engineers were impressed with the rover's durability, and this driving mode would allow the team to continue conducting science. Although it was mid-July, the Martian winter was approaching, but as it continued its slow climb and passed sol 200 (29 July), Spirit discovered rock outcrops that came under its examination. One rock in particular, named "Clovis" was examined by the rover's APXS, which found surprisingly high levels of bromine, chlorine and sulfur inside the rock.

"We have evidence that interaction with liquid water changed the composition of this rock,'' Dr. Steve Squyers of Cornell University said at the weekly MER mission update for the media. "This is different from the rocks out on the plain, where we saw coatings and veins apparently due to the effects of a small amount of water. Here, we have a more thorough, deeper alteration, suggesting much more water.''

In September 2004, Mars entered into planetary conjunction. It passed behind the Sun and communication with Spirit and Opportunity was lost for twelve days. The rovers remained in place but continued to make observations. This was the most difficult time for the rovers in terms of power generation in the midst of the Martian

At the start of sol 63, Spirit took this image of its home planet more than 250 million kilometers away. This is the first image ever taken of Earth by a robotic probe on the surface of another planet beyond the Moon. (NASA/JPL/Cornell/Texas A&M)

winter. Communications resumed when Mars appeared from behind the Sun, and JPL gave the MER program another extension.

"Although Spirit and Opportunity are well past warranty, they are showing few signs of wearing out,'' Jim Erickson, JPL's rover program manager said at a news conference during the third week of September. "We really don't know how long they will keep working, whether days or months. We will do our best to continue getting the maximum possible benefit from these great national resources.''

Spirit spent the next several months taking a cautious and winding route up the face of Columbia Hills, with the recalcitrant wheel slowing its progress. After weeks of diagnosing the problem at JPL, engineers succeeded in devising a work-around solution that restored the wheel's functionality. By 3 January 2005, Spirit had spent a full year on the planet, returning scientific data and startling images that continued to amaze and impress scientists. The rovers had succeeded in generating unprecedented interest around the world, with JPL's Martian Exploration Rover website having achieved more than nine billion "hits".

The rover Spirit was directed to begin its ascent of Husband Hill within the Columbia Hills. The hill was named after Rick Husband, who was Commander of the Space Shuttle Columbia that disintegrated upon re-entry on 1 February 2003. This part of the mission would mark a long phase of exploration, scientific discovery and return of many images. By the end of April, Spirit had climbed up half the elevation of Husband Hill and on 22 August 2005, the intrepid rover reached the summit, eighty-two meters above the plains of Gusev Crater. Spirit sent back a breathtaking panorama mosaic of its position on sol 582 (23 August), but this long climb to the top also had a definite purpose.

"This climb was motivated by science,'' said Steve Squyers at a news conference. "Every time Spirit has gained altitude, we've found different rock types. Also, we're doing what any field geologist would do in an area like this: climbing to a good vantage point for plotting a route.''

"We're finding abundant evidence for alteration of rocks in a water environment,'' deputy principal investigator for the rovers' science instruments Ray Arvidson stated during the same news conference. "What we want to do is figure out which layers were on top of which other layers. To do that, it has been helpful to keep climbing for good views of how the layers are tilted to varying degrees. Understanding the sequence of layers is equivalent to having a deep drill core from drilling beneath the plains.''

While on Husband Hill, Spirit made astronomical observations, taking images of the two moons Phobos and Deimos at night. The rover spent more than 100 sols performing detailed examinations of the varied rocks, outcroppings and soil, before

During its climb to the summit of "Columbia Hills'', MER Spirit took this mosaic of images toward "Clark Hill'' and the "Methuselah" Outcrop below, on sol 454 (13 April 2005). Engineers responsible for driving the rover had to drive a zigzag pattern to reach the top. (NASA/JPL/Cornell)

During its climb to the summit of "Columbia Hills'', MER Spirit took this mosaic of images toward "Clark Hill'' and the "Methuselah" Outcrop below, on sol 454 (13 April 2005). Engineers responsible for driving the rover had to drive a zigzag pattern to reach the top. (NASA/JPL/Cornell)

beginning its descent in mid-October with more than 630 sols under its wheels. On 20 November 2005, the Mars Exploration Rover team celebrated Spirit's first Martian year anniversary, equivalent to 687 Earth days. One of the benefits of its stay on Husband Hill was the wind gusts that kept the rover's solar panels relatively free of dust, allowing the rover to continue to receive its required amount of solar energy. As it was approaching the plain of Gusev Crater, it took images over a period of days at the end of December that made up a mosaic of the impressive sand dunes near a site identified as El Dorado. On 12 January 2006 (sol 721), Spirit stirred up the sandy soil with its wheels and revealed bright salts with iron-bearing sulfates, providing more evidence of liquid water having once been present.

The rover's next destination was Home Plate, a low plateau, to perform detailed studies of some of the uniquely-shaped rocks there. These rocks revealed many layers, with coarse granular structure at the bottom and finer structure at the top in a manner that indicated settled volcanic debris. The rover eventually left Home Plate and was directed toward McCool Hill, but on sol 779, Spirit's right front wheel seized completely. JPL calculated that the rover's wheels had performed more than thirteen million revolutions, traveling nearly seven kilometers. Mission planners moved the rover to a slope where its solar panels were better oriented toward the Sun in preparation for the long Martian winter. Here, Spirit would surpass sol 800.

Opportunity explores Meridiani Planum

Opportunity had made many wondrous discoveries of its own and returned images revealing the ancient history of Mars that would keep scientists poring over them for years. JPL spent a week preparing the rover, checking all its instruments, and raising it up from its stowed position before it rolled onto the surface of Eagle Crater on 31 January 2004. There was much for the rover to investigate within the crater. A photographic pan of the landing area revealed layered bedrock outcrops less than ten meters away, which project scientists identified as "rocks in place.'' These were rocks that had remained in the same place where they had originally formed. Such rocks hold a wealth of planetary history, and even from a distance, scientists studying the images could identify sedimentary layers, giving strong indications of the presence of water eons ago. Close inspection of the soil on the crater's floor with the microscopic imager revealed small spheres of hematite, a scientific fingerprint indicating that water had been present.

Opportunity spent weeks performing detailed examinations of the entire outcrop within Eagle Crater, stopping at particular rocks for study. Findings conclusively proved that water had at one time been present. This was a prime mission objective of the Mars Exploration Rovers.

"Liquid water once flowed through these rocks,'' said Dr. Steve Squyers at a press conference in March. "It changed their texture, and it changed their chemistry. We've been able to read the tell-tale clues the water left behind, giving us confidence in that conclusion. We think Opportunity is parked on what was once the shoreline of a salty sea on Mars.''

After spending more than two fruitful months exploring and revealing discoveries within Eagle Cater, Opportunity rolled up and out of the shallow crater on sol 57 and headed for a much larger crater over 700 meters away. This crater would be identified as Endurance Crater and would prove to be an even more spectacular find. The walls of Endurance Crater proved to be quite steep, and considerable discussion went on at JPL as to whether the rover should even attempt to enter it.

"This is a crucial and careful decision for the Mars Exploration Rovers' extended mission,'' said Dr. Edward Weiler, NASA's Associate Administrator for Space Science. "Layered rock exposures inside Endurance Crater may add significantly to the story of a watery past environment that Opportunity has already begun telling us. The analysis just completed by the rover team shows the likelihood that Opportunity will be able to drive to a diagnostic rock exposure, examine it, and then drive out of the crater. However, there's no guarantee of getting out again, so we also considered what science opportunities outside the crater would be forfeited if the rover spends its remaining operational life inside the crater.''

JPL methodically mapped the rover's entry route, its path of exploration within the crater and possible exit strategies. What the mission team did not know was that it would spend the next six months within Endurance Crater, exploring literally the history of Mars with Opportunity. The images the rover took within Endurance became some of the most amazing and revealing of its mission, and NASA proudly displayed the assembled mosaics as wide-angle panoramas. The rover brought all its instruments to bear upon the varied rock walls of the crater and found more evidence of water having once been present. It found significant levels of chlorine, which increased as it drove deeper into the crater, while concentrations of magnesium and sulfur decreased. During the Martian winter, the pace of Opportunity's exploration slowed in order to conserve and store precious solar energy.

Prior to leaving the crater, Opportunity spent considerable time inspecting exposed rock layers along the upper part of the crater wall, called Burns Cliff.

"In the lower portion of the cliff,'' Dr. Squyers stated in mid-December 2004, "the layers show very strong indications that they were last transported by wind, not by water like some layers higher up. The combination suggests that this was not a deep-water environment but more of a salt flat, alternately wet and dry.''

Opportunity successfully climbed up and out of Endurance Crater on sol 315 in December. The rover was then sent to make a thorough inspection of its battered heat shield, which had landed near Endurance, before heading off on a route directly south toward its next exploration target, Vostok Crater, more than a kilometer away. "Little did we know a year ago that we'd be celebrating a year of roving on Mars,'' Dr. Charles Elachi, director of the Jet Propulsion Laboratory, stated in January 2005. "The success of both rovers is tribute to the hundreds of talented men and women who have put their knowledge and labor into this team effort.''

Not far from the heat shield, the rover made a startling discovery: an iron meteorite. Its origin and composition was confirmed by the Mossbauer and the APXS instruments. "I never thought we would get to use our instruments on a rock from someplace other than Mars,'' Dr. Squyers said during the news conference that January. "Think about where an iron meteorite comes from: a destroyed planet or planetesimal that was big enough to differentiate into a metallic core and a rocky mantle.''

Panoramic

Alpha particle X-ray spectrometer imager

Moessbauer spectrometer

Navigation cameras

Mini-thermal emission spectrometer (at rear)

cameras

Low-gain antenna

Solar arrays

Calibration target

High-gain antenne

Magnet array

(forward)

Microscopic

Rocker-bogie mobility system

Rock abrasion too

This illustration shows key components of the MER rover from the top but does not show the bulk of the electronic equipment inside the body of the rover. (NASA/JPL)

The plain Opportunity traveled over was surprisingly smooth, unlike the rugged surface Spirit had to contend with, so its progress was relatively swift. Then, at the end of April on sol 446, the rover got bogged down in sand dunes. In one of JPL's laboratories, engineers formulated a Martian soil simulant and ran tests with a rover test vehicle with identical wheels to experiment with different methods of extracting Opportunity from its situation. The solution to incrementally move the rover without sinking further into the dunes took weeks to develop, test, and employ with the actual vehicle on Mars. Finally, after more than four weeks of effort, the JPL team succeed in getting the rover free of the dunes.

"After a nerve-wracking month of hard work, the rover team is both elated and relieved to finally see our wheels sitting on top of the sand instead of half buried in it,'' said Jeffrey Biesiadecki, a JPL rover mobility engineer. JPL decided to drive the rover more cautiously now, considering its surface conditions, and it took more than 100 sols before Opportunity arrived at Erebus Crater. This was the largest crater the rover had encountered so far, at 300 meters in diameter, and would prove to be

MER Opportunity took a panorama of images of Endurance Crater on sol 115 and 116 (21 and 22 May 2004). JPL used these images to plot Opportunity's entry into the crater and its path once inside. (NASA/JPL)

another rich exploration site. Exposed bedrock displayed cracks and fissures, indicating that the crater had repeatedly experienced wet and dry conditions over a long period of time.

On 26 November 2005 (sol 654), the robotic arm on the rover failed to function properly. After operating on the surface of Mars for the equivalent of nearly two Earth years, both rovers were starting to wear out. JPL engineers worked to determine the problem with the rover's robotic arm and Opportunity was parked on a rock outcrop called Olympia, with dark sandy dunes all around it, while a solution was sought to return the robotic arm back to service. The rover panoramic camera was put into service, thoroughly imaging the entire area and making yet another discovery. It found what JPL scientists called "festooned cross bedding'' formed by flowing liquid water. After weeks of conducting tests on a similar robotic arm at JPL, they were able to get Opportunity's robotic arm partially extended, and it would be used in this position from now on. It used the microscopic imager on 27 January 2006 (sol 715) to get close-ups of the rocks displaying "festooned cross bedding.''

The rover continued to explore Erebus Crater for the month of February and part of March, employing its microscopic imager on the crippled robotic arm and continuing to return superb images from the PanCam. Studying images taken by the Mars Orbital Surveyor camera, JPL decided to send Opportunity further south toward Victoria Crater two kilometers away. On sol 760, it began its trek to this crater, which measures approximately 750 meters in diameter. Both Spirit and Opportunity continued to amaze JPL's engineers, scientists and managers in their exploration of Mars.

"I don't think that any of us really seriously considered that the rovers would last this long,'' Andrew Mishkin admitted. "They could continue for a while longer or we could have a failure any day. One of the rovers one day may just not wake up or be able to communicate with us any more.''

The Jet Propulsion Laboratory knows that day for each rover will arrive, but the amount of scientific data and number of images they have sent back to Earth will keep scientists busy for years, a legacy that will continue long after the rovers themselves have ceased operating.

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