Opportunity Rover

Opportunity Rover


Opportunity, MER-B (Mars Exploration Rover – B), is a robotic rover active on the planet Mars since 2004. Launched on July 7, 2003, Opportunity landed on Mars' Meridiani Planum on January 25, 2004 at 05:05 Ground UTC (about 13:15 Mars local time), three weeks after its twin Spirit (MER-A), also part of NASA's Mars Exploration Rover Mission, touched down on the other side of the planet.[1] While Spirit became immobile in 2009 and ceased communications in 2010, Opportunity remains active as of 2013, having already exceeded its planned 90 sol (Martian days) duration of activity by 10 years, 92 days (in Earth time). Opportunity has continued to move, gather scientific observations, and report back to Earth for over 38 times its designed lifespan.

Mission highlights include the initial 90 sol mission, finding extramartian meteorites such as Meridiani Planum, and over two years studying Victoria crater. It survived dust-storms and reached Endeavour crater in 2011, which has been described as a "second landing site".[2]

The Jet Propulsion Laboratory (JPL), a division of the California Institute of Technology in Pasadena, California, manages the Mars Exploration Rover project for NASA's Science Mission Directorate in Washington, D.C..

Objectives

The scientific objectives of the Mars Exploration Rover mission are to:[3]

  • Search for and characterize a variety of rocks and soils that hold clues to past water activity. In particular, samples sought will include those that have minerals deposited by water-related processes such as precipitation, evaporation, sedimentary cementation or hydrothermal activity.
  • Determine the distribution and composition of minerals, rocks, and soils surrounding the landing sites.
  • Determine what geologic processes have shaped the local terrain and influenced the chemistry. Such processes could include water or wind erosion, sedimentation, hydrothermal mechanisms, volcanism, and cratering.
  • Perform calibration and validation of surface observations made by Mars Reconnaissance Orbiter instruments. This will help determine the accuracy and effectiveness of various instruments that survey Martian geology from orbit.
  • Search for iron-containing minerals, identify and quantify relative amounts of specific mineral types that contain water or were formed in water, such as iron-bearing carbonates.
  • Characterize the mineralogy and textures of rocks and soils and determine the processes that created them.
  • Search for geological clues to the environmental conditions that existed when liquid water was present.
  • Assess whether those environments were conducive to life.

During the next two decades, NASA will continue to conduct missions to address whether life ever arose on Mars. The search begins with determining whether the Martian environment was ever suitable for life. Life, as we understand it, requires water, so the history of water on Mars is critical to finding out if the Martian environment was ever conducive to life. Although the Mars Exploration Rovers do not have the ability to detect life directly, they are offering very important information on the habitability of the environment in the planet's history.

Design and construction

Opportunity (along with its twin, Spirit) is a six-wheeled, solar-powered robot standing 1.5 metres (4.9 ft) high, 2.3 metres (7.5 ft) wide, and 1.6 metres (5.2 ft) long and weighing 180 kilograms (400 lb). Six wheels on a rocker-bogie system enable mobility. Each wheel has its own motor, the vehicle is steered at front and rear and is designed to operate safely at tilts of up to 30 degrees. Maximum speed is 5 centimetres per second (2.0 in/s) although average speed is about a fifth of this (0.89 centimetres per second (0.35 in/s)). Both Spirit and Opportunity have pieces of the fallen World Trade Center's metal on them that were "turned into shields to protect cables on the drilling mechanisms".[4][5]

Solar arrays generate about 140 watts for up to four hours per Martian day (sol) while rechargeable lithium ion batteries store energy for use at night. Opportunity's onboard computer uses a 20 MHz RAD6000 CPU with 128 MB of DRAM, 3 MB of EEPROM, and 256 MB of flash memory. The rover's operating temperature ranges from −40 to +40 °C (−40 to 104 °F) and radioisotope heaters provide a base level of heating, assisted by electrical heaters when necessary.[6] A gold film and a layer of silica aerogel provide insulation.

Communications depends on an omnidirectional low-gain antenna communicating at a low data rate and a steerable high-gain antenna, both in direct contact with Earth. A low gain antenna is also used to relay data to spacecraft orbiting Mars.

Fixed science/engineering instruments include:

  • Panoramic Camera (Pancam) – examines the texture, color, mineralogy, and structure of the local terrain.
  • Navigation Camera (Navcam) – monochrome with a higher field of view but lower resolution, for navigation and driving.
  • Miniature Thermal Emission Spectrometer (Mini-TES) – identifies promising rocks and soils for closer examination, and determines the processes that formed them.
  • Hazcams, two B&W cameras with 120 degree field of view, that provide additional data about the rover's surroundings.

The rover arm holds the following instruments:

  • Mössbauer spectrometer (MB) MIMOS II – used for close-up investigations of the mineralogy of iron-bearing rocks and soils.
  • Alpha particle X-ray spectrometer (APXS) – close-up analysis of the abundances of elements that make up rocks and soils.
  • Magnets – for collecting magnetic dust particles
  • Microscopic Imager (MI) – obtains close-up, high-resolution images of rocks and soils.
  • Rock Abrasion Tool (RAT) – exposes fresh material for examination by instruments on board.

The cameras produce 1024-pixel by 1024-pixel images, the data is compressed with ICER, stored, and transmitted later.

The rover's name was chosen through a NASA sponsored student essay competition.

Mission overview


The primary surface mission for Opportunity was planned to last 90 sols. The mission has received several extensions and has been operating for 3836 days since landing. An archive of weekly updates on the rover's status can be found at the Opportunity Update Archive.[7]

From its initial landing, by chance, into an impact crater amidst an otherwise generally flat plain, Opportunity has successfully investigated soil and rock samples and taken panoramic photos of its landing site. Its sampling allowed NASA scientists to make hypotheses concerning the presence of hematite and past presence of water on the surface of Mars. Following this, it was directed to travel across the surface of Mars to investigate another crater site, Endurance crater, which it investigated from June – December 2004. Subsequently, Opportunity examined the impact site of its own heat shield and discovered an intact meteorite, now known as Heat Shield Rock, on the surface of Mars.

From late April 2005 to early June of that year, Opportunity was perilously lodged in a sand dune, with several wheels buried in the sand. Over a six-week period Earth-based physical simulations were performed to decide how best to extract the rover from its position without risking a permanent immobilization of the valuable vehicle. Successful maneuvering a few centimeters at a time eventually freed the rover, which resumed its travels.

Opportunity was directed to proceed in a southerly direction to Erebus crater, a large, shallow, partially buried crater and a stopover on the way south towards Victoria crater, between October 2005 and March 2006. It experienced some mechanical problems with its robotic arm.

In late September 2006, Opportunity reached Victoria crater and explored along the rim in a clockwise direction. In June 2007 it returned to Duck Bay, its original arrival point; in September 2007 it entered the crater to begin a detailed study. In August 2008, Opportunity left Victoria crater for Endeavour crater, which it reached on August 9, 2011.[8]

Opportunity's total odometry as of June 15, 2013 (sol 3339) is 22.83 miles (36.74 km).[9]

Mission timeline

2004

Landing site: "Eagle" crater

Main article: Eagle crater



Opportunity landed in Meridiani Planum at 1°57′S 354°28′E / 1.95°S 354.47°E / -1.95; 354.47, about 25 kilometres (16 mi) downrange (east) of its intended target on January 25, 2004 at 05:05.[10] Although Meridiani is a flat plain, without the rock fields seen at previous Mars landing sites, Opportunity rolled into an impact crater 22 meters in diameter, with the rim of the crater approximately 10 metres (33 ft) from the rover.[10] NASA Scientists were so excited about landing in a crater that they called the landing a "hole in one"; however, they were not aiming for the crater (or even knew it existed). Later, the crater was named Eagle crater and the landing site designated "Challenger Memorial Station".[11] This was the darkest landing site ever visited by a spacecraft on Mars. It would be two weeks before Opportunity was able to get a better look at its surroundings.

Scientists were intrigued by the abundance of rock outcrops dispersed throughout the crater, as well as the crater's soil, which appeared to be a mixture of coarse gray grains and fine reddish grains. This sweeping look at the unusual rock outcropping near Opportunity was captured by the rover's panoramic camera. Scientists believe the seemingly layered rocks are either volcanic ash deposits or sediments laid down by wind or water. It was given the name Opportunity Ledge.

Geologists said that the layers—some no thicker than a finger—indicate the rocks likely originated either from sediments carried by water or wind, or from falling volcanic ash. "We should be able to distinguish between those two hypotheses", said Dr. Andrew Knoll of Harvard University, Cambridge, a member of the science team for Opportunity and its twin, Spirit. If the rocks are sedimentary, water is a more likely source than wind, he said.[12]

These layered rocks measure only 10 centimetres (3.9 in) tall and are thought to be either volcanic ash deposits or sediments carried by water or wind. The layers are very thin measuring just a few millimeters thick in some cases.


"Opportunity Ledge" outcroppings

This panorama of Eagle crater shows outcroppings, which are thought to have water origins.

On Sol 15, Opportunity took a close up of the rock "Stone Mountain" in the outcrop area of the crater, raising speculation that the rock consisted of very fine grain or dust, in contrast to Earth sandstone, which is compacted sand with rather large grains. The weathering agent eroding away layers of this rock seemed to be visible as dark spots.[13]

A picture received on February 10 (taken on Sol 16) showed that the thin layers in the bedrock converge and diverge at low angles, suggesting that some "moving current" such as volcanic flow, wind, or water formed these rocks. The discovery of these layers was significant for scientists who had planned this mission to test the "water hypothesis" rigorously.

El Capitan outcropping


On February 19 the survey of "Opportunity Ledge" was declared successful. A specific target in the outcrop (dubbed "El Capitan"), whose upper and lower portions appeared to differ in layering and weathering characteristics, was selected for further investigation. El Capitan, about 10 centimetres (3.9 in) high, was named after a mountain in Texas.[14] Opportunity reached "El Capitan" on Sol 27, and took a first picture of the rocks with its panoramic camera.

On Sol 30, Opportunity used its Rock Abrasion Tool (RAT) for the first time to investigate the rocks around El Capitan. The image on the right-hand side shows a close up view taken after the drilling and cleaning process was complete. Due to chance, two spherules were also cut partially, and seem to show scratches and other marks made by the diamond-crusted grind tool. The black areas are artifacts of the imaging process, when parts of the picture are missing.

During a press conference on March 2, 2004, mission scientists discussed their conclusions about the bedrock, and the evidence for the presence of liquid water during their formation. They presented the following reasoning to explain the small, elongated voids in the rock visible on the surface and after grinding into it (see last two images below).[15]

These voids are consistent with features known to geologists as "vugs". These are formed when crystals form inside a rock matrix and are later removed through erosive processes, leaving behind voids. Some of the features in this picture are "disk-like", which is consistent with certain types of crystals, notably sulfate minerals.

Additionally, mission members presented first data from the MIMOS II Mössbauer spectrometer taken at the bedrock site. The iron spectrum obtained from the rock El Capitan shows strong evidence for the mineral jarosite. This mineral contains hydroxide ions, which indicates the presence of water when the minerals were formed. Mini-TES data from the same rock showed that it consists of a considerable amount of sulfates.

Opportunity digs a trench


The rover alternately pushed soil forward and backward out of the trench with its right front wheel while other wheels held the rover in place. The rover turned slightly between bouts of digging to widen the hole. "We took a patient, gentle approach to digging", Biesiadecki said. The process lasted 22 minutes.

The resulting trench—the first dug by either Mars Exploration Rover—is about 50 centimetres (20 in) long and 10 centimetres (3.9 in) deep. "It came out deeper than I expected", said Dr. Rob Sullivan of Cornell University, Ithaca, N.Y., a science-team member who worked closely with engineers to plan the digging.[16]

Two features that caught scientists' attention were the clotty texture of soil in the upper wall of the trench and the brightness of soil on the trench floor, Sullivan said.

By inspecting the sides and floor of a hole it dug, Opportunity found some things it did not see beforehand, including round pebbles that are shiny and soil so fine-grained that the rover's microscope could not make out individual particles.

What's underneath is different than what is at the immediate surface.[17] The soils consist of fine-grained basaltic sand and a surface lag of hematite-rich spherules, spherule fragments, and other granules. Underlying the thin soil layer, are flat-lying sedimentary rocks. These rocks are finely laminated, are rich in sulfur, and contain abundant sulfate salts.[18]


Endurance crater

Main article: Endurance crater


On sol April 20, 2004, the rover reached Endurance crater, which was known to have many layers of rocks.[19] In May the rover circumnavigated the crater, and made observations with Mini-TES and the panoramic camera. The rock "Lion Stone" was investigated on Sol 107[20] and found to be similar in composition to the layers found in Eagle crater.

On sol June 4, 2004 mission members announced their intention to drive Opportunity into Endurance, even if it should turn out to be impossible to get back out, targeting the various rock layers that were identified in the pictures from the crater rim. "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. Dr Squyres, principal investigator from Cornell University said: "Answering the question of what came before the evaporites is the most significant scientific issue we can address with Opportunity at this time."[21]

A first drive into the crater was executed on sol June 8, and Opportunity backed out again the same day.[22] It was found that the angle of the surface was well inside the safety margin (about 18 degrees), and the full excursion toward the rock layer of interest was started. During Sols 134 (June 12), 135, and 137 the rover drove deeper and deeper into the crater. Although some wheel slip was observed, driving was discovered to be possible even at slope angles up to 30 degrees.

Wispy clouds, similar to Earth's cirrus clouds, were spotted.

Opportunity spent roughly 180 sols inside the crater, before backing out of it again in mid December 2004, on Sol 315.[23] Scientific results of the sedimentary geology of the crater were published in the journal Earth and Planetary Science Letters[24]

Endurance Crater panorama (approximate true color)

2005

Heat Shield Rock

Main article: Heat Shield Rock

After exiting Endurance crater, in January 2005 Opportunity went to examine its own discarded heat shield. While in the vicinity of the heat shield, on Sol 345 it happened to come upon an object that was immediately suspected and soon confirmed to be a meteorite. The meteorite was promptly named Heat Shield Rock,[25] and is the first meteorite identified on another planet (although the Bench Crater and Hadley Rille meteorites were found earlier on the Moon).

After about 25 sols of observations Opportunity headed south for a crater named Argo, nearly 300 metres (980 ft) from the heat shield.[26]

Southern transit

The rover was commanded to dig another trench on the vast plains of Meridiani Planum, on Sol 366, and observations continued until Sol 373 (February 10, 2005). The rover then passed the craters "Alvin" and "Jason", and by Sol 387, approached a "crater triplet" on its way to Vostok Crater. Along the way, Opportunity set a distance record for one-day travel by either rover: 177.5 metres (582 ft), on sol February 19, 2005. On Sol (February 26, 2005), the rover approached one of the three craters, dubbed Naturaliste. A rock target named "Normandy" was chosen for investigation on Sol 392, and Opportunity remained there until Sol 395.

Opportunity reached Vostok Crater on Sol 399, finding it mostly filled with sand and lined by outcrops. It was then ordered south into what has been called "etched terrain", to search for more bedrock.

On March 20, 2005 (Sol 410) Opportunity set a new Martian record for the longest single day drive when it drove 220 metres (720 ft).[27][28][29]

By Sol 415, Opportunity stopped by some soil ripples to investigate the differences between soil in the trough of a ripple and its crest. Various soil targets included "Mobarak" in the trough, named in honor of Persian New Year, and "Norooz" and "Mayberooz" on the crest. By Sol 421, the rover left the ripple for "Viking" crater.

Stuck in sand

Between April 26, 2005 (Sol 446) and June 4, 2005 (Sol 484) Opportunity was stuck in a Martian sand dune.

The problem began on sol (April 26, 2005) when Opportunity inadvertently dug itself into a sand dune: Mission scientists reported that images indicated all four corner wheels were dug in by more than a wheel radius, just as the rover attempted to climb over a dune about 30 centimetres (12 in) tall. The sand dune was designated "Purgatory Dune" by mission planners.

The rover's condition was simulated on Earth prior to any attempt to move, out of concern that the rover might become permanently immobilized. After various simulations intended to mimic the properties and behavior of Martian sand were completed, the rover executed its first wheel movements on sol (May 13, 2005), intentionally advancing only a few centimeters, after which mission members evaluated the results.

During Sol 465 and 466 more drive commands were executed, and with each trial the rover moved another couple of centimeters. At the end of each movement, panoramic images were acquired to investigate the atmosphere and the surrounding dune field. The sand dune escape maneuver was successfully completed on sol (June 4, 2005), and all six wheels of Opportunity were on firmer ground. After studying "Purgatory" from Sol 498 to Sol 510, Opportunity proceeded southward toward "Erebus crater".

Erebus crater

Opportunity studied Erebus crater, a large, shallow, partially buried crater and a stopover on the way south toward Victoria crater, between October 2005 and March 2006.

New programming to measure the percentage of slip in the wheels was successful in preventing the rover from getting stuck again. Another "Purgatory"-like incident was averted on Sol 603, when onboard slip check software stopped a drive after slip reached 44.5%.[30] It proceeded over many ripples and 'half-pipes', taking photographs after each sol's journey.

On Sol (November 3, 2005) Opportunity woke up in the midst of a mild dust storm that lasted three days. The rover was able to drive in self-protective auto-mode during the storm, but it could not take any post-drive images. Less than three weeks later, another cleaning event cleared the dust off of the solar array so as to produce around 720 watt-hours (80% of max). On Sol (December 1, 2005), it was discovered the motor used to stow the robotic arm for travel was stalling. This problem took nearly two weeks to fix. Initially the arm was stowed only for travel, and was extended at night to prevent the arm from getting stuck. However further stalling convinced engineers to leave the arm extended at all times to avoid the arm becoming stuck in the stowed position and becoming unusable.

Payson outcrop on the western edge of Erebus crater

Opportunity observed numerous outcroppings around Erebus crater. It also collaborated with ESA's Mars Express by using the miniature thermal emission spectrometer and panoramic camera (Pancam), and took images of a transit across the Sun by Phobos. On Sol (March 22, 2006), Opportunity began the journey to its next destination, Victoria crater, which it would reach in September 2006 (Sol 951).[31] It would stay at Victoria crater until August 2008 (Sol 1630–1634).[32]

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Panorama taken on the rim of Erebus crater. The rover's solar panels are seen on the lower edge.

Shoulder troubles

The "shoulder" joint of Opportunity's arm has had troubles since Sol 2 (January 25, 2004), the rover's second day on Mars. Engineers discovered that the heater on the shoulder azimuth joint, which controls side-to-side motion of the robotic arm, was stuck in the "on" position. Closer investigation revealed that the on-off switch had probably failed during assembly, test, and launch operations on Earth. Fortunately for Opportunity, the rover was equipped with a built-in safety mechanism called a "T-stat box" (thermostatic switch) that provided protection against overheating. When the shoulder azimuth joint, also known as Joint 1, got too hot, the T-stat switch automatically opened and temporarily disabled the heater. When the joint got cold again, the T-stat closed. As a result, the heater stayed on all night but not all day.


The safety mechanism worked until Opportunity approached the first winter on Mars. As the Sun began to retreat lower in the sky and solar power levels dropped, it became clear that Opportunity would not be able to keep the batteries charged with a heater draining power all night long. On Sol (May 28, 2004), rover operators began using a procedure known as "deep sleep," during which Opportunity disconnected the batteries at night. Deep sleep prevented the stuck heater (and everything else on the rover except the clock and the battery heaters) from drawing power. When the Sun came up the next morning and sunlight began hitting the solar arrays, the batteries automatically reconnected, the robotic arm became operational, the shoulder joint warmed up, and the thermostatic switch opened, disabling the heater. As a result, the shoulder joint was extremely hot during the day and extremely cold at night. Such huge temperature swings, which tend to make electric motors wear out faster, were taking place every sol.

This strategy worked for Opportunity until Sol 654 (November 25, 2005), when the Joint-1 azimuth motor stalled because of increased electrical resistance. Rover operators responded by delivering higher-than-normal current to the motor. This approach also worked, though Joint 1 continued to stall periodically. Typically, the rover's handlers simply tried again the next sol and the joint worked. They determined that the Joint-1 motor stalls were most likely due to damage caused by the extreme temperature cycles the joint experienced during deep sleep. As a precaution, they started keeping the robotic arm out in front of the rover overnight, rather than stowing it underneath the rover deck, where it would be virtually unusable in the event of a Joint-1 motor failure. They stowed the arm only while driving and unstowed it immediately at the end of each drive.

This strategy worked for Opportunity until Sol 1502 (April 15, 2008), when the motor stalled at the beginning of an unstowing operation at the end of a drive, when the arm was still tucked underneath the rover. The motor continued to stall on all subsequent attempts, sol after sol. Engineers performed tests at various times of day to measure electrical resistance. They found that the resistance was lowest (essentially normal) when the joint was at its warmest—in the morning, following deep sleep, after the heater had been on for several hours, and just before the T-stat opened. They decided to try to unstow the arm one more time under these conditions.

At 08:30 local Mars time on Sol (May 14, 2008), they allowed Opportunity to direct as much current as possible to the warm, joint-1 azimuth motor in order to get the robotic arm into a usable position, in front of the rover. It worked.

Because Opportunity will likely never again stow the robotic arm, engineers devised a strategy for driving the rover safely with the arm deployed in front.[33]

2006

On March 22, 2006 (Sol 760), Opportunity left Erebus crater and began the journey to Victoria crater, which it reached in September 2006 (Sol 951[31]). It would stay at Victoria crater until August 2008 (Sol 1630–1634).[32]

Victoria crater

Main article: Victoria (crater)

Victoria crater is a massive impact crater approximately 7 kilometres (4.3 mi) from the original landing site. Victoria's diameter is six times larger than Endurance crater. Scientists believed that rock outcrops along the walls of Victoria would yield more information about the geologic history of Mars, if the rover survived long enough to investigate them.

On Sol (September 26, 2006) Opportunity reached the rim of Victoria Crater[34] and transmitted the first substantial views of Victoria, including the dune field at the bottom of the crater. The Mars Reconnaissance Orbiter photographed Opportunity at the rim of the crater.[35]

Victoria Crater as seen by the NASA Opportunity (MER-B) in 2006 using its Pancam instrument

2007

Software upgrade

On January 4, 2007, both rovers received new flight software for their computers. The update was received just in time for the third anniversary of their landing. The new systems let the rovers decide whether to transmit an image, and whether to extend their arms to examine rocks, which would save much time for scientists, as they would not have to sift through hundreds of images to find the one they want, or examine the surroundings to decide to extend the arms and examine the rocks.[36]

Cleaning events

A series of cleaning events beginning on Sol (April 20, 2007) allowed Opportunity's solar energy production to rise to above 800 watt-hours per Sol. By Sol (May 4, 2007) the solar array current was peaking above 4.0 amperes, values not seen since Sol (February 10, 2004).[37] However, the advent of extensive dust storms on Mars starting in mid-2007 (in-line with Mars' six Earth-year global dust storm cycle), dropped energy production levels to 280 watt-hours per day.[38]

Dust storms


Toward the end of June, 2007, a series of dust storms began clouding the Martian atmosphere with dust. The storms intensified and by July 20, both Opportunity and Spirit were facing the real possibility of system failure due to lack of power. NASA released a statement to the press that said (in part) "We're rooting for our rovers to survive these storms, but they were never designed for conditions this intense".[39] The key problem caused by the dust storm was a dramatic reduction in solar power. There was so much dust in the atmosphere that it blocked 99 percent of direct sunlight to the rover. The Spirit rover, on the other side of the planet was getting slightly more sunlight than Opportunity.

Normally the solar arrays are able to generate about 700 watt-hours of energy per day. During the storms, the power generated is greatly reduced. If the rovers get less than 150 watt-hours per day they have to start draining their batteries. If the batteries run dry, key electrical elements are likely to fail due to the intense cold. On July 18, 2007, the rover's solar-panel only generated 128 watt-hours, the lowest level ever. NASA responded by commanding Opportunity to only communicate with Earth once every three days, the first time that this had happened since the start of the mission.

The dust storms continued through July and at the end of the month, NASA announced that the rovers, even under their very-low-power mode were barely getting enough energy to survive. If the temperature of the Opportunity's electronics module continued to drop, according to the announcement, "there is a real risk that Opportunity will trip a low-power fault. When a low-power fault is tripped, the rover's systems take the batteries off-line, putting the rover to sleep and then checking each sol to see if there is sufficient available energy to wake up and perform daily fault communications. If there is not sufficient energy, Opportunity will stay asleep. Depending on the weather conditions, Opportunity could stay asleep for days, weeks or even months, all the while trying to charge its batteries with whatever available sunlight there might be."[40] It was quite possible that the rover would never wake up from a low-power fault.

By sol August 7, 2007 the storms appeared to be weakening, and although power levels were still low they were sufficient for Opportunity to begin taking and returning images.[41] By August 21 dust levels were still improving, the batteries were fully charged and Opportunity was able to make its first drive since the dust storms began.[42]

Duck Bay

Opportunity made a short drive into Duck Bay on sol September 11, 2007 and then reversed out again to test traction on the initial slope into Victoria Crater.[43] On sol September 13, 2007 it returned to begin a more thorough exploration of the inner slope, examining a series of layers of pale-coloured rock in the upper parts of Duck Bay and the face of the promontory Cape Verde in detail.

2008


Leaving Duck Bay

The rover exited Victoria crater's Duck Bay on August 24–28, 2008 (sol 1630–1634).[32] Before exiting the crater the rover experienced a current spike similar to the one that preceded the malfunction of the right front wheel of its twin Spirit. After Victoria crater and during its journey to Endeavour crater the rover investigated sets of "dark cobbles" on the Meridiani plains.[44]

Endeavour crater targeted

Endeavour is 22 km (14 mi) in diameter and is 12 kilometres (7.5 mi) south-east of Victoria.[45] Rover drivers estimated that this distance could be traversed in about two years.[45] Scientists expected to see a much deeper stack of rock layers at the crater than those examined by Opportunity in Victoria.[45] The discovery of phyllosilicate clay-bearing rock on the Endeavour crater rim promised exposure to a rock-type that is even more hospitable to life than types previously analyzed.[46]

Solar conjunction

The solar conjunction, where the Sun is between Earth and Mars, started on sol November 29, 2008 and communication with the rovers was not possible until December 13, 2008. During this time the rover team planned to have Opportunity use the Mössbauer spectrometer to examine a rock outcrop named "Santorini".[47]

2009

On sol (March 7, 2009) Opportunity first saw the rim of Endeavour after driving about 3.2 km (2.0 mi) since it left Victoria in August 2008.[48][49] Opportunity also saw Iazu crater that was about 38 kilometers (24 mi) away and is about 7 kilometers (4.3 mi) in diameter.[49]

On sol (April 7, 2009) Opportunity generated 515 watt-hours after a cleaning event of the solar arrays increased energy production by about 40%.[50] From 16 to 22 April (sol 1859 to 1865) Opportunity made a series of drives and during that week traveled a total distance of 478 meters (1,568 ft).[51] The drive actuator for the right front wheel, which had been rested while Opportunity studied a rock outcrop called "Penrhyn", had motor currents very close to normal levels.[50][51][52][53][54][55]

On sol (July 18, 2009) a large dark rock was noted in the opposite direction from which Opportunity was traveling and so the rover headed toward it, reaching it on sol (July 28).[56] The rock turned out to be a meteorite and was named Block Island. Opportunity spent until September 12, 2009 (Sol 2004) investigating the meteorite, before returning to its journey toward Endeavour Crater.[57]

Its journey was interrupted on Sol 2022 by the find of another meteorite, a 0.5 metres (1.6 ft) specimen dubbed 'Shelter Island',[58] which the rover investigated until Sol 2034. It then headed for another meteorite, 'Mackinac Island', which it reached four sols later on sol (October 17, 2009). The rover conducted a drive-by imaging sequence but otherwise did not investigate this meteorite, resuming its journey to Endeavour.[59]

On sol (November 10, 2009) the rover reached a rock target of interest, named 'Marquette Island'.[60] Prolonged study until sol January 12, 2010[61] ensued, as it was uncertain what type of rock this represented, but the eventual conclusion was that it was rock ejecta from deep within the surface of Mars rather than a meteorite.[62]

2010

On January 28, 2010 (Sol 2138) Opportunity arrived at Concepcion crater.[63] Opportunity successfully circumnavigated the 10 metres (33 ft)-meter diameter crater before continuing on towards Endeavour. Energy production varied from about 305 watt-hours to about 270 Wh during this period.[63]

On sol (May 5, 2010), due to potentially hazardous dune fields along the direct path between Victoria and Endeavour, a new route was charted that extended the distance to travel between the two craters to 19 kilometres (12 mi).[64]

On (May 19, 2010), Opportunity reached sols of operation, making it the longest Mars surface mission in history, breaking the record of 2245 sols set by Viking 1.[65]

In July 2010, it was announced that the Opportunity team would use the theme of names given to places visited by British Royal Navy Captain, Lieutenant James Cook, in his 1769–1771 Pacific Ocean voyage in command of HMS Endeavour, for informal names of sites at Endeavour Crater. These would include "Cape Tribulation" and "Cape Dromedary", "Cape Byron" (the most easterly point of the Australian mainland), and "Point Hicks" (the part of the Australian mainland first sighted by the Endeavour in 1770).[66]

On sol (September 8, 2010), the halfway point of the 19 kilometres (12 mi) journey between Victoria crater and Endeavour crater was reached.[67]

In November the rover spent a few days imaging a 20 metres (66 ft) crater called Intrepid while navigating through a field of small impact craters. On sol November 14, 2010 total odometry passed the 25 kilometres (16 mi) mark. Average solar array energy production in October and November was about 600 watt-hours.[68]

Santa Maria crater

On sol (December 15, 2010) the rover arrived at Santa Maria and spent several weeks investigating the 90 metres (300 ft) wide crater.[69] The results from Opportunity were compared to data taken from orbit by the CRISM instrument, a spectrometer, on the Mars Reconnaissance Orbiter.[69] CRISM had detected water-bearing minerals at Santa Maria crater, and the rover helped further analyze this.[69] Opportunity drove farther in that Martian year (that is about 2 Earth years), than in any previous year.[69]

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Santa Maria Crater panorama

2011

After its arrival at the edge of Santa Maria crater, the team positioned the rover at its southeastern rim and collected data.[70] They also prepared for the two-week solar conjunction of late January, when the Sun was between Earth and Mars and communication was blocked. In late March Opportunity began the 6.5 kilometres (4.0 mi) journey between Santa Maria and Endeavour, and on June 1, the rover passed the 30 kilometres (19 mi) traverse milestone (over 50 times its designed distance).[70][71] Two weeks later, on sol (July 17, 2011), Opportunity had driven 20 miles (32 km) on Mars.[72]

By sol (August 29, 2011), Opportunity had continued to function effectively 30 times longer than its planned 90-sol mission, aided by solar cell cleaning events, and performed extensive geological analysis of Martian rocks and planetary surface features with its instruments.[73]

Endeavour crater arrival

Opportunity arrived at Endeavour crater on sol (August 9, 2011), at a landmark called Spirit Point named after its rover twin, after traversing 13 miles (21 km) from Victoria crater, over a three-year period.[74] Endeavour is 14 miles (23 km) wide and offers scientists new terrain to explore, including older rocks than encountered heretofore, and clay minerals that may have formed in the presence of water. The rover's deputy principal investigator, Ray Arvidson, said it will probably not enter Endeavour crater as it appears to contain material observed previously. The rocks on the rim are older than any previously studied by Opportunity. "I think there's much more interest in driving around the perimeter of the rim," said Arvidson.[75]

Upon arriving at Endeavour, Opportunity almost immediately began discovering Martian phenomena not previously observed. On sol (August 22, 2011) the rover began examining Tisdale 2, a large ejecta block. “This is different from any rock ever seen on Mars," said Steve Squyres, principal investigator for Opportunity at Cornell University in Ithaca, New York. "It has a composition similar to some volcanic rocks, but there's much more zinc and bromine than we've typically seen. We are getting confirmation that reaching Endeavour really has given us the equivalent of a second landing site for Opportunity."[2][76]

In December the Homestake formation was analyzed, which was concluded to be formed of gypsum. Using three of the rover's instruments - the Microscopic Imager, the Alpha Particle X-Ray Spectrometer and the Panoramic Camera's filters - researchers determined the deposit to be hydrated calcium sulfate, or gypsum, a mineral that does not occur except in the presence of water. This discovery was called "slam dunk" evidence that "water flowed through underground fractures in the rock." [77]

Opportunity had driven more than 34 km (21 mi) by November 22, 2011 (sol 2783), as preparations were made for the coming Martian winter.[78] It moved to terrain that positioned it about 15 degrees to the north, an angle more favorable for solar energy production during the Martian winter.[79]

2012

In January 2012 the rover returned data from Greeley Haven, named after the geologist Ronald Greeley, while enduring its 5th Martian winter.[79] It studied the Martian wind, which has been described as "the most active process on Mars today", and conducted a radio science experiment.[79] By carefully measuring radio signals, wobbles in Martian rotation may show whether the planet has a solid or liquid interior.[79] The winter work site sits on the Cape York segment of the rim of Endeavor Crater. Opportunity reached the edge of this 14 miles (23 km) crater in August after three years of driving from smaller Victoria Crater, which it studied for two years.[80]

On Sol 2852 (February 1, 2012) the energy production from the solar array was 270 watt-hours, with a Mars atmospheric opacity (Tau) of 0.679, a solar array dust factor of 0.469, with total odometry at 21.35 miles (34.36 km).[81] By March (around Sol 2890), 'Amboy' rock was studied with the MIMOS II Mössbauer spectrometer and the Microscopic Imager, and the amount of Argon gas in the Martian air was measured.[82] The Mars winter solstice passed on March 30, 2012 (Sol 2909) and on April 1 there was a small cleaning event.[83] On Sol 2913 (April 3, 2012) solar array energy production was 321 watt-hours.[83]

The mission of Mars rover Opportunity continued, and by May 1, 2012 (Sol 2940), energy production had increased to 365 watt-hours, with the solar array dust factor at 0.534.[84] The team prepared the rover for movement and finished up collecting data on Amboy rock.[84] 60 Doppler radio passes were completed over the winter.[85]

Roving again

On May 8, 2012 (Sol 2947), the rover moved 12 feet (3.7 m).[86] On that day the Solar energy production was 357 watt-hours with a solar array dust factor of 0.536.[86] Opportunity had been stationary on Greeley Haven for 130 Sols (Mars' days), with a 15 degrees tilt to the North to help survive the winter; after the drive the northerly tilt decreased to 8 degrees.[86] The drive marked the end of the geodynamics science experiment, which used radio Doppler measurements while the rover was stationary.[86] By June 2012, it studied Mars dust and a nearby rock vein christened "Monte Cristo" as it headed North.[85]

3000 Sols

On July 2, 2012 Opportunity's 3000 Sols on Mars were celebrated.[87] By July 5, 2012, NASA published a new panorama (seen below) showing the surroundings of Opportunity at the Greeley Haven position.[88] Also, the other end of the Endeavour crater is seen in the right half of the scene, a crater that spans 22 kilometres (14 mi) in diameter. On July 12, 2012 (Sol 3010), solar arrays produced 523 watt-hours and 21.49 miles (34,580 m) was the total distance traveled from landing.[89] That month, Mars Reconnaissance Orbiter spotted a dust storm and water ice clouds near the rover.[89]


Greeley Haven panorama – a view of Cape York and the Endeavour crater – was taken while overwintering at the Greeley Haven position at Cape York in the first half of 2012. This false-color panoramic view was combined from 817 individual images taken in the near infrared, green and violet spectral bands.

Before Curiosity rover landed on August 6, 2012, Opportunity sent special Ultra High Frequency radio signals to simulate Curiosity for a radio observatory in Australia.[87] August activities for Opportunity included collecting data on atmospheric opacity,[87] visiting Sao Rafael and Berrio craters,[90] and achieving 35 kilometres (22 mi) of driving on Sol 3056 (August 28, 2012).[91] Also, on August 19, 2012 Mars Express orbiter automatically exchanged data with both Curiosity and Opportunity in one orbit, its first double contact.[92]


In the fall Opportunity headed south, exploring Matijevic hill and searching for phyllosilicate minerals.[91] Some data was sent to Earth directly using X-Band radio signals, as opposed to orbiter relays.[91] Finally, the number of power cycles on the rover's Inertial Measurement Unit were reduced.[91] Science work included testing various hypotheses about the newly discovered spherules.[93]

A small dust cleaning event occurred on Sol 3175 (Dec. 29, 2012), improving the energy production by about 40 watt-hours per sol. As of Sol 3180 (Jan. 3, 2013), the solar array energy production was 542 watt-hours with an atmospheric opacity (Tau) of 0.961 and an improved solar array dust factor of 0.633.
—NASA[94]

2013

Opportunity began the year at the edge of Endeavour Crater's Cape York,[94] and the total distance travelled since landing on Mars was 35 km (22 mi).[94][95] After completing work at Matijevic Hill the Opportunity rover headed south to the rim of Endeavour Crater. Next, the rover headed south across a gap in the rim to a place the researchers called Botany Bay, then up onto the next rim segment to the south. There are two hills to the south of it, one called Solander Point and farther south is Cape Tribulation.[96] The current aim is for Opportunity to reach Solander Point before winter reaches the Martian southern hemisphere as the area has ground tilted to the north allowing the rover to stay active during the winter months. In addition Solander Point has a large geological stack for Opportunity to explore.[97]

In April 2013, the rover passed through a three-week long solar conjunction, when communication with Earth was blocked because of the Sun.[98] The rover arm was positioned on a rock during that time so the APXS could collect data.[98]

On May 16, 2013, NASA announced that Opportunity had driven further than any other NASA vehicle on a world other than Earth.[99] After Opportunity's total odometry went over 35.744 kilometres (22.210 mi) it surpassed the total distance driven by the Apollo 17 Lunar Roving Vehicle.[99] The record for longest distance driven by a vehicle on another world is currently held by the Lunokhod 2 lunar rover that drove 37 kilometres (23 mi).[99] Based on wheel rotations Lunokhod 2 was thought to have covered 37 kilometres (23 mi), but Russian scientists have revised that to an estimated distance of about 42 kilometres (26 mi) based on orbital images of the lunar surface.[100][101]

On May 17, 2013, NASA announced that a preliminary analysis of one of the rock targets, named "Esperance", suggested that water in the past may have had a neutral pH.[102] This was later confirmed in further studies, supporting the notion that ancient Mars was a "water-rich world with conditions amenable for life".[103]

As of June 20, 2013 (Sol 3344), Opportunity's total odometry was reported at 22.89 miles (36.84 km), while en route to 'Solander Point.'[105] June 21, 2013 marked five Martian years on the 'red planet'.[106] The project manager, noting the harsh conditions of the planet, has said each day is "a gift".[107]

Solander

By early July 2013 Opportunity was approaching Solander Point, with daily drives ranging from dozens of meters (yards) to over a hundred.[109] It arrived at its base in early August 2013, after investigating a curious terrain patch along the way.[110] Solander can provide a northward facing slope to aid in sunlight collection, as the Martian winter is approaching (as the season changes, the angle of the Sun is shifting).[110] On Sol 3390 (Aug. 6, 2013) energy intake was 385 watt-hours, down from 395 on Sol 3384 (July 31, 2013), and 431 on Sol 3376 (July 23, 2013).[110] In May 2013 it had been as high as 546 watt-hours.[110] Other factors that impact collection include the atmospheric opacity (i.e. "Tau") and "solar array dust factor" that collects on the panels.[110] Although the rover cannot clean the dust off, such systems were considered for the rover during its development.[111]

In September, numerous surface targets and rocks around Solander were examined by the rover.[110] Solar array energy production dropped to 346 watt-hours by Sol 3430 (Sept. 16, 2013),[110] and 325 watt-hours by Sol 3452 (Oct. 9, 2013).[112] Before Spirit rover stopped responding back in 2010, it reported 134 watt-hours as temperatures plunged below minus 41.5 degrees Celsius (minus 42.7 degrees Fahrenheit).[113]

Scientific findings

Main article: Scientific information from the Mars Exploration Rover mission

Opportunity has provided substantial evidence in support of the mission's primary scientific goals: to search for and characterize a wide range of rocks and soils that hold clues to past water activity on Mars. In addition to investigating the water, Opportunity has also obtained astronomical observations and atmospheric data.

Honors

Honoring Opportunity's great contribution to the exploration of Mars, the asteroid 39382 has been named Opportunity.[114] The name was proposed by Ingrid van Houten-Groeneveld who, along with Cornelis Johannes van Houten and Tom Gehrels, discovered the asteroid on September 24, 1960. Opportunity's lander is Challenger Memorial Station.[11]

Pictures

Cirrus clouds in the Martian sky

See also

References

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External links

NASA links

MSSS and WUSTL links

Other links

Image map of Mars

The following imagemap of the planet Mars has embedded links to geographical features in addition to the noted Rover and Lander locations. Click on the features and you will be taken to the corresponding article pages. North is at the top; Elevations: red (higher), yellow (zero), blue (lower).

Spirit (2004) > Spirit

Opportunity (2004) > Opportunity

Pathfinder < Pathfinder/Sojourner (1997)

Viking 1 (1976) > Viking 1

Viking 2 (1976) > Viking 2

Phoenix < Phoenix (2008)

Mars 3 < Mars 3 (1971)

Curiosity (2012) > Curiosity