Opportunity’s eight years on Mars: A story of science and endurance

by Chris Gebhardt

Eight years ago today (January 25, 2004), the Mars Exploration Rover -B (MER -B) slammed into the Martian atmosphere and executed a successful Entry, Descent, and Landing on the Red Planet – beginning what was supposed to be 90 days of science operations on the surface of Mars. Eight years and 2,922 Earth-days later, Opportunity continues its mission of exploration of the Martian surface, unlocking the mysteries of Mars and serving as a symbol of endurance while paving the way for future human missions to the Red Planet.

Gearing up for an ambitious mission on Mars:
Like its twin rover, Spirit, Opportunity’s mission was based on 90-solar day mission on surface of Mars. A solar day is based on planetary Mars timekeeping based on Mars’ orbital rotation rate.
A solar day on Mars is clocked at 24 hours 39 minutes 35.24409 seconds. Compared to Earth’s 24 hour 00 minute 00.002 second solar day length, the difference in the Earth-Mars solar day results in the Martian solar day lasting 2.7% longer than Earth’s with a conversation factor of 1.027491 days to sols.
Thus, since landing on Mars, Opportunity has operated for 2,844 sols, equivalent to 2,922 standard Earth days (Earth sols).

In turn, this long-duration mission puts Opportunity 2,754 sols over its predicted and planned 90 sol-day mission – meaning that Opportunity has functioned 30.6 times longer than anticipated as the rover and its mission control team celebrates its 8th Earth-year anniversary on Mars.

Over these 8 Earth-years on Mars, Opportunity has searched for scientific knowledge based on its original mission objectives, including the search for and characteristic of rocks and soils.

Other objectives of Opportunity’s ongoing mission include the determination of the distribution and composition of minerals, rocks, and soils surrounding the landing site (and beyond, at this point); determination of what geologic processes have shaped the local terrain and influenced the chemistry, including water or wind erosion, sedimentation, hydrothermal mechanisms, volcanism, and cratering; and the performance calibration and validation of surface observations of Mars made by the Mars Reconnaissance Orbiter to help determine the accuracy and effectiveness of various instruments that survey the Martian geology from orbit.

Moreover, Opportunity’s objectives have and continue to revolve around the search for iron-containing minerals, including the identification and quantification of the relative amounts of specific mineral types that contain water or were formed in water; the characterization of the mineralogy and textures of rocks and soils to determine the processes that created them; the search for geological clues to the environmental conditions that existed when liquid water was present; and the assessment of whether the past Martian environment was conducive for life.

To accomplish the tasks given to it, Opportunity was truly built to last. At a height of 4.9 ft, a width of 7.5 ft, and a length of 5.2 ft, the six-wheeled utility craft was constructed to power itself via solar panels installed on its “back.”

These solar panels, at peak operating condition (clear of Martian dust and dirt), were designed to produce 140 watts of power for four hours per day. The energy produced from the solar panels is then transferred to the Opportunity’s lithium ion batteries for storage and distribution – thus allowing the rover to conserve power when not needed and use energy during non-sunlit portions of the day.

Weighing in a 400 lbs, the craft was built with mobility in mind, needing to not only drive itself to specific locations determined by its control team, but also to navigate around obstacles while driving toward specific targets of interest.

Thus, each wheel on Opportunity was given its own motor as well as steering at the front and rear drive sections.

With a maximum speed of 2 in/s (with an average speed about one-fifth of this), Opportunity was also built with the ability to navigate grades on the Martian surface of up to 30 degrees.

Opportunity was also affixed with nine scientific experiments, including a panoramic camera to examine the texture, color, mineralogy, and structure of the local Martian terrain; a navigation camera for driving purposes; the Miniature Thermal Emission Spectrometer to identify “promising rocks and soil” for examination; and two Hazcams with 120 degree views for “additional data about its surroundings.”

Opportunity’s robotic arm was fixed with the Mossbauer spectrometer for close-up investigations of the mineralogy of iron-bearing rocks and soils; the Alpha particle X-ray spectrometer for close-up analysis of the abundances of elements that make up rocks and soils; magnets for collects magnetic dust particles; a Microscopic Imager for close-up, high-resolution images of rocks and soils; and the Rock Abrasion Tool (RAT) to expose fresh rock material for examination by instruments on-board the rover.

Getting to Mars:

Like the Space Shuttle orbiter Endeavour and the Mars rover Sojourner before it, the Mars Rover ‘Opportunity’ was named through a student essay competition. The winning entry was written by a Russian-American student who spoke of the spirit and opportunity to achieve her dreams in the United States after living a portion of her life in an orphanage.

With its construction and ground test/validation complete, Opportunity was transported to Florida where the rover underwent final testing and preparations for its trip to Mars.

With final preparations complete, Opportunity was folded up inside its aeroshell. Following the launch of Opportunity’s twin rover Spirit on 10 June 2003, Opportunity was transported to Launch Complex 17B at the Cape Canaveral Air Force Station, where the assembly was hoisted up and placed atop a Delta II Heavy rocket in mid-June for a June 28th launch.

Bad weather, an insulation problem, and a battery issue on the Delta II rocket forced a nine day delay to Opportunity’s launch.

On 7 July 2003, Opportunity’s launch team targeted the first of two instantaneous launch windows for the day. With just seconds to go in the countdown, an automatic cutoff was ordered by the launch computers when a fill-and-drain value on the Delta II indicated a sluggish response.

The launch team backed out of the terminal count and reconfigured for the second of only two instantaneous launch windows of the evening.

With the fill-and-drain valve issue fixed, the “go” was given to proceed with the count, and the Delta II Heavy rocket lifted off at 23:18:15 EDT with the Opportunity rover.

The launch was the first flight of the Delta II Heavy rocket configuration and occurred six days before the close of the Earth-Mars planetary alignment launch window.

After a 6.5 month cruise to Mars, Opportunity hit the Martian atmosphere just before midnight Eastern Standard Time on 24 January 2004.

Confirmation of a successful landing on Mars was received at 00:05 EST (05:05 UTC) 25 January 2004.

A Hole-in-One landing and the first 90 sols on Mars:

After descending through the Martian atmosphere, Opportunity’s encasement was engulfed in airbags to cushion the rover for the drop down and bounce/roll onto the Martian surface.

Landing on the Meridiani Plamun 25km downrange of its targeted landed sight, Opportunity’s airbag enclosed capsule rolled into an impact crater on the Martian surface before coming to a complete stop.

Upon opening of Opportunity’s encasement, the rover’s control team was amazed to find the rover sitting in the bottom of an impact crater and quickly described the landing as an inter-planetary “hole in one” – even though the rover was not targeting that specific area for landing.

After landing, Opportunity’s landing team christened the crater “Eagle crater,” and, in following with twin rover Spirit’s landing site, officially named Opportunity’s landing site “Challenger Memorial Station” in honor of the Space Shuttle Challenger and her crew who were lost in the Challenger/STS-51L launch accident – the 18th anniversary of which was just 3 days after Opportunity’s landing.

Upon examination of the landing crater, Opportunity showed that the crater was the darkest landing site ever visited by a spacecraft on Mars.

However, the landing presented a challenge for Opportunity’s control team as the rover would now have to climb a relatively steep embankment to get out of the crater.

From a stationary position on its landing bed, Opportunity observed a rock outcropping along the rim of the crater and a compilation of course gray grains in the otherwise reddish sand within the crater.

During this stationary checkout time, Opportunity’s control team discovered a problem with the rover’s robotic arm in the Joint 1 heater – specifically, that the heather on the joint that controls the side-to-side motion of the arm was stuck “on.”

An investigation revealed that the heater most likely failed during final assembly, test, and launch operations.

Since the rover was built with a safety device for this possibility, the T-stat box on the rover terminated the heater at a specific temperature and reactivated the heater once the joint’s temperature fell below a certain degree point.

This meant that Opportunity’s Joint 1 heater turned all for the duration of the Martian night and turned off for significant portions of the Martian day – a not ideal but “livable” issue.

By Sol 15, Opportunity was mobile and examining the rock outcroppings at Eagle crater. Observations made by Opportunity at the time led to the hypothesis that the rocks were formed from “fine grain or dust” instead of compacted sand as Earth sandstone is.

This hypothesis in turn led to the belief that the rocks were formed from volcanic flow, wind, or water. With water as a potential forming agent for the Eagle crater rock outcroppings, Opportunity’s goal of determining the potential that water had once existed on the surface of Mars for a long enough period to effect local geology was underway.

While Opportunity’s exploration at Eagle crater continued, the rover used its robotic arm RAT for the first time on Sol 30. Examination of the cut rock, located at the El Capitan outcropping, indicated signs of erosion (small, elongated voids in the rock visible both on the surface of the rock and in its interior after Opportunity’s drilling) that suggested the presence of liquid water at one point in Mars’ past.

Specifically, scientists revealed that the voids were similar and “consistent” with vugs on Earth rocks.

Furthermore, Opportunity found evidence of water from the MIMOS II spectrometer. This instrument found evidence of the mineral jarosite, a mineral that contains hydroxide ions.

Opportunity’s crew also took this time to dig the first-ever trench by the Mars Rover pair by using the Opportunity’s front wheels. The process, which took less than an half-hour, created a trench 20 inches long by 4 inches deep.

The resultant dig revealed a “clotty texture” to the soil in the upper part of the trench and bright soil in the trench’s bottom.

The dig also revealed rounded, shiny pebbles and fine-grained soil particles too small for the rover’s microscope to discern.

Beyond the 90-sol-day warranty – Opportunity at Endurance Crater:

After leaving its landing site behind, Opportunity reached Endurance crater on Sol 95 – five days beyond its expected life time on Mars.

After completing a circumnavigation of the crater, Opportunity was directed toward the rock Lion Stone, which it arrived at 12 days after making it to Endurance crater.

Opportunity’s investigations of this rock found that it had a similar composition as those found at Eagle Crater.

By 4 June 2004, Opportunity’s team made the decision to send the rover itself into Endurance crater to examine an interesting area of rocks. This decision was made with the knowledge that the rover may not have been able to climb back out of the crater.

Opportunity began its descent into Endurance crater on 8 June 2004 before immediately backing out of the crater to test its descent angle. The information provided by this drive in/drive out maneuver confirmed that the angle of the crater’s surface was well within Opportunity’s operating limits.

After driving into Endurance crater on 12 June 2004, Opportunity spent 180 sols inside the crater examining the various rock formations – and even observing Earth-like wispy clouds in Mars’ atmosphere.

During this time, Opportunity returned valuable scientific data on the soil composition and sedimentary geology of Endurance crater.

A Stellar Find for Opportunity and a drive south:

After completing operations at Endurance crater, Opportunity’s team commanded the rover to begin driving toward its own discarded heat shield that protected it during Martian atmospheric entry almost one year prior.

While conducting this examination of its heat shield, Opportunity stumbled upon a rock that would prove to be one the rover’s most significant finds: a meteorite on the surface of Mars.

Discovered on Sol 345, the meteorite was the first one ever discovered on a planet other than Earth (though two meteorites had already been discovered on the Moon), and was first identified an “unusual” because it had an infrared spectrum similar in appearance to a reflection of the sky of Mars.

Measurements and examinations by Opportunity showed the meteorite was composed of 93 percent iron and 7 percent nickel.

Because of a lack of knowledge of Mars’ environment, whether the meteorite fell to Mars relative recently or several millions if not billions of years ago is unknown.

Opportunity has since found, to date, five similar meteorites.

After this discovery, Opportunity’s team directed the rover to dig another trench before setting off for Vostok crater.

After reaching Vostok crater and spending a few days in the vicinity, Opportunity was commanded southward to the “etched terrain.”

During this time, Opportunity set a single-day distance driving record by travelling 772 ft.

Stopping for six days to investigate soil surface ripples on the Meridiani Planum, Opportunity became the unwitting victim in a sand trap approximately 20 Martian days after leaving the rippled sands.

Opportunity became stuck in the sand on 26 April 2005 after attempting to climb over a dune that measured only 12 inches (30 centimeters) in height.

The dune was quickly dubbed “purgatory dune” because of the predicament it now posed.

Spending an agonizing 38 Sols stuck in the sand, Opportunity was eventually able to free itself after ground controllers simulated the condition here on the Earth.

Through a precise series of commands and maneuvers, Opportunity painstakingly moved only centimeters at a time so mission controllers could monitor progress and assess a best next move scenario after each labored movement forward.

After being freed, Opportunity spent 12 Sols studying purgatory dune before continue southward toward its target of Erebus crater.

The road to Victoria crater:

While Erebus crater was, in-hindsight (considering Opportunity’s longevity), always a stop-over on the way to Victoria crater, the year-long period between Opportunity’s arrival at Erebus (October 2005) and arrival at Victoria (September 2006) crater was a year filled with notable milestones for the mission, including the first dust storm endured by the rover, a cleaning event on its solar panels, and further problems with the rover’s robotic scientific arm.

During this time, a new program was uploaded to Opportunity that would prevent the rover from becoming stuck in another sand dune.

This program proved invaluable on Sol 603 when the program triggered an “all stop” command to Opportunity when the rover’s wheel-slip percentage reached 44.5 percent – thus preventing Opportunity from getting stuck in another sand dune.

By Sol 628, though, the rover was engulfed in a dust storm that lasted three days. The storm deposited numerous quantities of dust onto the rover’s solar panels and reduced total power generation on the rover.

However, as luck would have it, a sudden cleaning event took place less than three weeks after the dust storm, restoring Opportunity’s power generating capabilities to 80 percent of maximum.

The cleaning events occur when Martian winds blew the dust off the solar panels.

But by this point, Opportunity’s control team was battling a further issue with the rover’s Joint 1 heater.

As Opportunity approached its first Martian winter back in May 2004, the control team commanded the rover into deep sleep at night, a procedure which disconnected Opportunity’s systems from the main battery – thus preventing the Joint 1 heater from remaining “on” throughout the day and night as temperatures dropped in the Martian winter.

However, this procedure exposed the mechanical joint to extreme temperature swings during the day and night and eventually led to the stall of the Joint 1 motor on 25 November 2005.

At this point, Opportunity’s control team commanded the rover to send a higher-than-normal electrical current the arm to unstow it. This approach worked, though the joint would occasionally stall.

By late March 2006, after 760 sols on Mars, Opportunity departed Erebus crater for Victoria crater, arriving 191 sols later.

Time at Victoria crater – A struggle for survival:

Upon arriving at Victoria carter on 16 September 2006, Opportunity photographed the crater and returned the first substantial views of Victoria’s 7 kilometer wide impact crater.

During initial observations at Victoria, Opportunity revealed a dune field at the bottom of the crater as well as a slope leading into the crater itself.

While Opportunity investigated the rim of Victoria crater, mission controllers sent a software upgrade package to the rover that allowed it to make internal decisions on whether or not to transmit images back to Earth and whether or not to extend its robotic arm for scientific investigation.

By mid-May 2007, while crater rim observations and investigations continued, a series of significant cleaning events allowed for unprecedented power increases to the rover to levels not seen since Sol 18 of the mission.

This dramatic increase in power generating capability came at the best time possible as residual daily power was stored in Opportunity’s batteries just a month before devastating dust storms nearly claimed the rover.

Beginning in June 2007, Mars’ six Earth-year dust storm cycle began, clouding the Martian atmosphere in dust and blocking 99 percent of sunlight from reaching Opportunity’s solar panels – while at the same covering the rover’s solar panels and significantly reducing the rover’s ability to gather the small amount of sunlight actually reaching it.

As power level dropped to dangerously low levels, NASA released a statement saying, “We’re rooting for our rovers to survive these storms, but they were never designed for conditions this intense.”

Normal solar panel generation of 700 watt-hours energy per day dropped to only 128 watt-hours on 18 July 2007 on Opportunity. As a result, Opportunity began draining its batteries to preserve system power and heating requirements.

The rover’s control team, in response, commanded the rover to only communicate with Earth every three days to converse power for its heaters.

By late-July 2007, Opportunity was barely getting enough solar energy each day to survive, and the temperature in the rover’s electronics module was dropping. At this point, NASA stated that if temperatures continued to drop, Opportunity’s low-power fault program could trip, disabling the rover’s batteries and putting Opportunity into sleep mode.

“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.”

At this point, NASA also stated that there was a real chance that Opportunity, if placed into sleep mode, would never wake up.

But despite these abysmal odds, Opportunity never tripped its low-power fault, and by 7 August 2007, with the dust storms beginning to subside, power levels were sufficient for Opportunity to start taking pictures of the Martian dust storm again.

By 21 August, Opportunity’s batteries were fully charged, and the rover began driving again for the first time since the dust storm began – an amazing endurance story for the rover that had, by this point, survived the “un-survivable” scenario on Mars’ surface during full-fledged operations three years beyond its expected 90 sol day death date from low power levels because of predicted dust accumulation on its solar panels.

Recovering from the dust storm, Opportunity began its descent into Victoria crater on 11 September 2007 to test the terrain’s stability and slope gradient.

With final checks complete, Opportunity descended the Duck Bay ramp into Victoria crater on 13 September 2007 where it explored, for the next Earth-year, the rock composition of Duck Bay and the face of Cape Verde in great scientific detail.

By 15 April 2008, while still inside Victoria crater, Opportunity’s robotic arm once again failed to respond to commands, and the Joint 1 motor stalled at the beginning of unstowing operations.

The motor stalled on all follow-up unstow attempts – something the differed from previous unstow stalls where the motor worked on subsequent attempts.

A month of testing followed, during which controllers monitored resistance on the joint at various times in the day.

After rover wake up on Sol 1531 (14 May 2008), Opportunity was commanded to unstow its robotic arm. The command worked, and the arm extended from underneath the rover.

At this point, the decision was made to never stow the arm again, and a safe, arm-extended drive configuration was determined and implemented.

Thus, since May 2008, nearly 4 years ago and for half its time on Mars, Opportunity has driven across the surface of Mars with its robot arm fully extended out in front of it.

A new mission target – Endeavour crater:

With the rover in good health, Opportunity’s control team elected to send the rover on a 14 mile (22 kilometer) trek to Endeavour crater.

Emerging from Victoria crater between 24-28 August 2008 (Sols 1630-1634), Opportunity began the impressive trek for Endeavour crater, stopping along the way to investigate various “dark cobbles” on the Meridiani Planum.

Endeavour crater was chosen in large part due to expectations that deeper stacks of rocks would be seen at Endeavour crater than at Victoria crater. Furthermore, the team opted to send Opportunity to Endeavour crater following the discovery of phyllosilicate, clay-bearing rock at Endeavour crater – rock that is hospitable to life.

During the predicted two year drive to Endeavour crater, Opportunity was temporarily out of contact with Earth during the Solar conjunction of November/December 2008 at which time Earth and Mars were on opposite sides of the sun from one another.

By March 2009, Opportunity’s cameras could see the rim of Endeavour crater, as well as Iazu crater – which was 38 kilometers (24 miles) away from the rover at the time.

By 18 July 2009 (Sol 1850), Opportunity was directed to reverse course away from Endeavour crater and toward a large, black rock.

The rover reached the rock ten Earth-days later, at which point it was discovered that the rock was yet another meteorite.

After examination of the rock, Opportunity was again commanded to drive toward Endeavour crater, but was stopped again on Sol 2022 when it found yet another meteorite. After examining this meteorite for 12 Sols, Opportunity found yet another meteorite on Sol 2038.

This time, the rover did a “drive by” investigation, taking photographs of the meteorite while continuing on toward Endeavour crater.

Opportunity again stopped on Sol 2061 (10 November 2009) to investigate a rock target that’s identity was not initially clear.

It was eventually determined that the rock was rock ejecta material from deep within Mars.

Investigation of the rock ejecta concluded on Sol 2122 (12 January 2010), and the rover arrived at Concepcion crater on 28 January 2010.

After circumnavigating the crater, Opportunity once again set out for Endeavour crater.

By 5 May 2010, a new route to Endeavour crater was plotted to avoid potentially hazardous sand dunes.

Then, on Sol 2246 (19 May 2010), the Opportunity rover, despite arriving on Mars after its twin rover Spirit, became the longest-surviving surface mission on Mars, surpassing the previous 2245 Sol duration set by the Viking 1 mission from the late 1970s to early 1980s.

On Sol 2420 (14 November 2010), Opportunity’s odometer passed the 25 kilometer mark – shattering all estimates for how far the rover would actually drive on the surface of Mars.

In mid-December 2010, Opportunity began several weeks of observations at Santa Maria crater – observations that were compared to orbital data from the Mars Reconnaissance Orbiter (MRO).

At the conclusion of the 2010 Earth-year, Opportunity had driven more miles since leaving Victoria crater in August 2008 (the equivalent of 1 Martian year) than it had in any previous year – all while being 4-6 years beyond its originally estimated life span.

Opportunity spent the two-week solar conjunction of early 2011 at Santa Maria crater before beginning the final 6.5 kilometer journey to Endeavour crater in late March 2011.

By 1 June 2011, Opportunity passed the 30km life-time traverse mark – a distance 50 times greater than its operational designed traverse distance.

By 17 June 2011, Opportunity had driven 20 miles on the surface of Mars.

After 3 years of travels, Opportunity safely and successfully arrived at Endeavour crater on 9 August 2011 after traveling 13 miles from Victoria crater – a distance more than half of its total traversed distance on Mars.

The rover’s arrival point at Endeavour crater was quickly named “Spirit Point” by Opportunity’s control team in honor of Opportunity’s twin, Spirit, which did not survive the 2010 Martian winter.

Upon arriving at the crater, Opportunity quickly confirmed that the rocks on the rim of crater were older than any other rock previously studied by the rover, and quickly discovered Martian phenomenon not previously seen.

And then, in early December 2011, Opportunity made what is, at this time, its most important discovery while analyzing the “Homestake” formation.

Instruments on the rover were able to confirm that the “Homestake” formation is composed of gypsum – a mineral that does not occur except in the presence of water.

The rock was quickly nick-named “slam dunk” as it finally provided hard evidence that liquid water once flowed on Mars – thus providing substantial support for one of Opportunity’s primary mission scientific objectives.

An enduring legacy:

Throughout its eight year tenure on Mars, the rover Opportunity has greatly and in many ways drastically increased our knowledge of Mars as well as how our technology survives on the Martian surface.

Based on its tremendous scientific finds, life-span, and endurance beyond all odds, several honors have been conferred upon the Opportunity rover. Asteroid 39382 was officially named Opportunity in honor of the rover.

Furthermore, Opportunity is one of only 13 robots to be inducted into the robot hall of fame alongside the da Vinci Surgical System, fellow Mars rover Sojourner, Unimate (the first industrial robot which worked on the General Motors assembly line in 1961), and twin rover Spirit.

Moreover, while Opportunity’s landing site paid tribute to the Space Shuttle Challenger and her crew, Opportunity itself stands as a tribute and memorial to the men and women lost in the September 11th terrorist attacks on the World Trade Center, as metal from the twin towers was repurposed and used as cable protection shields on the twin rovers Opportunity and Spirit.

But perhaps the best way to continue to remember Opportunity, even though its time on Mars is not yet over, is the tremendous distance and longevity of the rover.

Travelling 21.33 miles, Opportunity has exceeded by more the 50 times the driving distance it was built for, it survived a severe Martian dust storm despite legitimate fears that it would not, it has conducted long-term investigations of four craters and entered, under its own power, two craters (not including the hole-in-one landing in Eagle Crater), and it has survived 30.6 times longer than originally planned.

(All Images via NASA, NASA JPL, NASA APOD).

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