Mars Exploration Rover

• 1. Introduction

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  Mars Exploration Rover was a NASA mission that sent two robots, Spirit and Opportunity, to the surface of Mars in January 2004, with a plan for each to last exactly 90 Martian solar days. Spirit survived more than six years. Opportunity lasted nearly fifteen. When engineers finally declared the mission over in February 2019, they had been operating rovers on another planet for over a decade and a half.

  The numbers are hard to absorb. Each rover was designed to drive a total of 600 meters. Opportunity eventually covered more than 45 km. At one point it passed the total distance driven by the Apollo 17 Lunar Roving Vehicle on the Moon. It then broke the record held by the Soviet Lunokhod 2. On the 23rd of March 2015, it crossed the 42.2 km mark, the full distance of a marathon, with a finish time of roughly 11 years and 2 months.

  But raw distance only hints at what the mission accomplished. The original scientific objective was to search for rocks and soils that carry signs of past water activity on Mars. What the rovers found, in crater walls and plains and layered outcrops, rewrote how scientists understand a planet once thought to be bone dry. How two machines, launched in the summer of 2003, managed to survive dust storms, mechanical failures, and Martian winters to return that story is the subject of this documentary.

• 2. The Names on the Rovers

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  Sofi Collis was nine years old and in third grade in Arizona when she won the essay competition that named the two rovers. She had been born in Russia and spent part of her childhood in an orphanage. Her winning entry read, in part: "I used to live in an orphanage. It was dark and cold and lonely. At night, I looked up at the sparkly sky and felt better. I dreamed I could fly there. In America, I can make all my dreams come true. Thank you for the 'Spirit' and the 'Opportunity.'" The names stuck in a way that the mission designations MER-A and MER-B never could.

  Before the competition, the rovers were identified internally as MER-1 Rover 1 and MER-2 Rover 2. Engineers at the Jet Propulsion Laboratory, which designed, built, and operated the whole mission, used MER-A for Spirit and MER-B for Opportunity based on the order each touched down on Mars. Two asteroids were eventually named in the rovers' honor, 37452 Spirit and 39382 Opportunity, a recognition of the scientific record both had accumulated.

• 3. Getting There

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  Spirit lifted off on the 10th of June 2003 aboard a Boeing Delta II 7925-9.5 rocket from Cape Canaveral Space Launch Complex 17A. Opportunity followed on the 7th of July 2003 from the adjacent pad, SLC-17B, on the heavier version of the same rocket, because it needed more energy for the Trans-Mars injection. The two pads sit right next to each other, which allowed mission planners to work the 15-day and 21-day planetary launch windows close together. The last possible launch day for Spirit was the 19th of June 2003; the first available day for Opportunity was the 25th of June 2003.

  The cruise stage that carried each rover across roughly 500 million kilometers was spin-stabilized at two revolutions per minute. Solar arrays on the outer ring could generate up to 600 watts near Earth and around 300 watts at Mars. Two aluminium-lined tanks held about 31 kg of hydrazine propellant for course corrections, and navigators planned up to six trajectory correction maneuvers along the way. A star scanner and a Sun sensor gave the spacecraft its orientation, with no backup system for the star scanner.

  Entry into the Martian atmosphere was the most violent phase of the journey. The aeroshell, built by Lockheed Martin Space in Denver, Colorado, used an ablator made of cork wood, binder, and silica glass spheres, a formula first developed for the Viking Mars lander missions and closely related to the materials used in the Mercury, Gemini, and Apollo crewed flights. The spacecraft slowed from 19,000 to 1,600 km/h in about a minute, generating roughly 60 meters per second squared of acceleration. A parachute 40% larger than the one flown on Mars Pathfinder, designed and built by Pioneer Aerospace in South Windsor, Connecticut, helped brake the descent. Three RAD rockets, each producing about a ton of force for nearly 4 seconds, brought the lander to a dead stop 10-15 meters above the surface. Then airbags made of Vectran, a material with roughly twice the strength of Kevlar, inflated and let the lander bounce across the Martian surface at approximately 100 km/h before coming to rest.

• 4. The Machines Themselves

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  Each rover stands 1.5 meters high, 2.3 meters wide, and 1.6 meters long, and weighs 180 kg, with 35 kg of that in the wheel and suspension system alone. Six aluminium wheels mount on a rocker-bogie suspension, the same basic design used on the smaller Sojourner rover, which keeps all wheels on the ground over rough terrain and allows the vehicle to cross obstacles larger than a wheel diameter of 250 mm. The wheels have cleats for grip in soft sand and rock faces. Each wheel has its own drive motor, and the front and rear wheels each carry individual steering motors, so the rover can turn on the spot through a full revolution. Maxon Motor, a Swiss company, made the drive motors.

  Power came from triple-junction solar arrays that generate about 140 watts when fully illuminated, enough to run the rover for up to four hours per Martian day. The rover needs around 100 watts just to drive. Two lithium-ion batteries weighing 7.15 kg each stored energy for the night. Engineers expected dust to cut solar output to roughly 50 watts by the end of the 90-sol mission. What actually happened was that wind-driven cleaning events removed dust from the panels far more often than anticipated, and power output remained between 300 and 900 watt-hours per day across much of the extended mission.

  At the heart of each rover is a radiation-hardened RAD6000 processor running at 20 MHz, paired with 128 MB of DRAM and 256 MB of flash memory. The operating system is VxWorks. Onboard instruments include nine cameras, a Miniature Thermal Emission Spectrometer built by Arizona State University, a Mössbauer spectrometer developed by Göstar Klingelhöfer at Johannes Gutenberg University in Mainz, an alpha particle X-ray spectrometer from the Max Planck Institute for Chemistry, also in Mainz, and a Rock Abrasion Tool built by Honeybee Robotics that can grind a hole 45 mm across and 5 mm deep in hard volcanic rock in about two hours.

• 5. Spirit at Gusev Crater

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  Gusev crater looked, from orbit, like a dry lakebed. When Spirit arrived on the plains inside it, the reality was more complicated. The surface rocks were basalt, volcanic in origin, containing olivine, pyroxene, plagioclase, and magnetite. Signs of water were subtle: thin coatings on the rocks, and some mineral deposits suggesting water had once moved through cracks.

  Spirit's most significant geology came when it climbed up from the plains into the Columbia Hills. On the 21st of August 2005, after 581 sols of driving and a journey of 4.81 km, it reached the summit of Husband Hill. Scientists categorized the rocks there into six groups, named Clovis, Wishbone, Peace, Watchtower, Backstay, and Independence, each after a prominent rock within the group. All six showed signs of alteration by water. The Clovis group contained goethite, detected by the Mössbauer spectrometer. Goethite forms only in the presence of water, making it the first direct mineralogical evidence of past water in those hills. Later in the mission, data from the Mini-TES confirmed carbonate-rich rocks in an outcrop called Comanche, another marker of ancient water.

  Spirit's front right wheel stopped working on the 13th of March 2006 while the rover was heading toward McCool Hill. Drivers tried dragging the dead wheel behind the rover, but soft sand on the lower slopes stopped that approach. Spirit spent the subsequent Martian winter parked on a feature called Low Ridge Haven, angled to collect enough sunlight to survive. Years later, in January 2010, NASA announced that Spirit had become permanently stuck in soft Martian sand and would serve as a stationary research platform. The last successful communication with the rover was on the 22nd of March 2010.

• 6. Opportunity and the Water Record

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  Opportunity landed in a small crater the science team nicknamed Eagle, on the flat plains of Meridiani Planum. Within the crater walls, the rover found something that had not been seen before on Mars: layered bedrock with sedimentary texture and, embedded in the soil, small spherical concretions the team called blueberries. Chemical analysis showed the blueberries were rich in hematite and had formed in an aqueous environment. The rock itself was primarily Jarosite, a ferrous sulfate mineral that forms as an evaporite when a salty body of water dries up.

  On the 23rd of March 2004, a news conference announced major discoveries of evidence for past liquid water on the Martian surface. Data from Meridiani showed a stratified pattern and cross-bedding in the rocks inside the crater. The irregular distribution of chlorine and bromine further suggested the site was once the shoreline of a salty sea.

  Opportunity kept moving. In February 2007, it became the first spacecraft to travel 10 km on the surface of Mars. It entered Victoria Crater in September 2007 and spent months exploring its interior before climbing out in August 2008. Project scientist Bruce Banerdt was quoted as saying the rover had done everything expected inside Victoria and more. On the 7th of March 2009, after driving about 3.2 km since leaving Victoria, Opportunity first caught sight of the rim of the much larger Endeavour crater, a 25-km-diameter feature whose orbital spectroscopy showed phyllosilicate rocks, indicative of older sedimentary deposits. It finally reached Endeavour's rim eight years after landing. By January 2009, the two rovers together had sent back 250,000 images.

• 7. Dust Storms and Endurance

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  In July 2007, during the fourth mission extension, a global Martian dust storm reduced sunlight so severely that engineers feared one or both rovers might be permanently disabled. Both hunkered down. Opportunity's power dipped to 128 watt-hours during that storm. The storm lifted, and both rovers resumed driving roughly two months after suspending operations.

  In June 2018, Opportunity was caught in a second global dust storm. Solar power fell below the threshold for normal operation, and the last contact with the rover came on the 10th of June 2018. NASA kept sending signals after the storm subsided, but the rover did not respond, possibly because a catastrophic system failure had occurred or because dust had settled thickly over the solar panels. On the 13th of February 2019, at a press conference, NASA officially declared the Opportunity mission over, closing a mission that had run for sixteen years.

  The fifth and final mission extension had been granted in October 2007, running through the end of 2009. The total cost of building, launching, landing, and operating the rovers for the initial 90-sol primary mission was 820 million US dollars. The first four extensions together added 104 million dollars, and the fifth cost at least 20 million. At their death, both rovers had long since paid back that investment in ways that went beyond the original mission brief: by January 2014, NASA had formally expanded its Mars objectives to include searching for evidence of ancient life, a goal that grew directly from what Spirit and Opportunity had found in the rocks of Gusev and Meridiani.