NASA's Mars Exploration Rover (MER) mission was a robotic space mission involving two Mars rovers, Spirit and Opportunity, exploring the planet Mars. It began in 2003 with the launch of the two rovers to explore the Martian surface and geology; both landed on Mars at separate locations in January 2004. Both rovers far outlived their planned missions of 90 Martian solar days: MER-A Spirit was active until March 22, 2010, while MER-B Opportunity was active until June 10, 2018.
Objectives
The mission's scientific objective was to search for and characterize a wide range of rocks and soils that hold clues to past water activity on Mars. The mission is part of NASA's Mars Exploration Program, which includes three previous successful landers: the two Viking program landers in 1976 and Mars Pathfinder probe in 1997.
The scientific objectives of the Mars Exploration Rover mission were to:
- Search for and characterize a variety of rocks and soils that hold clues to past water activity. In particular, samples sought 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 (MRO) instruments. This will help determine the accuracy and effectiveness of various instruments that survey Martian geology from orbit.
- Search for iron-containing minerals, and to 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 to 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.
The total cost of building, launching, landing and operating the rovers on the surface for the initial 90-sol primary mission was US$820 million. Each rover received five mission extensions, as they continued to function past their initially planned duration. The fifth mission extension was granted in October 2007, and ran to the end of 2009. The total cost of the first four mission extensions was $104 million, and the fifth mission extension cost at least $20 million. The mission was managed by the Jet Propulsion Laboratory (JPL), which designed, built, and operated the rovers.
In recognition of the vast amount of scientific information amassed by both rovers, two asteroids have been named in their honor: 37452 Spirit and 39382 Opportunity.
Mission timeline
Launch and landing
The MER-A (Spirit) and MER-B (Opportunity) were launched on June 10, 2003, and July 7, 2003, respectively. Though both probes launched on Boeing Delta II 7925-9.5 rockets from Cape Canaveral Space Launch Complex 17 (CCAFS SLC-17), MER-B was on the heavy version of that launch vehicle, needing the extra energy for Trans-Mars injection. The launch vehicles were integrated onto pads right next to each other, with MER-A on CCAFS SLC-17A and MER-B on CCAFS SLC-17B. The dual pads allowed for working the 15- and 21-day planetary launch periods close together; the last possible launch day for MER-A was June 19, 2003 and the first day for MER-B was June 25, 2003. NASA's Launch Services Program managed the launch of both spacecraft.
The probes landed in January 2004 in widely separated equatorial locations on Mars. On January 21, 2004, the Deep Space Network lost contact with Spirit, for reasons originally thought to be related to a flare shower over Australia. The rover transmitted a message with no data, but later that day missed another communications session with the Mars Global Surveyor. The next day, JPL received a beep from the rover, indicating that it was in fault mode. On January 23, the flight team succeeded in making the rover send. The fault was believed to have been caused by an error in the rover's flash memory subsystem. The rover did not perform any scientific activities for ten days, while engineers updated its software and ran tests. The problem was corrected by reformatting Spirit's flash memory and using a software patch to avoid memory overload; Opportunity was also upgraded with the patch as a precaution. Spirit returned to full scientific operations by February 5. Both rovers' missions were initially just 90-sol-long.
On March 23, 2004, a news conference was held announcing "major discoveries" of evidence of past liquid water on the Martian surface. A delegation of scientists showed pictures and data revealing a stratified pattern and cross bedding in the rocks of the outcrop inside a crater in Meridiani Planum, landing site of MER-B, Opportunity. This suggested that water once flowed in the region. The irregular distribution of chlorine and bromine also suggests that the place was once the shoreline of a salty sea, now evaporated.
Mission extensions
On April 8, 2004, NASA announced that it was extending the mission life of the rovers from three to eight months. It immediately provided additional funding of US$15 million through September, and $2.8 million per month for continuing operations. Later that month, Opportunity arrived at Endurance crater, taking about five days to drive the 200 meters. NASA announced on September 22 that it was extending the mission life of the rovers for another six months. Opportunity was to leave Endurance crater, visit its discarded heat shield, and proceed to Victoria crater. Spirit was to attempt to climb to the top of the Columbia Hills.
With the two rovers still functioning well, NASA later announced another 18-month extension of the mission to September 2006. Opportunity was to visit the "Etched Terrain" and Spirit was to climb a rocky slope toward the top of Husband Hill. On August 21, 2005, Spirit reached the summit of Husband Hill after 581 sols and a journey of 4.81 kilometers (2.99 mi).
Spirit's front right wheel ceased working on March 13, 2006, while the rover was moving itself to McCool Hill. Its drivers attempted to drag the dead wheel behind Spirit, but this only worked until reaching an impassable sandy area on the lower slopes. Drivers directed Spirit to a smaller sloped feature, dubbed "Low Ridge Haven", where it spent the long Martian winter, waiting for spring and increased solar power levels suitable for driving. That September, Opportunity reached the rim of Victoria crater, and Spaceflight Now reported that NASA had extended mission for the two rovers through September 2007. On February 6, 2007, Opportunity became the first spacecraft to traverse ten kilometers (6.2 miles) on the surface of Mars.
In July 2007, during the fourth mission extension, Martian dust storms blocked sunlight to the rovers and threatened the ability of the craft to gather energy through their solar panels, causing engineers to fear that one or both of them might be permanently disabled. However, the dust storms lifted, allowing them to resume operations.
Opportunity was poised to enter Victoria Crater from its perch on the rim of Duck Bay on June 28, 2007, but due to extensive dust storms, it was delayed until the dust had cleared and power returned to safe levels. Two months later, Spirit and Opportunity resumed driving after hunkering down during raging dust storms that limited solar power to a level that nearly caused the permanent failure of both rovers.
On October 1, 2007, both Spirit and Opportunity entered their fifth mission extension that extended operations into 2009, allowing the rovers to have spent five years exploring the Martian surface, pending their continued survival.
On August 26, 2008, Opportunity began its three-day climb out of Victoria crater amidst concerns that power spikes, similar to those seen on Spirit before the failure of its right-front wheel, might prevent it from ever being able to leave the crater if a wheel failed. Project scientist Bruce Banerdt also said, "We've done everything we entered Victoria Crater to do and more." Opportunity would return to the plains in order to characterize Meridiani Planum's vast diversity of rocks—some of which may have been blasted out of craters such as Victoria. The rover had been exploring Victoria Crater since September 11, 2007. As of January 2009, the two rovers had collectively sent back 250,000 images and traveled over 21 kilometers (13 mi).
After driving about 3.2 kilometers (2.0 mi) since it left Victoria crater, Opportunity first saw the rim of Endeavour crater on March 7, 2009. It passed the 16 km (9.9 mi) mark along the way on sol 1897. Meanwhile, at Gusev crater, Spirit was dug in deep into the Martian sand, much as Opportunity was at Purgatory Dune in 2005.
On January 26, 2010, after six years on Mars, NASA announced that Spirit would be used as a stationary research platform, after several months of unsuccessful attempts to free the rover from soft sand.
NASA announced on March 24, 2010, that Opportunity, which had an estimated remaining drive distance of 12 km (7.5 mi) to Endeavour Crater, had traveled over 20 km (12.4 mi) since the start of its mission. Each rover was designed with a mission driving distance goal of just 600 meters.
In March 2010 it was announced that Spirit may have gone into hibernation for the Martian winter and might not wake up again for months. On May 22, 2011, NASA ceased attempts to contact with Spirit, which had been stuck in a sand trap for two years. The last successful communication with the rover was on March 22, 2010. The final transmission to Spirit was on May 25, 2011.
On May 16, 2013, NASA announced that Opportunity had driven further than any other NASA vehicle on a world other than Earth. After Opportunity's total odometry went over 35.744 km (22.210 mi), the rover surpassed the total distance driven by the Apollo 17 Lunar Roving Vehicle. And on July 28, 2014, Opportunity had driven further than any other vehicle on a world other than Earth. Opportunity covered over 40 km (25 mi), surpassing the total distance of 39 km (24 mi) driven by the Lunokhod 2 lunar rover, the previous record-holder. On March 23, 2015, Opportunity had driven the full 42.2 km (26.2 mi) distance of a marathon, with a finish time of roughly 11 years and 2 months.
On January 24, 2014, NASA reported that then-current studies by the remaining rover, Opportunity, as well as by the newer Mars Science Laboratory rover Curiosity would now be searching for evidence of ancient life, including a biosphere based on autotrophic, chemotrophic and/or chemolithoautotrophic microorganisms, as well as ancient water, including fluvio-lacustrine environments (plains related to ancient rivers or lakes) that may have been habitable. The search for evidence of habitability, taphonomy (related to fossils), and organic carbon on the planet Mars was then switched to a primary NASA objective.
In June 2018, Opportunity was caught in a global-scale dust storm and the rover's solar panels were not able to generate enough power, with the last contact on June 10, 2018. NASA resumed sending commands after the dust storm subsided but the rover remained silent, possibly due to a catastrophic failure or a layer of dust covering its solar panels. A press conference was held on February 13, 2019, announcing that after numerous attempts to contact Opportunity, with no response since June 2018, NASA declared the Opportunity mission over, which also drew the 16-year long Mars Exploration Rover mission to a close.
Spacecraft design
The Mars Exploration Rover was designed to be stowed atop a Delta II rocket. Each spacecraft consists of several components:
- Rover: 185 kg (408 lb)
- Lander: 348 kg (767 lb)
- Backshell / Parachute: 209 kg (461 lb)
- Heat Shield: 78 kg (172 lb)
- Cruise Stage: 193 kg (425 lb)
- Propellant: 50 kg (110 lb)
- Instruments: 5 kg (11 lb)
Total mass is 1,063 kg (2,344 lb).
Cruise stage
The cruise stage is the component of the spacecraft that is used for travel from Earth to Mars. It is very similar to the Mars Pathfinder in design and is approximately 2.65 meters (8.7 feet) in diameter and 1.6 m (5.2 ft) tall, including the entry vehicle (see below).