In January 2004, NASA launched two new robotic geologists - Spirit and Opportunity. Their mission was to study geologically different regions of Mars. The original names were MER-A and MER-B, but they were changed when The Planetary Society and LEGO ran a “Name the Rovers” contest; open for K-12 American students. An essay was required to justify the name and the project involved thousands of individuals interested in Mars exploration.

Sofi Collis, a Siberian born third grader won the contest.  Her submission topped over 10,000 entries. In expressing her appreciation on being adopted and brought to America, her statements, “I used to live in an orphanage.  It was dark and cold and lonely.  At night I looked up at the sparkly sky.  I felt better.  I think I could fly there.  In America I can make all my dreams come true.  Thank you for the spirit and the opportunity,” won the contest, hands-down. NASA Administrator Sean O'Keefe, made the announcement at the June 8, 2003 press conference and stated, ”She has in her heritage and upbringing the soul of two great space faring countries, to be sure. We have names for these rovers that are extremely worthy of the bold mission they are about to undertake."

Once undertaking the mission, the rovers far exceeded their expectations. Highly mobile, they have the capacity to travel the length of a football field on a daily basis.

The rover design is extremely sophisticated. It is a solar-powered robot, height 4.9 ft (1.5 m), width 7.5 ft (2.3 m) and length 5.2 ft (1.6 m) and the wheel and suspension system occupies 80 lbs. of its total weight of 400 lbs. It has six wheels, each having cleats that provide grip for scrambling over rocks, or climbing in sand. The wheels are mounted on a “rocker-bogie” suspension system that keeps them on the ground while traveling rough terrain. This design allows the rover to go over obstacles and through holes that are more than 10 inches in size.  To allow the vehicle to turn, swerve, curve, and make a full revolution, each wheel has a motor and the two front and rear wheels have individual steering motors.

On flat, hard ground, the rover has the capacity to travel at a top speed of 50 mm/sec, but on the average, it moves at 10 mm/sec as a safety precaution.  It is programmed to stop every ten to twenty seconds to observe and comprehend the terrain it drives into. It can withstand a tilt of 45 degrees without capsizing and can grind deep into the terrain by spinning one of its front wheels while the rest of it remains motionless.  Hazard avoidance software has programmed it to avoid tilts of over 30 degrees.

Its electronic system is amazing to say the least.  It uses  multijunction photovoltaic cells (sub class of a solar cell) which has layers that each capture sunlight passing through its cell, allowing the cell to capture more of the spectrum and convert it into electricity.   This solar array generates approximately 140 watts per four hours per Martian day. At night, and when the sun is not shining, two rechargeable lithium ion batteries provide energy. Additionally, eight radioisotope heater units  keep the instruments at a safe temperature.

Its communication system consists of both a high-gain and low-gain antenna.  The high-gain antenna has a focused, narrow radio wave beam width, which allows precise targeting of the radio signal, and in transmitting increases the received signal strength. The low-gain antenna has a broad radio wave beam width that allows a more reliable signal regardless of terrain.

Nine cameras on the rovers produce 1024-pixel-by-1024-pixel images at 12 bits per pixel, which can be truncated to 8 bits per pixel. Three of the nine cameras are mounted onto one assembly called the Pan Cam Mast Assembly, and consists of:

1. The Panoramic Camera - determines texture, color, mineralogy, and structure of terrain.

2. Navigation Camera - used for navigation and driving and has a high field of view/low resolution and is monochromatic.

3. Thermal Emission Spectrometer (Mini-TES) - identifies which rocks and soils to choose for further examination and determines the processes that formed them.

The Rover’s arm or IDD (Instrument Deployment Device) has the ability to place instruments directly against rock and soil targets. It holds:

1. Mössbauer Spectrometer - used for close investigation of mineralogy of ion-bearing rocks and soils

2. Alpha Particle X-Ray Spectrometer (APXS) - used for close up analysis of the abundances of elements that make up rocks and soils

3. Magnets-used for collecting magnetic dust particles

4. Microscopic Imager (MI) - used for obtaining close-up, high-resolution images of rocks and soils

5. Rock Abrasion Tool (RAT)-used for removing dusty and weathered rock surfaces and exposing fresh material for examination by instruments on-board

The Rovers, Spirit and Opportunity are identical twins (in terms of sets of scientific instruments they carry), but their experiences differ.  NASA launched Spirit on June 10, 2003 and Opportunity, on July 7, 2003.  Spirit arrived on Mars January 3, 2004 Pacific Standard Time. Opportunity arrived on Mars, 21 days later-January 24, 2004 Pacific Standard Time. Both landed on opposite sides of the Red Planet.  They had only 90-day warranties and their primary mission was to examine geological evidence concerning past environments at their respective landing sites.

The crater Gusev, was Spirit’s targeted site. According to speculation, at some point in The Red Planet’s past, a channel system, (Ma’adim Vallis) drained into the crater and it may have carried water and ice. Gusev is filled with sediment approximately 3,000 feet thick and outcrops resemble landforms in some river deltas on Earth. Scientists assumed that water flows lasted longer than tens or hundreds of thousands of years. There are other indications that a lake near the source of Ma’adim Vallis could have provided this water. The possibility that Gusev is a former lake made this a promising target. The “dust devils” (whirlwinds) on Gusev’s floor attribute to Spirit’s longevity by cleaning its solar panels.

 The MER team named the landing site, “Columbia Memorial Station”.  The name honored the astronauts who lost their lives in the Space Shuttle Columbia tragedy.

Spirit’s early destination was Sleepy Hollow, a shallow depression in the crater.  Its name alludes to the Legend of Sleepy Hollow and the scientists designated it as a place for Spirit to “sleep” before its exploration of Mars.

Spirit had some hair-raising moments. On January 21, 2004, it ceased communications with Mission Control. It was not staying in “sleep mode” and was wasting battery power and overheating-a major risk factor. The command team sent a shutdown command-“SHUTDWN_DMT_TIL (‘Shutdown Dammit Until <time>’)”, which was seemingly ignored.  Spirit was stuck in a re-boot loop. The problem suggested that the error could be in flash memory and a radio-limited command set was given to tell Spirit to reboot without using flash.  The reboot cycle was broken.  The problem was due to the file management system in the software.  The engineers deleted excess files, reformatted the flash memory system, and on February 6, 2004, restored the rover. Spirit’s accomplishments include:

• On February 6, (Sol 34) Spirit performed History’s first grinding of a rock on Mars with its RAT performing well beyond expectations.  It also unearthed Mimi-a rock leading scientists to many hypotheses. The Rock Abrasion Tool’s grinding surface eventually wore down and its use is now limited to only brushing targets.
• On March 5, 2004, Spirit discovered hints of Mars’ water history in the rock “Humphrey”
• Reached many craters (Bonneville, Missoula, Lahontan) as well as the base of the Columbia Hills
• Explored the rock "Clovis"

It also investigated "Paso Robles", which contained the highest amount of salt found on Mars. In late 2005, it made multiple observations, including a lunar eclipse of the two Mars’ moons, Phobos and Deimos.

On February 7, 2006 (Sol 744), it arrived at Home Plate.  It moved on to Low Ridge Haven and returned on Sol 1126 to resume studies, and spend its third Martian winter.

Opportunity, on the other hand, had a landing that excited NASA Scientists. It landed approximately 24 km east of its intended target in Meridiani Planum, two degrees south of Mars’ equator. The rover rolled into an impact crater that scientists did not know existed, and later the landing was referred to as a “hole in one”.  They named it Eagle Crater and named the landing site, Challenger Memorial Station.  The site was so dark that it took Opportunity two weeks to be able to get a look at its surroundings.  The abundance of rock outcrops and soil-a mixture of reddish and grey grains was intriguing to NASA Scientists.  They assumed the seemingly layered rocks were either volcanic ash deposits or sediments left by wind or water.  They named the area of rock croppings “Opportunity Ledge”. This discovery was significant for the scientists whose purpose was to test the “water hypothesis”. The minerals uncovered by the RAT showed strong evidence of the presence of water when the minerals formed.

Opportunity also dug the first trench on Mars, finding major differences between the surface and beneath it.  On April 30, 2004, it investigated another site called Endurance Crater.  In the following month, the scientists made a critical and very careful decision to drive Opportunity into the crater with no assurance that it would be able to climb out again. It was vital to get information about what came before evaporates, even at the risk of stranding the rover.

On June 8, Opportunity descended into the crater and, like a trouper; it backed out the same day.  During Sols 134-137, the digging went much deeper.  There was minor wheel slip, proving to the scientists that driving was possible even at slopes angles up to 30 degrees. The rover spent 180 Sols inside the crater and the scientists published results of the crater’s sedimentary geology in the Journal of Earth and Planetary Science Letters.

Opportunity also discovered the first meteorite identified on another planet. In January, 2005, it was sent to examine its own discarded heat shield when it happened upon what was determined to be a meteorite and it was named Heat Shield Rock.

Additionally, the rover set the distance record for one-day travel, 177.5 meters (582 ft).  From February 10, (Sol 373) to February 26, (Sol 389) 2005, the trek included passing the craters, “Alvin” and “Jason”, “Vostok”, “Naturaliste”, and “Normandy”.

By Sol 415, it stopped to investigate soil ripples (sedimentary structures that indicate agitation by water). Targets included "Mobarak", "Mayberooz". By Sol 421, Opportunity left the ripple for "Viking" crater.

Problems, however, followed success. On April 26, 2005, the rover was stuck in a sand dune. The scientists feared that it would be permanently immobilized. They completed various simulations and by May 13, 2005, the simulations resulted in the rover advancing a few centimeters.  They named the dune, “Purgatory Dune”. Each trial afterwards moved the rover additional centimeters.  It escaped by June 4, 2005 (Sol 484).

November 3, 2005 (Sol 28) Opportunity was caught in a three-day dust storm and was unable to take images. By December 1, 2005, the motor used to stow the robotic arm was stalling. It took approximately two weeks to repair. To keep the arm from getting stuck , it was only stowed for travel and extended exclusively at night.

Like an arthritic old man, Opportunity’s shoulder joint was troubled. The heater on the azimuth joint was stuck in the “on” position-an error made during its assembly. However, it was equipped with a built-in safety thermostatic switch that protected against overheating.  The safety mechanism failed to work at Opportunity’s first winter on Mars. To resolve the problem, the operators used a method called “deep-sleep” that allowed it to disconnect its batteries at night. Unfortunately, every sol, the shoulder joint was extremely hot during the day and extremely cold during the night. These temperature swings had the potential to cause the electric motor to wear out.

The troubles were not over. June 2007 dust storms evaded the Martian atmosphere and by July, Opportunity was facing a system failure. With no chance to charge its solar batteries, the threat of permanent sleep emerged. In August 2007 the storms subsided, giving the rover the ability to re-charge its batteries and continue the drive.

The drive took the rover to Duck Bay, Victoria Cater and Cape Verde during the month of September 2007 and continued on to investigate Endeavour Crater.

Opportunity provided evidence to support the mission’s primary scientific goals-to distinguish an array of rocks and soils, which held clues to water activity in Mars’ past. Like Spirit, it was honored for a great contribution to Mars’ exploration and the asteroid 39382 was proposed and named, “Opportunity”, by Ingrid van Houten-Groeneveld, Cornelis Johannes van Houten and Tom Gehrels.

Scientists initially theorized that Mars was wet and warmer, but to prove the theory hard evidence was required. Spirit and Opportunity tested and proved the theory by landing on the Red Planet and sending back hard evidence in over 36 gigabytes of data and a quarter-million images. They drove over 13 miles, climbed mountains, descended into craters, escaped from sand traps, weathered dust storms, and survived, though their hardware was wearing out. They not only proved a history-changing theory, but also affirmed that Science can explore other planets.

The rovers are presently on Mars, carrying out the team’s exploration campaigns, but a new rover, the Mars Science Laboratory, will do the future explorations. Its instrument payload will be 10 times heavier than that of Spirit and Opportunity combined. It will be mobile and its 43-inch high deck will make climbing over obstacles more efficient.  The new mission will be to explore Mars’ past and present habitability. The team originally scheduled the mission for late next year, but then delayed it due to cost and technical difficulties. They will be cautious and patient because failure is not an option. The projected launch date is set for 2011.