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Space Exploration

Mars Exploration Rover Mission

Spirit spacecraft, Viking spacecraft, Meridiani Planum, Delta rocket, Lunar Prospector

Deeper web pages:

>  The Rover's Instruments and Navigation

>  A Typical Day, or Sol

>  Spirit's Landing Site

>  Scientific Findings From Spirit

>  The Opportunity Landing Site

>  Opportunity's Scientific Findings

Mars Exploration Rover Mission, robotic exploration of Mars carried out by the National Aeronautics and Space Administration (NASA) of the United States beginning in 2003. The primary goal of the mission was to land two highly mobile vehicles known as rovers at separate landing sites on Mars so that they could search for evidence that liquid water once existed on the planet’s surface. Equipped with scientific instruments, the rovers landed at sites chosen because they were likely to provide information on whether liquid water once existed on Mars. Water is essential to life, and scientists believe that if water once existed on Mars, then life might have evolved there in the distant past. The mission was regarded as a major scientific and engineering success, resulting in important new discoveries about the so-called Red Planet, including the finding that large areas of Mars once had liquid water.

The rovers were designed, built, and tested from 2000 to 2003 by a large team led by the California Institute of Technology’s Jet Propulsion Laboratory (JPL) in Pasadena, California. JPL is managed by the California Institute of Technology for NASA. The rover team included scientists and engineers from NASA, professors at U.S. and European universities, and private contractors. More than 1,000 people around the world were directly involved in the rovers’ design, assembly, and software development work. Once the rovers landed on Mars, a worldwide team of several hundred people became involved in the rovers’ day-to-day operations.

Assembly, test, launch, and a year of operations of each rover cost about $425 million, or about the same amount of money as it cost to make the movies Titanic (1997) and Pearl Harbor (2001). This amount was also equivalent to what it costs to launch a single space-shuttle mission. The rovers are part of a new class of less expensive NASA spacecraft, with costs similar to other recent Mars orbiters and smaller missions such as the Lunar Prospector. These missions cost hundreds of millions of dollars compared with the Viking spacecraft of the 1970s, or the more recent Hubble Space Telescope or Cassini Saturn orbiter missions, which each cost several billion dollars.

The first rover, Spirit, was launched on a Delta rocket from Cape Canaveral, Florida, on June 10, 2003. Spirit was targeted to land inside Gusev Crater, a 160-km (100-mi) wide crater in the southern hemisphere of Mars. Images and other data from orbiting spacecraft such as Viking, Mars Global Surveyor (MGS), and Mars Odyssey showed an enormous meandering channel, possibly a dry riverbed, which ends in Gusev Crater. This finding suggested that Gusev may once have been a water-filled lake. One of Spirit's primary goals was to search for evidence of whether Gusev ever contained liquid water, and if so, for how long.

The second rover, Opportunity, also part of a larger spacecraft, was launched on a similar Delta rocket from Cape Canaveral, Florida, on July 7, 2003. Opportunity was targeted to a landing site halfway around the planet from Gusev, in a smooth region just south of the equator called Meridiani Planum. Meridiani is among the flattest places on Mars and thus was judged to be a safer rover landing site than Gusev. The decision to land in Meridiani was mostly based on scientific observations from the MGS orbiter, which had detected evidence for deposits of the coarse-grained mineral hematite (Fe2O3) in this part of the planet. Coarse-grained hematite often forms on Earth in the presence of substantial amounts of liquid water. Opportunity's primary goals were to confirm the presence of hematite in Meridiani, to determine if it was formed by liquid water, and if so, to provide clues about how much water was there and how long it lasted.

After a seven-month interplanetary cruise to Mars traveling at a speed of about 19,000 km/h (12,000 mph), the spacecraft that carried each rover went through a six-minute thrill ride to decelerate and land. Each spacecraft used a heat shield to protect it from the heat of atmospheric entry, a parachute to slow the craft, retro-rockets to bring the craft to a near-hovered stop just above the surface, and finally a set of inflated airbags to cushion the blow of impact and allow the spacecraft to bounce around to a gentle stop. The Spirit spacecraft landed successfully on January 4, 2004, and the Opportunity spacecraft landed successfully on January 24, 2004. Once operators on Earth determined that it was safe to begin the mission, each spacecraft unfolded and deployed its various instruments, and the rovers rolled out on a ramp onto the surface of the planet. Spirit rolled onto the surface on January 15, and Opportunity was deployed onto the surface on January 31.

The landing procedure was similar to that of the successful 1997 Mars Pathfinder mission. However, the two identical rovers differ significantly from the earlier Sojourner rover on the Pathfinder mission. The Mars Exploration rovers are larger and heavier. Whereas Sojourner was 65 cm (2 ft) long with a mass of 10 kg (22 lb on Earth; 8 lb on Mars), each of the Mars Exploration rovers is 1.6 m (5.2 ft) long and has a mass of 174 kg (384 lb on Earth; 144 lb on Mars). The six-wheeled Mars Exploration rovers also have a suspension system that enables them to ride over rocks bigger than 26 cm (10 in) and to tilt up to about 30 degrees without turning over.


Bell, Jim, B.S., M.S., Ph.D.

Associate Professor of Astronomy at Cornell University who was in charge of the panoramic camerad on the Mars Rover Expedition. Author of "Postcards from Mars: The First Photographer on the Red Planet".

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