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Mars Exploration Rovers

Mars Exploration Rovers


The Rovers

The Mission

Mission Results



The exploration of Mars using robotic spacecraft began in the 1960s, when the US National Aeronautic and Space Administrations (NASAs) Mariner 4 flew past the planet and beamed back 21 fuzzy television pictures. In 1976, NASAs twin Viking landers touched down on different parts of the planet. Although the landers could not roam, they beamed back thousands of high-quality photographs, collected data on weather and chemistry, and performed sophisticated experiments on Martian soil to look for life. Although some confusing results were obtained from those experiments, most scientists today think that the Viking landers did not detect Martian life.

Several attempts were made by the Soviet Union (and later the Russian Federation) to send landers to Mars, but all failed. In 1996, the U.S. scored a second Mars lander success with its Pathfinder probe, which proved that a spacecraft could safely land on another world by bouncing inside a cluster of inflated airbags. Pathfinder released a tiny solar-powered rover called Sojourner that roamed a few yards from the lander.

Several other NASA attempts at landing on Mars failed. NASAs Mars Polar lander crashed in 1999, its Deep Space 2 surface penetrators returned no data when they impacted Mars in the same year, and the European Space Agencys Beagle lander failed in 2003. Then, in 2003, spectacular success: the large, sophisticated Mars Exploration Rovers Spirit and Opportunity, identical twins, successfully rolled out on the surface of Mars. It was the beginning of a mission that would continue for both rovers until at least late 2006, probably longer. (As of this writing, November 2006, both rovers were still functional.)

The Rovers

Each rover is about the size of a golf cart and consists of an instrument-packed chassis riding on six metal wheels. Each wheel has its own motor and can be steered and powered independently of all the rest. The top of the rover folds out flat to expose the solar panels that power the rover. A Pancam Mast Assembly rises out of the top of the rover, bearing several cameras at a height of 5 feet (a little less than 2 m). At the front of the rover, mounted on the end of a jointed robotic arm called the Instrument Deployment Device (IDD), is a circular grinding tool for polishing rocks to reveal their inner structure. The IDD also bears a Mössbauer spectrometer for determining what minerals are present in rocks, an alpha particle X-ray spectrometer for analyzing which elements are present in rocks, magnets for gathering iron-bearing dust, and a close-up camera called the microscopic imager. High- and low-gain antennas provide radio communications directly with Earth or with satellites orbiting Mars. In November, 2006 communications were established between the rovers and NASAs recently-arrived Mars Reconnaissance Orbiter, which can greatly speed up data return to Earth.

The rovers were not equipped with experiments designed to detect life.

The Mission

The rovers, named Spirit and Opportunity as a result of a school essay contest won by a third-grade girl, were launched from Cape Kennedy, Florida in June and July, 2003. Both landed on Mars in January 2004, on opposite sides of the planet. Borrowing technology pioneered by both the Viking missions of the 70s and the Pathfinder mission of the 90s, they first slowed themselves by riding large, saucer-shaped aeroshells into the upper Martian atmosphere. Friction with the atmosphere heated the aeroshells to a white glow and slowed the spacecraft down. Next, each lander deployed a parachute. Rockets stopped the final descent at a height of about 30 feet (10 m) above the surface, and the lander was released, packaged inside a roughly tetrahedral group of four airbags. (A tetrahedron is a pyramid with four sides shaped like equilateral triangles.) The spacecraft was still moving sideways as the airbag-protected landers were dropped, so each lander rolled and bounced for many yards over boulders and sand before coming to rest.

Next, each lander deflated its airbags and reeled them in to keep them from being an obstacle in the nearby landscape. The lander now consisted of a tetrahedral shell with the rover folded up inside. Three sides of the lander unfolded like petals of a flower, forcing the lander to roll, if necessary, so that the side with the rover clamped to it would be right side up on the ground. The rover was then commanded to unfold its camera mast, solar panels, and suspension system. Firing small explosive bolts cut cables holding the rover in place, and it was free to roll down one of the petals and onto the Martian surface. Both rovers completed all these steps successfully.

A scare occurred when the Spirit rover lost contact with Earth a few days after rolling off its lander. There were fears that the mission would be lost, but engineers discovered a software problem with the rovers flash memory management system. An upgrade was uploaded to both rovers and the failure did not recur.

Mission Results

As of November, 2006, the rovers had driven several miles each on the surface of Mars. Spirit had climbed (and descended) a nearby hill and Opportunity had traversed several kilometers of open desert to

arrive at the edge of a large crater named Endurance. Both had returned thousands of high-resolution images in color, black-and-white, and stereo and examined scores of rocks in detail. They had photographed Martian dust devils (small, tornado like air swirls picking dust up from the surface) and collected years of meteorological data. Geological data from both rovers had established firmly that Mars once, billions of years ago, went through a warm, wet period of its history. The duration of that warm, wet period, and whether it could possibly have allowed life to evolve, are still being debated by scientists.



Squyres, Steve. Roving Mars: Spirit, Opportunity, and the Exploration of the Red Planet. New York: Hyperion, 2005.


Squyres, S. W., et al. Two Years at Meridiani Planum: Results from the Opportunity Rover. Science. 313 (2006): 1403-1407.


National Aeronautics and Space Administration. Mars Exploration Rover Mission. November 22, 2006. <> (accessed November 29, 2006).

Larry Gilman

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