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MESSENGER: The Extreme Machine
Only one NASA spacecraft has visited Mercury and that was Mariner 10 in 1974 and 1975. It was programmed to fly by the planet three times to take images of its heavily-cratered surface. But the spacecraft saw essentially the same side of the planet on each pass.

Mercury image taken by Mariner 10 There's still more than half of Mercury we've never seen before. And it's not that NASA hasn't wanted to get there sooner! Scientists and engineers have spent nearly two decades developing new techniques and designing a spacecraft with the ability to survive the extreme conditions of Mercury.

Image Left: Nearly all of Mercury's surface will be imaged in stereo to determine the planet's global topography and landforms. MESSENGER will determine why Mercury is so much denser and more metal-rich than Venus, Earth, and Mars. Image credit: NASA

Their hard work is coming to fruition. The MESSENGER (MErcury Surface, Space ENvironment, GEochemistry and Ranging) mission is set to launch on Aug. 2 from Cape Canaveral Air Force Station, Fla., to further study the mysterious nature of Mercury.

Many of MESSENGER's basic components are very similar to other spacecraft, which kept project costs down. But MESSENGER has a unique quality that other crafts don't. Its structure was built using a composite material, making the spacecraft relatively lightweight. Although regularly used on other spacecraft, the composite material was never used to make an entire vehicle before MESSENGER.

Did you know that Mercury is so close to the Sun that it's up to 11 times brighter there than here on Earth? Mercury's surface temperatures can reach about 840 degrees Fahrenheit. But MESSENGER will stay cool (around average room temperature), sheltered behind a sunshade made of heat-resistant ceramic cloth. Sunshades and heat-protective blanketing were used on the Mariner 10 spacecraft, but MESSENGER's protective layer is thicker for the intense heat exposure during orbit.

Mercury's ice patches Image Right: Mercury's North Pole. These unusual images of what looks likes ice have sparked the imagination of scientists. It has been suggested that a tiny flow of ice from comets and meteorites could be cold-trapped in these polar deposits over billions of years, or that the polar deposits consist of sulfur that has seeped from minerals in the surface rocks over the eons. Image credit: NASA/Aricibo University

So how is it that the planet closest to the Sun has temperatures that possibly can sustain ice? Simply, Mercury's axis of rotation is such that sections of the planet, the deep floors and walls of craters near its poles, are always shaded. In these frigid areas of Mercury, temperatures can dip to minus 350 degrees Fahrenheit. Radar pictures from Earth show material in the craters that resembles ice, but its identity is one of Mercury's mysteries that NASA hopes to solve.

MESSENGER's science payload (or instrumentation) was selected to answer six key questions about the Solar System's second densest planet. Most of the instruments are rigidly fixed on the spacecraft's body, so taking each reading involves maneuvering the spacecraft into the correct position.

This is accomplished with the 16 small, monopropellant thrusters used for small orbit-corrections. Its main bipropellant engine will be used for large trajectory-correction maneuvers on the way to Mercury and to inject the spacecraft into orbit around the planet. Nearly 55 percent of MESSENGER's total mass of more than 2,400 pounds is propellant.

Mercury Trivia
Mercury was named for the swift Roman "messenger" god, since it travels around the Sun faster than any other planet.
MESSENGER's power comes mainly from its solar array. Power produced by the solar array is stored in a battery and then distributed to the other systems. The spacecraft is designed to rotate the panels away from the Sun to avoid overheating. Wisely, MESSENGER is built with a redundant system so if any one system fails, another can take over.

The spacecraft is scheduled to enter Mercury orbit in March 2011. No doubt, the findings will amaze and excite the NASA science team during the one Earth year that it will take to open the planet's doors for investigation.

By studying this extraordinary and least explored "terrestrial" planet in our Solar System, NASA researchers expect to understand how our own Earth was formed.

For further information, visit:
Kennedy Space Center's MESSENGER Web Site
The John Hopkins University's MESSENGER Web Site
Elaine M. Marconi
NASA's John F. Kennedy Space Center