NASA's MESSENGER spacecraft, headed toward the first study ofMercury from orbit, has swung by Earth for a gravity assist thatpropelled it deeper into the inner solar system.
Mission operators at the Johns Hopkins University Applied PhysicsLaboratory (APL) in Laurel, Md, said MESSENGER's systems performedflawlessly. The spacecraft swooped around Earth, coming to a closestapproach point of approximately 1,458 miles (2,347 kilometers) overcentral Mongolia at 3:13 p.m. EDT on August 2.
The spacecraft used the tug of Earth's gravity to significantlychange its trajectory. Its average orbit distance is nearly 18 millionmiles closer to the sun. The maneuver sent it toward Venus for anothergravity-assist flyby next year.
Launched Aug. 3, 2004, from Cape Canaveral Air Force Station, Fla.,the solar-powered spacecraft is approximately 581 million miles (930million kilometers) into a 4.9 billion mile (7.9 billion kilometer)voyage that includes 14 more loops around the sun. MESSENGER will flypast Venus twice and Mercury three times before moving into orbit.
The Venus flybys in October 2006 and June 2007 will use the planet'sgravity to guide MESSENGER toward Mercury's orbit. The Mercury flybysin January 2008, October 2008 and September 2009 will help MESSENGERmatch the planet's speed. These events will set up the maneuver inMarch 2011 that starts a year-long science orbit around Mercury.
"This Earth flyby is the first of a number of critical missionmilestones during MESSENGER's circuitous journey toward Mercury orbitinsertion," said Sean C. Solomon, the mission's principal investigatorfrom the Carnegie Institution of Washington. "Not only did it help thespacecraft sharpen its aim toward our next maneuver, it presented aspecial opportunity to calibrate several of our science instruments."
MESSENGER's main camera snapped several approach shots of Earth andthe moon during the past week. Today the camera is taking a series ofcolor images, beginning with South America and continuing for one fullEarth rotation. Science team members will string the images into avideo documenting MESSENGER's departure.
On Earth approach, the craft's atmospheric and surface compositionspectrometer made several scans of the moon in conjunction with thecamera observations. In addition, the particle and magnetic fieldinstruments spent several hours measuring Earth's magnetosphere. Thescience team will download the data and images through NASA's DeepSpace Network over the next several weeks, continuing assessment of theinstruments' performance.
MESSENGER will conduct the first orbital study of Mercury, the leastexplored of the terrestrial planets that include Venus, Earth and Mars.During one Earth year (four Mercury years), MESSENGER will provide thefirst images of the entire planet. It will collect detailed informationabout the composition and structure of Mercury's crust, its geologichistory, nature of its atmosphere and magnetosphere, makeup of its coreand polar materials.
MESSENGER, short for MErcury Surface, Space ENvironment,GEochemistry, and Ranging, is the seventh mission in NASA's DiscoveryProgram of lower-cost scientifically focused exploration projects. APLdesigned, built and operates the spacecraft and manages the mission forNASA's Science Mission Directorate.
For information about the spacecraft and mission on the Web, visit:
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