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At 6:30 a.m. (EST) today NASA's Mercury-bound MESSENGER spacecraft successfully fired its large bipropellant thruster for the first time since launch, completing the first of several critical deep space maneuvers that will help the spacecraft reach Mercury orbit.

The 524-second burn changed MESSENGER's velocity by about 316 meters per second (706 miles per hour), putting the solar-powered spacecraft on track for a 3,140-kilometer (1,951-mile) altitude flyby of Venus on October 24, 2006.

"This is a major accomplishment for the mission," said MESSENGER Mission Operations Manager Mark Holdridge, of The ÃØÃÜÖ±²¥ University Applied Physics Laboratory (APL), Laurel, Md. "That bi-prop engine is the last major component of the spacecraft that we haven't used in space and one we'll need at least five more times to orbit Mercury. The successful performance of this main engine proves that the spacecraft is up to the task."

Until today, only 16 of the MESSENGER spacecraft's 17 thrusters had been used in five small trajectory correction maneuvers. This latest maneuver, known as Deep Space Maneuver 1 (DSM 1), is the first to rely solely on the largest, most efficient thruster.

"Maneuvers performed with the largest thruster use about 30% less propellant, including both fuel and oxidizer, than the other thrusters, which use fuel only," explained APL's Jim McAdams, the mission design team leader. "About 18 percent of MESSENGER's propellant was used to complete DSM 1. Of all planned course-correction maneuvers for MESSENGER, DSM 1 is second only to the March 18, 2011, Mercury orbit insertion maneuver in velocity change."

MESSENGER controllers monitored the engine burn from the Mission Operations Center at APL. This change in the spacecraft's speed is about equal to the speed of a jet as it reaches the sound barrier.

"Credit for the completion of this important milestone belongs to the entire MESSENGER team," noted Dave Grant, MESSENGER program manager at APL. "We are very fortunate to have a highly skilled group of engineers, scientists and operations experts leading our journey to Mercury. Their untiring diligence in preparing for this maneuver has been rewarded with a great success."

Looking Forward

For the next 10 months, mission controllers at APL will perform routine housekeeping tasks and fine-tune instruments to prepare MESSENGER for the Venus flyby, the first of two Venus flybys that will use the pull of the planet's gravity to guide MESSENGER toward Mercury's orbit. This maneuver will occur near the beginning of an approximately two-week period when the apparent spacecraft position is too close to the Sun to allow communications with the spacecraft. So the team will spend the next several months getting the spacecraft ready to fly safely for an extended period of time without ground contact."

During a 7.9-billion kilometer (4.9-billion mile) journey that includes 15 trips around the Sun, MESSENGER will fly past Venus twice and Mercury three times before easing into orbit around its target planet. As with the October 2006 event, the second Venus flyby in June 2007 will be a gravity-assist maneuver. The Mercury flybys in January 2008, October 2008 and September 2009 will help MESSENGER match the planet's speed and location for an orbit insertion maneuver in March 2011 that starts the first-ever study of Mercury from orbit.

With just over 20% of the flight time completed between launch and Mercury orbit insertion, MESSENGER has traveled more than 1.3 billion kilometers (0.81 billion miles) around the Sun. Since its August 2004 launch, the spacecraft has completed 1.5 orbits of the Sun, including a successful flyby of Earth in August 2005. Follow the spacecraft on its path to Mercury on the "Where Is MESSENGER?" Web site.

MESSENGER, short for MErcury Surface, Space ENvironment, GEochemistry, and Ranging, is the seventh mission in NASA's Discovery Program of lower cost, scientifically focused exploration projects. Dr. Sean C. Solomon, of the Carnegie Institution of Washington, leads the mission as principal investigator. APL manages the mission for NASA, built MESSENGER and operates the spacecraft.

For more information, visit the MESSENGER Web site at .