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MESSENGER Mission News
October 24, 2011

Fourth Orbit Adjustment Stretches MESSENGER's Orbit around Mercury
The MESSENGER spacecraft successfully completed its fourth orbit-correction maneuver today to increase the period of the spacecraft's orbit around the innermost planet from 11 hours 46 minutes to a precise 12 hours.

MESSENGER was 198 million kilometers (123 million miles) from Earth when the 159-second maneuver began at 6:12 p.m. EDT. Mission controllers at The Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Md., verified the start of the maneuver about 11 minutes, 1 second later, when the first signals indicating spacecraft thruster activity reached NASA's Deep Space Network tracking station outside Goldstone, Calif.

This is the fourth of five maneuvers planned for the primary orbital phase of the mission to keep orbital parameters within desired ranges for optimal scientific observations. MESSENGER's orbital velocity was changed by a total of 4.2 meters per second (9.4 miles per hour) to make the corrections essential for continuing the planned measurement campaigns.

Most of the instruments were placed in a passive state during the burn, but the instruments were reconfigured at 7:05 p.m. EDT to resume scientific observations of the planet.

MESSENGER Mission Systems Engineer Eric Finnegan, of APL, said the engine burn was executed as planned. "The team was well-prepared for the maneuver, and MESSENGER is right where it needs to be to continue revealing new details about Mercury," he said.

The next orbit-correction maneuver is scheduled for December 5.

MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) is a NASA-sponsored scientific investigation of the planet Mercury and the first space mission designed to orbit the planet closest to the Sun. The MESSENGER spacecraft launched on August 3, 2004, and entered orbit about Mercury on March 17, 2011 (March 18, 2011 UTC), to begin a yearlong study of its target planet. Dr. Sean C. Solomon, of the Carnegie Institution of Washington, leads the mission as Principal Investigator. The Johns Hopkins University Applied Physics Laboratory built and operates the MESSENGER spacecraft and manages this Discovery-class mission for NASA.

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