The MESSENGER spacecraft successfully completed its fourth orbit-correction maneuver 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.