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Trajectory Correction Maneuver

This view of MESSENGER shows the orientation at the start of orbit correction maneuver 12 (OCM-12). The blue rectangles represent the front (sunlit) sides of the solar arrays. The large white feature is the spacecraft's sunshade, which points toward the Sun when the spacecraft is near or closer than Earth's distance from the Sun. Colored arrows indicate the directions of Earth, the Sun, the spacecraft's velocity with respect to Mercury, and the course-correction velocity change (delta-V or ΔV). The "spacecraft +x axis" label identifies an axis direction in the local spacecraft body-fixed coordinate system. Above and to the left of the MESSENGER spacecraft is a portion of Mercury’s southern hemisphere, with latitude lines at 15° increments and longitude lines at 30° increments. The curved purple line depicts MESSENGER’s orbit about Mercury.

The twelfth OCM since Mercury orbit insertion, OCM-12 raised the spacecraft’s minimum altitude above Mercury from 25.7 kilometers (16.0 miles) to 104.7 kilometers (65.3 miles). During OCM-12, a ΔV of 9.67 meters per second (21.62 miles per hour) was imparted by the four largest monopropellant thrusters, with a small contribution from eight of the 12 smallest monopropellant thrusters. Implemented when the spacecraft is at the farthest point in its orbit from Mercury, OCM-12 increased the spacecraft’s speed relative to Mercury. OCM-12 also added about 3.7 minutes to the spacecraft’s 8h 12.9m orbit period. During OCM-12, the sunshade will protect heat-sensitive parts from direct sunlight.  OCM-12 will be the first maneuver during the mission to intentionally use both fuel and gaseous helium pressurant to impart the desired ΔV. The propellant was drawn from both main fuel tanks, a small auxiliary fuel tank, and the gaseous helium was drawn from the main fuel tanks.

Mission controllers at The Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland, expect to verify the start of the maneuver about 6.6 minutes after the start of OCM-12, shortly after 1:34 pm Eastern Standard Time on January 21, 2015, when the first signals indicating spacecraft thruster activity reached NASA's Deep Space Network (DSN) tracking station in Goldstone, California. The 1.8-minute-long maneuver began at about 1:27 pm Eastern Standard Time.

Click here for detailed information on all of MESSENGER’s propulsive activity from launch to the present.



the orientation soon after the start of orbit correction maneuver 12 (OCM-12)
Click on the image above for a larger version

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