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Trajectory Correction Maneuver

This view of MESSENGER shows the orientation at the start of orbit correction maneuver 13 (OCM-13). 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. 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 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 thirteenth OCM since Mercury orbit insertion, OCM-13 raised the spacecraft’s minimum altitude above Mercury from 11.6 kilometers (7.2 miles) to 34.5 kilometers (21.4 miles). During OCM-13, a ΔV of 3.07 meters per second (6.87 miles per hour) was imparted by the four largest monopropellant thrusters, with a small contribution from four of the 12 smallest monopropellant thrusters. Implemented when the spacecraft was near the farthest point in its orbit from Mercury, OCM-13 increased the spacecraft’s speed relative to Mercury. OCM-13 also added about 1.1 minutes to the spacecraft’s 8h 16.5m orbit period. During OCM-13, the sunshade protected heat-sensitive parts from direct sunlight. OCM-13 used propellant from a small auxiliary fuel tank. The first OCM in the MESSENGER low-altitude hover campaign, also called the extension of the Second Extended Mission, OCM-13 was the first OCM for which the velocity change direction is offset from the spacecraft’s orbit plane.

Mission controllers at The Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland, verified the start of the maneuver about 10.3 minutes after the start of OCM-13, at 11:10 am Eastern Daylight Time on March 18, 2015, when the first signals indicating spacecraft thruster activity reached NASA's Deep Space Network (DSN) tracking station in Goldstone, California. The 33-second-long maneuver begin at about 11:00 am Eastern Daylight 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 13 (OCM-13)
Click on the image above for a larger version

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