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Emily LakdawallaDecember 5, 2008

MESSENGER steers for next September's Mercury flyby

The MESSENGER team issued a statement yesterday to the effect that the Mercury-bound spacecraft has just performed the first part of a two-part Deep Space Maneuver to position the spacecraft on course for a third flyby of the innermost planet. MESSENGER fired its main engines for 4.5 minutes, increasing its speed by 219 meters per second. Take a moment to think about something traveling 200 meters, two hundred-meter dashes, in one second. That's just the change in MESSENGER's velocity; it currently travels at about 31 kilometers per second in its orbit around the Sun. Stuff in space moves fast.

The second part of the maneuver, a smaller one, will be performed on December 8. Together, the two maneuvers will set MESSENGER up to fly past Mercury for one final flyby and gravity assist, next September. After that, it'll still have to orbit the Sun several more times before meeting Mercury again for its orbit insertion on March 2011. Matching Mercury's tiny orbit around the Sun is really hard to do.

MESSENGER's journey to Mercury

NASA / JHUAPL / Carnegie Institution of Washington

MESSENGER's journey to Mercury
MESSENGER's trip to Mercury requires a total of six gravity assists (one of Earth, two of Venus, and three of Mercury) to permit it to enter orbit at the small planet close to the Sun. This animation shows that journey and the motions of Venus and Mercury using a frame of reference that holds the Earth-Sun line fixed. The maneuver I'm talking about in this blog entry is the one labeled "DSM-4" on the orbit diagram and timeline.

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Emily Lakdawalla

Senior Editor and Planetary Evangelist for The Planetary Society
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