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.