The MESSENGER spacecraft has a complicated series of planetary flyby trajectory adjustments that allows it eventually to go into orbit about Mercury. A brief summary of the major mission milestones is shown below: a detailed discussion may be found on the mission design page. It is easy to find out where MESSENGER is at any time by going to the orbit calculator. The Delta Velocity in the rightmost column below clearly shows how the planetary flybys change MESSENGER's orbit far more than DSMs.

Summary of MESSENGER Orbital
Adjustments Per Major Event

EventDateRationaleO-VelocityM-VelocityΔVelocity
Earth Aug 2 2005Reduce perihelion and aphelion
33.1 km/sec--5.96 km/sec
DSM-1 Dec 12 2005Target Venus flyby 1
32.7 km/sec--0.32 km/sec
Venus 1 Oct 24 2006Reduce perihelion and aphelion
Rotate orbit Increase orbit inclination 		35.0 km/sec--5.46 km/sec
Venus 2 Jun 5 2007Reduce perihelion and aphelion
Rotate orbit Increase orbit inclination 		40.6 km/sec--6.96 km/sec
DSM-2 Oct 22 2007Target Mercury Flyby 1
40.7 km/sec--0.20 km/sec
Mercury 1 Jan 14 2008Reduce perihelion and aphelion
Rotate orbit Increase orbit inclination 		41.9 km/sec7.1 km/sec2.30 km/sec
DSM-3 Mar 17 2008Target Mercury Flyby 2
41.8 km/sec--0.07 km/sec
Mercury 2 Oct 6 2008Reduce aphelion
Rotate orbit 		43.7 km/sec6.6 km/sec2.46 km/sec
DSM-4 Dec 6 2008Target Mercury Flyby 3
43.4 km/sec--0.24 km/sec
Mercury 3 Sep 29 2009Reduce aphelion
Rotate orbit 		45.2 km/sec5.3 km/sec2.85 km/sec
DSM-5 Nov 29 2009Target Mercury Orbit Insertion
45.0 km/sec--0.18 km/sec
Mercury 4 Mar 18 2011Mercury orbit insertion
47.9 km/sec3.9 km/sec0.82 km/sec
O-Velocity = MESSENGER's average velocity relative to the Sun after the event
M-Velocity = MESSENGER's velocity relative to Mercury when closest to Mercury
ΔVelocity = effective velocity change in MESSENGER's trajectory
DSM = Deep Space Maneuver

A more detailed discussion of MESSENGER's trip through the inner solar system can be found in the frequently asked questions page and the mission design page.

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