Trajectory design and maneuver strategy for the MESSENGER mission to MErcury

Destined to become the first spacecraft to orbit the planet Mercury, the MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) spacecraft was launched on August 3, 2004. The 6.6-year ballistic trajectory to Mercury will utilize six gravity-assist flybys of Earth (one), Venus (two), and Mercury (three). Having completed three trajectory correction maneuvers (TCMs) by mid-November 2004, many more maneuvers will be necessary during the journey to Mercury and the subsequent one-year-duration Mercury orbit phase. The spacecraft's design and operational capability will enable real-time monitoring of every TCM. A complex mission plan will provide multiple opportunities to obtain observational data that will help fulfill the mission's scientific objectives. Soon after entering Mercury orbit in mid-March 2011, the initial primary science orbit will have 80 degrees orbit inclination relative to Mercury's equator, 200-km periapsis altitude, 60 degrees N sub-spacecraft periapsis latitude, and a 12-hour orbit period. With science goals requiring infrequent orbit-phase trajectory adjustments, pairs of orbit correction maneuvers occur at about the same time every Mercury year, or every 88 days. For the first time, the spacecraft's orbit design at Mercury accounts for the best available Mercury gravity model, small solar pressure perturbations due to changes in the solar array tilt angle, and an improved strategy for performing orbit correction maneuvers.