ENGINEERING MESSENGER'S GRAND FINALE AT MERCURY - THE LOW-ALTITUDE HOVER CAMPAIGN

Having completed its primary and first extended missions by mid-March 2013, the MESSENGER spacecraft in orbit about Mercury began a 2.1-year final mission extension that brought substantial opportunity for low-altitude science, along with many technical challenges successfully overcome by the flight operations and science teams. After four orbit-correction maneuvers (OCMs) between June 2014 and January 2015 targeted minimum altitudes near 25 km and 15 km, seven OCMs in March and April 2015 maintained minimum altitude between 5 km and 37 km. Engineering challenges at mission end included the efficient utilization of accessible propellant and helium gas pressurant to delay Mercury impact.