The MESSENGER SystemThe MESSENGER (MErcury Surface, Space ENvironment GEochemistry, and Ranging) propulsion system was built for and delivered to JHU/APL by Aerojet in 2003. MESSENGER is the seventh of a series of NASA Discovery Programs—all of which have included Aerojet propulsion.

 In March 2011 NASA’s MESSENGER spacecraft successfully achieved the first-ever orbit around the planet Mercury using Aerojet’s propulsion system. MESSENGER was launched aboard a Delta II on Aug. 3, 2004, and traveled approximately five billion miles and flown by Earth, Venus and Mercury. The successful Mercury orbit insertion (MOI) maneuver begins a year-long study phase of the closest planet to the Sun.

To slow the spacecraft down sufficiently to be ―captured by Mercury, MESSENGER’s 150 lbf bipropellant engine fired for about 15 minutes. This burn slowed the spacecraft nearly 2,000 miles per hour and consumed nearly a third of the propellant that the spacecraft carried at launch. Less than 10 percent of the usable propellant at the start of the mission remained after completing the orbit insertion maneuver. The supply was enough to finish an orbit adjustment in April, 2012.

After the burn, the spacecraft turned toward Earth and resumed normal operations. Data will be collected by Deep Space Network antennas and transferred for analysis to the Mission Operations Center at the Johns Hopkins University Applied Physics Laboratory (JHU/APL) in Laurel, Md. The maneuver — completed at a time that MESSENGER is more than 96 million miles from Earth — places the probe into an orbit that brings it as close as 124 miles to Mercury’s surface.

The MESSENGER propulsion system has an unusually high thrust-to-weight ratio enabled by a ―dual mode system (bipropellant main engine; monopropellant thrusters) and mission-enabling thin-walled propellant tanks as well as other innovative system features. Operating on hydrazine and nitrogen tetroxide, the 150 lbf bipropellant engine is accompanied by monopropellant hydrazine thrusters that will provide attitude control and wheel de-saturation as the spacecraft completes its mission.