MESSENGER Propulsion System Flight Performance

Abstract

Study of the planet Mercury is fundamental to acquiring insight into the evolution of the inner solar system. NASA’s seventh Discovery mission, the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) mission, will orbit a spacecraft around Mercury for 1 Earth year to gather scientific data. To make this mission possible, a lightweight dual-mode propulsion system capable of delivering 2,300 m/s was designed, developed, and qualified over a period of 30 months. Following integration with the spacecraft and an extensive checkout and test period, the spacecraft was launched by a Delta-II launch vehicle on 3 August 2004. The MESSENGER propulsion system includes three pressurized propellant tanks, an auxiliary fuel tank, propellant and pressurant control components, 16 monopropellant thrusters, and a single 667-N bipropellant large-velocity adjustment (LVA) thruster. The MESSENGER propulsion system has four operational modes: a passive thermal management or cruise phase mode and three active thruster operational modes. A mode-1 maneuver fires monopropellant thrusters with fuel fed in a blow-down mode from the auxiliary tank. A mode-2 maneuver fires monopropellant thrusters with fuel from pressurized main fuel tanks. A mode-3 maneuver fires the bipropellant LVA using propellants from pressurized fuel and oxidizer tanks. In both the mode-2 and -3 maneuvers, the propulsion system’s small auxiliary tank is refilled with fuel from one of the two main fuel tanks. In the passive thermal management mode, spacecraft and thermostatically controlled heaters maintain the propellant and propulsion components within their operational pressure and temperature ranges. This paper presents the performance of the MESSENGER propulsion system since launch. To date, all elements of the propulsion system have been exercised with the successful execution of nine propulsion maneuvers including five mode-1 maneuvers, three mode-2 maneuvers, and one mode-3 maneuver. Of the five mode-1 maneuvers, two were attitude control maneuvers only: one was used to detumble the spacecraft following launch while the second was a commanded momentum dump performed in early 2006. The single mode-3 maneuver, completed in December 2005, imparted the largest spacecraft velocity change to date. The 474-s burn of the propulsion system’s bipropellant thruster adjusted the spacecraft velocity by 315.72 m/s. * Aerojet Propulsion System Chief Engineer and MPS Integrated Product Team Lead and AIAA Member. † Aerojet MPS Systems Engineering Lead and AIAA Member. ‡ JHU/APL MPS Manager and Senior AIAA Member. § JHU/APL MESSENGER Spacecraft GN&C Manager and Senior AIAA Member. American Institute of Aeronautics and Astronautics 1 Nomenclature ACS = attitude control system BTI = burn time integration CMD = commanded momentum dump !V = delta-velocity DSM = deep space maneuver GN&C = guidance, navigation, and control JHU/APL = The Johns Hopkins University Applied Physics Laboratory LVA = large velocity adjustment MESSENGER = MErcury Surface, Space ENvironment, GEochemistry, and Ranging MPS = MESSENGER propulsion system MR = mixture ratio N2H4 = hydrazine N2O4 = nitrogen tetroxide PAUX-A = pressure, auxiliary tank side a PAUX-B = pressure, auxiliary tank side b PFF = pressure, fuel feed PVT = pressure, volume, temperature TVC = thrust vector control