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MESSENGER Mission News
April 20, 2012
http://messenger.jhuapl.edu/

MESSENGER Settles into Eight-Hour Orbit Around Mercury, Poised for New Discoveries
MESSENGER mission controllers at the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Md., conducted the second of two maneuvers required to reduce the spacecraft's orbital period about Mercury. The first maneuver, completed on Monday, shortened the orbital period from 11.6 to 9.1 hours and consumed the remaining oxidizer, one of two propellants that fuel the higher-efficiency large thruster. With today's maneuver, accomplished with the spacecraft's four medium-sized thrusters, MESSENGER is now in the 8-hour orbit from which it will operate for the next year.

MESSENGER was 133 million kilometers (83 million miles) from Earth when the 4-minute maneuver began at 7:05 p.m. EDT. Mission controllers at APL verified the start of the maneuver 7 minutes and 23 seconds later, after the first signals indicating spacecraft thruster activity reached NASA's Deep Space Network tracking station in Canberra, Australia.

The shorter orbit will allow MESSENGER's science team to address new questions about Mercury's composition, geological evolution, and environment that were raised by discoveries made during the first year of orbital operations.

"For instance," says APL's Patrick Peplowski, "during the first year of orbital operations, MESSENGER's Gamma-Ray Spectrometer and X-Ray Spectrometer provided the first measurements of the abundances of many elements on Mercury's surface, including magnesium, sulfur, calcium, and potassium. The eight-hour orbit gives us more observing time at low altitudes, which will permit measurements of variations in surface composition on shorter spatial scales. Such information will give us new insight into the chemical and geological processes by which Mercury's crust was formed."

An animation of the maneuvers that guided MESSENGER into its new orbit is available online at http://messenger.jhuapl.edu/the_mission/movies/OCM7and8_transition_to_8hour_orbit.mp4.

MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) is a NASA-sponsored scientific investigation of the planet Mercury and the first space mission designed to orbit the planet closest to the Sun. The MESSENGER spacecraft launched on August 3, 2004, and entered orbit about Mercury on March 18, 2011 (UTC), to begin its primary mission – a yearlong study of its target planet. MESSENGER's extended mission began on March 18, 2012. Dr. Sean C. Solomon, of the Carnegie Institution of Washington, leads the mission as Principal Investigator. The Johns Hopkins University Applied Physics Laboratory built and operates the MESSENGER spacecraft and manages this Discovery-class mission for NASA.

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