MESSENGER (an acronym of MErcury Surface, Space ENvironment, GEochemistry, and Ranging) is a robotic NASA spacecraft orbiting the planet Mercury, the first spacecraft ever to do so. The 1,069 pound spacecraft was launched aboard a Delta II rocket on August 3, 2004 to study Mercury's chemical composition, geology, and magnetic field. MESSENGER became the second mission after 1975's Mariner 10 to reach Mercury when it made a flyby in January 2008, followed by a second flyby in October 2008,and a third flyby in September 2009. Then MESSENGER entered orbit around Mercury on March 18, 2011. The MESSENGER mission is now expected to end in 2015 after the spacecraft uses the last of its maneuvering propellant and its orbit decays resulting in the spacecraft crashing into the surface of Mercury.