Thursday is the big day for the MESSENGER team. At 8:45 p.m. EDT, the spacecraft will begin to execute a 15 minute maneuver, inserting it finally into Mercury's orbit after six and a half years in space. If successful, MESSENGER will be the first spacecraft to orbit the planet, and only the second mission to visit Mercury after the 1975 Mariner 10 flyby.
For the last week, MESSENGER has been executing a last cruise command; when it finishes sometime today, it will begin the command sequence that will end with the orbit-insertion burn. In early February the team began configuring heaters to prepare the propellant, 'similar to pre-heating the diesel engine of a truck or car prior to starting in cold weather to allow ignition and prevent damage to the engine.'
The spacecraft has been using gravity assist maneuvers to slow it down, counteracting the pull of the sun. During its tour of the inner solar system, MESSENGER has performed flybys of the Earth (2005) and Venus (2006 and 2007) and three flybys of Mercury (two in 2008, one in 2009)
During its year orbiting the rocky planet, it will largely study the chemical and geological make-up and its magnetic field. MESSENGER has nine scientific instruments on board, which will map the surface through images and measuring the height of landforms, determine the compositios of surface materials and the planet's thin atmosphere, measure the strength, position, and amount of charged particles in the magnetosphere, and finally, study Mercury's gravity and the state of the planet's core.
Even before orbital insertion, MESSENGER has been making fascinating discoveries about the planet, including during its January 2008 flyby when it measured surprising amounts of water in the atmosphere and evidence of prior volcanic activity. Last month the team revealed a "family portrait' of the solar system constructed from images taken on its travels.
NASA's already planned a press conference for May 10 to discuss MESSENGER's early findings.
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