About MESSENGER
NASA's MESSENGER - set to become the first spacecraft to orbit the planet Mercury - was launched on August 3, 2004 aboard a Boeing Delta II rocket from Cape Canaveral. MESSENGER, short for MErcury Surface, Space ENvironment, Geochemistry, and Ranging, is the seventh mission in NASA's Discovery Program of lower cost, scientifically focused exploration projects. Johns Hopkins University Applied Physics Laboratory (APL) manages the mission for NASA's Office of Space Science, built the spacecraft and will operate MESSENGER during flight. MESSENGER is the 61st spacecraft built at APL.
The 1,100-kilogram spacecraft carries a package of seven science instruments to determine Mercury's composition; image its surface globally and in color; map its magnetic field and measure the properties of its core; explore the mysterious polar deposits to learn whether ice lurks in permanently shadowed regions; and characterize Mercury's tenuous atmosphere and Earth-like magnetosphere.
During a 4.9-billion mile (7.9-billion kilometer) journey that includes 15 trips around the sun, MESSENGER will fly past Earth once, Venus twice and Mercury three times before easing into orbit around its target planet. The Earth flyby, in August 2005, and the Venus flybys, in October 2006 and June 2007, will use the pull of the planets' gravity to guide MESSENGER toward Mercury's orbit. The Mercury flybys in January 2008, October 2008 and September 2009 help MESSENGER match the planet's speed and location for an orbit insertion maneuver in March 2011. The flybys also allow the spacecraft to gather data critical to planning a yearlong orbit phase.
The "brains" of the spacecraft are redundant integrated electronics modules (IEMs) that house two processors each -- a 25-megahertz (MHz) main processor and a 10-MHz fault-protection processor.
Attitude determination -- knowing where the spacecraft is and in which direction it's facing -- is performed using star-tracking cameras and an Inertial Measurement Unit containing four gyroscopes and four accelerometers, with six Digital Solar Sensors as a backup. Attitude control is mostly accomplished using four reaction wheels inside the spacecraft and, when necessary, MESSENGER's small thrusters. MESSENGER will receive commands and send data primarily through its circularly polarized X-band phased-array antennas.
A key MESSENGER design element deals with the intense heat at Mercury. The Sun is up to 11 times brighter than we see on Earth and surface temperatures can reach 450 degrees Celsius (about 840 degrees Fahrenheit), but MESSENGER will operate at room temperature behind a sunshade made of heat-resistant ceramic cloth.
Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington/Northwestern University