Messenger Spacecraft Approaches Mercury

The Messenger spacecraft launched into orbit from Cape Canaveral at 2 A.M. in the morning on August 3, 2004.  It first reached Venus in October 2006 for a couple of flybys and first reached Mercury in January 2008.  Today (Sept 29), it will fly past Mercury, approaching to within 142 miles of the surface.  With assistance from Mercury's gravity, the spacecraft will enter into Mercury orbit in 2011.

The spacecraft resembles the many telecommunications or instrumentation satellites in Earth orbit.  Except it has a special sunshade composed of ceramic cloth that protects it from the radiated temperatures of the planet and sun.  Because of the intense radiation so near the sun, the spacecraft has robust processors immune to upsets caused by energetic sub-atomic particles.  There is a cost for the immunity - the main processor operates at 25 MHz and the fault processor an even lower 10 MHz.

The instrumentation includes cameras, spectrometers, and neutron detectors.  It will orbit Mercury for a full year, with scientists anxious to watch how the planet reacts to varying energy from the sun.  NASA tells us that the spacecraft has completed almost three-quarters of its 4.9 billion mile journey.  This mission was part of the Discovery Program of low-cost, scientific missions.

The Discovery Program website tells us that the goals were: a) development schedule less than 36 months, b) less than $190 million for development costs, and c) total mission cost less than $299 million.  There have been eight missions launched, with only Contour (mission to fly past three comets) failing.  There are two more projects in progress.