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MESSENGER's installed scientific instruments
are bathed in a steady flow of extremely pure nitrogen, which
keeps both dust and moisture away from these sensitive components.
The silver box in the lower right of this week's image provides
this constant supply of nitrogen gas, known as a "purge."
(The engineers to the left of the box are checking MESSENGER's
Power Distribution Unit.)
The nitrogen gas is obtained by boiling a
large tank of liquid nitrogen; this keeps contaminants out of
the gas and, ultimately, away from the spacecraft. Any contaminants
that may have been in the liquid nitrogen remain (frozen or liquefied)
in the tank, so the gaseous form is extremely clean.
The yellow light on top of the supply box
would flash automatically in case of a flow or pressure problem.
MESSENGER will keep receiving its nitrogen purge right up to the
moment of ignition on the Delta II launch vehicle.
Last updated: August 19,
2003
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