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A Clean Purge

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.

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Last updated: August 19, 2003

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