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The turnover fixture allows engineers ready
access to any part of the spacecraft during assembly. Imagine
an auto repair shop that could rotate a car in any direction -
that's the job of the turnover fixture! Currently visible are
fill and drain valves for the propulsion system (marked with "Valves").
They perform a key function, ensuring that the engine gets just
the right mix of fuel and oxidizer at the right pressure during
thruster burns. Helium is simply used to help push the fuel and
oxidizer through the system to the engines.
The holes in the structure just below the valves will allow heat-conducting
devices (called "thermal vias") to pass from inside
the structure out to radiator panels, ensuring that MESSENGER's
critical components do not overheat. Soon these components will
be hidden behind hardware and thermal protection blankets.
Last updated: April 29,
2003
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