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of the innermost planet
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MESSENGER's Heartbeat

MESSENGER is now ensconced in the thermal vacuum chamber at NASA Goddard Space Flight Center. There are no windows in the chamber so our only way of observing and communicating with the spacecraft is through specialized test equipment, seen in this week's Webcam image.

The top panel (with red and green numbers) is the Power Monitor Control Unit that gives continuous information regarding the spacecraft's power system. These days MESSENGER gets its power from the flight spare battery, supported by a simulator that duplicates the voltage and current MESSENGER will get from its solar panels in space.

Just below the power monitor is an oscilloscope, which displays the transmission rate of commands sent to and data coming back from the spacecraft. Below that, with the green and red lights, is the Spacecraft Signal Distribution Unit, which distributes data between MESSENGER and various pieces of ground equipment supporting the spacecraft.

The lowest panel is the PAF/Propulsion Monitor Unit, which monitors pressure in the propellant tanks (marked by five green numbers across the top) and signals from the Payload Attach Fitting, a metal ring that will connect MESSENGER to its launch vehicle.

 The MESSENGER team constantly monitors these vital signs to check that the spacecraft is healthy and operating correctly. The team will use this mode of operating right up until liftoff -- after that, operators will communicate with MESSENGER through NASA's Deep Space Network of antennas.

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Last updated: February 6, 2004

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