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Upon Reflection...

MESSENGER will rely on solar panels for power during its long voyage to and orbit around Mercury. The custom-developed panels, installed on the spacecraft June 24-25, were the next-to-last major components to be attached before the spacecraft is moved to the Delta II launch vehicle this month.

(Click here for large and small time-lapse movies of the installation.)

To run MESSENGER's systems and charge its 23-ampere-hour nickel hydrogen battery, the panels, each about 1.5 meters (5 feet) by 1.65 meters (5.5 feet), will support between 385-485 watts of spacecraft load power during the cruise to Mercury and 640 watts during the science orbit. The panels could produce more than two kilowatts of power near Mercury, but to prevent stress on MESSENGER's electronics, onboard power processors take in only what the spacecraft actually needs.

The panels are 67 percent mirrors (called optical solar reflectors) and 33 percent triple-junction solar cells, which convert 28 percent of the sunlight hitting them into electricity. Each panel has two rows of mirrors for every row of cells; a total of 648 cells and 1,296 mirrors per panel. The small mirrors reflect the Sun's energy and keep the panel cooler. The panels also rotate, so MESSENGER's flight computer will tilt the panels away from the Sun, positioning them to get the required power while maintaining a normal surface operating temperature of about 150 degrees Celsius, or 302 degrees Fahrenheit.

Major events before moving the spacecraft include fueling - the team is loading the hydrazine fuel and nitrogen tetroxide oxidizer this week - and final installation of the sunshade.

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Last updated: July 2, 2004

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