A NASA Discovery mission to conduct the first orbital study
of the innermost planet
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A Matter of Thrust

The MESSENGER spacecraft has 16 small thrusters (arrows "1" and "5") in addition to the main engine (arrow marked "M"). Thrusters marked "1" indicate 1 pound of thrust, while those marked "5" develop 5 pounds of thrust. At launch the spacecraft at launch will carry about 611 kilograms (1,347 pounds) of fuel, about 90% of which will be used during main engine burns.

However, the small thrusters play several important roles. The 5-pound thrusters help hold the spacecraft steady during main engine burns and are also used alone for small course corrections. The smaller, 1-pound thrusters are used in conjunction with the gyroscopes to maintain the spacecraft's orientation during normal cruise and orbital operations. In this image, the small thrusters are temporarily covered (red caps) for protection during assembly - though the main engine bell is visible through its temporary four-pronged protective structure.

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Last updated: April 22, 2003

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