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of the innermost planet
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Spin Cycle

This week's image captures MESSENGER in four stages of a recent spin balance test. The test is critical to MESSENGER's early operations; the third (and final) stage of MESSENGER's Delta II launch vehicle is spin stabilized, so both spacecraft and rocket must be "balanced" to fly straight.

In this test, conducted Jan. 4, engineers measured MESSENGER’s center of gravity by spinning it to 25 rpm on its “z” axis – imagine a straight line running from top to bottom through the middle of the spacecraft. The testing machines then showed the team where to place weights on the spacecraft to balance it on this middle line, just like balancing a wheel on a car. Engineers conducted spin balance tests with MESSENGER’s tanks both empty and filled with water (to simulate fuel).

The top two frames in the image show the reflective front surfaces of the solar panels – at upper right the panel reflects the NASA logo on the wall of Goddard Space Flight Center’s acoustic testing chamber. The bottom left frame shows the back of the spacecraft with the Magnetometer boom in its stowed position, while the bottom right frame offers a full view of MESSENGER’s sunshade. Click here for a large or small movie of the test.

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Last updated: January 15, 2004

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