C
CalliArcale
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Yesterday, overshadowed by talk of STS-114, the spacecraft MESSENGER made a successful gravity-assist flyby of the Earth. It has been taking many pictures of Earth, which the team is going to assemble into a color movie depicting MESSENGER's final departure from its birthplace.<br /><br />Gravity-assists are often used to boost a spacecraft's orbit, such as Galileo or Cassini, to get it to the outer solar system. In this case, however, the technique is being used to gradually lower MESSENGER's heliocentric orbit so that it can approach Mercury in 2011 (after three gravity-assist flybys of Mercury) with a favorable relative motion so it can enter orbit around Mercury. This is the first of six planned gravity-assists for MESSENGER, and the only one involving Earth. It lowered MESSENGER's perihelion so that it can encounter Venus in the fall of 2006 for its next gravity-assist. <div class="Discussion_UserSignature"> <p> </p><p><font color="#666699"><em>"People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff."</em> -- The Tenth Doctor, "Blink"</font></p> </div>