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Dawn's changing orbit

Dawn's changing orbit
Dawn's changing orbit This shows how Dawn is changing its orbit in order to accomplish the opposition surge measurements. The perspective here is close to that of the figure from last month but shifted a little away from the north pole so you don’t see the orbit exactly along the edge. (As noted above, Dawn’s orbit has rotated slightly and is now more vertical than shown in January.) With the sun far to the left, the spacecraft starts in the vertical green orbit (known as extended mission orbit 3, or XMO3). When it is just to the left of Ceres, it is over the south pole, farther from you than the plane of the figure and traveling toward the bottom. Then the orbit takes it through your monitor, and it is closer to you as it skirts to the right of Ceres, over the north pole. The blue (which we’ll get to in a moment) obscures the right half of that green ellipse. The horizontal green orbit is the destination, and the plus sign shows where Dawn will be when it conducts the new observations. At that point, it will be on the line from Occator Crater to the sun. To maneuver to that new orbit, Dawn will follow the blue trajectory, thrusting with its ion engine where the trajectory is solid and coasting where it is dashed. As explained in the text in more detail, the spacecraft uses the first two thrusting segments (the solid vertical sections) to raise its orbital altitude. After the second one, Dawn’s orbit carries it to greater and greater heights. As it flies the arc at the top of the picture, it is receding from you, on the other side of the plane of this diagram, beyond your computer screen. It is not yet at its highest altitude, although it appears that way here because of the foreshortening of a two-dimensional figure. It is still ascending. When it does reach its highest altitude, it executes the third thrusting segment to accomplish the turn. Then with one more short thrust period (on the left of the figure), it reaches the desired new orbit. Dawn is flying north (and approaching you) when it reaches the plus sign. The two figures below show the same trajectory from different perspectives. NASA / JPL-Caltech