Science Opportunity Analyzer Images
By Steve Joy
The Dawn project members use an analysis tool called Science Opportunity Analyzer (SOA) to plan observations made by the spacecraft instruments.
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Image credit: NASA/JPL |
SOA allows the Dawn Science Team to test different image data acquisition strategies and evaluate how well they might accomplish the science objectives at the asteroids. This picture shows one example of how images might be acquired at Vesta during the High Altitude Mapping Orbit (HAMO). The figure shows the current Vesta shape model overlaid with a false texture maps (craters are not real, overall shape is). The Dawn ground track on the Vesta surface is colored green, the terminator is shown in white, sub-spacecraft point is the black square, and the sub-solar point is the red triangle. The Framing Camera surface footprints are shown in purple while the yellow squares show the "sky" footprints (i.e. where on the sky map the footprints would have fallen if Vesta were not in the way). Note that there are gaps in surface coverage between the images in the first and second orbits. These gaps would be filled in by data acquired in later orbits.
Dawn will be in a polar orbit around Vesta moving purely north to south. Why then do the lines marking the ground track appear inclined to the pole? The reason is the very rapid spin rate of Vesta. If Dawn was placed in a polar orbit around Mars, the ground track would very be nearly parallel to the meridians (lines of longitude). However, Vesta is spinning much more rapidly than Mars (or the Earth). This rapid spin motion of the surface creates a ground track on Vesta that is diagonal - as though the orbit plane was inclined by about 45 degrees.
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