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There is also a cool constraint allowing you to limit it to times above a certain elevation angle:
From STK(Introduction to STK (agi.com)): "You know that when you are on the ground trying to see something in space the lower you look along the horizon the more atmosphere you have to look through and the better the chance that something will be in the way. To help avoid the elevation angle problem, STK allows you to put an elevation angle constraint on a ground-based location. A good typical minimum elevation is 6-8 degrees, but it can be more depending on the area, the surrounding terrain, and even buildings."
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