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→Determination of Light/Eclipse region
==Determination of Light/Eclipse region ==
Here we are defining the dark region as umbra and rest is taken as the light region. We wish to calculate how long will the satellite be in Umbra. You can see from the figure that umbra region is formed by simply drawing the common tangents of earth and sun.
[[File:UmbraUmbra3.png|framethumb|center|1000px|Definition of the eclipse region. Image reproduced from [https://en.wikipedia.org/wiki/Umbra,_penumbra_and_antumbra here]]]
Let’s define first some of the parameters first.<br \>
Rs = Radius of Sun. <br \>
∅ = angle between sun vector and the vector formed be apex of umbra and satellite.<br \>
ru can be calculated by forming similar triangle.
The region of umbra would be when it follows two conditions:[[File:Equation76.png|frame|center]][[File:Umbra2.png|frame|center|Obtaining condition for satellite to be in umbra region]]
The knowledge of eclipse region is important from the power subsystem point of view. In this region there will no solar panel in the sunlight so the satellite functionalities have to depend solely on batteries. Also, in this region the sun vector can’t be calculated using the sun sensor. Any output coming on the sun sensor would be noise and we should not calculate sun vector using sun sensor in this region. <br \>
