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+% --------------------------------------
+% CHAPTER: Related Work
+% --------------------------------------
+\section{Related Work}
+\label{sec:Related Work}
+
+
+It is not possible to navigate the satellite since it has no rocket propulsion built in.
+Therefore it is also not possible to aim the camera to a certain object.
+This circumstance makes it quite hard to take pictures.
+
+So the first consideration is just
+to take any pictures and send them from the satellite down to the base stations on earth.
+But this method is not very feasible for some reasons. First we need to take a lot of pictures
+to get at least some good ones. This would need a lot of memory on the satellite, which is not 
+such a big deal, but the writing of data needs electric energy which is quite limited on the 
+satellite. The second problem is, that we also would need to transfer a big amount of data.
+Data transfer is limited through transfer rate and also through the time windows that allow
+communication with the satellite.
+
+It is quite obvious that there is a need of preselection of the pictures which shall be
+downloaded from the satellite. So we thought about a simple algorithm which could be able
+to do some evaluation if a picture wether it is 'interesting' or not. Totally black and 
+totally white pictures can be sorted out. Other pictures could show something intresting.
+The satellite travels on a n orbit which is about 318 km above the earths surface. Therefore
+the dihedral angle of earth in view is about \textbf{TOTO: check raumwinkel} which is rather 
+big compared to the one which is showing the sun. This means, that the likelyhood that a
+picture, which is not only black or white, is rather big that it shows some parts of the earth.
+
+In order to raise the likelyhood of shooting a picture at the right moment, we were searching
+for a way of how to find this right moment.
+Using the magnetic field of the earth is not an appropriate approach since the magnetic force 
+lines of the earth run approximately parallel to the earth surface (except of near the poles),
+which would not provide enough information to calculate the satellites orientation in a rather
+easy way. Furthermore, a teslameter that provides values of a usable accuracy would be to 
+expensive as well as too damageable.
+
+Finally we decided to use a 3D - light sensor. It shall help to find out the relative 
+orientation of the satellite to the earth. One photodiode on each side of a cube would provide 
+6 lines of different light intensities. When the satellite is spinning through space, the 
+photodiodes will give periodical signals, such way that three different periodes will be seen.
+The satellite will rotate around three axis, whereby each of these three periods corresponds to the rotation around one of these axes.
+
+\begin{figure}[h]  % [top, bottom, h ... where defined, p ... own page]
+\centering 
+\includegraphics[keepaspectratio,width=\hsize]
+%{drawings/Crc_Check.pdf}
+{figures/ligth_sens_1_ggb.pdf}
+\caption{Periodic output of 3 photodiodes.}
+\label{fig:lightsens1}
+\end{figure}
+
+In Figure~\ref{fig:lightsens1} we can see, that these periodes have one common periode,
+which is starting at t0. The point im time tp (here just an example) can the be taken as
+the point in time which is perfect for taking a picture. So the idea is to cumulate the
+photosensors measurements and download them to earth. After analysing and calculating a
+certain point in time tp, the satellite can be asked to take pictures at tp. If these
+pictures are not satisfying, tp can be tuned until the results fit to the expected outcome.
+