\section{CAU Requirements}
\label{sec:cau_req}
This section contains requirements from \ac{AHEPaM} on the \ac{ATHENA} spacecraft.

\subsection*{R-CAU-AHEPaM-001: Unobstructed Field of View}
\label{req:CAU-R-001}
The opening angle of AHEPaM is $\phi=20.5$\,degrees (half-angle) on both sides of the telescope (see \ac{MICD} \cite{ahepam-micd}). The solid angle described by these cones shall not be obstructed by more than 10\%.
%The field of view of both viewing directions of AHEPaM shall be only obstructed by small objects such as the spacecrafts booms in an opening angle of 20.6 degrees.

%\subsection*{R-CAU-AHEPaM-002: Purging}
%\label{req:CAU-R-001}
%AHEPaM shall be stored purged....
%Should this be really written here? Its already mentioned in R-AHEPaM-013: Storage....

\subsection*{R-CAU-AHEPaM-002: Accomodation}
\label{req:CAU-R-002}
An accommodation of \ac{AHEPaM} on a sun-obscured position on the space craft is required. 
This allows for an optimized thermal design without the additional mass and complexity that external radiators would introduce for a sun-exposed accommodation. The requirement is driven by the design temperature of the SSD detectors.


%The design temperature of \acs{AHEPaM}s particle detectors shall not exceed $0\,^\circ$C $\pm$ \acs{TBD}$\,^\circ$C.\\
%This requirement can be achieved by an adequate thermal design which bases on a mutual understanding between the prime and the instrument team regarding the detailed environmental thermal constraints. Most likely a certain combination of external radiators and op-/ non-op heating power will be required.\\


\subsection*{R-CAU-AHEPaM-003: GN2-Purge}
\label{req:CAU-R-003}
\acs{AHEPaM} will require GN2-Purge during storage.\newline
Max. allowed time without purge in a cleanroom environment shall not exceed \acs{TBD} 2\,hrs.