\chapter{Introduction}\label{introduction}

The SACAMOS software \cite{sacamos} enables the creation of Spice cable models from the description/ characterisation of cables and bundles of cables together with information required to specify a particular modelling scenario (for example the specification of incident field excitation or transfer impedance coupling model). 

Example models of cables used in spacecraft have been included with the software in a library of cable models referred to as 'MOD'.
MOD also includes example Spice cable bundle models which make use of these cable models.

The cable models in the library are based on the ESCC specification documents (references \cite{3901/019} to \cite{3401/071}) and include twisted pair power lines, shielded twisted pair low frequency signal lines and RS422 cables plus SpaceWire cable assemblies, including connectors.
This document describes the development of the library of cable models for spacecraft cables from these specifications and additional information where required i.e. how the information required in the cable specification \textbf{.cable\_spec} file \cite{sacamos_UG} is derived.

\subsection{Cable types in MOD}

The cable models defined in MOD are as follows:

\begin{enumerate}

\item Power lines: Twisted pairs with gauges 20, 22, 24, from 3 different standards \cite{3901/019},  \cite{3901/002} and \cite{3901/025}

\item Low frequency signals: variant 12 Shielded Twisted Pair from the standard  \cite{3901/025}

\item RS422 cables: variant 24 Shielded Twisted Pair from the standard  \cite{3902/002}

\item SpaceWire: gauges 28 and 26 from the standard \cite{3902/003} and low mass SpaceWire cable from the stsndard \cite{3902/004}

\item Connectors for SpaceWire: 9 contact connector from the standard \cite{3401/071}

\end{enumerate}

The cable naming convention combines the cable type (TP, STP, SPACEWIRE, LOW\_MASS\_SPACEWIRE) with the 
wire gauge (AWG 20, 22, 24, 26, 28), the ESCC specification document number and the particular 
cable variant number from within the specification.

The cable and connector models described here and made avaialble in MOD are as follows:

\textbf{Twisted Pair models}

\begin{verbatim}
TP_AWG_20_ESCC_3901002_V34

TP_AWG_20_ESCC_3901019_V14

TP_AWG_20_ESCC_3901025_V10

TP_AWG_22_ESCC_3901002_V33

TP_AWG_22_ESCC_3901019_V13

TP_AWG_22_ESCC_3901025_V09

TP_AWG_24_ESCC_3901002_V32

TP_AWG_24_ESCC_3901019_V12

TP_AWG_24_ESCC_3901025_V08
\end{verbatim}

\textbf{Shielded Twisted Pair models}

\begin{verbatim}
STP_AWG_26_ESCC_3901025_V12

STP_RS422_AWG_26_ESCC_3902002_V24
\end{verbatim}

\textbf{SpaceWire Cable models}

\begin{verbatim}
SPACEWIRE_AWG_28_ESCC_3902003_V1

SPACEWIRE_AWG_26_ESCC_3902003_V2

LOW_MASS_SPACEWIRE_AWG_28_ESCC_3902004_V1

SPACEWIRE_CONNECTOR
\end{verbatim}

%\subsection{Example sub-circuit models}
%
%For the practical use of the MOD library it would also be useful for the user, who needs cables "directly available" 
%(according to the SoW) to provide "single cable bundles" based on the above, and the relevant Spice models. 
%As, in practice, there is always a ground plane somewhere (a spacecraft structure panel, as discussed many times), 
%it would be useful to provide Spice models of a cable (from the list of cable to be agreed) above a ground plane. 
%The ground plane can be lossless, as, as discussed also several times, what tends to dominate is the impedance of 
%the connections of the ending circuits to the ground plane, rather than its own losses. I would suggest to consider 
%a height of the cable above the ground plane of 5 cm, as specified in most EMC standards. For the length: we can 
%stick to 1 metre, as long as you are sure that the cables can be cascaded (by the user) to achieve 2, 3, 5, 10 metres 
%without any unwanted effect. It seems to me that cascading 1 metre cables has the beneficial effect of spreading 
%a little the DC resistance of the conductors, which should result in more realistic circuits.
\section{Dielectric materials}

A number of different dielectrics are used in the construction of the cables specified. In all the cable models we assume that the dielectric material within each region is homogeneous, lossless and the relative permittivity is independent of frequency.

The relative permittivities used for the dielectrics used in spacecraft cable models are:

\begin{itemize}  

\item 
polyimide: 3.4
 
\item 
microporous PTFE: 1.3
 
\item 
fluoropolymer PFA: 2.1

\end{itemize}  
 
\cleardoublepage