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%\input dspace12.tex
%\input pstricks.tex
%\input psfig
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\newcommand{\eg}{{\it e.g.~}}
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\newcommand{\axaf}{{\em AXAF}}
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\large
%\vspace*{-0.5in}
\centerline {\bf 5.5\_V2.0 OPEN SMALL VENT VALVE IN EMERGENCY DEPLOYMENT } 
\vspace{0.25in}

\normalsize
\noindent{\it Last Revised: June 27,1999}\\
\noindent{\bf Filename: open\_svv\_emgdep} \\

\noindent {\bf BRIEF FUNCTIONAL DESCRIPTION:} \\
\normalsize

  This procedure is intended to be executed in the case of an
emergency deployment of AXAF during which it is still possible to
command the spacecraft.  This procedure should be implemented as an
script with no indefinite waits.  Once the first command is sent, the
script should only take 8~s to execute since there are 8 commands and
1~s delays between each command.  The following text
pertains to the opening of the little vent valve in general:


The little vent valve is planned to be opened once 
on orbit.  The current plan would open the valve while \axaf\/ is
still in the shuttle bay, 40~mins after the payload bay doors have
been opened.  The valve is opened to allow any residual
gas which has leaked into the ACIS detector housing to 
escape. There are two redundant vent valves located in parallel
downstream of a porous plug.  Thus, the opening of either of these valves
will be sufficient but it is planned to open both. Since
the pumping speed is limited by the porous plug, no advantage in time
or final pressure can be realized by opening both valves.  There is no
telemetry verifier that the valves have opened.  The only way to
verify the opening of the valves is to monitor the reading of the internal
pressure monitor.  Once opened the little valve should not be closed,
since the risk of contaminants reaching the focal plane through this
path is negligible. Initialy, the pressure will drop by a factor of
two every 30 minutes.  Typically in ground operations, 3 hours was the
standard waiting time or until the rate of change was less than 1 torr
per 30 minutes.  The eventual pressure should read $0\pm2$ torr.

\vspace{0.25in}
\noindent The sequence of actions will be: 
\be
\item turn on the pressure transducers A \& B
\vspace{-0.10in}
\item enable and open the little valve mechanism A \& B
\vspace{-0.10in}
\item disable the little vent valve mechanism A \& B
\vspace{-0.10in}
\item monitor the pressure as spacecraft telemetry is available
\ee


\vspace{0.15in}
\normalsize
\noindent {\bf ASSUMED INSTRUMENT STATE:} \\
\normalsize
Assumes that the PSMC has power from the spacecraft. \\


%\vspace{0.25in}
\normalsize
\noindent {\bf SPECIAL INITIAL CONDITIONS:} \\
\normalsize
%The environment must be clean enough to allow opening of the valve. \\
%Assumes that \axaf\/ ISIM RCTU is powered on and in telemetry format 6. \\
Assumes that the spacecraft has power and connections for commanding and telemetry. \\

%\newpage 

%\vspace{0.25in}
\normalsize
\noindent {\bf OPERATIONAL CONSTRAINTS/CAUTIONS:} \\
\normalsize
This procedure leaves the ACIS pressure transducers on during deployment.\\
There is no telemetry verifier and therefore it is crucial that the
internal pressure be monitored.  Both pressure monitors may be read
out, so they are both typically used. \\
CARD ACIS-002 \\


\normalsize
\noindent {\bf CHANGE HISTORY:} \\
\normalsize

{\bf V1.2}
\begin{itemize}
\item changed filenames from ``open\_lvv\_emgdep'' to ``open\_svv\_emgdep''
\end{itemize}

{\bf V1.3}
\begin{itemize}
\item deleted step 1 which turned on the DPA side A
\item deleted step 2.3 and 2.4 which provided a wait to measure the pressure
\item deleted step 5 which turned off the DPA side A
\item changed time delay between all commands to 1~s
\end{itemize}

{\bf V2.0}
\begin{itemize}
\item ACIS Team signed-off version, identical to previous version 1.3
\end{itemize}


\vspace{0.15in}
\normalsize
\noindent {\bf REFERENCES:} \\
\normalsize
ACIS Long Form Functional Test Procedure (36-01301.01)

\newcommand{\tablecaptiontext}{Open Small Vent Valve in an Emergency Deployment}
\input{open_svv_emgdep.tab}

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