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\begin{document}
%\input dspace12.tex
%\input pstricks.tex
%\input psfig
\newcommand{\be}{\begin{enumerate}}
\newcommand{\ee}{\end{enumerate}}
\newcommand{\bc}{\begin{center}}
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\newcommand{\bd}{\begin{description}}
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\newcommand{\eg}{{\it e.g.~}}
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\newcommand{\axaf}{{\em AXAF}}
\def\la{\hbox{\rlap{$<$}\lower0.5ex\hbox{$\sim$}\ }}


\large
%\vspace*{-0.5in}
\centerline {\bf 1.7\_V2.0 OPEN BIG VENT VALVE } 
\vspace{0.25in}

\normalsize
\noindent{\it Last Revised: June 23,1999}\\
\noindent{\bf Filename: open\_bvv} \\

\noindent {\bf BRIEF FUNCTIONAL DESCRIPTION:} \\
\normalsize
The ``big'' (previously referred to as ``large'')  vent valve is
planned to be opened once on orbit.
The big vent valve must be opened after the small vent valve has
been opened and before the ACIS door is opened. This valve provides 
efficient venting 
of the ACIS camera housing and the internal pressure will 
quickly reach the ambient pressure after the valve is open.
The pressure monitors are not sensitive below 1~torr so it 
is not possible to verify from the pressure that the
valve is open; however there is a telemetry verifier that the valve
has opened.
There is one valve with redundant paraffin actuators.  Extreme caution
must be exercised with these actuators, from the ACIS Long Form
Functional Test Procedure document:

\begin{quote}
\em{Because the Optical Blocking Filters are fragile and cannot 
withstand much differential pressure, mechanism motions may only 
be initiated when the differential pressure is less than 1 torr.
Be safe; check both transducers.  The mechanisms are driven by 
Starsys hot wax actuators. Power is applied directly from the 
space craft bus to heat the wax and, therefore, the time for a 
given motion to complete is dependent upon the bus voltage. To 
avoid failure of an actuator due to overheating--which would occur 
if the completion-of-motion switches failed, for instance--we 
monitor the actuator temperature. If the actuator temperature 
exceeds 135C, a command to abort the motion should be sent. Recovery 
from such a condition is never routine; no further motions should
be attempted without thorough analysis of the procedural failure.
 It is also imperative that the commanded actuator be allowed to 
cool below 50C before the opposing actuator is commanded, lest the 
afore-mentioned egregious situation occur.  It is not an error to 
command a valve open which is already open, etc., since the PSMC 
logic will know from the motion switches that the mechanism is 
already in the commanded state and not (falsely) apply power to 
the actuator.
}
\end{quote}

The side A actuator has an extra bit to monitor the status of the
actuator.  However, the logic which determines the value of this bit
is sufficiently obtuse, that it is typically easier to use side B.
The valve typically takes 3.5~minutes to open with a 28VDC bus
voltage; it will go faster with 32VDC on the bus.  The peak
temperature should be 120~C; damage can occur if the temperature
exceeds 135~C. An on-board regulator disconnects the voltage if the
temperature reaches 130~C.  Therefore, ground intervention to abort
the actuator motion should not be necessary or even possible, but 
is maintained as a backup to this automatic cutoff.  As the 
actuator warms above 70~C, it begins to move and the valve closed
bit should indicate the valve is no longer closed.  Once the motion 
is complete and the actuator
starts to cool, the valve open bit should indicate the valve is
fully open.  While in 
transition, both bits should indicate that the valve is neither open
nor closed.


The current timeline
indicates that the small vent valve will be opened while {\axaf} is
still in the shuttle bay and the big vent valve will be opened days
later after some of the rocket burns are complete and {\axaf} is still in 
its transfer orbit.   There is no stringent requirement as to the time at
which the big vent valve must be opened.  
%This assumes that there 
%are relatively few ACIS activities from final orbital insertion until
%the ACIS door is opened and therefore there is little time pressure.
It is desired that the big vent valve be opened at a time in which 
ACIS activities will be the highest priority and will not conflict
with other SC activities.  We heat the focal plane to -50~C and
maintain that temperature for 3 hours in order to allow any water
which has frozen on the CCDs to evaporate and escape the detector
housing.  It is desired to keep the FP temperature at -50~C after
this activity and going into the next activity which should be the 
``CCD Diagnostic Mode'' which is the major part of the ACIS
Short Form Functional test.  {\bf SO, THIS PROCEDURE ENDS WITH THE
FOCAL PLANE BAKEOUT ENABLED, THE FOCAL PLANE TEMPERATURE AT -50~C and
THE WARM BOOT FLAG OFF}.


\vspace{0.40in}
\noindent The sequence of actions will be: 
\be
\item turn on the pressure transducers A \& B, check the pressure, validate expectations
\vspace{-0.10in}
\item start DEA housekeeping to measure FP temperature
\vspace{-0.10in}
\item Dump configuration information
\vspace{-0.10in}
\item enable FP bakeout and heat FP to -50 C
\vspace{-0.15in}
\item enable the valve mechanism B and verify actuator temperatures
\vspace{-0.10in}
\item Open valve mechanism B
\vspace{-0.10in}
\item monitor the temperature and motion of the actuator
%\vspace{-0.10in}
%\item verify the close and open bits change
\vspace{-0.10in}
\item Turn off valve mechanism B when the motion is complete
\vspace{-0.10in}
\item verify the actuator temperature drops after the motion is complete
\vspace{-0.10in}
\item disable the vent valve mechanism B
\vspace{-0.10in}
\item {\bf On- orbit, WAIT FOR 3 HOURS}, Maintain elevated FP temperature 
\ee


%\vspace{0.25in}
\normalsize
\noindent {\bf ASSUMED INSTRUMENT STATE:} \\
\normalsize
Assumes that the PSMC has power from the spacecraft. \\
Assumes that instrument is in the canonical thermal standy state (the 
video boards and FEPs must be off for this procedure !!!!).\\
Assumes the small vent valve is open. \\

\vspace{0.25in}
\normalsize
\noindent {\bf SPECIAL INITIAL CONDITIONS:} \\
\normalsize
Assumes that RT contact is available for an extended period. \\
Assumes that \axaf\/ ISIM RCTU is powered on and in telemetry format
1 or 2. \\


%\newpage 

\vspace{0.25in}
\normalsize
\noindent {\bf OPERATIONAL CONSTRAINTS/CAUTIONS:} \\
\normalsize
The instrument is left in a state in which the focal plane bakeout is
enabled and the focal plane temperature is at -50~C. \\
The small vent valve must already be open. \\
The open and close mechanism must not be enabled at the same time.\\
{CARD ACIS-002} \\
{CARD ACIS-007} \\


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

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

{\bf V1.2}
\begin{itemize}
\item changed filenames from ``open\_vv'' to ``open\_bvv''
\end{itemize}

{\bf V1.3}
\begin{itemize}
\item changed title from ``large vent valve'' to ``big vent valve''
\item deleted ``CMD EGSE'' and ``SEQ KEY'' from the LaTeX table
\item changed HW TLM verifiers in steps 1.1 and 1.2 to ``ENB''
\item changed expected value of pressure in steps 1.3 and 1.4 to
$0\pm2$~T
\item changed required TLM format to 1or2 for all steps except step 2
\item changed ``Command echo'' in the Telemetry Description column to
``Check cmdResult == OK'' in the Telemetry EGSE column in steps 2.1,
4.2, 4.3, and 4.4
\item moved ``deaHousekeepingData'' in Telemetry Description column
to ``Telemetry EGSE'' column in steps 2.2, 2.3, and 4.5
\item changed expected focal plane temperature in step 2.3 to $<-50$~C
\item moved ``bepReadReply'' in Telemetry Description column to
Telemetry EGSE column and changed the verifier to ``Check cmdResult == OK''
\item put not in step 4.1 to warn that DEA A input current is noisy
\item added command to set the warm boot flag off in a new step 4.2
\item added a ``dumpSysConfig'' command in a new step 4.6
\item changed expected value of HW TLM verifiers in steps 5.1, 5.2, 
5.3, and 5.4 to ENB, $<30$~C, CLOS, and NOPE
\item added expected value of HW TLM verifier in step 6.1 
\item changed expected values of HW TLM verifiers in steps 8.1 and
10.1 to OFF and DIS
\item changed Time Req in step 9.1 to 30 minutes
\item changed HW TLM verifiers in step 11.1 to 1CBAT and 1CBBT
\item last step which disabled the focal plane bakeout and set the
focal plane temperature back to -120~C was deleted
\item edited Brief Functional Description to be consistent with edits
\end{itemize}

{\bf V1.4}
\begin{itemize}
\item added commandEcho values for steps 3.1--3.11 and 4.5 \& 4.6
\item changed ``Command Desription'' columns for steps 5.1, 6.1, and
8.1
\item added filename identification at top of procedure
\end{itemize}

{\bf V1.5}
\begin{itemize}
\item changed HW TLM verifier in step 4.1 to 1DE28AV0 from 1DEP3AVO,
and expected value to 27.0-35.0~V, and changed DEA A input current
to 0.60--0.78~A
\end{itemize}

{\bf V2.0}
\begin{itemize}
\item ACIS Team signed-off version
\item changed required TLM format to 1or2 for all steps except step 3
\item added step 12 to turn off the pressure XDCRs
\end{itemize}


\newcommand{\tablecaptiontext}{Big Vent Valve Opening Procedure}
\input{open_bvv.tab}

\end{document}


