Subject: HRI-SIM TV2 Flash report                                             
Date: Sun, 25 Aug 2002 23:16:51 -0400                                         
From: Dennis Wellnitz <wellnitz@astro.umd.edu>                                
                                                                              
Hi all,                                                                       
                                                                              
On Saturday, August 24, we opened up the chamber at about 8 am MDT,           
pulled out the SIM, performed safe-to-mate tests on the CCD and cabled        
up the CCD.  After changing the timing constant to 8 and resetting the        
FPGA, the CCD operated as expected.  We also checked the stimulator and       
found that the filament we were using (number 1) is now open.  We did         
not change the cabling to use filament number 2, because that would have      
taken too much time, and would have risked opening that filament as           
well.  We closed up the chamber at 4:15 pm MDT, and started flooding the      
shroud with liquid nitrogen at about 5:30 pm.                                 
                                                                              
This morning (Sunday, Aug 25), we starting running liquid nitrogen            
through the cold plate at about 7:30 am MDT, and monitored the CCD dark       
current every 5 degrees C as it cooled.  By late in the afternoon, we         
had verified that the dark current followed the curve measured in the         
lab down to about -60 C, but then continued following the exponential         
decrease shown at higher temperatures to at least -80 C, instead of           
flattening out to the minimum value of 0.3 to 0.4 BISC DN/pixel/second        
as measured in the lab.  The value at -81.3 C was 0.02 BISC                   
DN/pixel/second!  (One BISC DN is about 8 electrons, whereas one flight       
DN is about 30 electrons.)  At -81.3 C the integrations to measure dark       
current became too long (greater than 800 seconds) to keep up with the        
cooling rate, so we discontinued those measurements for now, but will         
make some more tomorrow as the temperature of the CCD stabilizes.             
                                                                              
This evening at 9 pm MDT we converted the cold plate from liquid              
nitrogen to liquid helium, and expect that the IR-FPA temperature will        
drop adequately to start telescope alignment sometime Monday morning          
(August 26).  By sometime in the afternoon, we expect to have                 
re-achieved telescope alignment and focus and will begin checking             
co-alignment of the IR spectrometer slit with the CCD, as well as             
running other checks on the operation of the CCD at HRI-CCD operating         
temperatures.  By Tuesday morning we expect to have achieved stability        
at the "warm" temperature (about 142 K) of the SIM bench, and will            
resume IR spectrometer calibration work.                                      
                                                                              
I expect to resume daily HRI-SIM TV2 Flash reports following this             
report.                                                                       
                                                                              
Please let me know if you have any comments or questions.                     
                                                                              
If you would prefer not to receive these Flash reports on HRI-SIM TV2,        
please let me know.                                                           
                                                                              
                Dennis