PROCEDURE: 6wh

TITLE: Semi-Parallel Long darks

CATEGORY: Calibration

PURPOSE: Measure darks with long enough exposures to get significant
counts.  Take HRC and WFC flats nearly concurrently so as to maximize
efficiency during TV capaign.  By "nearly" we mean juggle exposure times
and start times so that the read-outs do not temporally overlap.

FREQUENCY: Run over range of nominal operating T.  Use as filler when
not doing anything else.

DETECTORS: WFC and HRC

PREREQUISITES: none

HARDWARE REQUIREMENTS: none

SOFTWARE REQUIREMENTS: standard statistical analysis tool
                       stsdas.hst_calib.ctools.msbadpix

COMMAND MODE: SMS

PROCEDURE/EXPOSURES: 
	1.    bias (WFC)                   0s
	2.    bias (HRC)		   0s
	3.    dark (WFC)	        3600s  
	4.    dark (HRC)	       ~3600s  ****
	Record T_env, T_CCD at beginning, end and in the middle of each
	   dark exposure.  
	**** Jiggle exposure time so the HRC does not readout until WFC
	image is fully down-loaded.

TOTAL EXPOSURES: 2

TOTAL TIME: setup + 3600s + 2*overhead (WFC + HRC) = 1.57 hr
	(setup = 10min, overhead = 10min (WFC), 2min (HRC))

ANALYSIS: 

(1) Subtract overscan or master bias.

(2) Run basic statistical analysis tool.  Gives dark count rate.
Compare with previous darks to check if rate & shape remain constant.

(3) Plot dark rate vs. T_env, T_CCD, time.  Note trends.

(4) If more than one dark, combine and identify bad pixels.