Subject: Autumn 2003 Eclipse Season
Date: Thursday, August 7, 2003 3:43
From: Steve Hearn <shearn@pop400.gsfc.nasa.gov>

I re-examined all of the autumn 2001 eclipse performance data as well 
as recent bus load performance surrounding numerous instrument turn 
on/off and activation/deactivation periods.  Overall, the bus load 
penalty for leaving both TIDE Main Power and CEPPAD Power (all 
sensors) on is between 0.65 and 0.68 amps.  For the severe eclipses 
we expect to see during the autumn 2003 eclipse period, this increase 
in load will result in a little more than 2 percentage points of 
increase in battery depth-of-discharge (DOD) for each battery.

Maximum observed battery %DOD during the autumn 2001 eclipse season 
was 43%.  Maximum predicted %DOD for the most severe eclipse 
conditions during the autumn 2003 eclipse season is about 45%. 
(These numbers use somewhat conservative assumptions based on 
nameplate capacities of the batteries.  Real %DOD values are likely a 
little bit lower.)  This assumes the following conditions are met:

CAMMICE/HIT MAIN POWER OFF
CAMMICE/MICS MAIN POWER OFF (already done)
PIXIE MAIN POWER OFF
SEPS MAIN POWER OFF
PWI MAIN POWER OFF (during all shadow periods as stated below)
VIS HV OFF
HYDRA HV OFF
TIDE HV OFF
TIMAS HV OFF

If CEPPAD's three sensors (IPS, IES, HIST) are powered off (leaving 
the DPU powered on), an additional savings of approximately 0.22 amps 
will be achieved.  These sensors are not routinely disabled around 
maneuver or eclipse periods.

Although not advertised to endure such long shadows, the Polar 
batteries and power subsystem electronics continue to perform very 
well.  With Polar having survived an approximately 66% battery DOD 
during the autumn 2002 eclipse season, I see no technical reason why 
the CEPPAD and TIDE LV requests be denied.  The penalty is relatively 
small, although it occurs under rather extreme conditions for the 
power subsystem.

As for additional savings, if needed, the plan you've outlined below 
remains a good one.  I would prefer to place TIDE at the top of that 
list, if only because I believe their turn off sequence is simpler 
and better known to the FOT.  (CEPPAD commanding of any type is not 
often done by the FOT.)  The likelihood of needing these savings is 
pretty small.

Steve

Steve Hearn
GGS Wind/Polar Lead Engineer
Lockheed Martin Space Operations
301-286-0665