From: Mike Machado [Michael.J.Machado.1@gsfc.nasa.gov]
Sent: Monday, May 14, 2007 3:41 PM

Subject: Polar low power season load management

Importance: High

All,

It has been a long time since Polar experienced such a low power season due 
to high sun angle (1998). Unfortunately, due to solar array degradation 
over the years, we no longer have the power output that we did in 1998 and 
must resort to shedding loads to remain power positive and prevent the 
battery temperatures from going past the point of no return.

Last week, we avoided an under voltage condition and began managing loads 
by powering off PWI and reducing real-time contacts (communication system 
power) to minimum requirements for data recovery. That appeared to have the 
desired effect until a turn around this weekend caused more concern. 
Although the battery temps increased slightly above red low limits on 
Friday, they have once again dropped below the red low limit. As the sun 
angle continues to increase up to May 18, the situation will only get worse 
and our power margin less. In addition, there are fewer uplink supports 
available this week to command Polar due to major antenna maintenance and a 
high profile Ulysses event. As a result, more loads will need to be shed to 
improve the power situation. We're focusing on loads that would be shed 
should the under voltage condition be met. These include instrument loads 
as well as communication system loads and the catalyst bed heaters. The cat 
beds won't be on and the comm system power is required to monitor health 
and safety.

Tonight (135/0345-0445 UTC), the following instrument loads will be shed 
(instruments powered off):
CAMMICE/HIT
TIDE		(TIDHVRPDN129.RTC; TIDPWROFF129.RTC)
TIMAS		(TIM129.RTC)

These loads will remain off for approximately 2 weeks until the power 
margin improves.

Fortunately, this temporary sacrifice should allow Polar to transition the 
low power season in order to meet mission objectives for the remainder of 
the mission.

Thanks to everyone for quickly responding to FOT requests. Please contact 
me if you have questions.

Mike
301-286-0666 (office)
443-694-4317 (cell)