The spacecraft heaters shall operate from 25 to 35 V and survive indefinitely without damage from 0 to 40 V. It is a goal to be able to operate the heaters to 21 V with less than a 100% duty cycle.
If the heater specification went to 21 V like the rest of the spacecraft components, the nominal bus voltage would produce too much power dissipation. It is unlikely that we will have two battery cells fail and also require maximum heater power in our full sun orbit during the four month mission. The survival range is necessary for ground testing.
Keith Parrish on February 2, 1996.
The survival range is verified by analysis. The operating range is also verified by analysis. The thermal balance and thermal vacuum tests will verify the thermal model and the heater duty cycles at nominal bus voltages.
Revision: February 2, 1995