Power System

The power system consists mainly of two elements: the battery stack and the power controller. Meer Instruments of San Diego originally built the system. Because of the short duration of the SBI flight (< 14 hours), everything on board the gondola can be powered entirely by batteries. The absence of solar panels that can act as sails and add unwanted additional vibration modes will make pointing the SBI easier than pointing the FGE.

Before the September 1, 2003 flight we expected an average power consumption of about 502 Watts. We assumed a minimum operation of 15 hours, which includes two hours before the launch and 13 hours of actual flight. By including a 10% derating due to the below freezing temperature of operation, we expected a total power requirement of about 8.6 kW-hr. Commercially available Li-ion batteries have a performance of about 130 W-hr per kilogram of weight, therefore we required a total battery weight of about 66 kg. This means that the battery weight is not of considerable impact on the total gondola weight. For the flight we employed 12 Lithium batteries of 780 W-hr each, for a total of 9.3 kW-hour. The batteriaes were packed together in a thermally insulated container, mounted also on the mezzanine.

During the actual flight the power consumption resulted much lower than the expected. We have estimated that less that 50% of the available power was actually used.