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Design Objective

The power system is designed to be (i) Simple and efficient (ii) Compact and fits inside the specified mass (or) volume and (iii) Rugged and meet the stringent specification on, thermal, radiation and loading condition. The configuration has been selected to be simple and to make use of commercially available components for development and testing.
Major component of the power system configuration are summarized as follows.

Power Bus Formation

The power bus is formed connecting all the solar strings. It is an unregulated bus and is tied to the battery. Hence the battery, decides the bus voltage, and no control is required. The configuration does not extract the maximum power from the solar panel.

However, the nominal battery voltage is set near the maximum power point and as the life goes, the operating point moves towards the maximum power point. The power is named as unregulated Bus (URB). Figure shows the schematic of Power Bus formation.

The bus voltage selection is normally constrained by the requirement of satellite Sub systems and availability off-the-self component. Lower voltages allow use of solar-strings of short length providing lot of flexibility in cell arrangement. On the other hand, higher voltages result in lower current, simplifying the battery and distribution design. The Bus voltage is chosen to be 12V-16V for ANUSAT.

The orbital modes:

The Power system operates in the following orbital modes.
a) Detumbling mode: After deployment from the launcher the satellite will tumble until the attitude control System (ACS) stabilizes the satellite. b) Normal orbit mode: After successful detumbling, the satellite spins at the rate of 8 rpm. c) Emergency mode: This mode occurs when the battery voltage reaches the lowest safety value upon fully discharged condition. During this mode, the loads are cut-off from battery except for house keeping load. The System is brought back to nominal mode automatically upon reaching the required level or by ground command if necessary.

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