Power budget is the allocation, within a system, of the available electrical power among the various functions which need to be performed.

We need to know the power requirements of the system, that is to say, we need to know the average power that the system needs in order to work correctly during the whole orbit. We must bear in mind that, in the zone of eclipse, the power stored in the
batteries must be sufficient to totally satisfy the system needs.

The power subsystem of a spacecraft shall be able to generate, store, condition, distribute and monitor the electrical power used by the spacecraft throughout all mission phases in the presence of all environments actually encountered.

Power budget is designed to satisfy the following points:

• Simulation of the total power directly provided by the solar arrays.
• Power distribution among the different operation modes and satellite subsystems.
• Simulation of the total power CubeSat consumes during eclipse, which should be recharged during the daylight in order that CubeSat can be operated for long enough time.
• Simulations of the battery charging cycle.
• Ensure the minimum activity during the daylight in the event that all the batteries are lost.