Power Budget
Power budget is power utilisation and consumption calculation associated with a system. It can be seen as net power balance of the system while in operation. The power generated and consumed can vary according to mode of operation.
In case of a satellite, typically, solar panels generate power and battery stores it for use. While designing the satellite, we have to calculate how much power needs to be generated so as to cater the needs of all the electronics onboard. This calculation of how much power needs to be generated will be responsible for solar panel parameters. A storage capacity of battery is also dictated by the power needs in the eclipse region of the orbit, wherein solar panels do not generate power.It may seem as if the power budget can be calculated only when entire design of all the electrical components is known. But, a tentative budget calculation starts at the beginning. The parameters for the solar panels, battery and various loads get fixed iteratively and eventually the power budget get refined. Starting with ballpark values, helps us get to the initial design parameters which are later analysed and changed iteratively, as required to meet the requirements from various subsystems. The ballpark values can be obtained by studying the literature of previous satellite missions, from studying particular class of components etc. System Engineer plays an important role in making and maintaining the power budget of the system.
Case Studies of Power Budget
Power budget can be calculated by listing all the major components which consume some significant power. We will be calculating the power consumption of Pratham by taking one subsystem of Pratham and calculate the power consumed by it and do the same for other subsystem and add them up.
Power Budget of ADCS Subsystem of Pratham
The major components ADCS subsystem are-
| Component | Supply Voltage (V) | Load Current (mA) | Power consumed in nominal operation (mW) | Power consumed in Idle State (mW) |
| Magnetorquers | 3.3 | 220 | 700 | 0 |
| Magnetometer | 7.7 | 30 | 230 | 0 |
| GPS | 5 | 470 | 2300 | 0 |
| ATmega8 | 3.3 | 3.3 | 10.8 | 3 |
Power Budget of Pratham
In the manner shown above the power consumption should be calculated for all the major components, and added to get the overall power like given in the table below (a shorter version of the Power Budget is shown here, listing only the components that consume significant power)
| Component | Supply Voltage (V) | Load Current (mA) | Load Power (W) |
| Beacon | 5 | 548.6 | 2.74 |
| Downlink | 5 | 460.82 | 2.3 |
| Torquers | 3.6 | 865.7 | 3.12 |
| OBC | 3.3 | 24.77 | 0.08 |
| GPS | 5 | 470 | 2.3 |
| Battery | 8.4 | 130.84 | 1.1 |
| Total | 11.35 |
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