Power Budget Calculator

The sunlit duration is calculated as:

where:

• t_sunlit = sunlit duration (min)
• t_orbit = orbit period (min)
• t_eclipse = eclipse duration (min)

Energy generated per orbit is calculated as:

where:

• E_generated = energy generated per orbit (Wh)
• P_generation = power generation (W)
• Conversion factor 60 converts minutes to hours

Energy consumed per orbit is calculated as:

where:

• E_consumed = energy consumed per orbit (Wh)
• P_load,sunlit = load power during sunlit (W)
• P_load,eclipse = load power during eclipse (W)

Net energy per orbit is calculated as:

Power margin as a percentage is calculated as:

The orbit-averaged load power is calculated as:

where the orbit period is converted from minutes to hours.

Required battery energy during eclipse is calculated as:

Required battery capacity accounting for depth of discharge is:

where DoD is the depth of discharge (fraction, e.g., 0.2 for 20%).

Provide the following inputs to calculate your spacecraft power budget:

1. Power generation (W): Average power available from the solar array during sunlit time. This should account for solar panel efficiency, sun angle, and any degradation factors.
2. Orbit period (min): The total time for one complete orbital revolution around the central body.
3. Eclipse duration (min): The time spent in eclipse (in shadow) per orbit. This must be less than or equal to the orbit period.
4. Load power sunlit (W): Average total power consumption from all spacecraft loads during the sunlit portion of the orbit.
5. Load power eclipse (W): Average total power consumption from all spacecraft loads during the eclipse portion of the orbit.
6. Battery depth of discharge: Allowed depth of discharge as a fraction (e.g., 0.2 = 20%). Typical values range from 0.2 to 0.4 for lithium-ion batteries to maximize cycle life.

The tool calculates the following power budget parameters:

1. Sunlit duration: Time spent in sunlight per orbit (calculated as orbit period minus eclipse duration).
2. Average load power: Orbit-averaged power consumption from all loads over the entire orbital period.
3. Energy generated per orbit: Total energy generated by the solar array during one orbit (sunlit period only).
4. Energy consumed per orbit: Total energy consumed by all loads during one complete orbit (sunlit + eclipse periods).
5. Net energy per orbit: The difference between generated and consumed energy. Positive values indicate surplus energy, negative values indicate a deficit.
6. Power margin: Energy margin per orbit expressed as a percentage relative to total energy consumption.
7. Required battery energy: Energy that must be supplied by the battery during eclipse to power the loads.
8. Required battery capacity: Minimum battery capacity required based on the allowed depth of discharge limit.

Important considerations when using this tool:

1. The tool assumes constant power generation during sunlit periods and constant load power during sunlit and eclipse periods. Real missions may have variable power profiles.
2. Power generation should account for solar panel degradation, temperature effects, and incidence angle variations throughout the orbit.
3. A positive power margin indicates the system generates more energy than it consumes, allowing for battery charging and system reserves.
4. Negative net energy per orbit indicates the system cannot meet power requirements and requires either increased solar array capacity or reduced load power.
5. Battery depth of discharge should be selected based on battery chemistry and desired cycle life. Lower DoD values increase battery life but require larger battery capacity.
6. The eclipse duration must be less than or equal to the orbit period. If eclipse duration exceeds orbit period, sunlit duration is clamped to zero.