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Orbital Period Power Budget Planner

The Orbital Period Power Budget Planner estimates energy use over one orbit and sizes a simple generation requirement around sunlight and eclipse time. It combines orbital period, average spacecraft load, sunlight fraction, battery round-trip efficiency, and design margin. The results show orbit energy demand, eclipse energy that must come from storage, and average solar-array power required during the illuminated portion.

This is a practical early-stage check for satellites and other periodically illuminated spacecraft. It helps reveal whether a proposed load profile is compatible with the available charging window before detailed subsystem duty cycles are built. The model assumes a constant average load and a repeating sunlight fraction; thermal constraints, peak loads, battery depth-of-discharge limits, degradation, pointing losses, and seasonal beta-angle effects require separate analysis.

Mission inputs

min
W
%
%
%
Result
—
Calculated result
Load energy per orbit—
Stored energy for eclipse—
Sunlight time—
Required solar-array power—

1. Enter the orbital period
Set the duration of one repeating power cycle.

2. Set the average spacecraft load
Use the average electrical demand across both sunlight and eclipse portions of the orbit.

3. Enter the sunlight fraction
Specify the percentage of the orbit in which solar generation is available.

4. Account for battery losses
Round-trip efficiency increases the charging energy needed to replace eclipse energy drawn from storage.

5. Add design margin
Apply an explicit percentage margin to the required solar-array output.

6. Review energy and generation
Use eclipse energy for storage sizing context and required array power for first-pass generation sizing.

The planner balances load energy over one orbit while charging for eclipse losses during the sunlit interval:

Orbit energy = Load × orbital hours Eclipse energy = Load × eclipse hours Array energy during sunlight = Load × sunlight hours + Eclipse energy / battery efficiency Required array power = Array energy / sunlight hours × (1 + margin)

Load is in watts, time is converted from minutes to hours, energy is reported in watt-hours, and efficiency and margin are converted from percentages to decimals. The model assumes a constant average load and that all energy needed for eclipse can be replenished during sunlight. It does not enforce battery depth-of-discharge, peak-current, thermal, or degradation constraints.

What the result means

The main result is the average electrical output the solar array must deliver during sunlight to support the load and recharge eclipse energy, including the chosen margin.

For hardware sizing, account separately for array degradation, pointing and temperature losses, regulator efficiency, battery usable capacity, and peak loads.

Given

  • Orbital period: 95 min
  • Average load: 300 W
  • Sunlight fraction: 62%
  • Battery efficiency: 90%
  • Design margin: 20%

Calculation
Sunlight = 58.9 min = 0.9817 h; eclipse = 36.1 min = 0.6017 h. Eclipse energy = 300 × 0.6017 = 180.5 Wh. Array energy = 300 × 0.9817 + 180.5 / 0.90 ≈ 495.0 Wh. Required array power = 495.0 / 0.9817 × 1.20 ≈ 605.1 W.

Result
Required average sunlit array output ≈ 605 W.

That value supports the constant 300 W load, replenishes idealized eclipse discharge, and includes the selected 20% margin.

Is eclipse energy the required battery capacity?

Not necessarily. It is the energy drawn during the modeled eclipse. Battery capacity sizing also depends on usable depth of discharge, aging, temperature, cell limits, and reserve policy.

What if the spacecraft load changes by mode?

Convert the mode schedule into a weighted average load for a rough estimate, or use a time-resolved power profile for detailed sizing.

Why does lower battery efficiency increase array power?

More energy must be generated during sunlight to replace a given amount of energy delivered from storage when charging and discharging are not perfectly efficient.

Can sunlight fraction be 100%?

Yes. In that case eclipse energy is zero, and the array requirement reduces to the average load multiplied by the selected design margin.

Does the result include solar-array degradation?

Only if you represent it through the margin. Detailed design normally models beginning-of-life versus end-of-life output and additional pointing, temperature, and conversion losses explicitly.