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Satellite Power Mission Requirements Estimator

The Satellite Power Mission Requirements Estimator sizes the electrical generation capacity needed to support a spacecraft load through normal operation, eclipse recovery, and design margin. It is useful during early mission trades when engineers need a fast check of whether the planned solar-array or other generation system is large enough for the selected load profile.

The result focuses on required average generation power and the corresponding daily energy demand. By separating operating load, conversion efficiency, eclipse duty cycle, and margin, the estimator makes the main power-sizing assumptions visible and easy to revise as a mission concept matures.

Calculator inputs

W
min
min
%
%
Result
—
Required generation power
Daily load energy—
Sunlight fraction—
Generation with margin—

1. Enter the average load
Use the expected average electrical demand while the spacecraft is operating normally.

2. Define orbit and eclipse time
Enter the orbital period and the portion of each orbit spent in eclipse.

3. Set efficiency
Use an end-to-end charging and distribution efficiency that reflects conversion and storage losses.

4. Add design margin
Apply extra capacity for uncertainty, degradation, or growth allowance.

5. Review the requirement
Compare required generation power with the beginning- and end-of-life capability of the proposed power source.

Sunlight fraction = (orbital period − eclipse time) / orbital period
Required generation = average load / (sunlight fraction × efficiency) × (1 + margin)
Daily load energy = average load × 24 h

This simplified sizing model assumes the average load is representative across the orbit and that eclipse energy is replenished during sunlight. Detailed spacecraft power analysis may also model battery depth of discharge, seasonal illumination, array temperature, pointing, degradation, and transient peaks.

What the result means

This value is the average generation power needed during the available sunlight period after efficiency losses and the selected design margin are included.

It is a mission-planning estimate, not a substitute for a time-resolved spacecraft electrical power system analysis.

Given

  • Average load = 850 W
  • Eclipse = 36 min
  • Orbital period = 96 min
  • Efficiency = 88%
  • Margin = 20%

Calculation
Sunlight fraction = 60/96 = 0.625. Required generation = 850 / (0.625 × 0.88) × 1.20 = 1,854.5 W. Daily load energy = 850 × 24 = 20,400 Wh.

Result
Required generation ≈ 1.85 kW.

A generation system below this level would not, under these assumptions, replace eclipse energy and cover the stated margin.

Why does eclipse time increase the required generation power?

Energy consumed in eclipse has to be replenished during the shorter sunlight interval, so the generator must deliver more than the average spacecraft load while illuminated.

What efficiency should I enter?

Use an overall value for the path from generated power through regulation, charging, storage, and distribution. If those losses are modeled separately elsewhere, avoid counting them twice.

Does this replace a detailed solar-array sizing analysis?

No. It is an early-stage energy-balance estimator and does not model array orientation, cell temperature, radiation degradation, seasonal beta angle, or battery life constraints.

What happens if eclipse time equals the orbital period?

There is no sunlight interval available for recharge, so this sunlight-based model cannot calculate a finite generation requirement. The page flags that condition as invalid.

How should I use the design margin result?

Treat it as a planning allowance for uncertainty and growth. Compare it against both beginning-of-life and expected end-of-life generation capability.