Solar Array Sizing Calculator
Size a spacecraft solar array from orbit-average load and eclipse fraction. Uses the SMAD power-budget method: the array must carry the daylight load and recharge the battery through the next eclipse, after end-of-life degradation.
Inputs
Load
Orbit
LEO is typically 0.35–0.40; GEO averages about 0.02 (eclipse season only); dawn-dusk SSO can be 0.
Cell & array
Si ≈ 0.15, GaAs single-junction ≈ 0.19, triple-junction ≈ 0.28–0.32.
Packing factor, wiring, temperature, assembly losses. SMAD default 0.77.
Path efficiency
SMAD defaults: direct-energy-transfer 0.85/0.65, peak-power-tracking 0.80/0.60.
Result
Need battery depth-of-discharge sizing, per-subsystem power budgets, and thermal coupling in one model?
Sign up →Frequently asked questions
How is the required array power derived?
P_sa = (P_e·T_e/X_e + P_d·T_d/X_d) / T_d. The array works only in daylight, so everything the spacecraft needs during eclipse must also be generated then and pushed through the battery charge path — which is why X_e is the harsher of the two efficiencies.
What is inherent degradation?
Everything between raw cell efficiency and installed performance: cell packing factor, assembly and wiring losses, temperature derating, shadowing, and calibration uncertainty. SMAD's nominal value is 0.77, and it is applied before lifetime radiation degradation.
Why do BOL and EOL areas differ so much?
Radiation, thermal cycling, and UV erode cell output every year. At the default 2.75%/yr over a 5-year life the array keeps only about 87% of its beginning-of-life output — so it must be oversized on day one to still close the power budget on the last day.
What does this tool NOT account for?
Battery sizing and depth-of-discharge limits, array pointing and articulation losses beyond a fixed incidence angle, seasonal solar-distance variation, eclipse-duration variation around the year, or string-level failure margin. Those are in the Aerospace Pack's EPS sizing suite.
Upgrade for the full power budget
- Battery sizing with depth-of-discharge and cycle life
- Per-subsystem, per-mode power budgets with margin rollup
- Eclipse duration computed from the actual orbit, not a fixed fraction
- Thermal coupling — array temperature feeds cell efficiency
- Power budget feeds the CDR package directly