Spacecraft Battery Sizing Calculator

What It Does

The Battery Sizing Calculator computes the required battery capacity for a spacecraft from its eclipse load, eclipse duration, allowable depth of discharge (DOD), and end-of-life capacity loss. Input the average eclipse load and the calculator returns the required BOL and EOL ampere-hour capacity, the maximum allowable DOD by chemistry (Li-ion, NiH₂, NiCd), and the resulting battery mass. Includes harness loss and DC-DC converter efficiency.

Key Features

• Required BOL and EOL battery capacity from eclipse load and duration
• Chemistry-specific DOD limits (Li-ion, NiH₂, NiCd) with cycle-life curves
• Battery mass output for typical cell-level specific energies
• Harness loss and DC-DC efficiency in the load calculation

Why It Matters

Battery sizing is where eclipse duration meets electrical load. A LEO satellite cycling its battery 16 times per day for 5 years accumulates ~30,000 cycles, which forces aggressive DOD limits — typically 20% for Li-ion to maintain capacity margin. Sizing against the wrong DOD limit shortens battery life from 10 years to 3 and reduces the mission. The calculator enforces the chemistry-appropriate DOD limits and gives the right capacity at the start so you don't discover the problem at on-orbit checkout.

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