Spacecraft Battery Orbital DoD Calculator

Space Power Subsystems: Size spacecraft battery capacity (Wh & Ah), determine maximum allowable Depth of Discharge (DoD), and calculate orbital cycle life.

Eclipse Power & Mission Orbit

Orbit Mission Profile:

Eclipse Duration (minutes):

Eclipse Bus Load (W):

Maximum Allowable DoD (%): LEO: 20-30% DoD, GEO: 65-80% DoD

Nominal Bus Voltage (V):

Mission Design Life (years):

Discharge Path Efficiency η:

Battery Pack Sizing & Cycle Lifetime

Nameplate Capacity

-- Wh

Capacity (Ah)

-- Ah

Eclipse Energy

-- Wh

Estimated Mass

-- kg

Total Mission Cycles

-- cycles

Discharge Current

-- A

Li-ion String Topology: 8S (3.6V/cell nominal)

Specific Energy Density: 130 Wh/kg (Flight-Qualified Pack)

C-Rate during Eclipse Discharge: -- C

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Spacecraft Battery Sizing & Orbital Life Sizing

The spacecraft energy storage subsystem provides uninterruptible electrical power during orbital eclipses, launch/separation phases, and off-nominal attitude safe modes.

1. Required Nameplate Capacity Equation

To ensure end-of-life mission survival, nameplate capacity $C_{\text{bat}}$ is sized by:

C_bat (Wh) = [ P_eclipse · T_eclipse (hr) ] / [ DoD · η_dis · EOL_margin ]

P_eclipse: Average bus power consumption during shadow pass (Watts)
T_eclipse: Maximum orbital shadow duration (hours)
DoD: Maximum operational Depth of Discharge fraction ($0.20\text{--}0.30$ for LEO)
η_dis: Discharge converter and distribution wiring efficiency ($0.95$)
EOL_margin: Aging retention derating ($0.80\text{--}0.85$ over design life)

2. Ampere-Hour Rating

Capacity in Ampere-hours ($Ah$) is obtained by dividing nameplate energy by the nominal bus voltage:

Capacity (Ah) = C_bat (Wh) / V_bus,nominal

Frequently Asked Questions

Why is LEO satellite battery Depth of Discharge (DoD) kept so low (20–30%)?

A Low Earth Orbit (LEO) satellite completes roughly 15 to 16 orbits every single day, accumulating 5,500 charge-discharge cycles per year (over 27,000 cycles for a 5-year mission). To achieve tens of thousands of cycles without capacity fade or lithium dendrite failure, Li-ion batteries are restricted to 20% to 30% DoD. In GEO, where satellites experience only 90 eclipse cycles per year, DoD can safely reach 70% to 80%.

How does eclipse duration vary with orbit inclination and beta angle?

In LEO, maximum eclipse occurs when the orbit plane is edge-on to the sun (sun beta angle $\beta = 0^\circ$), with shadow duration spanning 35 to 37 minutes. At high beta angles ($|\beta| > \approx 65^\circ$), the satellite enters continuous sunlight (full sun orbit) where no battery eclipse discharges occur.

What bus voltages are standard in spacecraft electrical power architectures?

SmallSats and CubeSats typically use unregulated $8.4\text{ V}$ (2S) or $12\text{--}16\text{ V}$ (4S) buses. Large commercial and scientific satellites standardly operate regulated $28\text{ V}$ (8S Li-ion), $50\text{ V}$ (14S), or high-power $100\text{ V}$ (28S) buses to reduce harness copper mass and $I^2 R$ resistive distribution losses.