Spacecraft Power Budget

physics from SMAD 5th ed and ESA SPSEM; constants documented inline. beamed-instead? toggle swaps the array for a rectenna. real trade, no marketing math.

This calculator handles the solar array sizing, battery capacity, and power-system mass for a circular low Earth orbit (LEO) mission: orbit period from Kepler's third law, eclipse fraction from a spherical-Earth shadow geometry, array power from the sunlit fraction of the orbit, and battery capacity from the eclipse-period energy demand at a stated depth-of-discharge limit. Constants follow Space Mission Analysis and Design (SMAD) 5th ed. (Wertz & Larson, ch. 21) and the European Space Agency (ESA) Space Power Subsystem Engineering Manual - and every one is overridable, so it scales from a 3U CubeSat power budget to a several-hundred-watt Earth-observation microsat.

This calculator sizes the photovoltaic array, the battery, and the resulting power-system mass for a circular Low Earth Orbit mission. It is intended for early-stage mission design: the level of detail you'd run before formal SMAD-style sizing, the level a PI or programme manager wants to ground a power-subsystem conversation in. The model is pure physics: orbit period from Kepler's third law, eclipse fraction from a spherical-Earth shadow geometry with a parametric beta-angle assumption, array power scaled by the sunlit fraction of the orbit, and battery capacity sized for the eclipse-period energy demand at a stated depth-of-discharge limit.

Constants follow the consensus values you'd find in SMAD 5th ed. (Wertz & Larson, ch. 21) and the ESA Space Power Subsystem Engineering Manual. The solar constant is 1367 W/m²; rigid panels are sized at 2.8 kg/m²; mission-rated Li-ion batteries at 150 Wh/kg pack-level. Cell efficiency defaults to 0.28 (BOL, GaAs triple-junction), packing 0.85, BOL/EOL degradation 0.85, and a design margin of 0.25 on top of computed values. The eclipse model defaults to a worst-case sun-in-orbit-plane assumption for low- to mid-inclination orbits, and to a dawn-dusk SSO assumption (beta near 67 deg) for polar/SSO orbits, the design-conservative choices in each case. Every constant is overridable. Every input is overridable.

The "what if beamed instead?" toggle swaps the solar array for a 35 GHz rectenna sized for a beamed-power link, with the battery resized for safe-mode coast-through (a persistent, redundant beam makes eclipse-sized batteries overkill). The defaults model a sub-aperture rectenna at conservative received-power densities; tune them to your beam-design point. The model does not capture rectification efficiency drift with incidence angle, atmospheric loss for ground-to-space links, or stage-by-stage power conditioning. It is a first-order trade study, not a flight-design tool.

Share scenarios by URL: the share button packs every input into the page hash so you can paste the link into a design review without screenshots. The calculator runs entirely in your browser; no inputs leave your machine.