Power budget
Spacecraft Power Budget
Size the solar array, battery, and power-system mass for a typical satellite mission — then flip the toggle and see what swapping the array for a HawkLogic-style beamed-power link does to the 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.
About this model & its assumptions
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 (the beam is persistent and redundant in the HawkLogic architecture, so eclipse-sized batteries are 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.
// try a preset, then tweak. one tap loads every input.
// swap the array for a rectenna and resize the battery for safe-mode coast-through.
Orbit
// circular; SMAD spherical-Earth eclipse model.
Payload + bus
// duty cycle is fraction of orbit at active power.
Power system
// GaAs triple-junction defaults; tune for your stack.
Battery + margin
// DoD limit drives cycle life; design margin is on top.
Solar-array sizing
// avg load 11 W · orbit 94.6 min · eclipse 10.8%
0.056 m²
Array area
18 W
Array power BOL
15 W
Array power EOL
0.16 kg
Array mass
7.8 Wh
Battery capacity
0.05 kg
Battery mass
0.26 kg
Power-system mass
0.01 U
Stowed volume
// mass breakdown
- Array 0.16 kg
- Battery 0.05 kg
- Harness + deploy 0.05 kg
// shareable URL encodes every input. no backend.
// solar-array area vs orbit altitude
// ai-generated breakdown of what these numbers mean — with diagrams.
Common questions
How do I size a solar array for a CubeSat?
Start from the orbit-average load — payload power times duty cycle, plus bus housekeeping — and divide by the sunlit fraction of the orbit, since the array must recharge the battery for eclipse while carrying the load. Then the physical area follows from cell efficiency (0.28 default: beginning-of-life (BOL) triple-junction GaAs), packing factor (0.85), BOL-to-end-of-life degradation (0.85), and a design margin (0.25 on top). Those are the SMAD-consensus defaults this solar array sizing uses; override any of them for your cell stack.
What does a typical 3U CubeSat power budget look like?
The 3U preset — 500 km sun-synchronous, a 10 W payload at 30% duty cycle, 3 W of bus housekeeping — carries a 6 W orbit-average load. The model sizes it at roughly 8.4 W of end-of-life array power (about 0.03 m² of triple-junction cells), a battery of a few watt-hours, and on the order of 0.14 kg of array-plus-battery mass. Load the preset and tweak from there.
How is the battery sized for eclipse?
Capacity is the eclipse-period energy demand divided by the depth-of-discharge (DoD) limit, with the design margin on top; mass follows at 150 Wh/kg pack-level for mission-rated Li-ion. A shallower DoD costs capacity and mass but buys cycle life — the central battery trade for a LEO mission that sees an eclipse nearly every orbit.
What does the "what if beamed instead?" toggle do?
It swaps the solar array for a 35 GHz rectenna sized for a beamed-power link, and resizes the battery for safe-mode coast-through rather than every-orbit eclipse cycling. It is a first-order trade study of the receiving side; the transmitting side of such a link is the Microwave Power Link Budget tool's problem.
Does my design data leave the browser?
No — the calculator runs entirely in your browser and no inputs leave your machine. The share button packs every input into the page URL's hash so you can paste one link into a design review instead of screenshots.
References
- // Wertz, J. R., Everett, D. F., & Puschell, J. J. (eds.) (2011). Space Mission Engineering: The New SMAD, ch. 21 (Power Subsystems).
- // European Space Agency. Space Power Subsystem Engineering Manual (SPSEM), latest revision.
- // NASA. Battery Handbook for Aerospace Applications, 2024.
- // Vallado, D. A. (2013). Fundamentals of Astrodynamics and Applications, ch. 1 (orbit period, Kepler).
- // For the spherical-Earth eclipse model and beta-angle treatment, see Wertz & Larson (1999) section 5.1.
