Solar cell sizing, battery selection, MPPT charging, power budgets, thermal analysis, passive vs. active thermal control, and surviving eclipse cycles.
Power and thermal are linked. Power creates heat. Heat changes battery performance. Eclipse removes power and changes temperatures fast. You don’t “finish power” and then “do thermal” — they evolve together.
Power and thermal are coupled problems. Your power budget defines your thermal loads, and your thermal environment constrains your battery performance. Design them together.
Start with a load table: subsystem, mode (idle/active/peak), power (W), duty cycle (%), and energy per orbit (Wh).
| Subsystem | Idle (W) | Active (W) | Peak (W) | Duty Cycle |
|---|---|---|---|---|
| C&DH (Rook) | 0.3 | 0.5 | 0.8 | 100% |
| UHF Radio (RX) | 0.2 | 0.2 | 0.2 | 100% |
| UHF Radio (TX) | — | 1.5 | 2.0 | 10% |
| EPS | 0.1 | 0.1 | 0.1 | 100% |
| ADCS Sensors | 0.1 | 0.2 | 0.3 | 80% |
| Magnetorquers | — | 0.5 | 1.0 | 40% |
| Payload | — | 1.0 | 2.0 | 15% |
Always include margin. Use at least 20% power margin and treat payload power as guilty until proven innocent. The radio transmitter and payload are usually the biggest surprises.
Solar generation depends on several factors: cell efficiency (typical triple-junction GaAs ~30%, silicon ~20%), surface area, angle to sun, temperature, shadowing, and spacecraft attitude.
For body-mounted panels on a 1U CubeSat, each face is 10×10 cm = 100 cm². With ~30% efficient cells at AM0 (1361 W/m²), maximum power per face ≈ 2.3 W in direct sunlight. However, tumbling or non-optimal pointing cuts average generation significantly.
Deployable panels provide more area and are common for 3U+ missions that need higher power budgets.
A 400 km LEO orbit is approximately 60% sunlit and 40% eclipse. You must generate enough energy during sunlight to power all subsystems and recharge the battery for the next eclipse.
Batteries must survive charge/discharge cycles, temperature swings (–20°C to +40°C typical operating range), and peak current loads. Lithium-ion (Li-ion) and lithium-polymer (LiPo) are the standard chemistries for CubeSats. Typical capacity for a 1U is 10–20 Wh; for a 3U, 20–40 Wh.
| Parameter | Li-ion | LiPo |
|---|---|---|
| Energy Density | Higher | Moderate |
| Cycle Life | 500–1000+ | 300–500 |
| Temperature Range | –20 to 60°C | –20 to 45°C |
| Form Factor | Cylindrical cells | Flat pouch |
| Common Use | Most CubeSats | Compact builds |
Battery temperature is often the single biggest constraint on CubeSat thermal design. Most Li-ion cells lose significant capacity below 0°C and can be damaged by charging below –10°C.
Simple direct charging works for early prototypes, but more advanced missions use Maximum Power Point Tracking (MPPT) to extract up to 30% more energy from solar panels by dynamically adjusting the operating voltage.
Rook-based missions can standardize telemetry for power monitoring: voltages, currents, temperatures, reset causes, and battery health — giving your team real-time insight into EPS performance.
Thermal balance is the equilibrium between heat in (electronics dissipation + sun exposure), heat out (radiation to space through surfaces), and heat spreading (conduction through structure).
CubeSat thermal extremes can be dramatic: a sunlit face can reach +80°C, while a shadow face can drop to –40°C. Internal temperatures depend on power dissipation and conduction paths through the structure.
| Component | Min Operating | Max Operating |
|---|---|---|
| Li-ion Battery | –10°C | +45°C |
| Solar Cells | –100°C | +100°C |
| Electronics (general) | –40°C | +85°C |
| Radio Transceiver | –30°C | +60°C |
Many CubeSats don’t overheat — they freeze. Battery thermal management is often the first thermal priority. Plan heaters for the battery if your orbit has long eclipse periods.
Test your understanding of power and thermal design.
Explore CubeSat project ideas your team can start building today.