1. The station that orbited a world without a surface

Stanisław Lem’s Solaris returns as the recalled work because the Prometheus station hovers above an ocean that is, in some sense, alive, and the station itself is a fragile bubble of regulated temperature in an environment that does not care. A LEO desktop is the same: a small region of chosen temperatures surrounded by vacuum, sunlight, and the cold of Earth’s shadow. The first thing to understand about thermal management is that there is no air to carry heat away. The only paths are conduction through solid materials and radiation across empty space.

This entry reads about heat transfer and the LEO thermal environment.

2. Conduction inside, radiation outside

In a spacecraft, heat moves from hot parts to cold parts in two ways. Conduction transfers energy through direct contact: from a processor to its heat sink, from a heat sink to a heat pipe, from a heat pipe to a radiator panel. The rate depends on the material conductivity, the cross-sectional area, the length of the path, and the temperature difference. Metals like aluminum and copper are good conductors; composites and adhesives are usually worse.

Radiation is the only way to reject heat to space. Every surface emits thermal radiation according to its temperature and emissivity, and absorbs radiation according to its absorptivity and the incoming flux. A radiator is simply a surface designed to emit much more than it absorbs: high emissivity, low absorptivity, oriented away from the Sun and Earth when possible.

There is no convection in orbit. A fan inside a pressurized module can move air, but outside the shell the concept does not exist. This changes everything about thermal design. On Earth you can cool a chip with airflow; in space you must build a path to a radiator.

3. The LEO thermal environment

A spacecraft in LEO sees several heat sources and sinks:

  • Direct solar flux: roughly 1361 W/m² outside the atmosphere, varying slightly with solar cycle and distance.
  • Earth albedo: sunlight reflected from clouds, oceans, and land, which can add tens to hundreds of watts per square meter depending on the scene below.
  • Earth infrared: the Earth emits thermal radiation according to its own temperature, providing a modest but continuous input, especially on the nadir-facing side.
  • Deep space: the background acts as a sink at roughly 3 K, so any surface with a clear view of space can radiate heat away.
  • Eclipse: when the spacecraft passes through Earth’s shadow, all solar input disappears. The duration depends on orbit altitude, beta angle, and season.

The result is a thermal cycle: hot in sunlight, cold in eclipse, with gradients across the spacecraft depending on which surfaces see which sources.

4. The beta angle and the thermal season

The beta angle is the angle between the orbit plane and the Earth-Sun line. It determines eclipse duration and the fraction of each orbit spent in sunlight. At high beta angles, eclipses are short or absent. At low beta angles, especially near the equinoxes, eclipses can approach half the orbit. The thermal design must survive the worst-case eclipse and dissipate the worst-case heat load when the Sun is continuously available.

This is the orbital version of a season. The desktop does not get to choose it; it can only prepare for the full range.

5. What this changes

  • Thermal design starts with heat transfer by conduction and radiation only.
  • The LEO environment provides solar input, albedo, Earth infrared, and eclipse cold.
  • Beta angle drives the thermal season and the longest expected eclipse.
  • The next entry will read about radiators, heat transport, heaters, and thermal storage.