1. The astronaut who dusted off his panels

Andy Weir’s The Martian returns as the recalled work because Mark Watney’s survival depends on a row of solar panels that he has to keep clean, pointed, and accounted for. A LEO desktop does not have dust, but it has the same problem in a different form: the panels must be large enough, efficient enough, and oriented correctly enough to keep the batteries charged through every eclipse.

This entry reads about solar cells and arrays for LEO.

2. The physics of photovoltaic power in orbit

NASA’s Small Spacecraft Technology power chapter notes that solar power is the predominant energy source for small spacecraft. A photovoltaic cell produces current when photons excite electrons across a semiconductor bandgap. The power generated depends on:

  • the intensity of sunlight, which falls off with the inverse square of distance from the Sun;
  • the angle of incidence, which reduces output by the cosine of the tilt away from the Sun;
  • the cell temperature, which affects voltage and efficiency;
  • the area and packing factor of the array;
  • degradation from radiation, contamination, and thermal cycling over the mission life.

For LEO the intensity is essentially 1 AU, but the Sun angle changes continuously and eclipses occur every orbit. The design must therefore target orbit-average power, not peak instantaneous power.

3. Cell technologies

The current state of the art for space solar cells is multi-junction III-V devices, typically GaAs, InGaP, and Ge layers stacked to capture different parts of the solar spectrum. NASA reports beginning-of-life efficiencies in the 30–34% range, with laboratory demonstrations pushing toward 35–38% and concentrated-light records above 47%. Silicon single-junction cells are cheaper but limited to roughly 20% efficiency and are mostly used for cost-sensitive or short-life missions.

Emerging options include perovskite tandems, flexible thin-film CIGS, and organic photovoltaics. These promise lower mass and new form factors, but their long-term stability and radiation tolerance are still being proven in space.

4. Array architectures

AAC Clyde Space emphasizes that LEO subjects arrays to highly variable illumination and temperatures from roughly -40°C to +80°C during each orbit. The array can be:

  • body-mounted, simple and reliable but limited in area and often misaligned with the Sun;
  • deployable rigid panels, which add area and complexity;
  • flexible or roll-out blankets, which offer high specific power but require new deployment mechanisms.

NASA points out that specific power — watts per kilogram — is often more mission-limiting than raw cell efficiency. Arrays are life-limiting components, and their end-of-life performance at operating temperature is the critical metric.

5. What this changes

  • The desktop’s solar array must be sized for orbit-average power after end-of-life degradation, not for peak beginning-of-life output.
  • Pointing matters: a body-mounted panel on a nadir-pointing spacecraft will spend much of its time at a poor Sun angle.
  • Temperature swings in LEO mean the array voltage and maximum power point move continuously.
  • The next entry will read about batteries and power conversion.