1. The hostile farm

Andy Weir’s The Martian is not about orbit, but it is about the same problem: a machine that must keep working in an environment that tries to break it. Mark Watney’s habitat, rover, and life-support systems are ordinary engineering pushed to their limits by dust, cold, and radiation. His survival depends on knowing exactly what each subsystem can tolerate and having a workaround when it stops tolerating it. The desktop’s compute boards are not on Mars, but LEO is hostile in its own way, and the workaround logic is similar.

This entry reads about the LEO radiation environment and what it does to commercial off-the-shelf (COTS) compute electronics.

2. The radiation environment in LEO

The desktop will orbit inside Earth’s magnetosphere, which is a partial shield. The main threats to electronics are:

  • Trapped protons and electrons: concentrated in the Van Allen belts and especially dense in the South Atlantic Anomaly (SAA).
  • Galactic cosmic rays (GCR): high-energy heavy ions that penetrate most practical shielding.
  • Solar particle events (SPE): bursts of protons and ions from solar flares and coronal mass ejections.
  • Albedo neutrons and secondary particles: generated when primary particles interact with the atmosphere and spacecraft materials.

The MDPI survey notes that LEO dose rates are far lower than interplanetary or GEO missions, but they are not zero. For a typical low-inclination LEO, the total ionizing dose behind a few millimeters of aluminum can be on the order of a few hundred to a few thousand rad over a multi-year mission, depending on altitude, inclination, and solar cycle.

3. Two categories of damage

Radiation harms electronics in two ways:

  • Total ionizing dose (TID): cumulative charge trapping in oxides and interfaces. It shifts thresholds, increases leakage, slows switching, and eventually causes parametric failure. TID is a wear-out mechanism measured in rad or krad.
  • Single-event effects (SEE): a single high-energy particle deposits enough charge in a sensitive node to cause a transient or permanent fault. SEEs include single-event upsets (SEU, a bit flip), single-event latch-up (SEL, a destructive short that may be recoverable by power cycling), single-event burnout (SEB, permanent destruction), and single-event functional interrupt (SEFI, a device lockup).

The Orbital Transports survey cites Sinclair and Dyer’s finding that more than 40% of COTS-based CubeSat missions have experienced in-orbit anomalies potentially linked to radiation. Most of these are SEUs or SEFIs, not permanent burnouts.

4. COTS tolerance ranges

The literature gives rough bounds for unhardened COTS parts:

  • Typical TID tolerance: a few krad to a few tens of krad for older or less robust parts; some modern CMOS devices survive 50–100 krad or more because thin gate oxides trap less charge.
  • SEL susceptibility: highly variable. Some devices are immune to latch-up at 60+ MeV·cm²/mg; others latch at much lower linear energy transfer (LET).
  • SEU rates: depend on orbit, shielding, device cross-section, and memory architecture. SRAM is more upset-prone than DRAM, which is more upset-prone than hardened latch-based memory.

The MDPI study emphasizes that model predictions can differ from measured doses by factors of 3 to 30, depending on the model and shielding assumptions. This means a desktop that relies on model-predicted dose alone is flying blind unless it also has on-orbit dosimetry or component test data.

5. What this changes

  • The desktop’s compute boards must be evaluated for both TID and SEE, not just one or the other.
  • The South Atlantic Anomaly is the dominant daily radiation stress for most LEO orbits.
  • COTS parts can survive LEO, but survival is not guaranteed; it must be demonstrated by testing or heritage.
  • The next entry will look at what the radiation literature says about storage, which has its own failure modes.