1. The invisible storm

Michael Crichton’s The Andromeda Strain returns as the recalled work because the novel’s threat is not seen directly; it is inferred from the failure of instruments, the behavior of cultures, and the statistics of contamination. Radiation in orbit is the same kind of antagonist. It cannot be aimed at or argued with, only characterized by the damage it leaves behind.

This entry reads about what radiation actually does to spacecraft electronics.

2. Where the particles come from

Space radiation has three main sources, none of which are negotiable:

  • Galactic cosmic rays (GCR): high-energy heavy nuclei from outside the solar system. They are relatively rare but extremely penetrating and ionizing.
  • Trapped radiation belts: protons and electrons captured by Earth’s magnetic field. In LEO the South Atlantic Anomaly is a region where the inner radiation belt dips low enough to increase flux significantly.
  • Solar particle events: bursts of protons and heavier ions associated with flares and coronal mass ejections. They are episodic but can raise dose rates by orders of magnitude.

A NASA report on space radiation effects describes how charged particles ionize semiconductor material as they pass through, depositing charge where it does not belong.

3. Total ionizing dose

Total ionizing dose (TID) is the cumulative damage caused by long-term exposure. It shifts transistor thresholds, increases leakage current, and eventually degrades performance until a part no longer meets specification. The damage is invisible until it isn’t; a device that passed every ground test may quietly drift out of tolerance after months or years in orbit.

TID is measured in kilorads or megarads of silicon absorbed dose. Rad-hard parts are designed and tested to survive specific TID levels, often hundreds of kilorads or more. Commercial parts may begin to degrade at a few kilorads.

4. Single-event effects

Single-event effects (SEE) are the result of one particle hitting one device. They are the most immediate radiation concern for digital electronics. Common categories include:

  • Single-event upset (SEU): a bit flip in memory, a register, or a flip-flop. It is a soft error; the device is not damaged, but the data or state is wrong. Beidou navigation satellite monitoring found that SEUs accounted for the majority of on-orbit failures in their sample.
  • Single-event latchup (SEL): a particle triggers a parasitic thyristor structure, creating a low-impedance path from power to ground. The device draws excessive current. Power cycling usually clears it, but without fast current limiting it can destroy the device or collapse the power bus.
  • Single-event burnout (SEB): a catastrophic, permanent failure, often in power transistors. It is not recoverable.
  • Single-event gate rupture (SEGR): dielectric breakdown in power MOSFETs, also permanent.
  • Single-event functional interrupt (SEFI): a transient loss of function, often in complex devices like FPGAs or memory controllers, requiring reset or reconfiguration.

ESA’s spacecraft electronics effects presentation notes that corrupted memory can lead to erroneous commands, which is why SEE mitigation is not only a hardware problem but a system-level one.

5. What this changes

  • Radiation is not one hazard but several: cumulative dose, single-particle upsets, and catastrophic single-particle failures.
  • LEO is less hostile than deep space or the radiation belts, but it is not safe; the South Atlantic Anomaly and solar events matter.
  • The desktop’s compute, power, and storage electronics all need a radiation strategy, not just the main processor.
  • The next entry will read about how components are classified and selected for radiation environments.