Radiation effects & COTS screening

Total ionizing dose vs single-event effects in LEO

At $500\text{-}550\text{km}$ Sun-synchronous orbits, a PocketQube has relatively thin shielding—often $1\text{mm}$ of aluminium or $1.6\text{mm}$ of FR-4—yet its short orbital lifetime ($1.5\text{-}3\text{years}$) keeps cumulative Total Ionizing Dose (TID) around $1\text{-}4\text{krad(Si)}$[1]. Most modern commercial off-the-shelf (COTS) CMOS microcontrollers, transceivers and LDOs survive $5\text{-}20\text{krad(Si)}$ without parametric failure[2].

The primary radiation hazard in LEO is instead Single-Event Effects (SEE) triggered by high-energy protons ($>30\text{MeV}$) trapped in the South Atlantic Anomaly (SAA) and galactic cosmic rays near the poles[3]:

• Single-Event Upset (SEU): Non-destructive bit flip in SRAM, processor registers or flash configuration cells.
• Single-Event Latch-up (SEL): Parasitic thyristor triggering in bulk CMOS that creates a low-impedance short between supply and ground, destroying the IC thermally unless power is cut within milliseconds.

Circuit and architectural mitigations

1. Per-rail over-current foldback and power cycling: Every COTS subsystem rail on the EPS is routed through a fast current-limiting switch ($t_{\text{trip}}<1\text{ms}$) that quenches SEL currents and re-powers the branch after a cooldown delay[2].
2. FRAM and MRAM for critical state: Ferroelectric RAM (e.g., TI MSP430FR series or external SPI FRAM) stores boot counters, orbital parameters and configuration tables in polarization states immune to proton bit flips, paired with Triple Modular Redundancy (TMR) and CRC-32 scrubbing[3].