Space
Radiation And Why Spacecraft Electronics Are Old
Space hardware often uses processors decades behind consumer devices because radiation tolerance, qualification history and thermal limits matter more than raw speed.
Spacecraft frequently fly processors that would look outdated in a household appliance. The choice is deliberate, and it follows from what happens to electronics outside the atmosphere.
Charged particles disrupt circuits directly
Space contains high-energy particles from the sun and from beyond the solar system, and the atmosphere and magnetic field that shield the ground are absent or weakened.
A single particle passing through a transistor can deposit enough charge to flip a stored bit, producing a value the software never wrote.
More energetic strikes can trigger a latch-up, a condition in which the device draws excessive current and may destroy itself unless power is cycled quickly.
Smaller features are more vulnerable in some ways
Modern processors store information using very small amounts of charge, so less deposited energy is needed to disturb a stored value.
Older designs with larger features hold more charge per cell, making them inherently more tolerant of single-particle disruption.
The relationship is not entirely one-directional, since smaller devices also present a smaller target, but the practical result favours conservative designs for critical functions.
Total dose accumulates over the mission
Beyond individual events, continuous exposure gradually changes the electrical characteristics of semiconductors, shifting thresholds until circuits misbehave.
This ageing sets a mission lifetime limit that depends on orbit, since radiation environments differ enormously between low orbits, the belts and interplanetary space.
Shielding helps but adds mass, and it can worsen matters by producing secondary particles when very energetic primaries strike it.
Qualification takes years
A part intended for flight must be tested against radiation, vibration, vacuum and temperature extremes, then documented thoroughly enough to satisfy the mission authority.
That process is slow and expensive, so the qualified catalogue lags the commercial market by a long interval regardless of engineering preference.
Using an already-flown part also carries evidence of reliability that no amount of ground testing on a newer device can match.
Redundancy substitutes for hardening
Some programmes now fly commercial processors in multiples, comparing their outputs and discarding any unit that disagrees with the others.
This delivers far more computing capability per unit mass, which suits missions that need onboard processing of imagery or autonomy.
The approach suits short-duration or replaceable spacecraft better than long missions where a failure cannot be tolerated or repaired. Constellations of many small satellites can accept the occasional loss in a way a single deep space probe cannot.
Hybrid designs are now common, pairing a hardened processor that handles command, attitude and survival functions with a commercial one that handles payload work and may be restarted freely if it misbehaves.
