What is the difference between a soft fault and a hard fault in spacecraft avionics?

What is the difference between a soft fault and a hard fault in spacecraft avionics?

• A. A soft fault is transient and recoverable; a hard fault is persistent and typically requires remediation.
• B. A soft fault causes permanent damage; a hard fault is temporary.
• C. Soft fault affects only sensors; hard fault affects actuators.
• D. Soft fault occurs during launch; hard fault occurs in orbit.

Answer: (A)

The key idea is recoverability: soft faults are transient and recoverable, while hard faults are persistent and require remediation. A soft fault looks like a temporary anomaly—often from something like a radiation-induced bit flip or a momentary power fluctuation. It can typically be cleared with a reset, a memory scrub, or reinitialization, and the system returns to normal without hardware changes. A hard fault, by contrast, indicates a failed or severely degraded component whose problem does not go away with a simple reset; addressing it usually means switching to redundant hardware, reconfiguring the system to bypass the bad part, or putting the subsystem into a safe/degraded mode, possibly followed by physical replacement or servicing.

This distinction helps spacecraft fault management decide when to try quick recoveries versus when to switch to backups or change operation modes. The other descriptions don’t match how faults are categorized in avionics—soft faults aren’t defined by causing permanent damage, they aren’t limited to sensors versus actuators, and they aren’t tied to launch versus orbit conditions.