Fallback hierarchy for safe degradation

Design and validate a fallback hierarchy that provides safe degradation when the ARC V3A growth-rate controller encounters actuator saturation, diagnostic degradation, surrogate extrapolation, or other failure conditions.

Background

The control architecture includes a conceptual fallback position controller, but the present study does not implement an integrated hierarchy for transitions among growth-rate control, position control, and other protective actions. Such a hierarchy is needed because the simulations show failures under limited voltage authority, combined degradations, and large disturbances.

References

The principal open questions are robustness to diagnostic noise and reconstruction errors, systematic characterization of surrogate gradient accuracy, generalization of the surrogate beyond the training distribution, real-time implementation on PCS hardware with deterministic timing guarantees, and design of a fallback hierarchy for safe degradation.

— On the feasibility of model-based feedback control of vertical instability growth rate using out-vessel coils in ARC-like scenarios  (2608.22677 - Kumar et al., 24 Aug 2026) in Section 6, Conclusions