AGC 1201 & GRID LOAD SHEDDING
A comparison of Apollo 11's graceful degradation and power grid load shedding protocols.
FILM
Film rendering in the background. Will be live on my 4ort.mov channel soon.
COMPANION NOTES
Apollo 11 AGC Alarm 1201
The Apollo Guidance Computer (AGC) used a fixed-priority preemptive scheduler. During the lunar descent, the rendezvous radar flooded the system with interrupts, triggering Alarm 1201 (Executive Overflow). The AGC gracefully degraded by shedding lower-priority tasks, ensuring critical functions like guidance and navigation continued.
Grid Load Shedding
In power dispatch, load shedding is used to maintain grid stability during peak demand or system overloads. Non-critical loads are shed in pre-defined priority cycles to ensure critical infrastructure remains operational.
KEY PARALLELS
- Priority Handling: Both systems use pre-defined priority lists to determine which tasks or loads are critical.
- Graceful Degradation: Both systems are designed to shed non-essential functions to maintain core operations.
- Deterministic Behavior: Both systems are designed to behave predictably under overload conditions.
LESSONS FOR MODERN SYSTEMS
Modern power grids are increasingly reliant on inverter-based resources like solar and wind. These resources lack the inertia of traditional spinning turbines, making frequency changes faster and more unpredictable. The lessons from Apollo 11's graceful degradation are more relevant than ever:
- Design systems with deterministic behavior under overload.
- Pre-define priority lists and ensure they are immutable.
- Test graceful degradation scenarios rigorously.