Modeling a Launch Abort System
This example shows how to model a launch abort system. An aircraft is launched into outer space. If an anomaly or fault occurs during the launch, the operation is aborted, and the aircraft is sent back down to Earth.
The Launch Abort Controller state chart is used to control the mode logic and launch abort behavior. The state chart consists of two parallel states: ModeLogic and Abort. Within the Mode Logic state, the aircraft can be in either one of four states:
- RTLS: Return to Launch Site
- DRL: Downrange Landing
- AOA: Abort Once Around
- ATO: Abort to Orbit
The aircraft transitions from one mode to the next based on the altitude of the aircraft (a simplification).
The second parallel state controls the behavior of the aircraft if an anomaly is detected. If an anomaly occurs, the system transitions to the abortLogic substate and the following 3 actions can occur, depending on the current state of the system:
- Dump the fuel
- Release the tanks
- Release the stage
Although Stateflow® is used to schedule when these events occur, the fuel, tank, and stage subsystems are modeled in Simulink®. Since this is a simplified example, the dynamics of the subsystems are not modeled here. However, a visualization of the fuel dump, tank release, and stage release can be seen through the use of Simulink® 3D Animation™.
Nelson, D. K., Bradford, J. E., Olds, J. R., "Abortability Metrics: Quantifying Intact Abort Mode Availability for Reusable Launch Vehicles," AIAA-2006-7293, Space 2006, San Jose, California, September 19-21, 2006.