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Model a Launch Abort System

This example shows how to model a launch abort system for an orbiter heading into outer space. If a fault occurs during the launch, the orbiter aborts the launch. Depending on when the fault occurs, the orbiter returns to the launch site, returns to a downrange landing site, attempts to land after orbiting once around the Earth, or proceeds to a lower, stable orbit. A Simulink 3D Animation™ window displays a visualization of these steps. This simplified example does not model the dynamics of the fuel, boosters, and tank subsystems.

Monitor Orbiter Altitude

In this example, a Stateflow® chart monitors the flight of the orbiter and schedules the appropriate launch abort actions when the orbiter encounters an anomaly.

The chart consists of two parallel states: ModeLogic and Abort. The ModeLogic state contains four substates that describe the possible launch abort scenarios based on the altitude of the orbiter:

  • Return to Launch Site (RTLS) — If the altitude is less than 10,000 meters, the orbiter dumps the fuel, releases the solid rocket boosters and the external tank, and returns to the launch site.

  • Downrange landing (DRL) — If the altitude is between 10,000 and 100,000 meters, the orbiter releases the solid rocket boosters and the external tank and returns to a downrange landing site.

  • Abort Once Around (AOA) — If the altitude is between 100,000 and 400,000 meters, the orbiter releases the external tank, circles the Earth once, and proceeds to re-entry.

  • Abort to Orbit (ATO) — If the altitude is greater than 400,000 meters, the orbiter abandons the intended orbit and proceeds to a lower, stable orbit.

Schedule Launch Abort Actions

The Abort state controls the behavior of the orbiter when an anomaly is detected. If an anomaly occurs, the system transitions from the Normal substate to the AbortLogic subchart before transitioning to the AbortComplete substate.

The transition into the AbortLogic subchart connects to an entry port. Similarly, the transition out of the subchart begins at an exit port. Each port has a matching junction that marks the entry or exit point inside the subchart. The junctions isolate the internal logic of the subchart which, depending on the launch abort scenario, schedules three possible actions:

  • Dump the fuel.

  • Release the sold rocket boosters.

  • Release the external tank.

If the orbiter is in the ATO scenario, none of these actions is required.

For more information about entry and exit ports, see Create Entry and Exit Connections Across State Boundaries.

Simulate the Model

To run a simulation of the model:

  1. Double-click the Inputs block. In the Signal Editor dialog box, select a launch abort scenario from the Active Scenario list. The default scenario is RTLS_Abort.

  2. Click Run. The Simulink 3D Animation window displays a visualization of the launch.

  3. To view the orbiter from different perspectives, in the Simulink 3D Animation window, use the Viewpoint dropdown menu. For example, you can see entire flight of the orbiter by selecting Chase Plane.

Reference

Nelson, Douglas, John Bradford, and John Olds. "Abortability Metrics: Quantifying Intact Abort Mode Availability for Reusable Launch Vehicles." In Space 2006. San Jose, California: American Institute of Aeronautics and Astronautics, 2006. https://doi.org/10.2514/6.2006-7293.

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