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In the flight software, certainly not as a string. Strings are just nasty in this regard. Almost all flight software is written in one of three languages: Ada, C, or C++. All three of those languages support the concept of an enumeration. In the flight software code, it is best to the enumeration value by name (but not a string) rather than integer value in ...
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There was no escape system for shuttle so N/A there.
See this Q&A Why not turn off the main engines while using the launch escape system on liquid fuelled engines? and especially the documents referenced in the answer, namely
Technical Information Summary AS-501 p. 13+ (Emergency Detection System diagram)
CSM15 Launch Escape System
There's a full ...
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