Hi, I found some acronyms/abbreviations in this post. This is how they expand:

Acronym	Explanation
ATK	Alliant Techsystems, predecessor to Orbital ATK
EM-1	Exploration Mission 1, first flight of SLS
EUS	Exploration Upper Stage
MSFC	Marshall Space Flight Center, Alabama
RS-25	Rocketdyne-developed rocket engine used for Shuttle; see SSME, SLS,Space Shuttle Main Engine
SLS	Space Launch System heavy-lift

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