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 |