| Abbreviation | Definition |
|---|---|
| IFRU | In-Flight Replacement Unit |
| IFT | In-Flight Test |
| IFTM | In-Flight Test Maintenance |
| IFTS | In-Flight Test System |
| IFU | InterFace Unit |
| IG | IGloo |
| IG | Inertial Guidance |
| IGA | Inner Gimbal Angle |
| IGAX | Inner Gimbal Axis |
| IGDS | Iodine Generating and Dispensing System |
| IGM | Interactive Guidance Mode |
| IGN | Ignition |
| IGN | Ignition, Ignite |
| IGOR | Intercept Ground Optical Recorder |
| I-GPRF | Isothermal General Purpose Rocket Furnace |
| IGS | Inertial Guidance System |
| IGSE | In-Space Ground Support Equipment |
| IGV | Inlet Guide Valve/Vanes |
| IGV | Inlet Guide Vane |
| IH/SR | Integration Hardware and Software Review |