| Abbreviation | Definition |
|---|---|
| IRAR | Internal Variable |
| IRD | Information Requirements Document |
| IRD | Initiating Reference Document |
| IRG | Inertial Rate Gyroscope |
| IRG | Inner Roll Gimbal |
| IRIG | Inertial Rate Integrating Gyro |
| IRIG-B | Inter-Range Instrumentation Group B |
| IRIS | Intelligent Rotation In Space |
| IRIS | Italian Research Interim Stage |
| IRL | Initiating Reference Letter |
| IRL | Interface Requirement List |
| IRL | Intermediate Range Lander |
| IRME | Initiator Resistance Measuring Equipment |
| IRR | Infra Red Resistant |
| IRR | Inspection Rejection Report |
| IRR | Integral Rocket Ramjet |
| IRS | Inertial Reference System |
| IRSPECT | Infrared Spectrometer |
| IRTCM | Integrated Real-Time Contamination Monitor |
| IRU | Inertial Reference Unit |