| Abbreviation | Definition |
|---|---|
| IRV | Improved Inter-Range Vector |
| IRV | Isotope Reentry Vehicle |
| IRVE | Inflatable Reentry Vehicle Experiment |
| IS | Installation Support |
| IS | Interconnecting Station |
| IS | Internal Stabilization |
| ISA | Initial Sun Acquisition |
| ISA | Interim Stowage Assembly |
| ISAS | Institute of Space and Astronautical Science |
| ISBD | Inter- Sub- Band Detector |
| ISBD | Inter-Sub-Band Detector |
| ISC | Interstellar Space Craft |
| ISCM | Initial Software Configuration Map |
| ISCO | Innermost Stable Circular Orbit |
| ISE | Integrated Synthesis Environment |
| ISEE | International Sun-Earth Explorer |
| ISES | International Space Environment Service |
| ISF | Industrial Space Facility |
| ISG | ISTP Scheduling Group |
| ISI | Initial System Installation |