| IAPPP | International Amateur/Professional Photoelectric Photometry | - | Atmospheric Research Center |
| IAU | International Astronomical Union | - | Atmospheric Research Center |
| IAUC | IAU Circular | - | Atmospheric Research Center |
| IBSS | Infrared Background Signature Survey | - | Atmospheric Research Center |
| IC | Index Catalog | - | Atmospheric Research Center |
| ICE | International Cometary Explorer | - | Atmospheric Research Center |
| IDA | International Dark-sky Association | - | Atmospheric Research Center |
| IDL | Interactive Data Language | - | Atmospheric Research Center |
| IFEA | Integrated Furnace Experiment Assembly | - | Atmospheric Research Center |
| IGBP | International Geosphere/Biosphere Programme | - | Atmospheric Research Center |
| IGM | InterGalactic Medium | - | Atmospheric Research Center |
| IGY | International Geophysical Year | - | Atmospheric Research Center |
| IKI | Institut Kosmischeskikh Issledovaniya | - | Atmospheric Research Center |
| IML | International Microgravity Lab | - | Atmospheric Research Center |
| IMO | International Meteor Organization | - | Atmospheric Research Center |
| IMU | Inertial Measurement Unit | - | Atmospheric Research Center |
| INCO | Integrated Communications Officer | - | Atmospheric Research Center |
| INMARSAT | International Maritime Satellite | - | Atmospheric Research Center |
| INTELSAT | International Telecommunications Satellite | - | Atmospheric Research Center |
| IOA | Institute Of Astronomy (Cambridge) | - | Atmospheric Research Center |
| IOBM | In Ocean By Mistake | - | Atmospheric Research Center |
| IOC | In-Orbit Checkout And Calibration | - | Atmospheric Research Center |
| IOTA | Infrared-Optical Telescope Array | - | Atmospheric Research Center |
| IOTA | International Occultation Timing Association | - | Atmospheric Research Center |
| IPAC | Infrared Processing & Analysis Center | - | Atmospheric Research Center |
| IPMP | Investigations Into Polymer Membrane Processing | - | Atmospheric Research Center |
| IPS | Inertial Pointing System | - | Atmospheric Research Center |
| IR | InfraRed | - | Atmospheric Research Center |
| IRAF | Image Reduction And Analysis Facility | - | Atmospheric Research Center |
| IRAS | InfraRed Astronomical Satellite | - | Atmospheric Research Center |
| IRFNA | Inhibited Red Fuming Nitric Acid | - | Atmospheric Research Center |
| ISAMS | Improved Stratospheric And Mesospheric Sounder | - | Atmospheric Research Center |
| ISAS | Institute Of Space AND Astronautical Science | - | Atmospheric Research Center |
| ISEP | Isolated/Stabilized Exercise Platform | - | Atmospheric Research Center |
| ISM | InterStellar Medium | - | Atmospheric Research Center |
| ISO | Imaging Spectrometic Observatory | - | Atmospheric Research Center |
| ISO | Infrared Space Observatory | - | Atmospheric Research Center |
| ISO | International Standards Organization | - | Atmospheric Research Center |
| ISPM | International Solar Polar Mission | - | Atmospheric Research Center |
| ISRO | Indian Space Research Organisation | - | Atmospheric Research Center |
| ISTS | Institute For Space And Terrestrial Science | - | Atmospheric Research Center |
| ISU | International Space University | - | Atmospheric Research Center |
| ISY | International Space Year | - | Atmospheric Research Center |
| ISZ | Iskusstvenniy Sputnik Zemli | - | Atmospheric Research Center |
| IUE | International Ultraviolet Explorer | - | Atmospheric Research Center |
| IUS | Inertial Upper Stage | - | Atmospheric Research Center |
| IVT | Interface Verification Test | - | Atmospheric Research Center |
