| Abbreviation | Definition |
|---|---|
| INSY | International Near Space Year |
| IO | Interacting Object |
| IO | Interaction Objects |
| IOA | Institute of Astronomy |
| IPC | Inter Planetary Commission |
| IPE | Initial Pointing Error |
| IPN | InterPanetary Internet |
| IPNS | Intense Pulsed Neutron Source |
| IPPW | International Planetary Probe Workshop |
| IRAS | Infra Red Astronomical Satellite |
| IRS | International Reference Star |
| ISM | InterStellar Medium |
| ISRO | India Space Research Organisation |
| ISRO | Indian Space Research Organisation |
| ISRO | Indian Space Research Organization |
| ISS | International Space Station |
| ISV | Inter-Stellar Void |
| ITRF | International Terrestrial Reference Frame |
| IWARA | International Workshop on Astronomy and Relativistic Astrophysics |
| IYA | International Year of Astronomy |