| Abbreviation | Definition |
|---|---|
| JCP | Joint Power Conditions |
| JCT | Junction |
| JD | Jovian Diameter |
| JDEM | Joint Dark Energy Mission |
| JDX | Joint Damping Experiment |
| JEA | Joint Endeavor Agreement |
| JED | Julian Ephemeris Data |
| JELM | Japanese Experiment Logistics Module |
| JEM | Japanese Element Module |
| JEM | Japanese Experiment Module |
| JES | Joint Environment Simulator |
| JESS | Joshi's External Stabilization System |
| JETS | Joint Electronics Type (Designation) System |
| JETT | Jettison |
| JG | John Glenn |
| JGR | Journal of Geophysical Research |
| JH | Dr. Joe Harrington |
| JIFFS | Joint Institute for Acoustics and Flight Sciences |
| JIMO | Jupiter Icy Moons Orbiter |
| JIP | Just Iss Planetary |