| Abbreviation | Definition |
|---|---|
| GCL | Ground Control Landing |
| GCL | Ground Coolant Loop |
| GC-MS | Gas chromatograph/mass spectrometer |
| GCN | GRB (Gamma-Ray Burst) Coordinates Network |
| GCN | Ground Communications Network |
| GCO | Ground CheckOut |
| GCOS | General Computer Operational System |
| GCOS | Ground Computer Operating System |
| GCR | Galactic Cosmic Ray |
| GCR | Ground Controlled Radar |
| GCS | Ground Communications System |
| GCS | Guidance Cutoff Signal |
| GCTS | Gas Component Test Stand |
| GCTS | Ground Communications Tracking System |
| GCU | General Control Unit |
| GCU | Generator Control Unit |
| GCU | Ground Cooling Unit |
| GCU | Gyro Coupling Unit |
| GCV | Gaseous Oxygen Control Valve |
| GD | GuarD |