- 3D imaging
- Acquisition
- Actor-Observer Bias
- Aerial Reconnaissance
- Aeroacoustics
- Aerospace
- Aggregate economics
- Alien World
- Allocative inefficiency
- Anchoring and Adjustment
- Anchoring Bias
- Angel Investor
- Antimatter
- Apollo
- Apollo Lunar Module
- Apollo Program
- Artificial Intelligence
- ASI
- Asset management
- Asset purchase program
- Asteroid
- Asteroid Deflection
- Asteroid Mining
- Asteroid Mining
- Astrobiology