S-66A (also called BE-A, acronym of "Beacon Explorer",) was an artificial NASA satellite launched on March 19, 1964 by means of a Delta B rocket, but it could not reach orbit due to a vehicle launcher failure.
- Launch mass: 114 kilograms (251 lb)
- Dimensions: 24.5 by 45.7 centimetres (9.6 in × 18.0 in)
- Manufacturers: Applied Physics Laboratory
- Launch place: Cape Canaveral LC-17A
- Instruments: Radio Beacons, Doppler Navigation System, Electrostatic Probe, Passive Laser Tracking Reflector
- Beacon Explorer-A. NASA GSFC