| Explorer S-66 | |
| Names List: | BE-A Beacon Explorer-A NASA S-66 |
| Mission Type: | Ionospheric research |
| Operator: | NASA |
| Cospar Id: | EXS-66A |
| Mission Duration: | Failed to orbit |
| Spacecraft: | Explorer S-66 |
| Spacecraft Type: | Beacon Explorer |
| Spacecraft Bus: | Transit-Bus |
| Manufacturer: | Johns Hopkins University Applied Physics Laboratory |
| Power: | 4 deployable solar arrays and batteries |
| Launch Date: | 19 March 1964, 11:13:41 GMT |
| Launch Rocket: | Thor-Delta B (Thor 391 / Delta 024) |
| Launch Site: | Cape Canaveral, LC-17A |
| Launch Contractor: | Douglas Aircraft Company |
| Destroyed: | Failed to orbit |
| Orbit Reference: | Geocentric orbit (planned) |
| Orbit Regime: | Low Earth orbit |
| Apsis: | gee |
| Instruments: | Langmuir Probe Laser Tracking Radio Frequency Beacon |
| Programme: | Explorer program |
| Previous Mission: | Explorer 19 |
| Next Mission: | Explorer 20 |
Explorer S-66 (also called BE-A, acronym of Beacon Explorer-A), was a NASA satellite launched on 19 March 1964 by means of a Thor-Delta B launch vehicle, but it could not reach orbit due to a vehicle launcher failure.
Beacon Explorer-A was a small ionospheric research satellite instrumented with an electrostatic probe, a 20-, 40-, and 41-Hz ionospheric radio beacon, a passive laser tracking reflector, and a navigation experiment. Its primary objective was to obtain worldwide observations of total electron content between the spacecraft and the Earth. The spacecraft was an octagonal right prism -diameter terminated on top with a truncated octagonal pyramid on which the laser reflectors were mounted. Appended were four hinged paddles carrying solar cells. Each paddle was .
During the third stage operation, a malfunction of unidentified origin prevented successful orbit. Satellite and third stage descent were in the south Atlantic Ocean with no useful scientific data obtained.[1]