SNAP-10A system being tested in preparation for launch.

SNAPSHOT was the first, and so far only, American flight of an operational nuclear space reactor. The SNAP-10A reactor produced 650 watts of power from 1.3 kilograms of used uranium-235 fuel (embedded in uranium zirconium hydride) to run a small ion propulsion system.


Twelve hours after launch, the reactor was automatically brought up to operating temperature. Following 43 days of successful operation, it was shut down as the result of a high voltage failure in the electrical system of the Agena spacecraft. All flight test objectives were met with the exception of the expected length of operation. The reactor remains in polar orbit today.


launch date Apr 3, 1965
launch vehicle Atlas-Agena D
launch site Vandenberg Air Force Base
mass 440 kg
orbit 1,270 × 1,314 km × 90°