Satellite 2120 saw a switch to the Agena B stage, and was launched as SAMOS 3 with the 0.9-meter (36-inch) focal length E-2 steerable reconnaissance payload. However, the Atlas exploded on the pad at the moment of takeoff. The rocket reached an altitude of 1 meter when the engine shut down because of a signal from an umbilical cable which failed to detach. The rocket fell back to the launch pad and exploded. The intended orbit was 480 x 480 km x 83 deg.
According to TRW Space Log, launch mass was 1900 kg, but this may be an unreliable extrapolation from SAMOS 2.
In addition to the SAMOS E-2 camera and F-1 ferret, satellite 2120 carried scientific experiments . SAMOS 3 was the only Program 101A satellite. A second satellite, Agena no. 2121, appears never to have been launched. It was originally intended that 2120 and 2121 would each carry only one payload, interchangeably either E-2 or F-2.
|SAMOS 3 (Agena 2120)|
|1961 Sep 9||1928||Launch by Atlas Agena B||NMFPA LC1 Pad 1|
|1928||Atlas engine shutdown (T+0:01)|
|1928||Atlas impact on pad, explosion (T+0:01)|
|1928||Agena explosion (T+0:02)|