It was 5 feet in diameter, three axis stabilized (for the benefit of the reconnaissance system cameras) and its Bell 8096 engine produced 16,000 lbs thrust using hydrazine (UDMH) and nitrogen tetroxide as propellants. The engine could be restarted multiple times in orbit. This engine started life as the power plant for the canceled rocket-propelled nuclear warhead pod for the Convair B-58 Hustler bomber. Agena was thus known as Hustler early in its development.
Agena seems to have come in three versions:
; A : 7,000 kg thrust Bell 8048 engine, 120 second burn time, used on Thor and Atlas. ; B : 7,250 kg thrust Bell 8081 engine, 240 second burn time, used on Thor and Atlas. Launched early SAMOS and MIDAS military satellites and the Ranger lunar probes. ; C : Proposed but never built. ; D : 7,250 kg thrust Bell 8096 engine, 265 second burn time, used on Thor, Atlas, and Titan. Launched early KH-7 GAMBIT spy satellites and the two Mariner Mars probes.
Extensive information about Agena is hard to come by; perhaps due to its reconnaissance roots.
Agena may have last flown in 1987.