Plural of Agena . In the military field, it is the name of the upper stage of rockets for United States reconnaissance satellite programs. They were designed by Loockheed Martin. The internal designation was RM-81. It was mixed with Thor, Atlas or Titan rockets. Colloquial or popular way of calling bright stars. Agena is another of the names of the star Beta Centauri or Hadar, which belongs to the constellation Centaurus.