This is the antenna assembly from an engineering test model of the approach radar set used to land on the moon. The antenna was mounted on the lower exterior surface of the Apollo program Lunar Module (LM). The signal from the antenna was fed to a continuous wave doppler radar set that controlled the powered landing. This instrument provided velocity, slant and altitude measurement data to the guidance computer used to manage the retrorockets that slowed the descent of the LM. The radar set was manufactured by the Teledyne Corporation. This antenna and its electronics (A 19740640000) were transferred to NASM from NASA's Johnson Space Flight center in 1974.