Vela 3B was one of two polyhedral satellites comprising the third in a series of six Vela launches. The orbits of the two satellites on each launch were basically circular at a radial distance of about 17 earth radii and spaced 180 deg apart. The satellites were spin stabilized at about 2 rps and had their spin axes inclined at about 60 deg to the ecliptic. Data acquisition was mainly real time and averaged 25% (1 out of every 4 h) coverage per day. Data coverage was increased for special events. The satellite operated well during the period of major data coverage, i.e., from launch until the April 1967 launch of the Vela 4 satellites. After this time, data acquisition from the Vela 3 satellites became increasingly sporadic.