ESSA 4 was a sun-synchronous operational meteorological satellite designed to provide real-time earth cloudcover TV pictures to properly equipped ground receiving stations for use in weather analysis and forecasting.
The satellite carried the APT (Automatic Picture Transmission) system with two redundant APT cameras with 2.54 cm diameter vidicons and 108° wide angle 1/1.8 objective lense with a focal length of 5.7 mm. The imaging system was programmed to take four or eight APT pictures per orbit

With the exception of the failure of one of the APT cameras, the spacecraft performed normally after launch. It was turned operationally off on December 6, 1967, and was finally deactivated on May 5, 1968.