N-4 n°3 is a satellite of the N-4 constellation. The N-4 heavy science satellites were developed by Vladimir Chelomei's OKB-52 in the early 1960s. Baptized "Proton", they will give this name to the UR-500 launcher which will put them into orbit.

They are designed to study very high-energy particles in low Earth orbit, assess the hazard they represent, and determine the intensity and energy spectrum of electrons and gamma rays. These studies are not possible on Earth, because the charged particles are mainly absorbed by the atmosphere.

They are sized to operate in orbit for forty-five days, and are equipped with four solar panels, several batteries and a thermoregulation system. The batteries are located in small capsules placed between the central body and the external envelope of the satellite.

The satellite was destroyed in the atmosphere because of the failure of the launch.