The Proton was a model of Soviet scientific artificial satellites. The maximum mass was about 17 tonnes. Four "Protons" were launched between 1965 and 1968. The satellite was developed by NPO Mashinostroyenia. The aim of the project was to study high and ultra-high energy particles.
The Proton satellites were the source of the name for the Proton rocket, which launched them as some of its first payloads.