On this day in 1965, the first Proton booster rocket was launched. Almost 50 years later, this booster remains one of the most powerful in the world, and also one of the most controversial. It's been used in almost 350 launches.
Like all Soviet rockets designed during the Cold War, Proton was originally made for military purposes. The rocket booster was designed specifically for the task of launching 100 megaton atomic bombs. However, since it was never put into mass production as a weapon-carrying missile, it was repurposed for launching satellites and other gear. Its first mission was the launch of a scientific research satellite. It was also used for lifting the Salut, Almaz and Mir space stations.
These days, the Proton booster is used most frequently to launch American telecommunication satellites. The booster has been improved over the years to include longer fuel tanks and more stages in the rocket. These innovations mean that it's able to lift 45,000 pounds into low orbit, making it useful for testing lunar orbit ships and even research stations into deep space. The Proton booster is on track to be replaced by a new model by 2030, but for now, it remains one of the most successful heavy boosters in the history of space flight.