Proton Rocket

The Proton is a Soviet and Russian heavy-lift rocket that became one of the longest-serving and most-used large launchers in history. Since 1965 it has lofted space station modules, planetary probes, and big communications satellites, doing much of the heavy hauling of the Soviet and Russian space programs.

Quick facts

• First flight: 1965.
• Origin: the Soviet Union; later operated commercially by Russia.
• Class: heavy-lift, able to send large payloads to orbit and beyond.
• Propellants: a storable but highly toxic mix of UDMH fuel and nitrogen tetroxide oxidizer.
• Notable cargo: the core modules of the Salyut and Mir space stations, and the Zarya and Zvezda modules of the ISS.

How it works

Proton uses propellants that stay liquid at room temperature, so the rocket can be fueled and held ready without the super-cold tanks that other rockets need. That made it dependable for heavy and deep-space missions. The trade-off is that those propellants are very toxic and corrosive, which raises safety and environmental concerns, especially because spent stages fall on land rather than into the ocean.

Why it matters

For more than half a century Proton was the backbone of Soviet and Russian heavy launches. It carried every major Soviet space station core to orbit and delivered the first two building blocks of the International Space Station. In the 1990s and 2000s it became a major commercial launcher, sending Western communications satellites to high orbits. As newer rockets like Angara are phased in to replace it, Proton’s record stands as one of the great workhorses of the space age.