File image of a Proton rocket lifting off. Photo: ILS

Proton is the most capable, commercial, expendable launch vehicle presently in operational service. It offers larger beginning-of-life (BOL) masses in geostationary orbit (GSO) than any other commercial launch system, as well as larger delivered payload masses into most low-, intermediate, and high-energy orbits. Proton's three-stage configuration is used primarily to launch large payloads into low earth orbit, while the four-stage configuration is used to launch spacecraft into high-energy trajectories (geo-transfer, geosynchronous, geostationary, and interplanetary).

Proton's fourth stage possesses a multiple restart capability that allows it to perform all orbit change maneuvers necessary to place a spacecraft into its final orbit, without requiring use of the spacecraft's on-board propellant supply. Proton can deliver payloads of up to 22 metric tons to low-earth orbit, or up to 2.1 metric tons to geosynchronous orbit.

Development of the Proton launch vehicle was undertaken in the early 1960s, under the direction of the Soviet academician, V. N. Chelomey. The first launch took place in July 1965. The two-stage D version, last flown in 1966, was used to launch four flights of the Proton satellite series, from which the launch vehicle takes its name. The two-stage D version has been superseded by the three-stage D-1 (SL-13) model and the four-stage D-1-e (SL-12) model, both of which are currently in use. An improved version of the Proton (Proton M) is now in service.

Proton has flown more than 300 missions and has orbited the Salyut series space stations and the Mir Space station modules. It has launched the Ekran, Raduga, and Gorizont series of geostationary communications satellites (which provided telephone, telegraph, and television service within Russia and between member states of the Intersputnik Organization), as well as the Zond, Luna, Venera, Mars, Vega, and Phobos inter-planetary exploration spacecraft. The Proton has also launched the entire constellation of Glonass position location satellites. All Russian geostationary and interplanetary missions are launched on Proton. Approximately 90% of all Proton launches have been the four-stage version.

The Proton launch vehicle has a long history of outstanding reliability. From its first operational launch in 1970 to the present day, Proton has averaged a 92.5% success rate. The Proton launch vehicle has a 92% (moving average) success rate over its last 50 launches.

Proton/W3A vehicle

Proton booster
The Khrunichev State Research and Production Space Center-built Proton booster is 4.1 m (13.5 ft) in diameter along its second and third stages, with a first stage diameter of 7.4 m (24.3 ft). Overall height of the three stages of the Proton booster is 42.3 m (138.8 ft).

First stage
The first stage consists of a central tank containing the oxidizer surrounded by six outboard fuel tanks. Each fuel tank also carries one of the six RD-253 engines that provide first-stage power. Total first stage sea-level thrust is approximately 9.5 MN (2,140,000 lbf) with a vacuum-rated level thrust of 10.5 MN (2,360,000 lbf). The first stage engines are flown at a 107% thrust level.

Second stage
The second stage, of conventional cylindrical design, is powered by four RD-0210 engines and develops a vacuum thrust of 2.3 MN (570,000 lbf).

Third stage
The third stage is powered by one RD-0210 engine, developing 583 kN (131,000 lbf) thrust, and a four-nozzle vernier engine which produces 31 kN (6,900 lbf) thrust.

Breeze M upper stage
The Breeze M is powered by one pump-fed gimbaled main engine developing 19.6 kN (4,400 lbf) thrust. The Breeze M is composed of a central core and a jettisonable additional propellant tank. Inert mass of the stage at liftoff is approximately 2,370 kg (5,225 lbm). The quantity of propellant carried is dependent on the specific mission requirements and is varied to maximize performance for the mission. The Breeze M is capable of operating on-orbit for a minimum of 24 hours and is controlled by a closed loop, triple redundant guidance system that is commandable in flight.