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.

Background and History
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 The two-stage D version has been superseded by the three-stage D-1 (SL-13) model and the four-stage D-1-e (SL-12) model, both of which are currently in use.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) has been developed and flown once.

A Proton is erected upright on its Baikonur Cosmodrome launch pad. Photo: ILS

The Block DM fourth stage of the Proton was developed independently during the 1960s as the fifth stage of the Russian manned lunar launch vehicle, the N1-L3. It was originally known in Russia as the Block D ("block" is the common translation of the Russian word denoting a rocket "stage", while "D" is the fifth letter in the Russian alphabet). The vehicle was upgraded during the 1970s to the current Block DM (modernized) version. The Proton model numbers D, D-1, D-1-e, SL-13, and SL-12 are the designations currently in common use in the United States, with the D numbers having been applied by the Library of Congress and the SL numbers originating with the U.S. Department of Defense.

Proton has flown more than 200 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.

The Proton family
The Proton is currently available as a three-stage D-1 (SL-13) model and as a four-stage D-1-e (SL-12) model which will be used for commercial launches. A variety of supplemental orbital propulsion units, in a range of capabilities, can be used with either the three- or the four-stage Proton. In addition, there are multiple fairing designs presently qualified for flight. A "Standard Commercial Payload Fairing" has been developed specifically to meet the needs of commercial satellite customers.

Illustration of Proton/Block DM rocket. Photo: ILS

The lower three stages of the Proton are produced by the Khrunichev State Research and Production Space Center (KhSC) plant in Moscow. Production of the Block DM fourth stage is carried out by Russian Space Complex (RSC) Energia, also in Moscow. Current production capacity for the Proton is approximately 15 vehicles depending on launch rate.

Overall height of the vehicle in either configuration is approximately 61 m (200 ft), while the diameter of the second and third stages, and of the first stage core tank, is 4.1 m (13.5 ft). Maximum diameter of the first stage, including the outboard fuel tanks, is 7.4 m (24.3 ft). The Block DM fourth stage, when present, has an external diameter of 3.7 m (12.1 ft). Total weight of the Proton at launch is approximately 691,500 kg (1,524,000 lbm).

D-1-e (Four-Stage) Configuration
The Proton D-1-e (which will launch EchoStar 8) is a series-staged vehicle consisting of four stages. The lower three stages are identical to those of the three-stage Proton D-1, and use nitrogen tetroxide (N 2 O 4 ) and unsymmetrical dimethylhydrazine (UDMH) as propellants. The fourth stage, known as the Block DM, uses liquid oxygen and synthetic kerosene, or synthin.

The Block DM (fourth stage) is optimized for multi-burn space transfer operations. Its main engine (model number 11D58M) delivers a vacuum thrust of 83.5n (1.88 x 10 4 lbf), is gimbaled to provide three-axis control during powered flight operations, and can be restarted as many as seven times during flight. The stage is 3.7 m (12.1 ft) in diameter, 6.28 m (20.6 ft) in length, with an inert mass at separation of 2,440 kg (5,378 lbm) and a total propellant mass of 15,050 kg (33,180 lbm). It is three-axis stabilized in unpowered flight by a storable bipropellant (N 2 O 4 /UDMH) attitude control system, comprised of two "SOZ" (or "micro") thruster units located at the base of the Block DM. Guidance, navigation, and control of the fourth stage are provided by a triple redundant digital avionics package, which can be ground commanded in flight, if necessary.

Multiple payload fairings are available for the Proton. It is a two-piece, hinged, clamshell structure of monocoque composite sandwich construction. It does not incorporate separation rocket motors, and no pyro gases are released during operation.