The largest Russian launch vehicle in regular use is the Proton-K, used in a 3-stage configuration for heavy, LEO missions and in a 4-stage configuration for high altitude deployments. The former variant is capable of lifting 20-metric-ton-class spacecraft into very low altitude orbits of about 200 km, while the latter supports semi-synchronous (GLONASS), geosynchronous, and deep-space missions, such as lunar and planetary probes.
The Proton originally was introduced in 1965 as a booster for heavy military payloads and for space stations. It was designed by the Salyut Design Bureau and is manufactured by the Khrunichev State Research and Production Space Center in Moscow. The Proton is among the most reliable heavy-lift launch vehicles in operation, with a reliability rating of about 98 percent.
The first three stages of the Proton-K were originally developed by the Chelomei Design Bureau in the early and mid-1960's. Today, design and production responsibilities lie with the Khrunichev State Space Research and Production Center in the Moscow region. All three stages burn UDMH and N204 hypergolic propellants. The first stage is powered by six 11 D48 (RD-253) engines, the second stage by three 8D411 K (RD-0210) engines and by one 8D412K (RD-0211) engine, and the third stage by a single 8D48 (RD-0212) engine. The first stage engines were developed by the Glushko Design Bureau (now the Energomash Scientific Production Association), whereas the Kosberg Design Bureau (now the Khimavtomatiki Design Bureau) created the second and third stage engines.
The first stage includes six engines that are fed propellants from a single, center oxidizer tank surrounded by six outboard fuel tanks. At launch, the first stage engines combine to provide about 1.9 million pounds of thrust. The first stage, which measures about 68 feet long by 24 feet in diameter, burns out and is jettisoned two minutes, six seconds after launch at an altitude of 27 statute miles and traveling more than 3,700 miles per hour.
Four engines creating 475,000 pounds of thrust power the Protonís second stage, which measures 56 feet long by 13.5 feet in diameter. While the second stage is in operation, the protective fairing covering Zvezda for liftoff is jettisoned at three minutes, three seconds into the flight. The second stage burns for a total of about three minutes, 28 seconds and is jettisoned at about five and half minutes after launch. When the second stage is jettisoned, the spacecraft is at an altitude of about 86 miles, traveling more than 9,900 miles per hour.
The Proton's third and final stage measures 13.5 feet long by 13 feet in diameter, and is powered by a single engine that creates 125,000 pounds of thrust.
The fourth stage of the Proton-K is produced by the Energiya Rocket and Space Corporation (formerly the Korolev Design Bureau) and utilizes liquid oxygen and kerosene derivatives as propellants, much like the original Sputnik launch vehicle. The main engine is restartable and is known as the 11D58M (RD- 58M). The fourth stage comes in two major variants: the Block D without an independent navigation and guidance unit for deep-space missions and the Block DM with such a unit for most Earth orbital missions. Three models of the Block DM are now in use for semi-synchronous missions (11S861), for normal geosynchronous missions (11S86), and for heavy geosynchronous spacecraft (11S861-1).The last was first used in 1994 for the maiden flight of the Gals spacecraft.
During the 1993-1994 period no 3-stage versions of Proton-K were flown, but 19 flights of the 4-stage model were conducted. All were successful except the mission of 27 May 1993 which failed to achieve orbit due to propellant contamination in the second and third stages. The vehicle returned to flight the following September (References 259-276). Four launch pads for the Proton-K were built at Baikonur (Complexes 81 left and right and 200 left and right), but only two were operational at the end of 1994. The other two were undergoing major overhauls.
One of the principal topics concerning the Proton-K launch vehicle in recent years has been its entry into the international commercial launch services market. An agreement between the US and the Russian Federation was finally reached in 1993 to allow limited use of Proton launch vehicles for commercial geosynchronous flights through the year 2000. In all, nine Proton missions to GEO (including the previously approved INMARSAT 3 contract} were allowed if the cost was not less than 7.5% below the international market value and more than two missions were conducted in a 12-month period. Three LEO missions of US Iridium spacecraft were also permitted, but other LEO commercial contracts were subject to future negotiations and mutual agreement.
Marketing of Proton launch vehicles was to be handled via the newly formed Lockheed-Khrunichev-Energia joint venture. By the end of 1994 no commercial Proton launches had been undertaken, and the first such mission was unlikely before the spring of 1996. Meanwhile debates concerning the raising of the numbers of GEO launches and how to count the leasing of Russian GEO spacecraft often became heated (References 277-286).
Before the US-Russian deal had been ironed out, Russian officials had already committed to a modernization of the nearly 30-year-old launch vehicle. The new Proton-KM launch vehicle will eventually be able to place 23.7 metric tons into LEO and 4.5 metric tons directly into GEO. With a standard Block DM fourth stage the Proton-KM will handle 3-metric-ton GEO payloads (compared to a 2.5-metric-ton limit for the Proton-K), but a new liquid oxygen/liquid hydrogen fourth stage will permit carrying the heavier 4.5-metric-ton spacecraft. In addition, new shrouds with larger volumes, some as large as 120 m3, will also be available.
Other elements of the modernization program include a new guidance system, more efficient energy and propellant management procedures, more benign payload launch environments, and more accurate landing zones for sub-orbital stages. Proton-KM will also be able to use a version of Khrunichev's new Breeze upper stage or Lavochkin's Fregat as anauxiliary fifth stage. Plans also call for replacing most Ukrainian suppliers of Proton components with new Russian vendors. Tentative plans announced in 1992 to build Proton launch facilities at the Plesetsk Cosmodrome were later abandoned when a program for a new generation heavy-lift booster was approved.