MOSCOW (Yuri Zaitsev, for RIA Novosti) - Forty years ago, on July 16, 1965, the world's heaviest research station was launched into space.

The Proton weighed 12.2 tons, carried 3.5 tons of instruments and research equipment, and was designed to study space rays and their interaction with ultra-high-energy particles.

The research was later continued with the Proton-2, Proton-3 and Proton-4 stations. The Proton-4 weighed about 17 tons, while its equipment weighed 12.5 tons. All the stations were put into orbit by the Ural UR-500 multi-purpose rocket, developed at Vladimir Chelomei's design bureau. The rocket's performance characteristics by far exceeded those of carrier rockets of the time in the Soviet Union and abroad. The military version was intended to be used for retaliation in case of an attack on the Soviet Union, and could deliver a 50-megaton nuclear warhead at intercontinental distance.

It was an immense project. The first stage of the rocket consisted of a central block with six side blocks around it. Each block had an engine with a 150-ton jet thrust. The second stage consisted of one block of the same diameter as the central block of the first stage. The rocket was fuelled at the launch site by aggressive fuel components, where nitric tetroxide was used as an oxidizer and non-symmetric dimethyl hydrazine (heptyl) as fuel.

The launch weight of the rocket was about 600 tons. While the rocket was being designed, it appeared that with its set parameters the size of the first-stage airframe would make it impossible to carry it by rail, which was a problem as the military, which had ordered the rocket, insisted that it should be carried only by rail. Chelomei decided to link the fuel tanks with the oxidizer tank, forming a kind of a packet scheme. Such an arrangement suited the military and was accepted as the standard.

The launch system was original as well. For the first time, a scheme was proposed using two similar launchers. They were placed 600 meters away from each other and shared facilities for preparing and conducting a launch.

Initially both ground and silo variants of the launch pad were to be created, but work on the silo variant was abandoned some time later.

The first experimental launch of the UR-500 was carried out on May 15, 1964. However, testing of a nuclear warhead at Novaya Zemlya showed that a 50-megaton nuclear explosion would cause a global catastrophe, and the plan was scrapped. Thus a rocket to deliver such a warhead became unnecessary, and work on the development of the Ural UR-500 ballistic rocket was stopped in the same year.

A space carrier rocket was developed in two-stage and three-stage versions based on a two-stage IBM. Since Proton space vehicles were launched during testing, the two-stage carrier rocket was called Proton, and the three-stage one Proton-K. The design appeared to be successful.

After the Energia-Buran reusable shuttle program was discontinued, the Proton was Russia's only heavy-class space carrier rocket. The three-stage version was used to launch modules for the Mir orbital station, and then for the International Space Station. It was decided to add a booster (i.e., a four-stage version) to launch space vehicles to high-energy orbits (the European Integral astrophysical laboratory), and also to switch to a geostationary orbit (GLONASS navigational space vehicles and communications satellites, and also on the trajectory of departure from the Earth (Mars-Phobos, Mars-96).

The Proton-K won a reputation as the world's most reliable, best tested and profitable heavy carrier. It has been used for commercial launches since April 1996. And to the end of 2000, when quotas for using it on the world launch-services market were still valid (they were cancelled in December 2000), Russia made 23 commercial Proton launches, which brought it about $2 billion. Sales of the carrier rocket were not at dumping prices but ranged between $65 million and $90 million per launch.

At present the load carrying capacity of the Proton-K to an orbit at 200 km altitude, when launched from Baikonur, is 20.6 tons, and to geostationary orbit 2.6 tons. In April 2001, the first successful launching of a Proton-M (M for modernized) was carried out. A new booster, the Breeze-M, was added to the carrier, thus considerably improving conditions of placing space vehicles under the nose fairing, which has become especially attractive to commercial customers.