Proton (UR-500)

The figures here are for the original two-stage UR-500 as it first flew on 16 July 1965, because that is the variant RussianSpaceWeb specifies: 44.3 metres without warhead or upper stages, 7.4 metres across, 620 tonnes fuelled, and 12 to 13 tonnes to orbit. Liftoff thrust is six RD-253 engines at 150 tonnes each on the ground, 900 tonnes of thrust, about 8,826 kilonewtons. The later three-stage Proton-K raised the first stage to 9.5 meganewtons and the payload well beyond 20 tonnes.

The distinctive silhouette, a fat core with six slim tanks strapped around it, is not aerodynamics. RussianSpaceWeb is explicit that sectioning of the first stage was dictated by transportation restrictions rather than flight dynamics: the 4.1 metre core tank is the absolute maximum that could be delivered by rail even on a custom carriage. The oxidiser lives in the core, the fuel in six 1.6 metre bolt-on tanks, and the cluster spans 7.4 metres. A rocket designed around a tunnel profile.

Chelomei’s bureau sold it to the military as a 500 tonne two-stage machine capable of carrying a 30 megaton warhead, which is how a space launcher got funded. It never carried one. What it did carry, in its three-stage form, is most of the Soviet and Russian heavy-lift record: Salyut, the world’s first space station, on 19 April 1971; the base block of Mir on 19 February 1986; and Zarya, the first module of the International Space Station, on 20 November 1998.

The dates on this record run the length of the Soviet-era vehicle, from the first UR-500 on 16 July 1965 to the last Proton-K on 30 March 2012, which carried the final Oko early warning satellite. The commercial Proton-M outlived it. The physical figures above are the 1965 original and nothing later.

The chemistry that makes it convenient makes it a diplomatic problem. Hypergolic propellants ignite on contact and need no ignition system, and they sit at ambient temperature so the rocket can stand fuelled. They are also unsymmetrical dimethylhydrazine and nitrogen tetroxide, both severely toxic. When a Proton carrying JCSAT-11 crashed in September 2007 it still held an estimated 218 tonnes and 979 kilograms of propellant, and left a crater 20 metres deep and 45 metres across. As after previous accidents, the Kazakh government imposed a formal ban on further Proton launches. That veto has been used repeatedly, and it is the real constraint on the vehicle, not its engineering.