Commercial Rockets

PROTON (Протон) — Russia, 1965

Like other rockets of the era, this was originally built for use as an ICBM. This one in particular was designed to hurl hydrogen bombs of titanic size. It was never deployed in that role. This was a big-ass rocket for the time, comparable in grunt to today’s Delta IV Heavy. But the thing is surprisingly compact for the amount of muscle it has. It launched the Salyut and Mir space stations, and some modules of the International Space Station. When used for satellites, they often load a dozen or more into one flight, distributing them around to various orbits. They were quite secretive about the rocket in the early days, allowing no pictures of the bottom stage.

Unlike the Delta or Atlas or even the Soyuz, it uses hypergolic fuels (unsymmetrical dimethylhydrazine and dinitrogen tetroxide, this being the most common of several available hydrazine mixes). As explained in the Stats & Specs section about engine type and fuel codes, “Hypergolic” means they need no igniter, as they immediately combust on contact with each other, but it also means they are very toxic in unburned form and nasty polluters when burned. The principal advantage of hypergolics is that they can be stored for long periods at room temperature, which makes sense for an ICBM.

Like other Russian designs, this rocket widens at the bottom, with six gimballed nozzles mounted in a ring around the central tank. But these do not detach; there is no central nozzle. Each engine is surmounted by an outboard fuel tank, while the central cylinder holds the oxidizer. The reason for this construction was just that they didn’t have any good way of transporting rocket bodies of larger diameter; this allowed the side parts to be bolted on at the launch site. Because of this radial design, the engines (Energomash RD-275M) are notably lopsided when viewed in the open.

The second and third stages are of a conventional cylindrical shape, using the same hypergolic fuel, and enormous by upper stage standards: over 200 tons for the pair. A fourth stage for high orbits or reaching escape velocity is optional, and there are a few choices for which to use. (In the early days, the Proton specialized in interplanetary probes, and the fourth stage was always used. The top stage used kerosene and lox, which made no sense. Nowadays the fourth stage is usually a “Briz-M”, which uses the same fuel as the rest of the rocket.) Unlike the R-7, this rocket has not evolved very much; it’s still much as it was in its early days. And unlike the R-7, it does not manage to pull off the tapered look with elegance and grace; even some who are fans of the rocket will admit that it’s butt-ugly.

The Proton has never done a crewed flight, but it was almost used a couple of times, and at one point was going to send two people on a circumlunar mission. Repeated failures with unmanned vehicles forced them to reconsider. I will note that the great Korolev felt that hypergolic fuels were inherently too unsafe to use on crewed flights... but then, the Proton team was competing for support with his N-1 moon rocket.

In an effort to lower costs, they were designing lightened variants of the rocket, including a version with only four engines instead of six. The first stage would be stretched a bit, and the huge second stage would be eliminated. But they never persuaded anyone to fund this. The head of the Roscosmos agency announced in June of 2018 that Proton production will now be halted so the facilities can start building Angaras instead. Some of the Proton’s workload will probably go in time to the Irtysh, a remake of the Zenit which has been widened to have the same exterior diameter as the Proton (the maximum diameter that can be transported by rail) and be compatible with much of its infrastructure. It seems strange that the light Angara will officially replace the heavy Proton, while the heavy Irtysh will replace the light Soyuz... I guess that’s Russian politics. And it means that during the transition, there might be a period where Russia has no heavy rocket in operation, so the only way to launch a twenty-ton payload will be by combining five Angara boosters, which can’t be cheap.

At present, it appears that the Proton will be retired once its currently booked launch contracts are completed. But that list still has about twenty launches over the next two to three years.

Proton M, three stage: mass 683 t, diam 4.1 m (7.4 at base), thrust 10000 kN, imp 3.1 km/s, type ZOd, payload 21.6 t (3.2%), cost $5M/t, record 374/0/46.
Stage name 8S810KM 8S811KM 8S812KM Blok-DM * Briz-M
Role (pos) count core (1) upper (2) upper (3) kick (4), opt kick (4), opt
Diameter (m)     7.40 *   4.10   4.10   3.70   4.10
Liftoff mass (t) 448    167    50   17.6 19.6
Empty mass (t) 29   11    3.5  2.2  2.4
Fuel mass (t) ~114     ~43.3  ~13.1  ~4.4 ~5.8
Oxidizer mass (t) ~305     ~113     ~33.4  ~11.0  ~11.7 
Fuel type UDMH UDMH UDMH kerosene UDMH
Engine Energomash
RD-275M ×6
RD-0210 ×3,
RD-0211 ×1
Power cycle Staged (ZO) Staged (ZO) Staged (ZO) Staged (ZO) gas gen
Chamber pres. (bar) 165    147    147   78   98  
Ox./fuel ratio   2.67   2.60   2.54   2.48   2.00
Thrust, vac max (kN) 11000      2400     630    83   19.6
Thrust, SL initial (kN) 10100     
Spec. imp, vac (km/s)   3.10   3.21   3.19   3.42   3.20
Total imp, vac (t·km/s) 1325     523    148   53.5 64.2