Commercial Rockets

ZENIT (Зеніт), IRTYSH (Иртыш) / SOYUZ-5, and YENISEI (Енисе́й) — Ukraine/Russia, 1985

Designed to replace the Proton, though not as powerful, they had some hope it could largely replace the Soyuz as well... this is a much more modern design than either, but it suffered from the turmoil of the Soviet breakup. It then went on to find a market elsewhere. Some versions were launched at sea by a company called the Sea Launch Consortium, from a converted drilling rig based in Long Beach. Others launch from Baikonur. But the relationship with the Ukrainian factory is kaput after the Crimean annexation, which appears to have also killed off Ukraine’s Dnipr rocket. There has only been one Zenit launch since 2015, so it may be a dead duck... Sea Launch claimed they’d be back to a regular launch schedule starting in 2019, but this was very overoptimistic, as delivery of Russian engines to either Ukraine or the USA remains problematic, and many of the skilled workers at the Yuzhnoye Design Office and associated PA Yuzhny Machine-Building Plant (commonly known as Yuzhmash / Южмаш), where the rocket is built, have now departed. Back in the day, Yuzhmash also built the Dnipr and Tsyklon rockets.

The Russian government would definitely like to get Sea Launch going again, because it’s their only launch option that can take off from near the equator... but the Ukrainian government would prefer to keep Sea Launch unavailable to them. The S7 Group, which bought the company in 2016, finally admitted that there are no foreseeable launches, but blamed the delay on Covid-19, which was of course affecting the whole industry. They moved the platform and its support ship to Vladivostok, but now they basically need to find a new rocket for it.

The Zenit’s first stage has a kerosene engine with a quadruple nozzle — the RD-171M. Its four combustion chambers are fed by a single set of turbopumps. It’s a variant of the RD-170, and is the most powerful liquid-fueled engine ever made, outperforming the mighty F1 used in the Saturn V. The engine weighs ten tons, and the whole thing gimbals as a unit. (Improved gimballing is the main difference between the 170 and the 171.) This belongs to the same family as the RD-180 used by the Atlas, which is basically half of an RD-171, and like that engine it has exceptional performance for a kerosene burner because it uses a closed cycle and can maintain an extremely high pressure in the combustion chambers. It took eleven years to engineer this staged-combustion motor, but it has proved worth the effort. Not only does the engine (and its many descendants) have world-leading performance, it also has the durability to be put into a reusable rocket, able to do ten flights before replacement. Some engines have reportedly survived up to twenty flights worth of test firings.

This big engine was originally used in the monstrous Energia (Энергия) rocket which once flew the Buran (Бура́н) shuttle. The Zenit’s main stage started out as a side booster on the Energia, which had four of these strap-ons attached asymmetrically to a hydrogen-burning core stage, and could lift 100 tons. There is still talk about bringing back the Energia, despite its high cost. The question of whether Russia can get away with just the cheap little Angara or whether it needs a much bigger rocket is apparently still being argued, but it looks like the case for the Angara-only approach has been lost. There were unfinished plans to build an Energia 2 which would allow them to recover and reuse both the Zenits and the core stage; if pursued, this might make the cost much more reasonable, even though with that version they planned to increase its capacity to a whopping 170 tons. But I don’t know, the plans looked a bit nutty... they involved giving each Zenit a big pair of folding airplane wings! Even in the original Energia,the side boosters used parachutes for a semi-soft landing, so they could be recovered and examined after use. These plans for a reusable superheavy rocket were interrupted by the fall of the Soviet Union, which is why the Buran (which means “blizzard”) never made a second flight.

The present-day Zenit’s RD-171M is a less expensive, mildly simplified version of the engine. Its second stage has two kerosene engines, the main one being a non-gimballing RD-120, with a four-nozzled RD-8 encircling it to provide steering. It’s the only vernier engine to use staged combustion. A third stage — usually a stubby Russian model also used atop the Proton, known as Blok-DM — is generally used for sea launches but not from land; this is for reaching geostationary and other high orbits. A Fregat kick stage can also be used. These fit inside the fairing. The Zenit has high performance for its cost, but the tradeoff has been a pretty bad failure rate.

With Yuzhmash out of the picture, the plan they settled on was to build a new Zenit-based rocket and call it the Sunkar (Сұңқар), an improved all-Russian version. Sunkar means “falcon” in Kazakh... in Russian it was going by the name Feniks (Феникс), then they said it was officially going to be Soyuz-5 (a complete misnomer as it shares no heritage with the Soyuz and doesn’t even come from the same manufacturers), but then they said the Russian name is going to be Irtysh (Иртыш), which like Angara and Dnipr is the name of a river. The Sunkar name is apparently being discarded along with Feniks. But they might be sticking with Soyuz-5 after all — it’s not clear. The engine would be a new version called RD-171MV, with improved controls and no imported components.

Apparently one minor part of the rocket’s purpose is to rebuild business ties with the Baikonur launch facility in Kazakhstan, which the Russians had been pulling away from in favor of new launch pads on Russian soil. They may be regretting that because none of those new pads have as low a latitude as that of Baikonur. If this gets built, it might kill off the rival proposals for a lightened Proton and for a methane-burning Soyuz replacement, and also make a significant dent in the ambitions of the struggling Angara system. Each design comes from a different rival aerospace outfit: the Soyuz coming from RKTs Progress in Samara, the Angara from the Khrunichev Center (which also makes the Proton), and the Irtysh from RKK Energia. If the Irtysh wins — and for the short term, it seems to be doing so — the two losing companies will probably each get some subcontracting work. But the latest plot twist is that a methane rocket, now dubbed the Amur, is the one with which they will go for reusability. They have not yet said who will build it. Those plans are described in the article for the Angara.

One condition the Kazakhs had was that any new rocket should use clean fuel. They were tired of the environmental hazards of the Proton, and knew what it was like to see one smack into the ground and not only shatter windows in the next town, but also leave behind a huge patch of poisoned soil.

The Irtysh would be widened from 3.9 to 4.1 meters, so its middle part would be externally compatible with the Proton. This would increase its payload capacity to 17 metric tons, maybe even 18. The base would be narrower, to be compatible with that of the Zenit. It would keep its overall height compatible with the Zenit 3. Keeping to these pre-existing constraints minimizes the changes needed for launch pads and transporters. (As with the Zenit and Proton, the stages would be shipped by rail.) To fit this height goal, they’re designing the new second stage to have eight small nozzles (divided between two RD-0124MS engines) to keep its base as short as possible. They hope to fly this in 2023, and to then restart Sea Launch with it.

There are plans to also restore the Irtysh to its role as a side booster in a superheavy rocket like the Energia. Some plans are to just update the classic Energia design, but there’s another approach which argues that by just hooking up five or six Irtysh cores horizontally, and then piling three more stages on top of the central one, they could lift payloads exceeding 100 tons without needing any oversized central stage.

And in 2018, it was a version of this plan which got the go-ahead for further development: a new superheavy launcher to be called Yenisei (Енисе́й — Russia’s largest river) would have four or six side boosters based on the Irtysh first stage, surrounding a core booster which would be similar but use the smaller RD-180 engine instead of the RD-171MV. Four of the side boosters would be used right away, while the other two (if used) would be delayed and stay attached longer. So the nomenclature they’re using is that the four early boosters would be designated as stage 1, the two late ones as stage 2, the core as stage 3, the upper (which would use dual RD-0146 motors that burn hydrogen in an expander cycle) would be stage 4, and at the top they could add a little stage 5 with an RD-58MF engine... which is odd as this is a kerosene engine, and I’ve never heard of a kerosene stage being carried by a hydrogen stage before. They plan to lift 100 tons with this design. In silhouette this stack would look scarcely bigger than a Falcon Heavy, but then you’d notice the four additional boosters.

The sneaky bit is that the the core booster may look like another Irtysh, as it’s 4.1 meters across and uses a similar engine, but it isn’t: it’s actually a super-fattened Angara rather than a slightly fattened Zenit. It would be built in the Angara factory. I assume there were good political reasons for distributing the construction contracts between the rival companies. But there may also be good engineering reasons, as the Angara was designed from the start to have an airframe capable of supporting large external boosters. They never planned on hanging this much mass and power off of it, but at least it’s only a matter of scaling up the thing’s structural strength by some percentage, rather than building up such a framework from scratch. It’s not clear that this saves much design effort when the diameter is drastically different, though.

But that’s just one version of the Yenisei proposal: in earlier ones the core would be Energia-like and burn hydrogen. It could change again if the Angara program continues to struggle.

Zenit 2M (no third stage): mass 462 t, diam 3.9 m, thrust 7550 kN, imp 3.3 km/s, type ZOk, payload 13.7 t (3.0%), cost $6M/t,record 65/7/12 (final?).
Stage name Zenit Blok-DM-SL * Fregat-SB
Role (pos) count core (1) upper (2) kick (3), opt kick (3), opt
Diameter (m)   3.90   3.90   3.70   3.35
Liftoff mass (t) 354    91  17.4 11.6
Empty mass (t) 27.6 ~8.4  2.1  1.4
Fuel mass (t) 90.2 22.8 ~3.4
Oxidizer mass (t) 236.6  58.9 ~6.8
Fuel type kerosene kerosene kerosene UDMH
Engine RD-171M RD-120 +
RD-8 vernier
RD-58M Lavochkin
S5.92
Power cycle staged (ZO) staged (ZO) staged (ZO) gas gen
Chamber pres. (bar) 245    163    78   98? 
Ox./fuel ratio   2.60   2.72   2.00
Thrust, vac max (kN) 7890     990    85   19.9
Thrust, SL initial (kN) 7550    
Spec. imp, vac (km/s)   3.30   3.42   3.45   3.27
Total imp, vac (t·km/s) 1065     280    56   32.7