RD-171MV. One engine for three rockets.
On April 30, 2026, the 45th platform of the Baikonur Cosmodrome was launched RocketSoyuz-5 launch vehicle. The first and second stages performed normally. A payload mockup landed in an area of the Pacific Ocean closed to shipping. Nine years of development, four delays, one launch.
Nine years from drawing to launch
The Soyuz-5 program began in the mid-2010s under the working names Phoenix, Sunkar, and Irtysh. Each name reflected a stage. Phoenix was an attempt to revive the mid-range rocket line after the loss of the Ukrainian Zenit. Sunkar was Kazakhstan's contribution to the Baiterek project. Irtysh was the final Russian version for serial production.
Initially, the rocket was planned to run on methane. The designers at the Progress Rocket and Space Center abandoned this idea in favor of the proven combination of liquid oxygen and kerosene-naphthyl. The decision was driven by the need to minimize technical risk. At that time, methane engines in the country existed only as prototypes. Oxygen-kerosene represents fifty years of production experience and a functioning process chain.
The first launch was planned for the second half of 2022. Then it was pushed back to the end of 2025. Then to March 2026. Then to April 30th. Each postponement was explained by modifications based on the results of ground tests. By the end of 2025, the rocket was assembled and formally ready for launch, but Roscosmos management scheduled an additional round of checks for the onboard electronics and ground equipment. Nine years before the first launch is a long time by the standards of commercial programs like the Falcon 9. It's not unusual by the standards of large-scale state-run rocketry from scratch.
What is the RD-171MV?
The heart of the Soyuz-5 is the RD-171MV engine developed by NPO Energomash. It is a four-chamber, closed-cycle liquid-propellant rocket engine. Its two propellants are liquid oxygen and kerosene. Its thrust at sea level is approximately 800 tons. In simple terms, the engine produces a thrust equivalent to the weight of 800 tons at the Earth's surface. Its vacuum thrust is approximately 880 tons. Its specific impulse at sea level is 309 seconds, and in a vacuum, 337 seconds. This is the world's highest performance for oxygen-kerosene engines.
A closed cycle with afterburning of the oxidizing generator gas is the key principle. In an open cycle, part of the working fluid, after spinning the turbopump turbine, is ejected overboard past the combustion chamber. In a closed cycle, all the gas after the turbine enters the combustion chamber and is burned there. The fuel's energy is utilized more completely, and the specific impulse is higher. The design is an order of magnitude more complex. The turbopump operates in an environment where temperatures exceed 500°C and pressures reach hundreds of atmospheres.
Four chambers on a single turbopump is a signature solution of the Glushko school. A single-chamber engine with comparable thrust would have to be built with a chamber large enough to fit a person, and such a design is technologically unfeasible due to combustion instability. Four smaller-diameter chambers, fed by a single supply unit, provide the combined thrust of a single-chamber giant without process failure. Each chamber oscillates in a single plane to control the thrust vector. This is the difference between the RD-171 and the RD-170. In the RD-170, all four chambers oscillate in two planes, while in the RD-171, each oscillates in a single plane. Control is simpler and reliability is higher.
From RD-170 to MV
The engine line of this family has been in production since 1976. The RD-170 was developed for the first stage of the Energia super-heavy rocket for the Buran program. Its thrust at sea level is approximately 740 tons. It is the most powerful liquid-propellant rocket engine ever created, with a weight comparable to the American F-1 engine from the Saturn V. The F-1 was single-chamber and operated on an open cycle. Its specific impulse was lower, but its design was simpler. The RD-170 opted for complexity for efficiency.
The RD-171 is a modification for the Ukrainian Zenit rocket. The RD-171M is a 2001 version with a 5% increase in thrust due to a redesigned turbopump assembly and control systems. The RD-171MV is the current version for the Soyuz-5, with updated control electronics and improved hot-section materials.
What exactly was changed? In terms of electronics, a digital control system replaces analog, providing more precise thrust and vector control. In terms of materials, heat-resistant alloys are used in the injector head and the critical nozzle section, where temperatures reach 3500–3700 K. In terms of the cooling system, the regenerative cooling channels have been optimized, where kerosene passes through the chamber and nozzle cooling jacket before being injected into the chamber, absorbing heat. The turbopump unit has been modified for higher feed pressure, allowing for additional seconds of specific impulse.
The strategic significance extends beyond the Soyuz-5 itself. The RD-171MV is becoming the reference engine for an entire line. The RD-191 on the Angara is structurally equivalent to one chamber of the RD-170 family. The RD-180, which previously powered the American Atlas V, is equivalent to two chambers. A complete RD-171MV is four. Between these three engines, there are no identical components in the sense of "remove from one and install on another." Standardization is taking place at a different level. A common Glushko school, shared closed-cycle principles, common materials, and a common component base. Technological interrelationships are estimated at 70%. The serial production rate of each component is higher than it would have been with separate development. This is engineering economics at the level of a state program.
Second stage and numbers
The second stage is powered by the RD-0124MS engine, developed by the Voronezh-based Chemical Automation Design Bureau (KBKhA). It is a modification of the RD-0124 that powers the Soyuz-2.1b. It produces 60 tons of thrust. Its specific impulse in a vacuum is approximately 360 seconds, a record for oxygen-kerosene liquid-propellant rocket engines. The second stage is 7,77 meters long, 4,1 meters in diameter, and weighs approximately 5,9 tons dry and approximately 65 tons fueled.
A design feature of the second stage is the combined bottom of the oxidizer and fuel tanks. This means one common element instead of two. This reduces several hundred kilograms of dry weight and overall length. The interstage compartment is made of composites. The tank bodies are made of high-strength aluminum alloy, welded using friction stir welding. This is a solid-phase welding process: the material is not melted. A rotating tool heats the metal to a ductile state and stirs it at the joint. The resulting weld is stronger than traditional fusion welding, with no heat-affected zones or porosity.
The overall length of the Soyuz-5 is between 58 and 65 meters, depending on the fairing. Its launch weight is approximately 525–530 tons. Its payload into a low-altitude circular orbit at an altitude of 200 kilometers and an inclination of 51,6 degrees when launched from Baikonur is 17 tons. The payload into a geostationary transfer orbit with the Fregat upper stage is 5 tons. For comparison, the Soyuz-2.1b launch vehicle can launch approximately 8 tons into low-altitude orbit. The payload capacity has roughly doubled.
"Zenith"
The Soyuz-5 has a direct technological ancestor—the Zenit rocket, developed from 1976 to 1985. The lead developer was the Yuzhnoye Design Bureau named after Academician M.K. Yangel in Dnepropetrovsk. At the time of the main work on the Zenit, Vladimir Utkin was the design bureau's chief designer. The first-stage engine is the RD-170 developed by Energomash. The second-stage engine is the RD-120, developed by Energomash and manufactured at Yuzhmash. The first launch took place on April 13, 1985.
The Zenit was conceived as a universal medium-class launch vehicle powered by environmentally friendly fuel, as opposed to the Proton with its toxic heptyl and dinitrogen tetroxide. The concept of the rocket as a unit from which a family of launch vehicles of varying payload capacities could be assembled also originated with the Zenit. This same concept was inherited by the Soyuz-5.
After the collapse of the USSR, Zenit production remained divided between Russia and Ukraine. In 1995, the Sea Launch program was launched—an international consortium involving RSC Energia, Yuzhmash, the American Boeing, and Norway's Kvaerner. Launches were conducted from the Odyssey floating platform, a 137-meter-long, converted Norwegian drilling rig. The launches were conducted from the Pacific Ocean off Christmas Island, on the equator. An equatorial launch increases the launch mass due to the Earth's rotational speed.
From 1999 to 2014, the Sea Launch program conducted 36 launches, 32 of which were successful. After 2014, Ukrainian participation became impossible for political reasons. Zenit production ceased in 2015. The Odyssey platform was transferred to the Russian company S7 in 2018. A dilemma arose: lose the floating spaceport's operational infrastructure or adapt a new rocket to it. The decision was made to adapt the Soyuz-5.
Launch sequence. Minute by minute.
A rocket launch isn't just the push of a button. It's a cyclogram, a schedule of hundreds of commands, counted from the moment of impact. Before impact, time is counted with a minus sign. After impact, it's counted with a plus sign. The launch crew has a "shooter," a coordinator, who holds a card with the exact timing of each operation.
What happened on April 30th. One minute before launch, the "One-Minute Ready" command was given. The systems entered final preparation mode. Then, "Key to Launch." Turning the key switches the controls to automatic. "Protyazhka-1" and "Protyazhka-2" begin recording telemetry from onboard and from the launch pad. "Purge." Nitrogen purges fuel vapor from the engine lines, preventing an explosion.
"Drain key." The valves that evaporated liquid oxygen from the tanks are closed. Up until this point, the rocket had been suspended in a cloud of white vapor. The evaporation was constant, and the oxygen in the tanks was constantly being replenished. Now the refilling is stopped, and the tanks are sealed. "Ground to air." The cable mast is undocked, and the rocket switches to onboard power.
"Start." Component feed valves open. "Ignition." The four RD-171MV chambers ignite simultaneously. "Preliminary," "Intermediate," and "Main"—a sequential increase in thrust to nominal values. When thrust exceeds the launch mass, the rocket begins to ascend. The lift contact sensor is triggered. The "Lift" command is given. The broadcast reads "Let's go."
From this point on, everything is determined by the mathematics of ballistics. The first stage burns for approximately two and a half minutes, launching the second stage to an altitude of approximately 60 kilometers. Separation is accomplished using the hot-separation principle. The second stage ignites its RD-0124MS rocket before the first stage fully separates, to maintain control. Operation then continues on the second stage alone until the calculated trajectory is reached.
What the critics say
The project also has its downside. Criticism comes from three sources: the rocket concept, the architectural solutions, and the market niche.
The first line is the concept. Andrei Ionin, a corresponding member of the Tsiolkovsky Russian Academy of Cosmonautics, publicly stated that the Soyuz-5 was originally designed as a sidecar for the Yenisei super-heavy rocket, not as an independent commercial launch vehicle. When attempting to use the sidecar as a separate rocket, problems of optimality arise.
A specific indicator is the first stage's fall range. For an optimally designed two-stage medium-class rocket, this is approximately 900 kilometers from launch; for Zenit, this figure was practically identical. For Soyuz-5, it's 1100–1200 kilometers. This means the first stage is overweight for its intended role. According to estimates provided by RSC Energia, redesigning it for a purely commercial launch vehicle would increase the payload from 17 to approximately 20 tons.
The second line is architecture. Sergei Sopov, the former head of S7 Space, back in 2018 called the Soyuz-5 "a grown-up and beefed-up Zenit." The phrase is offensive, but meaningful: the rocket is an evolution of a 1980s Soviet rocket, not a new platform. The same logic was expressed by former Khrunichev Center managers regarding the Angara-A5 and Soyuz-5 combination: both launch vehicles were designed with the technological level of the 1990s in mind and became obsolete before they entered production.
The most specific issue is fuel. The global trend is toward methane: it's cheaper to produce, soot-free, and more compatible with reusability. Blue Origin's methane-fueled BE-4 is already flying on the American Vulcan. The RD-171MV is the pinnacle of the oxygen-kerosene rocket school, but it's the pinnacle of a school that most new projects consider to be on the decline.
The third line is the market. Eric Berger of Ars Technica articulated a fundamental doubt: Soyuz-5 is no different from the new mid-range launch vehicles entering service in the second half of the 2020s. Nine years of development—and the result is a completely disposable rocket, while competitors are already reusing their first stages. At a unit cost of 300 rubles per kilogram versus 230 for the Falcon 9 at the current exchange rate—the Russian rocket is approximately a third more expensive. The Falcon 9 also lifts 25 tons into low orbit versus 17. A separate question is who will buy the launches. Most international contracts expired after 2022, and critics estimate that the Soyuz-5 in its current form will not be able to break through the sanctions barrier with a purely commercial advantage.
What follows from this? Some of the criticisms are mitigated by the context. The decision to develop the Soyuz-5 as a unified unit for the Yenisei wasn't a mistake, but a conscious choice: a single component base for the medium and super-heavy classes, saving on production. The price of this choice is a suboptimal, independent rocket. Some criticisms are not mitigated by anything. An expendable first stage in 2026 is a technological disadvantage by definition, and a mass-produced Amur-SNG with stage recovery won't appear until the early 2030s.
What's next
The flight test plan calls for four launches. The first, on April 30, 2026, took place. Next comes debugging of the flight sequence, validation of the onboard systems in various modes, and operation with standard payloads. Following the completion of the tests, Progress Rocket and Space Center plans serial production, launching no more than one Soyuz-5 per year, with subsequent scaling based on demand.
The main sequel is the manned version. The Soyuz-5 is being designed, among other things, to carry the Oryol spacecraft, which is intended to replace the Soyuz MS. In its current form, the Oryol is a reusable reentry vehicle for near-Earth and lunar missions, designed to accommodate four cosmonauts. The program is evolving at a variable pace: the ship's readiness date for routine manned launches has been pushed back several times, with the current target being the late 2020s. Certification of the Soyuz-5 for manned launches is a separate, lengthy process. Reliability requirements are higher than for the cargo version: an emergency escape system, engine certification for a significant service life, and multiple unmanned launches are required. Based on the experience of the manned Soyuz-2.1a, this process took approximately five years from the rocket's first launch to the first manned launch. For Soyuz-5 and Orel, this means that the crewed debut of the combination is not realistically expected until the early 2030s.
The most distant horizon is the Yenisei super-heavy rocket. According to various project versions, it is designed to launch 100–160 tons into low orbit. The Yenisei's first stage is assembled from a bundle of Soyuz-5-based units: five or six units, depending on the configuration. The RD-171MV will serve as the supporting engine for both the medium and super-heavy rockets. It was this role that largely dictated the Soyuz-5's architectural decisions, for which the rocket is currently being criticized. If the Yenisei makes it to the hardware stage, the Russian lunar program will receive its own launch vehicle, and then the entire unified logic of the project will be retroactively justified. If not, the country will be left with a medium-class launch vehicle with a suboptimal first stage and the potential for commercial loading in limited markets. The Yenisei program is currently in the preliminary design stage with regularly shifting deadlines; the first launch, according to various estimates, is scheduled for the late 2030s.
At the same time, the rocket is being adapted for launches from the Vostochny Cosmodrome and the Odyssey floating platform; an equatorial launch from Sea Launch will add 10-15% to its payload capacity due to its geographic location. The methane-fueled Amur-LNG with a reusable first stage has been pushed back from the late 2020s to the early 2030s; knowledge gained from debugging the Soyuz-5 will form its foundation. Oxygen-kerosene is a proven technology. Methane with a reusable first stage is next.
On April 30, 2026, the rocket lifted off from pad 45. The mockup was released into the Pacific Ocean. The RD-171MV engine performed normally. This isn't the end of nine years of work. This is its beginning, in the hardware itself. With all the caveats that come with that hardware.
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