Russia’s Soyuz-2.1b Rocket Powers Progress MS-35 Toward ISS in Strategic Capability Demonstration
By Khawar Nehal
19 September 2026
PLESETSK COSMODROME, Russia — Russia successfully launched the Progress MS-35 cargo spacecraft aboard a Soyuz-2.1b rocket, marking a significant milestone in the nation’s space logistics capabilities and paving the way for heavier payload deliveries to both the International Space Station and Russia’s planned future orbital facility.
The launch, which lifted off from the Plesetsk Cosmodrome, showcased Russia’s commitment to utilizing the enhanced Soyuz-2.1b variant for critical cargo missions—a strategic shift from the more commonly used Soyuz-2.1a configuration.
Enhanced Payload Capacity for Future Missions
The Soyuz-2.1b rocket represents a substantial upgrade over its predecessor, offering significantly increased cargo capacity that will prove essential for Russia’s ambitious space infrastructure plans. According to space historian Alexander Zheleznyakov, who spoke to Sputnik about the mission, this flight serves dual purposes: supporting current ISS operations while validating capabilities for Russia’s future independent orbital station.
“The Soyuz-2.1b rocket offers greater cargo capacity than the lighter Soyuz-2.1a, usually used for Progress cargo ships and crewed missions,” Zheleznyakov explained. “This enhanced capability is crucial not only for current ISS resupply operations but also for the larger, more complex modules that will comprise Russia’s planned orbital station.”
Technical Superiority: The RD-0124 Engine Advantage
The key differentiator between the Soyuz-2.1a and 2.1b variants lies in the third-stage propulsion system. The 2.1b configuration replaces the RD-0110 engine with the more advanced RD-0124, an oxygen-rich staged-combustion engine that delivers superior performance metrics.
The RD-0124 engine increases specific impulse from 326 to 359 seconds—a substantial improvement that translates directly into enhanced payload capacity. While maximum thrust was marginally reduced from 298 to 294 kilonewtons, the extended burn time with the same propellant load results in markedly improved overall performance.
From the Baikonur Cosmodrome, the Soyuz-2.1b can deliver approximately 8,670 kilograms (19,110 pounds) to low Earth orbit, compared to the 2.1a’s 7,430 kilograms (16,380 pounds)—an increase of roughly 1,240 kilograms. Even from the higher-latitude Plesetsk facility, the 2.1b variant maintains its advantage, capable of lifting 7,730 kilograms versus the 2.1a’s 6,800 kilograms to comparable orbits.
Experimental Flight Profile
The Progress MS-35 mission employs a partly experimental flight profile that extends the traditional rendezvous timeline. Rather than the rapid same-day or two-day approach commonly used for Progress missions, this cargo spacecraft is following a three-day trajectory to the ISS.
The extended journey serves a critical purpose: providing additional time for comprehensive system checks and performance monitoring of the Soyuz-2.1b’s upgraded systems under actual flight conditions. Engineers at mission control will utilize the extra hours to validate telemetry, navigation equipment, and propulsion performance before the spacecraft initiates its final approach sequence.
Docking with the International Space Station is scheduled for September 19, 2026, where the Progress MS-35 will deliver essential supplies including fuel, food, water, and scientific equipment to support the orbital crew.
Proven Heritage with Expanded Applications
While the Progress MS-35 mission represents an expanded operational envelope for the Soyuz-2.1b in cargo configurations, the rocket variant itself boasts a solid flight heritage. The 2.1b previously demonstrated its reliability in 2021 when it successfully delivered the Progress M-UM spacecraft carrying the Prichal nodal module to the Russian segment of the ISS.
That 2021 mission validated the rocket’s capability to handle critical infrastructure deliveries requiring precise orbital insertion. The current mission builds upon that foundation by testing the vehicle’s performance with extended flight profiles and heavier cargo loads.
The Progress Spacecraft: Russia’s Orbital Lifeline
The Progress MS-35 spacecraft itself represents the latest evolution in a lineage dating back to 1978. The modern Progress MS series features enhanced redundancy, improved micrometeoroid protection, and advanced digital systems compared to earlier variants.
With a mass of approximately 7 tonnes and a length of 7.9 meters, the Progress spacecraft can transport roughly 2.5 tonnes of cargo, including both pressurized freight and gaseous propellants. The MS-35 variant incorporates upgraded flight control systems and enhanced autonomous docking capabilities, ensuring reliable delivery of critical supplies to the ISS.
Strategic Implications for Russian Space Operations
The successful deployment of the Soyuz-2.1b for Progress missions carries significant strategic implications for Russia’s space program. As the nation prepares to eventually transition from the International Space Station to its own Russian Orbital Station (ROS), the ability to lift heavier payloads becomes increasingly critical.
Future ROS modules are expected to be larger and more complex than those currently attached to the ISS, requiring the enhanced lift capacity that the Soyuz-2.1b provides. Additionally, the rocket’s improved performance enables more flexible mission planning, including the potential for dual-payload configurations or heavier single payloads that would exceed the 2.1a’s capabilities.
Rocket Specifications at a Glance
The Soyuz-2.1b stands approximately 46.3 meters (152 feet) tall with a core diameter of 2.95 meters and a maximum diameter of 10.3 meters including its four strap-on boosters. The vehicle’s total liftoff mass reaches approximately 312,000 kilograms.
The rocket’s first stage consists of four tapered strap-on boosters, each powered by an RD-107A engine burning RP-1 kerosene and liquid oxygen. The core stage utilizes a single RD-108A engine with the same propellant combination. The upgraded third stage features the RD-0124 engine, the heart of the 2.1b’s performance advantage.
For missions requiring precise orbital insertion or higher-energy trajectories, the Soyuz-2.1b can be paired with the Fregat upper stage—a restartable propulsion module that provides exceptional orbital maneuvering capability.
Launch Infrastructure and Operations
The Plesetsk Cosmodrome, located in Arkhangelsk Oblast in northwestern Russia, serves as Russia’s primary military spaceport and has been operational since the Soviet era. The facility’s high-latitude location makes it ideal for polar and Sun-synchronous orbit missions, though it can also support ISS resupply flights.
The launch complex features extensive ground support equipment, including the distinctive red-and-white service tower visible during the rocket’s vertical erection sequence. The facility has undergone continuous modernization to support the Soyuz-2 family of rockets, with upgraded processing facilities and launch infrastructure.
Looking Ahead
As the Progress MS-35 continues its three-day journey to the ISS, the success of this mission will inform future operational decisions regarding rocket configuration selection for Russian cargo and crewed missions. The validation of the Soyuz-2.1b’s enhanced capabilities opens new possibilities for payload mass and mission complexity.
With Russia’s space program increasingly focused on developing independent orbital infrastructure, the Soyuz-2.1b’s proven performance provides a reliable foundation for future ambitious projects. The rocket’s combination of heritage, reliability, and enhanced capability ensures its continued role as a cornerstone of Russian space operations for years to come.
The Progress MS-35 is expected to remain docked with the ISS until February 2027, providing cargo storage and waste disposal capabilities before its eventual undocking and destructive reentry over the Pacific Ocean—the standard end-of-mission profile for Progress spacecraft.
