Progress MS-35 re-supplies ISS

After a week-long delay caused by a technical problem, the third Russian cargo mission to the ISS in 2026 lifted off from Baikonur on September 16 to support Expedition 75 aboard the outpost. The Progress MS-35 supply vehicle followed a three-day rendezvous profile with the station and waas scheduled to remain at the ISS until February 2027.

The 96th Progress re-supply mission to the ISS was initially planned for November 2026, but by 2025, it was advanced to April 28, 2026. By October 2025, the launch slipped to June 17, 2026. Following the service platform collapse at Site 31 in November 2025, and the resulting domino effect of delays, the Progress MS-35 mission was re-scheduled for Sept. 9, 2026.

According to the official data, the Progress MS-35 carried "more than 2,400 kilograms" of supplies to the International Space Station, ISS, including 275 kilograms of food, 357 kilograms of sanitary and hygiene items, 20 kilograms of medical supplies and means of battling microgravity conditions, as well as 525 kilograms of supplies and equipment for maintaining the station and scientific work. The latter included materials and hardware for the following experiments: Gazoanalizator-FS, Teledroid, Biopolimer, Virtual, Vampir, Uragan and Separatsiya.

For the Teledroid experiment, the Progress MS-35 carried the so-called exoskeleton working place for a cosmonaut to interact and control a humanoid robot, which was scheduled for delivery with the next cargo mission, Roskosmos said.

The refueling section (INSIDER CONTENT) also carried 842 kilograms of propellant, 420 kilograms of water and 50 kilograms of oxygen.

The Progress MS-35 mission also marked a transition of Russian cargo launches from the Soyuz-2-1a to Soyuz-2-1b variant in the continuous effort to consolidate the production of the Soyuz rocket family through the retirement of the Soyuz-2-1aa variant, which would require test launches of the cargo ship before a switch of piloted Soyuz-MS vehicles.

After a series of factory checks, Progress MS-35 was shipped from its production plant in Korolev around April 1, 2026, and reached Baikonur around five days later. The initial inspection of the spacecraft ahead of an active launch campaign started at Site 254 on June 30, 2026. Between Aug. 3 and 11, 2026, RKK Energia reported testing the spacecraft for air leaks in the vacuum chamber at Site 254, after which, the vehicle was returned to its processing stand.

On Aug. 21, 2026, the ship's solar panels went through a routine test with the exposure to an array of artificial lights.

On Aug. 25, 2026, the assembly of the booster stages of the Soyuz rocket for the Progress MS-35 mission was reported completed. On Aug. 28, 2026, RKK Energia reported that a meeting of the technical management in Baikonur had cleared Progress MS-35 for irreversible operations, including fueling of its Integrated Propulsion System (INSIDER CONTENT) and of the Refueling System (INSIDER CONTENT). Before the transfer to the fueling facility, the vehicle went through the weighting and balancing process at Site 254. The fueling operations were reported completed on August 29.

The spacecraft was then returned to its processing facility at Site 254, where it was integrated with the launch vehicle adapter and a payload fairing, after which the resulting payload section was transferred to the vehicle assembly building at Site 31, where it was integrated with the rocket.

The completed launch vehicle with the cargo ship was rolled out to the launch pad at Site 31 on the morning of Sept. 6, 2026. The liftoff was planned for Sept. 9, 2026, at 19:15:03 Moscow Time, allowing the docking with the ISS on Sept. 11, 2026, at 21:37 Moscow Time (2:37 p.m. EDT).

However soon after the installation of the rocket on the launch pad on September 6, Russian and Kazakh sources reported a problem with the third stage, which was serious enough to require the return of the rocket to the vehicle assembly building. According to the KazTAG news agency, the Soyuz-2-1b vehicle was expected to be removed from the pad and rolled back to the processing building at Site 31 on Sept. 7, 2026, following a decision of a State Commission overseeing the launch campaign.

According to an unofficial source, the rocket had an issue with a hydraulic system. The launch was re-scheduled for Sept. 16, 2026, at 16:33:53 Moscow Time, shifting the ship's arrival at the ISS to Sept. 19, 2026, at around 16:46 Moscow Time.

For the second launch attempt, the rocket was rolled out to the launch pad on the morning of Sept. 13, 2026.

A Soyuz-2-1b rocket, carrying the Progress MS-35 cargo ship, lifted off from Pad 6 at Site 31 in Baikonur on Sept. 16, 2026, at 16:33:54.560 Moscow Time: (9:33 a.m. EDT).

Following a vertical liftoff under the combined thrust of the four RD-107 engines (INSIDER CONTENT) on the first stage and the single RD-108 of the second (core) stage, the launch vehicle headed eastward from Baikonur matching its ground track to an orbit inclined 51.67 degrees to the plane of the Equator.

The four first-stage boosters separated 1 minute 58 seconds after liftoff (at 16:35:51 Moscow Time; Launch+116.61 seconds), at an altitude of around 43 kilometers. In the meantime, the second stage continued firing until 16:38:39 Moscow Time.

The third stage then ignited moments before the separation of the second stage, firing its RD-0124 engine through a lattice structure connecting the two boosters and ensuring a continuous thrust during the separation process. A fraction of a second later, the boosters of the second and third stage parted ways at L+284.50 seconds and the aft cylindrical section of the third stage will split into three segments and dropped off at L+292.69 seconds, ensuring the fall of the second stage and the aft section into the same drop zone on the ground.

The second stage separation was followed by the split and drop of the two halves of the payload fairing at 16:38:48 Moscow Time, at an altitude of around 165 kilometers.

The third stage completed firing its engine at L+550.73 seconds and released the cargo ship into an initial parking orbit at 16:43:08 Moscow Time or L+554.02 seconds into the flight.

The Progress MS-35 launch on Sept. 16, 2026, targeted a 240.0 by 193.1 initial orbit, with an inclination 51.67 degrees toward the Equator and the 88.53-minute orbital period. At the time of the cargo ship's liftoff, the ISS was orbiting the Earth over the Southern Pacific Ocean, which required a three-day, 45-orbit rendezvous profile between the cargo ship and the station.

The Progress MS-35 was scheduled to begin an autonomous rendezvous with the ISS during the cargo ship's 45th orbit, which was expected to have the following parameters: a perigee — 384.534 kilometers and an apogee — 436.614 kilometers. At the time, the ISS was flying in the 415.932 by 433.310-kilometer orbit.

The autonomous rendezvous process included six major orbit-correction maneuvers using main SKD engine and small DPO thrusters of the cargo ship on Sept. 19, 2026.

The autonomous rendezvous process between Progress MS-35 and the ISS was planned according to the following timeline on Sept. 19, 2026:

Start of the autonomous rendezvous	14:20:14 Moscow Time
Activation of the rendezvous equipment on the Zvezda Service Module	15:09:14 Moscow Time
Activation of the rendezvous equipment on the cargo ship	15:10:14 Moscow Time
Flyaround starts	16:21 Moscow Time
Flyaround completed	16:33 Moscow Time
Station-keeping period begins	16:33 Moscow Time
Station-keeping period end	16:35 Moscow Time
Final approach to Poisk module begins	16:35 Moscow Time
Final approach completed	16:46 Moscow Time
Contact	16:46:33 Moscow Time
Docking process begins	16:47 Moscow Time
Docking process ends	16:54 Moscow Time

Progress MS-35 was scheduled to perform an automated docking at the zenith (sky-facing) port of the Poisk (MIM2) module, a part of the Russian ISS Segment on Sept. 19, 2026, at 16:46 Moscow Time (9:46 a.m. EDT).

Following a long-range rendezvous, Progress MS-35 initiated flyaround of the ISS to align itself with the destination docking port on the Poisk module at around 16:20 Moscow Time. The maneuver was completed at around 16:32 Moscow Time at a distance of around 185 meters from the station. The ship than made a roll maneuver for the final attitude at docking and maintained a station-keeping for a couple of minutes, before the final approach was initiated at around 16:34 Moscow Time.

The actual contact between the two spacecraft was registered at 16:44:20 Moscow Time (9:44 a.m. EDT) on Sept. 19, 2026, according to mission control in Moscow.

The cargo ship is expected to remain at the ISS for around five months, before undocking and performing destructive reentry into the Earth's atmosphere in February 2027.