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Progress MS-31 re-supplies ISS

The second Russian mission to resupply the International Space Station, ISS, lifted off from Baikonur Cosmodrome in Kazakhstan, on July 3, 2025. The Progress MS-31 cargo ship made a two-day trip to the orbital outpost delivering propellant and cargo to the Expedition 73 crew.

Progress MS-31 mission at a glance:

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Progress MS-31 cargo mission

According to Roskosmos, Progress MS-31 was scheduled to deliver 2,625 kilograms of cargo to the station. It included more than 540 kilograms of hardware and equipment, as well as various materials for the following experiments: Impuls (Phase 2), Mirazh, Biopolymer, Virtual, Fulleren, Splankh, Biodegradatsiya, Orbita-MG, Vampir and Separatsiya.

The dry cargo also included 317 kilograms of personal supplies for the members of Expedition 73, such as clothing, medical and hygiene materials, as well as 344 kilograms of food. All this cargo was loaded into the pressurized forward compartment of the vehicle.

At the same time, the cargo ship's tanker module was filled with 950 kilograms of propellant for refueling (INSIDER CONTENT) the station's propulsion system (INSIDER CONTENT), 420 kilograms of drinking water and 50 kilograms of compressed nitrogen for replenishing the atmosphere of the ISS, Roskosmos said.

Roskosmos assigned the Progress MS-31 mission to the Soyuz-2-1a No. 075 rocket, which was originally procured for the commercial launch of the second CAS-500 remote-sensing satellite for South Korea. For promotional purposes, the State Corporation's commercial arm, Glavkosmos, had ordered the rocket to be painted mostly white, apparently because its executives erroneously believed that such a paint scheme had been used on the Vostok rocket which launched the first human into space in 1961. The rocket was stuck on the ground after South Korea cancelled the deal as a result of Russia's full-scale invasion of Ukraine in 2022.

According to the ISS flight manifest in 2024, the launch of Progress MS-31 was expected on May 28, 2025, but before the end of that year, the mission shifted to July 3, 2025.

Progress MS-31 launch campaign

On March 14, 2025, RKK Energia reported that the Progress MS-31 spacecraft had completed its factory tests and been shipped to Baikonur by rail. It reached the launch site four days later.

The active launch campaign for Progress MS-31 in Baikonur started in mid-May 2025, when specialists placed the spacecraft into the anechoic chamber within the processing complex at Site 254 for radio tests. The operation was completed on May 15. On May 29, 2025, Roskosmos reported the successful completion of tests in the vacuum chamber which were started on May 23. Progress MS-31 entered the irreversible phase of the launch campaign with the start of propellant components and pressurized gases loading on June 22, 2025.

On June 27, the cargo ship was mounted on its launch vehicle adapter designed to serve as an interface with its Soyuz-2-1a rocket. On June 29, specialists conducted traditional visual inspection of the spacecraft and then lowered it into horizontal position and rolled it into the payload fairing. The resulting assembly was then returned into vertical position for final tests. The stack was then lowered again, loaded into a rail transporter and moved to the Vehicle Assembly Building at Site 31 for the final integration with the launch vehicle. The assembly process was completed on June 30, 2025.

The rocket with the spacecraft was rolled out to the launch pad at Site 31 on the morning of July 1, 2025.

Progress MS-31 launch profile

A Soyuz-2-1a rocket, carrying the Progress MS-31 cargo ship, lifted off from Pad 6 at Site 31 in Baikonur on July 3, 2025, at 22:32:40.257 Moscow Time (3:32 p.m. EDT).

Following a vertical liftoff under the combined thrust of the four RD-107 engines 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 an altitude of around 43 kilometers, followed by the split and drop of the two halves of the payload fairing slightly more than a minute later at an altitude of around 91 kilometers, just above the dense atmosphere and around 200 kilometers downrange. In the meantime, the second stage continued firing until 4 minutes and 47 seconds into the flight, bringing the vehicle to around 143 kilometers above the planet and a speed of around four kilometers per second, some 500 kilometers downrange from the launch site.

The third stage ignited moments before the separation of the second stage, firing its RD-0110 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 and the aft cylindrical section of the third stage split into three segments and dropped off, ensuring the fall of the second stage and the aft section into the same area on the ground.

The third stage completed firing its engine and released the cargo ship into an initial parking orbit at 22:41 Moscow Time, or 8 minutes 49 seconds after liftoff.

Progress MS-31 docks at ISS

The Progress MS-31 mission will follow a two-day, 34-orbit rendezvous profile with the ISS. The cargo ship was slated to perform a fully automated docking with the Poisk module, MIM2, a part of the Russian Segment on July 6, 2025, at 00:27 Moscow Time (5:27 p.m. EDT on July 5).

Progress MS-31 was scheduled to begin an autonomous rendezvous with the ISS during the cargo ship's 33rd slightly elliptical orbit, which was expected to have the following parameters: a perigee — 399.543 kilometers and an apogee — 431.541 kilometers. Around the same time, the ISS was flying in a 414.238 by 432.726-kilometer orbit.

The autonomous rendezvous process between Progress MS-31 and the ISS was planned according to the following timeline during the night from July 5 to July 6, 2025:

By around 23:55 p.m. Moscow Time on July 5, 2025, as the Progress was around a kilometer from the ISS, cosmonauts Sergei Ryzhikov and Aleksei Zubritsky completed testing of the TORU remote control system inside the Zvezda Service Module and put it in a stand-by mode in case of problems with the automated rendezvous system aboard the cargo ship.

Progress MS-31 completed its final scheduled rendezvous maneuver just around midnight Moscow Time on July 6, 2025, and minutes later, initiated a 15-degree flyaround of the ISS to align itself with Poisk. It was completed in less than 15 minutes and the spacecraft performed a short period of station keeping and the final approach was initiated right before 00:15 Moscow Time, a few minutes ahead of schedule.

The contact of the docking ports between the cargo ship and the station took place at 00:25:45 Moscow Time on July 6, 2025, (5:25 p.m. EDT on July 5, 2025), as the two spacecraft were over the Atlantic Ocean.

(To be continued)

This page is maintained by Anatoly Zak; last update: July 6, 2025

Page editor: Alain Chabot; last edit: July 3, 2025

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Progress MS-31 spacecraft is integrated with the launch vehicle adapter on June 26, 2025. Click to enlarge. Credit: Roskosmos

Click to enlarge. Credit: Roskosmos

Assembly of the launch vehicle for the Progress MS-31 mission. Click to enlarge. Credit: Roskosmos

View of the ISS via an engineering camera aboard the approaching Progress MS-31 spacecraft. Click to enlarge. Credit: Roskosmos