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Progress MS-21 re-supplies the ISS, suffers coolant leak

The third and final Russian cargo mission to the International Space Station, ISS, in 2022 lifted off in the early hours of October 26 and successfully docked at the outpost two days later. However, at the end of its tenure at the station, the spacecraft suddenly lost all its coolant fluid, right after the subsequent Progress MS-22 spacecraft docked at a neighboring port on Feb. 11, 2023.

Previous mission: Progress MS-20


Progress MS-21 mission at a glance:

Spacecraft designation(s) Progress MS-21, 11F615 No. 451, ISS mission 82P
Launch vehicle Soyuz-2-1a 14A14-1a No. Ya15000-057
Payload fairing 11S517A2 No. Ya15000-127
Launch site Baikonur, Site 31, Pad 6
Mission Cargo delivery to the ISS
Launch date and time 2022 Oct. 26, 03:20:09.237 Moscow Time
Docking date and time 2022 Oct. 28, 05:48:54 Moscow Time
Docking destination ISS, Russian Segment, Poisk module (MIM2), zenith port
Mission duration 247 days (planned as of early 2022)
Spacecraft mass ~7.4 tons
Deorbit date 2023 Feb. 19

Preparations for the Progress MS-21 mission

In a preliminary ISS flight manifest drafted in 2014, the third Russian cargo mission to the ISS in 2022 was penciled for October 16, but in early January 2022, Roskosmos announced the plan to launch Progress MS-21 on October 26 of that year. At that time, the 82nd Progress flight to the station was expected to last 247 days.

According to Roskosmos, the spacecraft was expected to carry 2,520 kilograms of cargo to the station, including 702 kilograms of propellant for refueling the station, 420 kilograms of drinking water, 41 kilogram of nitrogen, as well as 1,357 kilograms of supplies in its pressurized compartment for Expedition 68 aboard the ISS. A total of 47.78 kilograms of deliverable materials aimed to support following experiments: Splankh, Neiroimmunitet, Korrektsiya, Impakt and Terminator, Matreshka-R, OMIKi-SPK, Vzaimodeistvie-2, Biodegradatsiya, Separatsiya, Dispersiya. The cargo also included filament rolls for the experimental 3D printer on the station.

Mass breakdown of the cargo delivered aboard Progress MS-21, according to the mission control in Korolev:

Hardware for onboard systems
427 kilograms
Means of medical support
45 kilograms
Personal protection equipment
64 kilograms
Sanitary and hygiene equipment
238 kilograms
Means of servicing and repair
12 kilograms
Means of crew support
38 kilograms
336 kilograms
12 kilograms
Additional hardware
184 kilograms

Preparations for flight

The newly manufactured spacecraft arrived at Baikonur by rail from Korolev on Oct. 25, 2021. The cargo ship underwent vacuum tests between September 12 and 20, after which it was installed at its processing rig inside the spacecraft processing building at Site 254 and where it was connected to diagnostics equipment kicking off its active pre-launch operations. Processing operations included pressurization tests of the propellant lines, loading of thermal-control fluids and filling of the Rodnik water delivery system, final operations with onboard computer and radio systems and the loading of the ship's pressurized compartment with cargo for the ISS.

The 22-car train carrying components of the Soyuz-2-1a rocket for the Progress MS-21 mission arrived at Site 112 in Baikonur from a production factory in Samara in the second half of June 2022 and its unloading proceeded on June 29. The payload fairing for the mission arrived at the site in the second half of August 2022.

The active campaign for the launch started around Sept. 1, 2022, when specialists attached the four strap-on boosters of the first stage to the core stage of the Soyuz-2-1a rocket. In the meantime, the cargo ship was transferred into the anechoic chamber inside processing building at Site 254 for testing of its radio equipment. From September 12 to 19, the ship was undergoing air leak tests in the vacuum chamber at Hall 103.

On Sept. 30, 2022, a routine testing of the ship's solar panels started, involving their exposure to an array of electric lights.

On Oct. 10, 2022, a meeting of technical management in Baikonur cleared the spacecraft for irreversible operations, including loading of propellant into the ship's re-fueling section and into its own integrated propulsion system. Ahead of the trip to the fueling facility at Site 31, the ship underwent weighing and balancing inside the processing building at Site 254. The fueling operations began on October 11 and were completed on October 13. The vehicle was then returned to Site 254 and installed back at its processing rig for closeout operations.

On October 17, Progress MS-21 was integrated with its launch vehicle adapter ring serving as an interface with the Soyuz rocket. The operation was concluded with a test activation of the ship's command and telemetry system and with the preparation for the final visual inspection of the vehicle, which took place on October 19. On the same day, the spacecraft was rolled inside its payload fairing. After a simulation of launch readiness, the payload section was prepared for the transfer to the rocket assembly building at Site 31.


The fully assembled vehicle was rolled out to the launch pad at Site 31 on the morning of Oct. 22, 2022.

According to the Russian mission control, key operations on the launch pad had the following timeline:

  • 48:00:00 - 00:50:00: Thermal conditioning of the spacecraft;
  • 03:30:00 - 03:00:00: Loading of fuel aboard the launch vehicle;
  • 03:00:00 - 00:30:00: Testing of equipment and of onboard systems;
  • 02:50:00 - 00:30:00: Loading of the oxidizer aboard the launch vehicle;
  • 02:45:00 - 01:30:00: Cooling and loading of the liquid nitrogen;
  • 02:20:00 - 01:50:00: Loading of the hydrogen peroxide aboard the rocket;
  • 00:45:00 - 00:30:00: Retraction of the lower access platform and access gantry.

Progress MS-21 enters orbit

A Soyuz rocket carrying the Progress MS-21 cargo ship (ISS mission 82P) lifted off from Site 31 in Baikonur on Oct. 26, 2022, at 03:20:09.237 Moscow Time (8:20 p.m. EDT on October 25).

Following 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 nearly two minutes after liftoff at an altitude of around 43 kilometers at 03:22:07 Moscow Time, 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 90 kilometers, just above the dense atmosphere and around 200 kilometers downrange at 03:23:12 Moscow Time. 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 the speed of around four kilometers per second, some 500 kilometers downrange from the launch site at 03:24:56 Moscow Time.

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 after the boosters of the second and third stage parted ways, 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 drop zone.

The third stage continued firing and inserted the cargo ship into an initial parking orbit nearly nine minutes after liftoff at 03:28:58 Moscow Time. The mission targeted the 240 by 193-kilometer orbit with an inclination 51.67 degrees to the Equator. Mission control later reported that the spacecraft separation command was issued at 03:28:19 Moscow Time and the parameters of the initial orbit were as following:

  • Orbital period: 88.55 minutes;
  • Inclination: 51.67 degrees toward the Equator;
  • Perigee: 193.05 kilometers;
  • Apogee: 241.24 kilometers.

At the time when Progress MS-19 entered orbit over Siberia, the ISS was ahead over the Pacific, near the cost of Japan, in a 414,299 by 436,696-kilometer orbit.

According to NASA, Progress MS-21 successfully deployed its solar arrays and antennas immediately after the separation from the launch vehicle. The Russian mission control showed the following timeline for initial operations in orbit:

  • 03:32 - 03:36 Moscow Time: Test of the Kurs rendezvous equipment;
  • 04:58 - 05:06 Moscow Time: Extension of the docking mechanism probe into the operational position.

Upon reaching orbit, mission control in Korolev displayed time confirmations for completed milestones:

  • 03:29:00 Moscow Time: Separation of from the third stage of the launch vehicle;
  • 03:29:15 Moscow Time: Deployment of the antennas of the RTS radio system;
  • 03:29:23 Moscow Time: Deployment of solar panels;
  • 03:29:13 Moscow Time: Deployment of the rendezvous antennas.

Progress MS-21 arrives at ISS


Originally, the docking of Progress MS-21 with the ISS was scheduled to take place two days after launch, but in May 2022, Head of Roskosmos Dmitry Rogozin said that a one-orbit (2-hour 46-minute) rendezvous profile could be tested during a cargo mission in the Fall of that year. Based on publications in the official Russian press, the "one-orbit" rendezvous scenario remained on the books as late as September 2022, but it was ultimately replaced with a two-day (34-orbit) flight profile to the station. As usual, it included six major orbit-correction maneuvers using main SKD engine and small DPO thrusters planned during the autonomous rendezvous with the station on Oct. 28, 2022:

Moscow Time
Range to ISS
Velocity change
Burn duration
Engine used
487.72 kilometers
35.78 m/s
90.4 sec.
188.36 kilometers
1.35 m/s
35.0 sec.
80.92 kilometers
39.81 m/s
99.4 sec.
2.20 kilometers
5.82 m/s
17.4 sec.
1.04 kilometers
5.67 m/s
73.8 sec.
0.61 kilometers
1.61 m/s
28.0 sec.

The autonomous rendezvous process between Progress MS-21 and the station was planned according to the following timeline:

Start of the autonomous rendezvous 03:26:23 Moscow Time
Activation of the rendezvous equipment on the Zvezda Service Module 04:15:23 Moscow Time
Activation of the rendezvous equipment on the cargo ship 04:16:23 Moscow Time
Flyaround starts 05:26 Moscow Time
Flyaround completed and station-keeping period 05:40 Moscow Time
Final approach starts 05:40 Moscow Time
Final approach completed 05:51 Moscow Time
Contact 05:51:20 Moscow Time
Docking process begins 05:51 Moscow Time
Docking process ends 06:08 Moscow Time

Progress MS-21 was expected to perform an automated rendezvous and docking with the zenith (sky-facing) port of the Poisk module, MIM2, a part of the Russian ISS Segment on Oct. 28, 2022, at 05:49 Moscow Time (10:49 p.m. EDT on October 27).

In preparation for docking, Russian cosmonauts aboard the ISS conducted a test of the TORU manual rendezvous system, which was expected to be in a standby mode during the final approach of the cargo ship in case of proplems with the automated rendezvous system.

In the meantime, Progress MS-21 fired its DPO thrusters on Oct. 27, 2022, at 04:09:43 Moscow Time, delivering a velocity change of 1,126 meters per second and climbing the 257.17 by 292.75-kilometer orbit, as it continued its chase of the ISS.

After a total of six orbit corrections, the cargo ship was expected to climb to a 377.262 by 426.004-killometer orbit during the 34th revolution of the mission, with an apogee around 10 kilometers below that of the ISS, predicted to be in a 413,974 by 436.974-kilometer orbit at that time.

Following the successful rendezvous, Progress MS-21 performed a flyaround of the station to align itself with the destination docking port and, after a few moments in station keeping, proceeded with an automated final approach around 05:36 Moscow Time on October 28 (10:36 p.m. EDT on October 27). The contact between the cargo ship and the station took place as planned at 05:48:54 Moscow Time on Oct. 28, 2022, (10:48 p.m. EDT on October 27), as the two vehicles were approaching the coast of Chile over the Sothern Pacific. The hard docking was successfully completed around five minutes later, at 05:54 Moscow Time on October 28, (10:54 p.m. EDT on October 27).

Progress MS-21 loses coolant, departs ISS


An apparent leak from the Progress MS-21 spacecraft appeared to be less extensive than the loss of fluid from the Thermal Control System of the Soyuz MS-22 spacecraft in December 2022, but seemingly originated from the same area of the radiator.

On February 11, Roskosmos, citing data from mission control, said that the Progress MS-21 cargo ship docked at the station had lost pressure. According to the State Corporation, the hatch connecting the ship's pressurized compartment with the rest of the station was closed and the vehicle was fully isolated from the ISS' habitable volume.

Roskosmos added that the reasons for the depressurization were being evaluated and that the incident would not affect the subsequent ISS flight manifest (INSIDER CONTENT) and stressed that the temperature and pressure inside the station were normal.

According to unofficial sources, the spacecraft lost all its cooling fluid from its Thermal Control System, SOTR. (INSIDER CONTENT) Several hours after the incident, NASA confirmed that the breach had been limited to the cooling system. At the same time, the US space agency said that the hatches between the cargo ship and the station had remained open, while temperatures and pressures aboard the outpost had stayed normal.

The accident apparently took place just half an hour after docking of the fresh Progress MS-22 cargo ship at a different docking port of the Russian Segment and resembled the situation with the Soyuz MS-22 crew vehicle in December 2022.

The subsequent publicly available exchange between NASA mission control in Houston and US astronaut Frank Rubio, aboard the ISS, indicated that the coolant system of the Progress MS-21 spacecraft had been completely emptied before the leak stopped. NASA also indicated that the plans to undock the vehicle from the ISS according to its original schedule had remained in place for the time being but were subject to change.

Prior to the coolant leak, Progress MS-21 was scheduled to undock from the zenith (skyward facing) port of the Poisk module, MIM2, on Feb. 18, 2023, at 03:55:30 Moscow Time (7:55 p.m. EST on Feb. 17) to make way for the arrival of the unpiloted Soyuz MS-23 spacecraft replacing the damaged Soyuz MS-22.

The spent cargo ship was expected to be deorbited on Feb. 18, 2023, at around 07:05 Moscow Time over a remote region of the Pacific Ocean. Any surviving debris were estimated to hit the ocean surface at around 07:45 Moscow Time.

According to Dmitry Strugovets, a former Roskosmos spokesman, an emergency meeting at RKK Energia held on February 11 established that the leak had started after 09:40 UTC on February 11 (4:40 a.m. EST) and the Russian specialists planned to request an inspection of the damaged Progress with the Canadarm, despite the less-than-ideal vantage points available to the robotic arm for observing this particular area of the station.

At the time, Russian officials left the Soyuz MS-23 spacecraft on schedule for launch on February 20, while also planning to revisit the results of the investigation into the Soyuz MS-22 leak according to Strugovets, apparently in search for a possible commonality between the two incidents. The meeting did not establish a leading theory on the cause of the problem with Progress MS-21, Strugovets said, but another gathering at Roskosmos was scheduled for Monday, Feb. 13, 2023.

In a video statement issued on February 11, Sergei Krikalev, the head of piloted space flight at Roskosmos, admitted that the leak aboard Progress MS-21 resembled the incident with Soyuz MS-22 and hinted that the original conclusion about its causes was now in doubt. He said that careful analysis would have to rule out the possibility of a common issue affecting the upcoming launches.


The Canadarm moving into position for the inspection of Progress MS-21 on Feb. 14, 2023.

On Feb. 13, 2023, the head of Roskosmos Yuri Borisov said that the State Corporation was taking steps to reach the affected area on the Progress by optical means to conduct photography of a possible hole in the radiator system. The inspection using the Canadarm was performed on Feb. 14, 2023.

As of February 15, the undocking of Progress MS-21 was re-scheduled for 05:26 Moscow Time on Feb. 18, 2023, (9:26 p.m. EST on February 17) or one orbit later than in the original plan.

On the morning of February 17, NASA officials said that shortly after its undocking from the ISS, Progress MS-21 would be commanded by cosmonauts Sergei Prokopiev and Dmitry Petelin at the TORU control console inside the Zvezda Service Module of the ISS to turn 180 degrees for the additional inspection of the leak area on the cargo ship using the station's cameras. At the time, specialists still evaluated images of the damage obtained by the Canadarm-2 and the investigation into the cause of the leak was ongoing, according to NASA.

According to exchanges between the Russian mission control and the ISS crew, Progress MS-21 was scheduled to perform roll maneuver at a distance of 10 meters from the station and two minutes after undocking.


Progress MS-21 undocked from the ISS as planned at 05:26 Moscow Time on Feb. 18, 2023, and after the completion of the roll maneuver, which lasted until around 05:40 Moscow Time, departed the vicinity of the station.

According to Roskosmos, no visible damage was found on the vehicle. However, the State Commission overseeing the flight considered two options for the further flight of Progress MS-21, Roskosmos said. One scenario was to re-dock the cargo ship to the Prichal Node Module, UM, for further investigation into the cause of the ship's thermal control failure or the deorbiting. As a result, the planned deorbiting scheduled for 07:03 Moscow Time on Feb. 18, 2023, had been postponed.

The extended autonomous flight provided some data on the conditions of the spacecraft without operational Thermal Control System, SOTR (INSIDER CONTENT).

However, several hours later, Roskosmos announced that the Chief Operational Control Group, GOGU, at RKK Energia made a decision to deorbit the spacecraft a day later than planned on Feb. 19, 2023.

The start of the deorbiting maneuver was scheduled for 06:15 Moscow Time (10:15 p.m. EST on February 18) and any surviving debris of the vehicle were projected to hit the remote area of the Pacific Ocean at 06:57 Moscow Time on Feb. 19, 2023, (10:57 p.m. EST on February 18).

External impact blamed for Progress MS-21 accident


On February 21, Roskosmos announced that the State Commission was continuing its analysis of the incidents with the Soyuz MS-22 and Progress MS-21 transport ships.

"Based on the preliminary assessment of the situation with Progress MS-21 at RKK Energia, the cargo ship had experienced an external impact," the State Corporation said. "This conclusion was made based the photos which revealed changes on the exterior of the vehicle, including those on the radiator of the Instrument and Aggregate Module and on the solar panels of the ship," Roskosmos said, "the holes discovered (on the photos after undocking) had not been seen either during the manufacturing of the Progress MS-21 at the factory, nor during its preparation for launch, nor during its flight and docking with the ISS."

Roskosmos also reported that in order to exclude the hypothesis of a manufacturing defect, RKK Energia reviewed the history of anomalies (INSIDER CONTENT) in the Thermal Control System (INSIDER CONTENT) of the Soyuz and Progress vehicles in the past 15 years. The State Corporation cited a report from the company stating that "No anomalies that could lead to such an incident had been found. The reliability of the Thermal Control System is guaranteed for one year from the launch of the spacecraft and, therefore, it is ensured to work reliably under nominal operational conditions."

In the meantime, the specialists continued the analysis of the available information, according to Roskosmos. Ground experiments were planned to simulate the damage found aboard Progress MS-21. That work would help in the final testing of all possible scenarios and the development of measures for eliminating such risk during the design and production of spacecraft, Roskosmos said.

Roskosmos also reconfirmed that the available information allowed the State Commission to clear Soyuz MS-23 for launch on February 24.



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This page is maintained by Anatoly Zak; Last update: February 21, 2023

Page editor: Alain Chabot; Edits: October 25, 2022, February 12, February 21, 2023

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Progress MS-21 during tests in anechoic chamber in early September 2022. Click to enlarge. Credit: RKK Energia


Progress MS-21 shortly after its integration with the launch vehicle adapter. Click to enlarge. Credit: Roskosmos


Integration of the payload section with the third stage, which was emblazoned with a design dedicated to the Rostov Region. Click to enlarge. Credit: Roskosmos


Soyuz-2-1a rocket with Progress MS-21 is installed on the launch pad. Click to enlarge. Credit: Roskosmos


Opening of a solar panel aboard Progress MS-21 shortly after reaching orbit as seen by an onboard camera. Credit: Roskosmos



Progress MS-21 fires its thrusters during the planned flyaround of the ISS as seen by the station's camera around 05:33 Moscow Time on Oct. 28, 2022. Credit: NASA