Russia’s Soyuz MS-25 arrives at ISS

Soyuz MS-25 arrives at ISS

After a 48-hour delay, the Soyuz-2-1a rocket lifted off from Baikonur Cosmodrome, Kazakhstan, sending the Soyuz MS-25 spacecraft with a crew of three on its way to the International Space Station, ISS. The crew vehicle successfully docked at the outpost on March 25, 2024.

Soyuz MS-25 mission at a glance:

Soyuz MS-25 mission

As of 2014, the first launch of a Soyuz crew vehicle to the ISS in 2024 was penciled for March 30, but during most of 2023, the Soyuz MS-25 mission was expected to lift off on March 13, 2024. However by the end of 2023, the launch was re-scheduled for March 21, 2024.

According to the original plan for the Soyuz MS-25 mission, Russian cosmonauts Aleksei Ovchinin and Oleg Platonov were to be joined by a visiting crew member from Belarus. As of May 2023, Belorussian authorities were expected to appoint Marina Vasilevskaya, a flight attendant from the Belavia airline, as the primary candidate and Anastasia Lenkova, a pediatric doctor, as her backup. Vasilevskaya and Lenkova arrived at Star City to begin their eight-month training for the flight on July 23, 2023. By that time, Vasilevskaya was expected to make a 12-day visit to the ISS, accompanied by Roskosmos cosmonaut Oleg Novitsky and a NASA astronaut Tracy Dyson. Vasilevskaya and Novitsky were slated to land aboard the returning Soyuz MS-24 spacecraft, as members of Visiting Crew 21, along with NASA astronaut Loral O’Hara, completing a long-duration stay on the ISS. In the meantime, Dyson would remain aboard the ISS for a multi-month shift during Expedition 71.

The Soyuz MS-25 backup crew included Roskosmos cosmonaut Ivan Vagner and NASA astronaut Donald Pettit.

Soyuz MS-25 launch campaign

The Soyuz-2-1a rocket for the Soyuz MS-25 mission arrived at Baikonur and was delivered to vehicle assembly building at Site 112 on Sept. 11, 2023. Then, Soyuz MS-25 was delivered to the launch site from RKK Energia, along with the Progress MS-27 cargo ship, on Sept. 14, 2023.

After a period in a storage since the second half of December 2023, the preparations for the Soyuz MS-25 mission resumed on Jan. 11, 2024, with test activation of equipment aboard he spacecraft, followed by a series of integrated electric tests. On January 25, Roskosmos announced the return of the spacecraft from the anechoic chamber at Site 254 after testing of radio equipment in the ship’s Kurs-NA rendezvous system.

From Feb. 7 to Feb. 13, 2024, Soyuz MS-25 was transported into the vacuum chamber at Site 254 for air leak checks. The tests continued until February 13, when the spacecraft was returned to its work site for testing the propulsion (INSIDER CONTENT) and descent control systems, followed by onboard flight control computer and radio system tests. Also, the ship’s thermal control system (INSIDER CONTENT) was filled with coolant.

On Feb. 19, 2024, the Emergency Escape System, SAS, for the Soyuz MS-25 mission was delivered to the launch site and on February 27, the ship’s solar panels were put to a routine test.

By March 6, 2024, specialists working inside the vehicle assembly building at Site 31, connected the four boosters of the first stage to the core (second) stage booster of the Soyuz-2-1a rocket for the Soyuz MS-25 mission. On the same day, the primary and backup crews of the Soyuz MS-25 mission arrived at Baikonur after landing at the spaceport’s Krainy airfield. On March 7, 2024, both crews conducted the first “fit tests” inside the Soyuz MS-25 spacecraft, including donning their Sokol-KV2 pressure suits and taking their seats inside the Descent Module (INSIDER CONTENT). On the same day, a meeting of the technical management at the launch site cleared the spacecraft for irreversible operations including loading of propellant components and pressurized gases. The fueling was completed on March 11, 2024, when the spacecraft was returned to its processing building at Site 254.

On March 12, 2024, Soyuz MS-25 was integrated with its launch vehicle adapter, which serves as an interface between the spacecraft and the third stage of the Soyuz-2-1a rocket. Before the operation, specialists performed final weighting of the spacecraft and completed placement of cargo onboard.

On March 13, specialists completed the traditional visual inspection of the spacecraft, after which it was lowered in horizontal position and rolled inside its payload fairing. The resulting assembly was then prepared for launch readiness simulation and then specialists loaded cargo intended for delivery to the ISS into habitable compartments of the spacecraft.

On March 15, the crews conducted second and final familiarization training inside the flight-ready Soyuz MS-25 spacecraft, which included taking seats inside the Descent Module (INSIDER CONTENT) and inspecting cargo inside the Habitation Module. The payload section with the spacecraft was then loaded on a rail transporter and transferred from the spacecraft processing building at Site 254 to the launch vehicle assembly building at Site 31. The integration of the payload section with its Soyuz-2-1a rocket was completed on March 16, after which the State Commission overseeing the campaign, authorized the rollout to the launch pad which took place as scheduled on March 18, 2024.

According to the Russian mission control, the Soyuz MS-25 mission had the following countdown timeline:

• 78:21:00 — 01:01:00: Thermal conditioning of the spacecraft;
• 04:11:00 — 03:46:00: Fueling of the launch vehicle;
• 02:46:00: Arrival of the crew at the launch facility;
• 02:41:00 — 02:16:00: Crew boards the spacecraft;
• 01:30:00 — 00:30:00: Checks of the spacecraft onboard systems;
• 00:45:00 — 00:33:00: Retraction of the access gantry;
• 00:30:00 — 00:15:00: Systems configuration to launch readiness;
• 00:25:00: Powering up of the Emergency Escape System;
• 00:10:00: Launch vehicle flight control system ready for flight;
• 00:06:00: Issuing of pre-launch commands;
• 00:00:00: Liftoff.

Soyuz MS-25 launch attempt scrubbed

A moment of the scrub during launch attempt on March 21, 2024.

A Soyuz-2-1a rocket carrying the Soyuz MS-25 spacecraft was originally scheduled to lift off from Site 31 in Baikonur on March 21, 2024, at 16:21:19 Moscow Time (9:21 a.m. EDT, 13:21 UTC). At the time of the crew vehicle launch, the ISS would be orbiting the Earth over Southwest Kazakhstan and it was expected to pass over Baikonur 36 seconds later. The Soyuz would then enter orbit with a 14.6-degree phasing angle relative to the station, enabling the docking at 19:39 Moscow Time (12:39 p.m. EDT, 16:40 UTC) on the day of the launch, or 3 hours 19 minutes (two orbits) after its departure from Baikonur. Soyuz MS-25 was expected to perform a 45-degree flyaround of the ISS before docking at the Prichal Node Module, UM.

All preparations for liftoff on March 21 went without a hitch until around L-20-second mark when the Emergency Engine Cutoff, AVD (from the Russian Avariynoe Vyklyuchenie Dvigatelya), command interrupted the final countdown. At that moment, the launch control had already issued the “Pusk” (launch) command (normally issued at L-19 seconds), however, one umbilical mast, VKM (from the Russian Verkhnyaya Kabel Machta), located above the surface of the pad, remained connected to the rocket, with its nominal retraction usually taking place at L-15 seconds in the countdown.

The Russian launch control then instructed the personnel to prepare for a 24-hour stay on the pad, but according to NASA, the next opportunity to launch Soyuz MS-25 would not come until March 23 (at 15:36:10 Moscow Time). If it made that launch opportunity, the Soyuz would enter orbit 201 degree away from the ISS in the phasing angle, requiring a 50-hour (two-day, 34-orbit) rendezvous profile with the station and docking on March 25, 2024, at around 18:10 Moscow Time (11:10 a.m. EDT). A similar flight scenario (with the 294-degree phasing angle) would be available during a backup launch opportunity on March 24, 2024, at 15:13:33 Moscow Time.

Within minutes after the scrub, the launch control authorized lifting the access gantry and bringing the lower service platform into position for servicing the rocket and draining cryogenic liquid oxygen and nitrogen from its tanks. The vehicle and the crew were declared safe for deactivating of the emergency escape system and the subsequent evacuation of the crew.

Coming out from a meeting of the State Commission following the aborted launch attempt, Head of Roskosmos Yuri Borisov was quoted as saying that a voltage drop in chemical batteries caused the mishap. According to Borisov, the culprit had already been established. Around the same time, an official NASA press release said that the launch “was automatically scrubbed by ground support equipment due to low voltage reading in the Soyuz rocket electrical system.”

According to unofficial reports on the Novosti Kosmonavtiki forum, a sudden voltage drop from normal 27 volts to three volts was detected in backup chemical batteries KhIT (from the Russian Khimichesky Istochnik Toka) in two out of five boosters (Block A and G) comprising the first and second stage of the Soyuz rocket, immediately after the third stage (Block I) of the rocket had been switched to the internal power supply. In the meantime, the voice AVD command was reportedly anounced by mistake, because the propulsion system of the first stage had never been activated. Unofficial reports also said that on March 22, specialists were replacing an avionics unit in the flight control system, indicating that the culprit was not in the batteries themselves. There was also an unofficial report stating that the batteries could have failed as a result of an interruption in their heating circuits responsible for thermal conditioning to the KhIT system. The problem apparenyl led to overheating of the batteries and to a leak of alkaline electrolyte from the nikel-cadmium batteries.

Yet, another poster on the same forum said that the following the transition of the vehicle to the onboard power supply, the main batteries had experienced a voltage drop, which investigators had apparently attributed to excessive loads bordering on a short circuit and originating from the backup batteries. The question remained how the two electrically isolated battery systems on two different boosters would short-circuit at the same time.

On March 22, 2024, the meeting of the State Commission in Baikonur officially cleared the Soyuz MS-25 mission for another launch attempt on March 23. The same meeting also re-scheduled the return of the Soyuz MS-24 mission from the ISS back to Earth with two members of the Soyuz MS-25 crew and a US member of Expedition 70 from April 2 to April 6, 2024. The resulting change would keep the 12-day duration of a visit by two members of the Soyuz MS-25 crew but extend their overall flight to 14 days, counting added two days in the Soyuz autonomous flight required to reach the station.

Soyuz MS-25 launch scenario

After a 48-hour delay, the Soyuz-2-1a rocket with the Soyuz MS-25 spacecraft lifted off on March 23, 2024, at 15:36:10.573 Moscow Time. Propelled by the simultaneous thrust of the four engines of the first stage and the single engine of the second stage, the vehicle headed almost exactly east to align its ascent trajectory with an orbital plane inclined 51.6 degrees toward the Equator. Slightly less than two minutes into the flight (L+113.47 seconds), at an altitude of around 45 kilometers and a velocity of 1.75 kilometers per second, the ship’s main emergency escape rocket was jettisoned, immediately followed by the separation of the first stage (at L+117.8 seconds). The emergency escape rocket and four boosters of the first stage then impacted the ground 330 and 350 kilometers downrange from the launch site respectively.

Around 35 seconds after the first stage separation, as the vehicle exited the dense atmosphere at an altitude of 79 kilometers and a velocity of 2.2 kilometers per second, the payload fairing protecting the spacecraft split into two halves and fell away (at L+153.33 seconds). They were projected to fall 500 kilometers downrange from the launch site.

In the meantime, the second (core) stage of the rocket continued firing until 4.8 minutes into the flight. Moments before the second stage completed its work, the four-chamber engine of the third stage will ignited, firing through the lattice structure connecting the two stages. Moments after the separation of the core booster at an altitude of 157 kilometers and a velocity of 3.8 kilometers per second (at L+287.70 seconds), the aft skirt of the third stage split into three segments and separated as well (at L+296.12 seconds). The second stage booster and the sections of the aft skirt were to impact the ground 1,550 and 1,570 kilometers downrange from the launch site respectively.

Following the 8-minute 49-second climb to orbit, the propulsion system of the third stage was cut off (at L+525.93 seconds), releasing Soyuz MS-25 into a 200.0 by 242.0-kilometer initial orbit at L+529.229 seconds after liftoff.

Rendezvous and docking operations

At the time of the Soyuz MS-25 liftoff on March 23, 2024, the ISS was orbiting the Earth over the Southwestern Atlantic of the coast of Argentina in the 415.530 by 436.562-kilometer orbit.

Within three minutes after the separation of the crew vehicle from the third stage of the launch vehicle at 15:44:59 Moscow Time, the Soyuz was scheduled to deploy its solar panels and radio antennas. NASA confirmed that all initial operations went as scheduled.

Between 15:51 and 15:57 Moscow Time on March 23, 2024, the first in-orbit tests of the Kurs-NA rendezvous system and the Motion and Control and Navigation Systems, SUDN, were planned, followed by the extension of the docking probe in the ship’s active docking mechanism.

By the 33rd orbit of the autonomous flight, the Russian mission control projected Soyuz MS-25 to climb to the 385.388 by 420.469-kilometer orbit, just below the ISS, which was in the 415.135 by 436.545-kilometer orbit. By that time, the crew vehicle was in the autonomous rendezvous process with the station, which was projected to have the following milestones:

• 15:46:33 Moscow Time: Beginning of autonomous rendezvous with the ISS;
• 16:35:40 Moscow Time: Activation of the Kurs rendezvous system aboard the Zvezda Service Module, SM;
• 16:36:40 Moscow Time: Activation of the Kurs rendezvous system aboard Soyuz MS-25;
• 17:45 — 17:52 Moscow Time: Fly-around of the station;
• 17:52 — 17:58 Moscow Time: Station-keeping of the spacecraft near ISS before final approach;
• 17:58 — 18:09 Moscow Time: Final approach to the Rassvet module, MIM1;
• 18:09:28 Moscow Time: Contact.

As usual, the Russian mission control in Korolev planned six maneuvers with the ship’s SKD and DPO engines during the autonomous rendezvous with the station:

As planned, Soyuz MS-25 approached the station to a distance of around 400 meters around 17:45 Moscow Time (10:45 a.m. EDT) on March 25, 2024, when it began a 51-degree flyaround of the station to align itself with the nadir (Earth-facing) port of the Prichal Node Module, UM, a part of the Russian ISS Segment.

After a two-day, 34-orbit autonomous flight, Soyuz MS-25 docked with the ISS at 18:02:51 Moscow Time (11:03 a.m. EDT) on March 25, 2024, as the two spacecraft were flying over Central Kazakhstan. Following leak checks, hatches between the transport ship and the station were opened at 1:26 p.m. EDT (20:26 Moscow Time), according to NASA.

Soyuz MS-25 crew members: