Union MS-11: An accident that did not exist?

    The landing of Soyuz MS-11 on June 25 was supplemented by intrigue - at first the information about the accident appeared in the media, then Roscosmos officially stated that the landing was regular, and some news agencies reached the wording "Roscosmos" hid the incident with Soyuz MS-11 "" . Based on open sources, let's try to figure out what happened.

    Soyuz slows down for orbit, screenshot from Orbiter simulator


    The complete process of landing the ship, for our happiness, is recorded and uploaded to YouTube.

    On June 25, Soyuz MS-11 undocked from the ISS at 02:25 Moscow time ( 4:10:34 in the video).
    At 04:55 the next important stage began - the ship began braking ( 06:40:12 ). The maneuver was successfully completed after four minutes and 39 seconds, the speed of the ship, as planned, decreased by 127.98 meters per second. And after three minutes ( 6:48:06 ) the alarming sounded:
    A generalized K1B accident has passed, 05:02:54.
    MCC clarified "switched to the second collector?". And then, alas, the negotiations were blocked by the translator and commentator of NASA-TV, and it is impossible to make out.

    The separation of the compartments took place at 05:22, as planned. The ship made a successful landing in the calculated area at the expected time (05:48 Moscow time).

    And after landing, Roscosmos published an official message:
    According to the results of the analysis of telemetric information during the landing of the crew of the transport manned spacecraft, all on-board systems and units of the Soyuz MS-11 (including the combined propulsion system) worked out normally, in strict accordance with the flight program. There are no comments.

    After complete completion of the landing tasks, a backup manifold (KDU pneumatic-hydraulic system circuit) was prepared for use (in case of a possible need).

    Thus, the messages distributed by some media about the occurrence of certain “emergency situations” during landing are unreliable.


    What is K1B? This is the first collector of mooring and thrust orientation engines. On the previous version of the ship, Soyuz TMA-M, to control the position of the ship in space and maneuver when approaching / docking, there were 16 large thrust engines DPO-B and 12 small ones (DPO-M). On the Soyuz-MS flying now, they implemented a completely duplicated system of two sets of 14 high-thrust engines with one collector (switchgear) per set.

    Soyuz TMA-M, DPO-B closed with red, DPO-M

    Soyuz-MS visible , all engines the same.

    Accordingly, in case of failure of the main collector, the ship switches to standby and continues flying.

    Questions and answers

    Let's try to answer the most obvious questions.

    Was there an accident at all?
    Judging by the NASA-TV broadcast, there was a signal about the accident because cosmonauts reported it. The information message of Roscosmos admits that a reserve collector has been prepared, but not informative enough to clearly say what exactly happened. For example, the signal could turn out to be false or disappear after some time. Broadcast talks are blocked by NASA-TV announcers, and what happened next is unknown.

    How dangerous was that?

    The scenario “the braking engine has failed at the spacecraft and it cannot return to Earth” is mortally dangerous, therefore, engineers laid down emergency systems for this case even at the dawn of astronautics. The Soviet "Vostoks" launched into such an orbit that they would have left in an acceptable time even in the event of a complete failure of the brake propulsion system, the American "Mercury" carried three solid fuel brake engines, which were reliable due to their simplicity, and their total momentum was chosen with a large by reserve - the ship would return even if two of the three engines failed. Specifically, in the case of Soyuz-MS, the ship regularly brakes with the SKD marching engine (in the photo below, in the center of the stern, it is closed with a lid), and in case of failure, two more sets of DPO-B engines remain.

    In addition, Soyuz MS-11 has already managed to perform a braking maneuver on the SKD marching engine. Mooring and orientation engines in any case would have been reset together with the aggregate compartment in twenty minutes, and after separation of the compartments, the descent vehicle is already controlled by its orientation engines. Another confirmation that the flight program was not violated - the ship landed in a regular area at the expected time. In case of problems, the automation of the descent vehicle enters ballistic descent mode, and the ship lands with a large shortage in the reserve landing area. So the general conclusion is that there was no danger to the astronauts.

    Were there similar incidents in the history of space?

    In 2015, the docking of the Soyuz TMA-19M spacecraft with the ISS was obtained only on the third attempt and in manual mode, because one of the DPO engines did not give out full thrust. At Soyuz MS, a similar accident would not have affected the docking because the automation would have switched to the backup manifold engine.

    September 6, 1988 a rather unpleasant situation arose at the Soyuz TM-5. Uncertain operation of the orientation sensor was perceived by the on-board computer as a failure, and braking at the estimated time was blocked. Orientation was restored after 7 minutes, and it was necessary to turn off the engines manually started by the computer, so as not to sit in China. After two turns, the on-board computer began to execute the erroneously loaded docking program, and it was necessary not only to turn off the engine manually, but also urgently to block the automatic separation system, so as not to remain in orbit without engines and oxygen reserves. The astronauts had to wait a day without a toilet (the household compartment was planned to be reset in advance), but the landing the next day, September 7, went without any problems.

    On April 10, 1979, problems arose with the Soyuz-33 main engine. The astronauts successfully returned on the backup. This modification of the ship still had two marching engines and a separate additional fuel oil circuit. A single fuel system for SKD and DPO appeared in 1986 at TM Soyuz.


    In general, it should be noted that the huge number of space flights that remained in history as "regular", in reality, faced various problems, too small to get on the pages of encyclopedias. This is normal - space technology is complex and can never be 100% reliable.

    And, finally, stories like the one that happened on June 25 say, however paradoxical it may seem, about the reliability of the Unions and that they were well designed.

    PSAt the end of May, the hubts of the former Giktayms were transferred to non-core ones on Habré. Together with the changes in the rules that allowed repost, in my opinion, this looks like a direct recommendation “try to write to specialized publications, and then you can repost here”. I am grateful to Habr for a good and pleasant venue, and I accept the fact that time is running out and everything is changing. By a lucky coincidence, representatives of already several resources came to me at the same time as news, so I didn’t even have to throw a cry in social networks “But does anyone need a space columnist?” I have not gone anywhere and continue to engage in popularization, but the tradition of weekly publications, alas, has ordered a long life, and now the materials will be released without any schedule.

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