One bad day on Soyuz 33

[WallE]

After Soyuz 32 cosmonauts Vladimir Lyakhov and Valery Ryumin established the third crew residency on Salyut 6, they were looking forward to receiving visitors when Soyuz 33 arrived on an Intercosmos mission with Nikolai Rukavishnikov and Bulgaria's Georgi Ivanov. After lifting off on the evening of April 10, 1979 and reaching orbit, the crew approached Salyut 6 and attempted to dock at the station's rear docking port. At about 3,200 feet from the station, the Soyuz's engines cut off after three seconds of operation. The spacecraft shook violently when this happened.

Ground control gave permission to try again. Rukavishnikov activated the engine but could see flames shooting sideways out the back. He disabled it and was told to abort the mission and return to Earth. As with previous Soyuz docking failures, the cosmonauts had no choice but to power down non-essential systems to conserve battery power while waiting for reentry.

The attitude control jets could be used to complete the docking if Salyut 6 was close enough but the two spacecraft were drifting apart at a rate of 90 feet per minute. The Soyuz's backup propulsion system had never been used on an actual flight and could have been damaged by the problem with the main engine. Using the attitude control thrusters to deorbit Soyuz 33 was also a dubious idea; there might not be enough propellant for that and it was hard to say where the spacecraft might land. It would take ten days for the spacecraft to decay naturally and consumables onboard wouldn't last that long.

With no other options, it was decided to risk firing the backup engine, which had to be fired long enough to allow deorbit but not so long as to subject the crew to high G loads. The engine worked but the autopilot ran it for 213 seconds until the cosmonauts manually shut it down. They were subjected to up to 10 Gs during reentry but landed close to the intended recovery area in the USSR. The cosmonauts were recovered alive and well despite the rough reentry, but it was an embarrassing fiasco especially during a high profile Intercosmos mission.

Postflight investigation found that a pressure sensor in the engine terminated thrust as a safety cutoff when it detected abnormal combustion. The Soyuz engine was an extremely reliable piece of hardware that had never failed in countless firings, but it was redesigned afterward although Roscosmos has never specifically stated what the failed component was (perhaps a fuel valve?)

The unmanned Soyuz 34 was launched on June 6 with hardware modifications and it replaced Soyuz 32, which had been in orbit five months and was past its "expiration" date. Soyuz 32 returned to earth unmanned after the crew loaded it with various items that needed to be brought back to Earth, including the results of scientific experiments. However, the planned guest missions to Salyut 6 were unable to take place and it left Lyakhov and Ryumin in a foul mood as they had been looking forward to their planned visitors. They completed the rest of the residency by themselves until it wrapped up in August and they returned to Earth.

[Nicolas PILLET]

Rukavishnikov activated the engine but could see flames shooting sideways out the back.

Rukavishnikov didn't see anything, since the portholes location did not allow him to see the engine plume. It was the Salyut-6 crew who observed flames in lateral direction.

The Soyuz's backup propulsion system (...) could have been damaged by the problem with the main engine.

And it was the heart of the problem ! Main and backup engines are functionnally independant, but physically side by side. And it was the case : the explosion of main engine's gas generator did damage the backup engine.

The engine worked but the autopilot ran it for 213 seconds until the cosmonauts manually shut it down.

The nominal, calculated duration was 187,8 seconds. With this duration, the spaceship would have landed in the backup landing area. But Rukavishnikov heard non nominal sound during the work of the backup engine, and he decided to manually cancel the automatic shutdown and to give 25 seconds more to the engine. It was very unlikely and completely unintentional, but these 25 seconds made the spaceship land exactly in the main landing area, like if nothing had happened !

Soyuz-33 is the most underrated mission in space history. It was maybe more dangerous than Apollo 13. And Rukavishnikov role was really impressive.

[mn]

Rukavishnikov activated the engine but could see flames shooting sideways out the back.

Rukavishnikov didn't see anything, since the portholes location did not allow him to see the engine plume. It was the Salyut-6 crew who observed flames in lateral direction.

The Soyuz's backup propulsion system (...) could have been damaged by the problem with the main engine.

And it was the heart of the problem ! Main and backup engines are functionnally independant, but physically side by side. And it was the case : the explosion of main engine's gas generator did damage the backup engine.

The engine worked but the autopilot ran it for 213 seconds until the cosmonauts manually shut it down.

The nominal, calculated duration was 187,8 seconds. With this duration, the spaceship would have landed in the backup landing area. But Rukavishnikov heard non nominal sound during the work of the backup engine, and he decided to manually cancel the automatic shutdown and to give 25 seconds more to the engine. It was very unlikely and completely unintentional, but these 25 seconds made the spaceship land exactly in the main landing area, like if nothing had happened !

Soyuz-33 is the most underrated mission in space history. It was maybe more dangerous than Apollo 13. And Rukavishnikov role was really impressive.

Wikipedia has a slightly different narrative on the deorbit burn. Obviously no way of me knowing which version is more accurate.

I guess you can go ahead and edit the Wikipedia page if you have accurate sources for your version of events.

[WallE]

The autopilot ran the engine longer than planned because the backup engine had lower ISP than the main one and the autopilot wasn't designed to compensate for that so the cosmonauts finally shut it off after 213 seconds of burn time (the Soyuz 7K-T had primitive avionics with no reprogrammable computer). The reentry was accurate but they did get kind of banged around with high G loads.

I had remembered that it was the Soyuz 32 crew that saw the abnormal engine burn but I forgot to edit the OP text and correct that.

Also yes it was quite perilous and the Soviet program had lots of close calls like that. On the Soyuz 15 and T-8 docking failures they very nearly crashed into the Salyut station at a high rate of speed. Quite terrifying, really. As for Apollo 13 comparisons you can liken it to the astronauts having no way to know if the command module heat shield was damaged by the service module explosion.

Lyakhov and Ryumin were apparently surly enough about the mission failure that they cut off all communications with ground control for a while and refused to speak to them.

[mn]

The autopilot ran the engine longer than planned because the backup engine had lower ISP than the main one and the autopilot wasn't designed to compensate for that so the cosmonauts finally shut it off after 213 seconds of burn time (the Soyuz 7K-T had primitive avionics with no reprogrammable computer). The reentry was accurate but they did get kind of banged around with high G loads.

I had remembered that it was the Soyuz 32 crew that saw the abnormal engine burn but I forgot to edit the OP text and correct that.

Also yes it was quite perilous and the Soviet program had lots of close calls like that. On the Soyuz 15 and T-8 docking failures they very nearly crashed into the Salyut station at a high rate of speed. Quite terrifying, really. As for Apollo 13 comparisons you can liken it to the astronauts having no way to know if the command module heat shield was damaged by the service module explosion.

Lyakhov and Ryumin were apparently surly enough about the mission failure that they cut off all communications with ground control for a while and refused to speak to them.

I'm not following, if the autopilot was not designed to compensate for the lower thrust, why was it running the engine longer than 'planned' (planned by who/when? original plan for regular engine, new calculated number for backup lower isp engine?)

[WallE]

I'm not following, if the autopilot was not designed to compensate for the lower thrust, why was it running the engine longer than 'planned' (planned by who/when? original plan for regular engine, new calculated number for backup lower isp engine?)

It's on the Wikipedia article.

The main option was to fire the backup engine, but this option was not guaranteed to work, even if the engine fired. The nominal burn time was 188 seconds, and as long as the burn lasted more than 90 seconds, the crew could manually restart the engine to compensate. But this would mean an inaccurate landing. If the burn was less than 90 seconds, the crew could be stranded in orbit. A burn longer than 188 seconds could result in excessive G-loads on the crew during reentry.

In the end, the backup engine did fire, though for 213 seconds, 25 seconds too long, resulting in the craft taking an unusually steep trajectory and the crew having to endure an acceleration of 10 gs. Rukavishnikov and Ivanov were safely recovered It was the second ballistic entry reported by the Soviets, Soyuz 1 being the first (although Soyuz 18A was a ballistic reentry, and Soyuz 24 reportedly also was one).

The high G-loads during reentry were a mix of crew error and a design flaw in the autopilot; because the backup engine produced less thrust than the main engine, the autopilot tried to run it until the proper delta V was achieved, but the cosmonauts issued a manual shutoff command after 213 seconds of burn time. This unwise decision resulted in a ballistic reentry. This would have caused the Soyuz to land uprange of the planned landing point, but the low delta-V (as the result of the crew manually shutting off the engine early) resulted in the opposite effect and instead, the capsule touched down very close to the target area.

The computer on the Soyuz 7K-T was not re-programmable; it had a hard-wired number of actions it could do and the program for the burn time was supposed to be 188 seconds but since the backup engine had lower ISP than the main engine the computer kept running it well past the intended burn time as it didn't detect the correct delta-V so Rukavishnikov manually shut it off.

On Soyuz T and later they could have modified the autopilot program for the backup engine but this was not possible on earlier Soyuz variants.

Apparently the cause of the engine failure was indeed the gas generator. It was difficult to get complete information on the status of Soyuz 33 since telemetry tapes had to be studied which take a while but the gas generator was rather quickly determined to be the culprit. Aside from that being redesigned afterward, the procedural instructions the cosmonauts were issued for operating the engine were revised and clarified.

[Big RI Joe]

Wasn't Rukavishnikov the first civilian Soviet spacecraft commander?

[Nicolas PILLET]

I guess you can go ahead and edit the Wikipedia page if you have accurate sources for your version of events.

My source is this wonderful website (), who gives its (primary) sources at the bottom of the page.

https://www.kosmonavtika.com/vaisseaux/dos/missions/soyouz33/chrono.html

[WallE]

No cause of failure listed for the 8/19/71, 4/12/74, 6/12/82, 7/9/88, and 11/11/88 launches.

https://www.kosmonavtika.com/vaisseaux/voskhod/missions/voskhod1/photos/photos.html

I believe the photos of Voskhod 1's liftoff are also incorrect (spacefacts.de has the same apparent mistake) as Voskhod had a very distinctive payload shroud that could not mistaken for anything else. This is probably a planetary probe mission (which one is anyone's guess). Outside chance it's a Zenit or Molniya launch but I'd be inclined to think the former is most likely.

On that note Voskhod 1 and 2's boosters also had very distinctive black and white roll bars painted on the Blok I stage. I've never seen another photo of an R-7 vehicle with those and I wonder what if any reason there was for doing that.

[Nicolas PILLET]

No cause of failure listed for the 8/19/71, 4/12/74, 6/12/82, 7/9/88, and 11/11/88 launches.

I've added the explanations for the failures.

I believe the photos of Voskhod 1's liftoff are also incorrect

You believe right. I've deleted the pictures. I'll add the good pictures when I find time !

On that note Voskhod 1 and 2's boosters also had very distinctive black and white roll bars painted on the Blok I stage. I've never seen another photo of an R-7 vehicle with those and I wonder what if any reason there was for doing that.

There was a camera on Voskhod spaceship to record the separation of Blok I. The black and white paint was here to allow for angular rate measurement during video analysis.