Discussion Soviet N1 Discussion Thread

[GigaG]

I don't play Orbiter any more - I'm more of a Kerbal Space Program guy. However, I still love space, and I figured that this would be a better place to discuss this than the KSP forum.

Anyways, I used to be obsessed with the N1 Soviet lunar rocket. For those of you who don't know, it was a rocket of comparable size to the Saturn V (I believe it was heavier, but couldn't carry as much.) It used giant clusters of small engines rather than the Saturn V's smaller clusters of large engines. The first stage, in particular, had 30 engines.

The N1 had 4 unmanned test flights. All 4 failed before the first stage separated.

The first launch of the N1 didn't happen until February of 1969, and it failed when a fire in the first stage reached the engine control system, shutting down the engines at about 69 seconds and (I believe) forcing range safety to destroy the vehicle.

The next launch in July of 1969 happened just before Apollo 11. A bolt got sucked into a fuel pump. The pump exploded, and the engine control system shut down 29 of the 30 first stage engines. The rocket fell back to the pad and generated the largest explosion in the history of rocketry, comparable to a small nuclear bomb. The blast destroyed the launch pad and severely damaged the next one.

The third launch happened in June of 1971. This rocket went into a roll and was destroyed (range safety, probably) at 51 seconds. This was actually promising - the first stage, while unable to halt the roll, still had all 30 engines burning up until the rocket was destroyed.

The fourth launch happened in November of 1972. The rocket experienced "pogo oscillations" - which were also an issue with the Saturn V. Just before 107 seconds into the flight, the engines cut off due to pogo oscillations. A shutdown of some engines to prevent over-stressing led to an oxygen pump explosion in engine 4. The rocket exploded - although I am unsure whether the explosion was directly caused by the series of failures or range safety. The Wikipedia entry for this words it quite vaguely. The first stage's burn should have lasted 125 seconds - this was the closest the N1 ever got to staging.

The program was shut down by the Soviet government before the 5th launch could commence. As far as I know, the Soviet government destroyed much of the footage of the failures (although a fair bit is available online, it annoys me that there could be much more) and kept the N1 program under wraps until 1989.

So this thread is for discussion of history's "forgotten lunar rocket." I hope that sometime, we get more footage of this rocket. Maybe the Russian government still has some footage that they either don't want to be released or don't know exists. Although, the way Russia is going, and with all the controversy they are involved in giving them other priorities, I don't think they'll open up about this anytime soon.

If I have any of my historical facts incorrect, please tell me.

 

[Urwumpe]

The first launch of the N1 didn't happen until February of 1969, and it failed when a fire in the first stage reached the engine control system, shutting down the engines at about 69 seconds and (I believe) forcing range safety to destroy the vehicle.

Actually, the fire was caused by a fluid hammer in the fuel lines to the center engines. When they shut the engines down and closed the valves, the many tons of flowing fuel stopped suddenly, dynamic pressure turned into static pressure and exceeded the burst pressure of some welds.

The biggest problem of the N1 was never the number of engines... it had been the fact that it was never system tested before launch. There was no test stand for testing the whole first stage of the rocket.

 

[Dantassii]

Some N1 Links I've found

Over the years, I've found quite a bit of information about the N1 rocket and it's trials and tribulations. The main one is here:

http://www.astronautix.com/lvs/n1.htm

There are links inside this document to additional details.

It may not have worked in its 4 flights, but it was a pretty rocket none the less. It is interesting to read the ASTF articles on this site because they give some insight into the reasons why the USSR had so many problems with their rockets and their spacecraft. In a word, telemetry.

Dantassii
HUMONGOUS IMS shipbuilder

 

[GigaG]

Yeah, the N1 probably would have been a great rocket, if a bit inefficient. Maybe if they improved on it, they could have gotten a much better heavy-lifter. I know it was untested. The Saturn V went through lots of issues with its F1 engines during testing, but these were obviously worked out. Am I correct?

Urwumpe - how do you know this? I'd like to see wherever you got this info - the N1 fascinates me.

One more thing - I've seen the famous video of N1-5L exploding. One still (courtesy of Astronautix) shows the falling rocket. I am unsure what is what, though.

Is this the second or third stage, with the interstage section in the bottom of the frame?

 

[Urwumpe]

Is this the second or third stage, with the interstage section in the bottom of the frame?

Should be the interstage between first and second stage, the large fairing for the external propellant lines are a good hint.

 

[GigaG]

Should be the interstage between first and second stage, the large fairing for the external propellant lines are a good hint.

Ah. I once saw a video of N1-5L's launch showing the escape system firing as the rocket reached its peak. It didn't show the explosion, though. You can't see the top of the rocket until the escape system goes off, but you can make out the rocket leaning over precariously. If cosmonauts were on board, this would be pretty terrifying (although there has been launch aborts such as the high-altitude Soyuz 18a incident which did not use the escape tower or Soyuz T-10a where the escape tower saved the crew from a rocket that was exploding on the pad.) In fact, the video is here-

https://www.youtube.com/watch?v=AyoBHBOnscY

Although, despite the terror, it would be an interesting story for the cosmonauts had it been manned and there were survivors. "Yeah, you all walked on the moon? Well, we survived the largest explosion in the history of rocketry!"

Anyways, this video appears to have been recorded from the opposite side, seeing as we are seeing the white side of the rocket (5L was half white, half black I believe), while the other one (I posted a still from it earlier) seems to show the black side as it falls back, although this could just be a silhouette of sorts. I wonder how what seems to be a rather candidly taken video survived the Soviet cover-up. I guess whoever took it kept it secret.

This failure is definitely 5L - although I don't know the exact times, I do know that 3L and 5L were the only 2 with a functioning escape tower, and 3L failed much later into the flight.

Another sad note - Astronautix says that it was determined that if 7L had jettisoned the first stage a few seconds early, they could have made it to orbit.

 

[Dantassii]

Another sad note - Astronautix says that it was determined that if 7L had jettisoned the first stage a few seconds early, they could have made it to orbit.

Actually, they shut down the interior 6 motors a few seconds from the rest in the hope of reducing the shock of shutting down all 36 engines at the same time. Turns out, if they had just left all 36 motors run to the end of the burn and shut them all down at the same time, they probably would have had a 2nd stage ignition. Exactly where it would have gone from there is anyone's guess as the 2nd and 3rd stages had never been fired before in a flight.

Dantassii
HUMONGOUS IMS shipbuilder.

 

[GigaG]

^Interesting, although one should note that the N1 had 30 engines, and the 6 center ones are part of the 30 (2 rings, 24 engines on the outside and 6 on the inside.)

Didn't the Saturn V do something similar where the center engine of the first stage would cut off before the rest of them (and the same on the second stage?) This was planned.

As for the N1, what happened? I have 2 interpretations-
-The problems started right before the center 6 engines were planned to be shut down, and the shutdown made the problem worse, leading to the failure. (In this case, the shutoff was planned a la Saturn V. I think this is what happened, considering that it has been cited that the cutoff was to "reduce g-force", just like the Saturn V did.)
-The problem was detected and the 6 engines were shut down to try to solve the issue, but the problem just became worse. (The shutoff was unplanned, which I don't think happened, but I'm not sure.)

Which one of these is correct?


Here is an acceleration graph of the Saturn V showing center engine cutoff-

http://en.wikipedia.org/wiki/File:Apollo_8_acceleration_2.svg

By the way, how much acceleration did an N1 produce on launch? Yes, I know the wisecrack answer would be "however much acceleration the escape tower needed to launch the capsule free of a small nuclear bomb's worth of exploding kerosene."

Oh yeah - Dantassii - OHIO!

 

[PeterRoss]

Here is the book written by one of Korolev's assistants who participated in creation of the whole Soviet rocket science starting from aquiring German rockets and ending with Energia. The book is translated into English and is being distributed as .PDF by NASA for free:

http://www.nasa.gov/connect/ebooks/rockets_people_vol1_detail.html

It is boring sometimes, too much is said about people you never heard about (and the book's title is saying about it honestly), but it has a good description of the process of development of N1 and about all its failures.

 

[Dantassii]

Didn't the Saturn V do something similar where the center engine of the first stage would cut off before the rest of them (and the same on the second stage?) This was planned.

As for the N1, what happened? I have 2 interpretations-
-The problems started right before the center 6 engines were planned to be shut down, and the shutdown made the problem worse, leading to the failure. (In this case, the shutoff was planned a la Saturn V. I think this is what happened, considering that it has been cited that the cutoff was to "reduce g-force", just like the Saturn V did.)
-The problem was detected and the 6 engines were shut down to try to solve the issue, but the problem just became worse. (The shutoff was unplanned, which I don't think happened, but I'm not sure.)

Which one of these is correct?

On the Saturn 5, the center engine on the 1st stage was shut down early on all the flights. The center engine on the 2nd stage was also shut down early but not on Apollo 4, 6, and 8. I don't know exactly when they started shutting down the center engine on the 2nd stage. On Apollo 13 the center engine on the 2nd stage shut down prematurely but it wasn't planned. By Apollo 15 it was definitely done as a fuel usage optimization measure. I think it was part of the mid-life improvement process to allow the heavier payloads of the J missions (Apollos 15, 16, and 17). I read on the Apollo Mission Journal (http://history.nasa.gov/afj/) that the Lunar Injection payload of Apollo 8 was around 89,000 pounds but by Apollo 17 it had increased to 108,000 pounds. That's quite an improvement if you ask me.

On the final mission of the N1, the center 6 engines were shut down 6 seconds early as planned, however, this caused vibrations in the rest of the 1st stage plumbing and first stage came apart before the rest of the engines on the first stage could shut down and the second stage ignite.

When the ASTF was getting setup, one of the things that surprised the USSR engineers was the sheer quantity of telemetry that was available in real-time from the Saturn boosters. It was several (at least 2 and possibly as high as 4) orders of magnitude more telemetry than they ever had on one of their rockets. This was not only during flight, but during the test runs on the ground. Even if they had built a test stand that they could run a full N1 first stage, they may no have found all the problems due to the lack of telemetry during the test.

Although a full N1 first stage was never test fired on the ground, individual engines were tested. Also it was noted in the article I read about the N1, the USSR did not test fire their flight engines or flight stages prior to launching them. Each Saturn 5 stage was test fired fully assembled prior to putting it on the pad. The Soviet method was that engines that were test fired on the ground did not fly on a mission. So the first time an engine on a rocket was fired for a full mission length burn was when the rocket was used in an actual launch.

A side note:

Several times during that ASTF, there were politicians who tried to scuttle the ASTF because they were fearful that the Soviet rockets and spacecraft were not safe. Did you know that early Soviet spacecraft were built super air-tight because they had no means on board to add atmosphere to the spacecraft once it left the ground. If it sprung a leak, they had no means to replenish the atmosphere. I suspect they had special tanks put inside the spacecraft for EVA use, but if the mission didn't have an EVA, they had no extra gas on board. This was a change they had to make to participate in the ASTF. The fact that they had no backup pressure gasses on board was discovered by US engineers when the Soviet engineers got extremely worried that the leaky US Apollo spacecraft was unsafe and would kill their cosmonauts.

Dantassii
HUMONGOUS IMS shipbuilder

 

[Urwumpe]

I am not sure if this was triggered by time or by acceleration, but the center engines have been shutdown on the Saturn V for reducing acceleration. Also this limited Pogo a lot, since the center engines had been most sensitive to it.

 

[GigaG]

^^ Apollo 8 had CECO on the S-II the graph I linked to shows a drop in g force which goes with CECO. That graph was recorded on Apollo 8.

 

[Urwumpe]

There is also a technical manual about the Saturn V, which contains all that information...

http://history.nasa.gov/ap08fj/pdf/sa503-flightmanual.pdf