AHC: The USSR builds and launches the equivalent of Sea Dragon

[Anime Ninja]

Your challenge is to have the USSR in the 60's or early 70's build and launch an equivalent to the Sea Dragon.

This can be for a moon shot or a very large station or both.

How would the US react?

Could they have used the Black Sea as a launch point or would have been some place else?

 

[unclepatrick]

The Soviet had problems with Large Engines .
Their moon rocket the N1 had 30 smaller engines to the Saturn 5 5 engines on their first stages .
A Sea Dragon style rocket would involve even larger engines.
I not sure they could build the necessary engines for a Sea Dragon style rocket.

 

[GTStinger]

Was there a specific cause for the historic trouble making large engines? Lack of necessary metallurgy, lack of ability with computer simulations, etc?

Or was it just engines get exponentially more difficult as size increases and the Soviets didn’t have time to catch up?

 

[TDM]

Was there a specific cause for the historic trouble making large engines? Lack of necessary metallurgy, lack of ability with computer simulations, etc?

Or was it just engines get exponentially more difficult as size increases and the Soviets didn’t have time to catch up?

IIRC it has something to do with getting enough fuel steadily into the larger engine's combustion area to ignite all at the right time without getting too much at the wrong time and it blowing up.

 

[fasquardon]

Was there a specific cause for the historic trouble making large engines? Lack of necessary metallurgy, lack of ability with computer simulations, etc?

Or was it just engines get exponentially more difficult as size increases and the Soviets didn’t have time to catch up?

My understanding is that it is just more difficult to mix two fluids as throat diameter grows. The US solved that by using injector plates that were basically giant shower heads (which cost some performance) and the USSR solved that by using more combustion chambers on each nozzle (which added complexity, but also let them achieve far higher chamber pressures).

Making it harder is that making Sea Dragon a hypergolic engine would simply be suicidal. Handling that much of such nasty stuff simply could not be done without leaks, and even a small portion of propellant of something Sea Dragon sized is still alot of toxic crud. Sea Dragon would need to be LOX/hydrocarbon or LOX/LH2.

Building a rocket engine on Sea Dragon's scale is certainly a difficult thing, but some parts of engine design actually become more simple as the engine grows in scale, which was part of why Truax thought Sea Dragon might be a good idea. Of course, no-one has attempted to build something that massive, so we don't know if the problems of increasing turbulence in the nozzle would out-weigh the advantages of big nozzles, like reduced need for high pressures and easier cooling.

And I've read that Sea Dragon would have been loud enough to deafen most marine life in its launch area (and for whales "launch area"="the same ocean", so launching these monsters in the black sea, while less harmful than launching from the Atlantic, is going to be absolutely brutal on the local ecology. Together with all the pollution being washed into the sea, it could become a microbial life only zone.

Your challenge is to have the USSR in the 60's or early 70's build and launch an equivalent to the Sea Dragon.

This can be for a moon shot or a very large station or both.

How would the US react?

Could they have used the Black Sea as a launch point or would have been some place else?

The Soviets were always more interested in setting up a lunar base than the US was. It may be that in TTL they are even more keen on the idea for some reason, and develop a truly massive rocket to make such a base economical (I believe a Sea Dragon could achieve launch costs a couple orders of magnitude below the costs per kilo of the 60s).

fasquardon

 

[e of pi]

Was there a specific cause for the historic trouble making large engines? Lack of necessary metallurgy, lack of ability with computer simulations, etc?

Or was it just engines get exponentially more difficult as size increases and the Soviets didn’t have time to catch up?

The word behind the issue is "combustion stability". The mixing of propellants and their combustion is prone to minor fluctuations--say a burst of LOX doesn't vaporize quite as much through the injector plate, and so there's a brief moment where a spot in the chamber had lower pressure, then everything gets shoved towards, it, making altered pressure and combustion elsewhere, causing more fluctuations and so on. This creates pressure wavefronts on the face of the injector. Undamped, these can become larger and larger, until eventually the engine fails, one way or another. The larger the injector plate, the more area there is for things to go wrong (so it's more likely to happen) and the larger the waves can get as they get out of hand. The solutions in the 60s were experimental, not analytical: back off from maximum performance and stick a bunch of baffle walls into the chamber until it can damp out any waves that start. This is a lot of why the F-1 took from 1959 to 1964 to achieve enough stability to flight rate--they kept exploding from combustion instability at the start. To test it, they resorted to sticking explosive charges up inside the bell and setting them off to deliberately induce worst-case waves and check that the engine could damp them. Computer simulations capable of the kinds of turbulent flow happening inside rocket engines really weren't a thing until years later.

The Soviet program didn't go in as much for engine testing as the Americans did, as I understand it. At the very least, Kuznetsov's early NK-15 could only be fired once, seriously impairing testing. Finding someplace to test an engine of Sea Dragon's class would be tremendously challenging--it will need the kind of full-stage test stand they never even built for N-1.

A point to be noted is that the issue gets worse the larger the chamber pressure, so low-pressure engines like the pressure-fed original Sea Dragon concept are less susceptible to it. Nevertheless, Truax's design did call for an engine larger in diameter than the entire Saturn V. This all said, Sea Dragon is really only worth building if you're looking to launch payloads of at least 300 metric tons several dozen times. That'd almost have to be a massive moon base or a sustained Mars campaign.

 

[fasquardon]

The solutions in the 60s were experimental, not analytical: back off from maximum performance and stick a bunch of baffle walls into the chamber until it can damp out any waves that start. This is a lot of why the F-1 took from 1959 to 1964 to achieve enough stability to flight rate--they kept exploding from combustion instability at the start. To test it, they resorted to sticking explosive charges up inside the bell and setting them off to deliberately induce worst-case waves and check that the engine could damp them.

I thought they were also trying adding more holes to the injector plate as well?

fasquardon

 

[e of pi]

I thought they were also trying adding more holes to the injector plate as well?

They did a lot of things--they fiddled with the layout, number, and size of baffles, they moved injector holes around, they changed the angle of impingment of the propellant flows to change how they mixed, and they changed the size of the injector holes. I was trying to simplify, but a more complete and correct summary can be found in Stages to Saturn: https://history.nasa.gov/SP-4206/ch4.htm

 

[jsb]

build and launch an equivalent to the Sea Dragon.

Sea Dragon is really only worth building if you're looking to launch payloads of at least 300 metric tons several dozen times.

Does the Sea dragon need to be as large to get the cost advantages or could anybody build a small dragon and still be cheaper to orbit than OTL pump feed rockets?

 

[fasquardon]

Does the Sea dragon need to be as large to get the cost advantages or could anybody build a small dragon and still be cheaper to orbit than OTL pump feed rockets?

I think pump fed engines on any size Sea Dragon type vehicle would be an improvement. Large scale pressure fed systems have always proven to be more complex than anticipated when they've been tried and some of the practical engineering and pad handling challenges of gigantic pressurized propellant tanks are a bit thorny. A smaller Sea Dragon is certainly possible. Personally I think something in the Saturn V class would actually be a much more useful vehicle than the max sized sea dragon. The payload size would be useful on a realistic timescale, the noise problems are much less, handling is easier, engineering is easier, the mixing between atmosphere layers as the rocket punches between them are less.

fasquardon

 

[jsb]

I think pump fed engines on any size Sea Dragon type vehicle would be an improvement. Large scale pressure fed systems have always proven to be more complex than anticipated when they've been tried and some of the practical engineering and pad handling challenges of gigantic pressurized propellant tanks are a bit thorny. A smaller Sea Dragon is certainly possible. Personally I think something in the Saturn V class would actually be a much more useful vehicle than the max sized sea dragon. The payload size would be useful on a realistic timescale, the noise problems are much less, handling is easier, engineering is easier, the mixing between atmosphere layers as the rocket punches between them are less.

I was interested in if they need the pressure tanks to survive landing and not cost a fortune refitting for flight the engines post submersion? I was more thinking something even smaller SIb, F9 or SRB sized as a recoverable cheap first stage without needing the fancy computers of the F9 for landing?

Say a small (only compared to SV or SD) water landing reusable rocket, not even that new a concept as did some of Von Braun Ferry Rockets did the same to reduce costs?

 

[RanulfC]

Does the Sea dragon need to be as large to get the cost advantages or could anybody build a small dragon and still be cheaper to orbit than OTL pump feed rockets?

Truax himself was dismissive of anything less than the full size Sea Dragon on both cost and capability. When NASA paid him to study a smaller scale Sea Dragon called "Excalibur" (http://www.astronautix.com/e/excalibur.html) he derisively called it "sub-caliber" in both capability and economics. Mostly I suspect it was that the smaller vehicles retained all the complex manufacturing and operations of a 'normal' LV while having none of the scale and manufacturing advantages ascribed to Sea Dragon. Sea Dragon is essentially built in a ship-yard using associated technology and skills so it (in theory) was going to be very cheap to build.

A lot of companies found when they studied smaller (but still in the heavy to super-heavy payload class) launchers than Sea Dragon, called "Big Dumb Boosters", that they could see some incredible savings over more conventional, higher performance LVs. But that came at a price of a projected higher failure rate of launches themselves along with a lack of payloads to justify such designs.

So what would 'justify' such an LV? Arguably this his how the US and USSR would get their Cis-Lunar Deterrence Forces ships into space

Randy

 

[fasquardon]

I was interested in if they need the pressure tanks to survive landing and not cost a fortune refitting for flight the engines post submersion? I was more thinking something even smaller SIb, F9 or SRB sized as a recoverable cheap first stage without needing the fancy computers of the F9 for landing?

It is still possible to build a fairly solid wall to the tanks and have a pump-fed engine.

fasquardon

 

[RanulfC]

I was interested in if they need the pressure tanks to survive landing and not cost a fortune refitting for flight the engines post submersion? I was more thinking something even smaller SIb, F9 or SRB sized as a recoverable cheap first stage without needing the fancy computers of the F9 for landing?

Say a small (only compared to SV or SD) water landing reusable rocket, not even that new a concept as did some of Von Braun Ferry Rockets did the same to reduce costs?

The S1B was studied for recovery initially, not so much for reuse but so they could study the stage after use. The H1 engines were extensively immersion and refurbishment tested and found to be reusable at a cost of about 5% of the initial engine price per turn around. Later there was study of both the S1B and S1C as recoverable-at-sea stages with various means of final landing. (One had the S1C stabilized in a forward-down position using parachutes and air-brakes and blowing off the forward LOX dome to use it as a pneumatic piston to cushion the landing) For the most part about the ONLY pump-fed rocket stage that can't handle an ocean landing are the pressure supported designs such as the Atlas and Centaur.

Water landing and recovery in and of itself isn't all that complicated or expensive but if you CAN land it back at the launch site that cuts your refurbishment time and expense.

Randy

 

[juanml82]

And I've read that Sea Dragon would have been loud enough to deafen most marine life in its launch area (and for whales "launch area"="the same ocean", so launching these monsters in the black sea, while less harmful than launching from the Atlantic, is going to be absolutely brutal on the local ecology. Together with all the pollution being washed into the sea, it could become a microbial life only zone.

Couldn't the Soviets launch from the Caspian sea or other inner lake? It can make logistics easier for them while avoiding the international repercussions of extinguishing all whales in the world by breaking their collective ears

 

[RanulfC]

Couldn't the Soviets launch from the Caspian sea or other inner lake? It can make logistics easier for them while avoiding the international repercussions of extinguishing all whales in the world by breaking their collective ears

The main reason "Sea Dragon" launched from the ocean is how easy it is to access in the US. The Soviets don't have that much access so launching from land has more of an advantage for them. You also have to consider the damage that would occur to those lakes due to even successful launches let alone a failed one...

Randy

 

[fasquardon]

The main reason "Sea Dragon" launched from the ocean is how easy it is to access in the US. The Soviets don't have that much access so launching from land has more of an advantage for them. You also have to consider the damage that would occur to those lakes due to even successful launches let alone a failed one...

Well, there's also the problem that the sound waves from the engine would liquefy any conceivable launch pad. To say nothing of what the hot exhaust gasses would do.

Couldn't the Soviets launch from the Caspian sea or other inner lake? It can make logistics easier for them while avoiding the international repercussions of extinguishing all whales in the world by breaking their collective ears

Sure. Though Iran might get upset at the caviar industry being destroyed and Baikal is kinda far from where the rocket would be manufactured. The Aral sea might have deep enough parts. And the deepest parts of Lake Balkhash might be deep enough for some sort of Sea Dragon type vehicle to be launched there. Though maybe not a full size one.

fasquardon

 

[RandomChance]

I’d think the Soviets would be more likely to look at something like Project Orion - blast off from the remote reaches of Kazakhstan or Siberia, safely distant from Moscow. Especially in the Krushchev era - There’s a guy not afraid of letting rip with nukes to further the Soviet cause (Tsar Bomba anyone?)

 

[juanml82]

I’d think the Soviets would be more likely to look at something like Project Orion - blast off from the remote reaches of Kazakhstan or Siberia, safely distant from Moscow. Especially in the Krushchev era - There’s a guy not afraid of letting rip with nukes to further the Soviet cause (Tsar Bomba anyone?)

Why not both? Sea Dragon to lift the pulse nuclear ship outside the ionosphere, pulse nuclear when the nukes radiation can't reach the biosphere. Double the madness!

 

[e of pi]

It is still possible to build a fairly solid wall to the tanks and have a pump-fed engine.

One of my favorite examples, from Gemini 5. No parachutes, no nothing, just recovering what survived when it hit the water. It's only about half the stage, but it's still impressive for all the caveats.