Max size of a rocket?

[Frozen_Heart]

There is a few heavy lift vehicles on the horizon now which has set me wondering...

Does anyone know what the theoretical maximum is possible to launch into space using chemical rockets?

Here I saw it suggested that a tri-core BFR could perhaps lift 700tons to LEO! http://www.reddit.com/r/spacex/comments/2b4lqx/updated_bfrmct_estimates_with_new_raptor_thrust/

[Bill Phil]

Theoretically? No limit. Practically? A GCR rocket proposal said 1000 tons to LEO, and 1000 tons from LEO to surface with a powered landing. Now I don't know about the powered landing part, but it seems that it's the neighborhood of 1000 tons to LEO.

[Dkmdlb]

Wot? ?

[kerbiloid]

There are at least two limits:

1. A strength of the struts holding a massive rocket.

2. Increase an engine size means increase gas flow turbulences in the combustor and nozzle causing a combustion instability.

[EzinX]

There are at least two limits:

1. A strength of the struts holding a massive rocket.

2. Increase an engine size means increase gas flow turbulences in the combustor and nozzle causing a combustion instability.

Well, make the struts thicker.

Point is, you could clearly build two saturn 5s and connect them together with a girder between the rockets. While this would be a bad idea, you could probably make the 2 connected rockets hold together well enough to reach orbit.

If you can do it with 2, you can do it with any number of Saturn 5s, although there is a problem that impulses could spread across the 2d mesh of rockets and cause some of the rockets to point the wrong way, causing further wobble, til the whole assembly flies apart. This is probably a solvable problem, you could use computer controlled dampers on the interconnects among other things.

So even if there is a practical limit on how big a rocket shaped like a saturn 5 can scale to, due to surface area : volume constraints, you could bolt together smaller rockets and call the assembly a bigger rocket.

[kerbiloid]

Well, make the struts thicker.

Struts  maybe. But you must attach them to some, say, brackets mounted in a rocket itself, and to be sure that a thin rocket wall won't be screwed out by its weight.

So, the bigger is rocket  the heavier its construction mass relative to total mass, until you can't lift any useful payload at all.

If you can do it with 2, you can do it with any number of Saturn 5s, although there is a problem that impulses could spread across the 2d mesh of rockets and cause some of the rockets to point the wrong way, causing further wobble, til the whole assembly flies apart. This is probably a solvable problem, you could use computer controlled dampers on the interconnects among other things.

And as a result, you get dozens of engines per stage. Any of them goes wrong  and... Wait, that's the story about N-1.

[cicatrix]

Theoretically? No limit. Practically? A GCR rocket proposal said 1000 tons to LEO, and 1000 tons from LEO to surface with a powered landing. Now I don't know about the powered landing part, but it seems that it's the neighborhood of 1000 tons to LEO.

I think the limitations are not in fuels but in materials. If you increase the size of your rocket then sooner or later the material it's built of would become not strong enough. You'll need thicker body to support its weight and the thicker it is the more fuel you would need to lift it up then you'd need even stronger construction which, in turn, require more weight, etc. At some point there won't be a known material with necessary load bearing capabilities.

As far as I know, chemical rocket engines are nearly at the upper limits of fuel efficiency. We shouldn't expect any new engine significantly outstripping the existing ones by performance.

[magnemoe]

Struts  maybe. But you must attach them to some, say, brackets mounted in a rocket itself, and to be sure that a thin rocket wall won't be screwed out by its weight.

So, the bigger is rocket  the heavier its construction mass relative to total mass, until you can't lift any useful payload at all.

And as a result, you get dozens of engines per stage. Any of them goes wrong  and... Wait, that's the story about N-1.

Falcon 9 does well with 9 engines it can even handle an engine out situation.

Think N-1 was more about pressing the limits to the edge and that the 60's style engine control system was not able to handle engine out situations.

Real max size for rockets is the lack of need to launch payloads weighting 500 tons or more. Rocket efficiency goes up with size, secondary systems and air resistance don't grow linear with weight. Tanks get lighter for the fuel weight. Problem is cost, it become more expensive to build and test. Also lots of fixed costs making it cheaper to use multiple smaller rockets who is also used for other cargo.

Most heavy rockets are updated of other ones.

[Guest]

There is two "engine-out" situations:

1) Graceful shutdown, with probability "a1"

2) Violent explosion and fire, with probability "a2"

If you have engines without situation 2 (in reality they not exist), you want a huge cluster of tiny engines.

Sadly, in real world, a2 is non zero.

So you need to determine a1 and a2, and balance your design for maximum reliability.

You do not want too many engines because of case (2) and you want to be able to continue flight in case of (1) happened 1-2 times.

[Ralathon]

You also run into the cube square law. Say you take a Saturn V and make it twice as large in all dimensions. Its F-1 engines are now twice as wide and have 4 times the thrust (fuel flow is a function of surface area). But it is 8 times as heavy, so it won't have the TWR to leave the pad. So larger rockets have to be stubby to ensure they can lift their own weight. Also, you have 4 times the surface area so that means the aerodynamic pressures on the hull exert 4 times the force.

So, if you keep trying to build ever bigger rockets you'll end up with a giant pyramid shaped rocket with terrible aerodynamics. So you'll need ever stronger reinforcements that eventually outcompete payload increases. To say nothing about the budget...

[Frozen_Heart]

You also run into the cube square law

I've ran into that problem with KSP. As I keep making larger launchers they have to get progressively stubbier. Concept art of the Spacex BFR suggests that its pretty stubby as well.

And as a result, you get dozens of engines per stage. Any of them goes wrong  and... Wait, that's the story about N-1.

I assumed that multiple engines provided redundancy as engines could fail yet the rocket could continue? The Falcon 9 is designed this way. So was the Saturn V.

[Bill Phil]

The N-1's engines were fine, mostly. It was KORDS and poor workmanship that ruined the N-1.

[Tommygun]

There is also the Sea Dragon concept that could put 550 metric tons into LEO.

Although I think launching from the sea would have made things much more difficult and expensive, the rocket itself is an interesting idea.

http://en.wikipedia.org/wiki/Sea_Dragon_%28rocket%29

[Frozen_Heart]

There is also the Sea Dragon concept that could put 550 metric tons into LEO.

Although I think launching from the sea would have made things much more difficult and expensive, the rocket itself is an interesting idea.

http://en.wikipedia.org/wiki/Sea_Dragon_%28rocket%29

550 tons!

Would a single engine that large have worked? Someone mentioned earlier about larger engines having combustion instability issues?

[Bill Phil]

Yeah... That's why they invented clustering.

[zekes]

There is a few heavy lift vehicles on the horizon now which has set me wondering...

Does anyone know what the theoretical maximum is possible to launch into space using chemical rockets?

Here I saw it suggested that a tri-core BFR could perhaps lift 700tons to LEO! http://www.reddit.com/r/spacex/comments/2b4lqx/updated_bfrmct_estimates_with_new_raptor_thrust/

I'd say that's about right - my KSP lifter puts about 800 tonnes to LKO, and it's 7000 tonnes.

[kerbiloid]

Falcon 9 does well with 9 engines it can even handle an engine out situation.

Falcon 9 total mass is 500 tons. Not too impressing. Saturn V/Space Shuttle/Energiya are 2500..3000 tons, and use 5..20 engines on start.

Also how many times Falcon already have been launched to talk about statistics?

Soyuz and Energiya have/had 20 engines (or nozzles if you want), but every stage module itself has only 4 of them.

There is also the Sea Dragon concept that could put 550 metric tons into LEO.

How many SeaDragons were at least built?

Edited December 6, 2014 by kerbiloid

[Frozen_Heart]

How many SeaDragons were at least built?

None. But I'm asking about what's theoretically possible, not what's the heaviest mass that has been lifted.

[Whirligig Girl]

Aren't there extremely powerful concepts for a "Nuclear Lightbulb" Rocket Engine that is not only far more efficient but considerably higher thrust than the F-1 engine? My guess is, if you're going for payload capacity, a sea-launched nuclear lightbulb rocket (Nuclear Sea Dragon) would be a heavy-lifting monster. (A nuclear lightbulb rocket the size of a Saturn V could lift the ISS into orbit in one go!)

- - - Updated - - -

550 tons!

Someone mentioned earlier about larger engines having combustion instability issues?

Eh, just punch a bunch of holes in different patterns until the instability stops.

[Ralathon]

Aren't there extremely powerful concepts for a "Nuclear Lightbulb" Rocket Engine that is not only far more efficient but considerably higher thrust than the F-1 engine? My guess is, if you're going for payload capacity, a sea-launched nuclear lightbulb rocket (Nuclear Sea Dragon) would be a heavy-lifting monster. (A nuclear lightbulb rocket the size of a Saturn V could lift the ISS into orbit in one go!)

OP asked specifically about chemical rockets. Those are limited in energy density by the chemical properties of the fuel. If you go with nuclear designs you'll be able to lift much bigger payloads obviously.

[Frozen_Heart]

Aren't there extremely powerful concepts for a "Nuclear Lightbulb" Rocket Engine that is not only far more efficient but considerably higher thrust than the F-1 engine? My guess is, if you're going for payload capacity, a sea-launched nuclear lightbulb rocket (Nuclear Sea Dragon) would be a heavy-lifting monster. (A nuclear lightbulb rocket the size of a Saturn V could lift the ISS into orbit in one go!)

Wouldn't launching such a large nuclear rocket be pretty dangerous? And I thought that they weren't great as launchers due to a lower TWR?

[Javster]

Maximum size? Rocket? YOU CAN ALWAYS ADD BOOSTERS.

[Bill Phil]

Wouldn't launching such a large nuclear rocket be pretty dangerous? And I thought that they weren't great as launchers due to a lower TWR?

Actually, a nuclear lightbulb with a closed cycle is very safe. Especially with three levels of failsafes. The thrust is actually a lot, because the reactor is a different kind. But, the tech required isn't really achievable right now.

[Bill Phil]

Hmmm...............

I'd say 200 tons with just chemical, but that's arbitrary.

[kerbiloid]

None. But I'm asking about what's theoretically possible, not what's the heaviest mass that has been lifted.

Of course. But hydrodynamics is yet more empirical science than theoretical.

The question is: would such big nozzle even be ignited and work, or its gas flow would be so unstable that such engine just stops or bursts.

The largest one definitely works is F-1 (and maybe 1-2 similar to it), and it has taken a lot of efforts to create it.