Embedded Nozzles into hull VS Outward Nozzles

[Spacescifi]

There seem to be some advantages to hull embedded nozzles, yet they are not popular choice.

Seems to me the main reason is staging.

Embedded nozzle holes on a flat side of the hull are perfect if there was an SSTO that could do it with a reasonably useful mass of payload. You could have big vacuum rated nozzle in the center and a ring of smaller atmospheric nozzles surrounding it.

During reentry if you fly belly down your nozzles are shielded.

Hull embedding on a flat side also makes fuel transfer docking in space easy. Just dock butt to butt with the flat sides between like ships and pump fuel.

 

Reasons why not do it: Staging. SSTO's are not practical. But if they were, embedded nozzles in the hull might catch on. Nozzles don't move, so you need really good RCS thrusters to compensatem

 

In the meantime we have starship, while not embedded nozzles it does have a skirt to protect nozzles during reentry.

Edited August 20, 2021 by Spacescifi

[DDE]

You forget cosine losses. Any deviation from vertical is thrust, energy and propellant wasted.

[monophonic]

Try thrust vectoring when your nozzle is affixed to the skin of the space craft.

Well, vanes or propellant injection would still work, but there must be a good reason why most TVC capable motors go for the moving nozzle system.

[magnemoe]

Is it any orbital rocket with enclosed nozzles? Except starship who need it for reentry. 

And the reason is weight and heat, interstages makes separation more complex. Some has an interstage fairing who is dropped after separation like saturn 5 but this also add some weight. 
With an open engine you don't need to cool the outer part of an vacuum engine nozzle. 

Guess drag is not that important for orbital rockets, guess people has thought about adding an aerodynamic skirt to first stages. 
Missiles outside of ICBM tend to have enclosed engines as they fly in the atmosphere. Drag is much more serious with an small rocket in atmosphere and you can use fins for control.  

 

[RyanRising]

You say there are a few advantages to embedded nozzles, but the only one I see mentioned is reentry/aerodynamic shielding. That is a practical purpose for them, and, for example, is why RCS thrusters in reentry vehicles are sunken into the hull. But covering main engines would require more mass, and for questionable utility if you can just keep those engines out of the airflow by more sparse shielding - the winds of reentry should only come from one direction, after all.

[Spacescifi]

18 minutes ago, RyanRising said:

You say there are a few advantages to embedded nozzles, but the only one I see mentioned is reentry/aerodynamic shielding. That is a practical purpose for them, and, for example, is why RCS thrusters in reentry vehicles are sunken into the hull. But covering main engines would require more mass, and for questionable utility if you can just keep those engines out of the airflow by more sparse shielding - the winds of reentry should only come from one direction, after all.

 

Yes... more mass indeed. Which is why TWR would have to be unusually high as well as specific impulse for it to be viable at all.

Futurstic for sure.

I know in popular scifi on TV embeddsd nozzles are popular, but I suppose it is because of tropes.... and maybe someone is aware of the reentry shielding.

[Ultimate Steve]

Another advantage of a non embedded nozzle is that you can radiatively cool your nozzle in some cases without it affecting your hull.

[cubinator]

My two cents: putting the nozzle outside the main hull gives you more volume for fuel and/or saves the mass of the skirt. Of course there are tradeoffs and depending on your flight profile and range of uses either one could be the better option.

[RCgothic]

On some rockets embedding the nozzles would mean putting at least some thrusters inside a propellant tank. That's non-ideal.

[DDE]

51 minutes ago, RCgothic said:

On some rockets embedding the nozzles would mean putting at least some thrusters inside a propellant tank. That's non-ideal.

I'm offended om behalf of the Makeev Design Bureau

Spoiler

The only rrason there's an interstage under the third stage is that's where the nukes go.

 

Edited August 24, 2021 by DDE

[magnemoe]

39 minutes ago, DDE said:

I'm offended om behalf of the Makeev Design Bureau

  Hide contents

The only rrason there's an interstage under the third stage is that's where the nukes go.

 

Now this was an interesting design. I assume this is for submarines as here space is an premium.
You might get some pressure issues in lower tank in first stage but you can vent gas if it get to bad. 
I would not try this with cryogenic however. 
Hard to service the engines but you would not do that on an fueled stage anyway nor above an submarine. 

 

[DDE]

15 minutes ago, magnemoe said:

You might get some pressure issues in lower tank in first stage but you can vent gas if it get to bad. 

Well, over in the other corner, Yuzhnoe's R-36/Satan created tank pressure by dribbling some of the hypergolic propellant into the other's tank. Given that the Sarmat is basically Makeyev giving the Satan a full make-over to squeeze more performance out of the same size of missile, it's probably one truly fascinating machine.

[kerbiloid]

2 hours ago, DDE said:

Given that the Sarmat is basically Makeyev giving the Satan a full make-over to squeeze more performance out of the same size of missile, it's probably one truly fascinating machine.

An on-ground ICBM  from the SLBM bureau.

A Swamp Thing. To launch from bogs and mask with frogs.