Gnom ICBM. Is this design really use ramjet propulsion ?

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stealthflanker

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So yeah, i think this one is quite famous. The Soviet era Gnom

Gnom

Gnom
www.astronautix.com www.astronautix.com

This ICBM use a propulsion system in one of the stage which if i'm reading correctly is a ramjet. So after 1st stage burnout, the rocket motor will be ejected/dropped and the Ramjet starts and will propel it to Mach 5.5 which then it will also be ejected and the 3rd stage rocket motor starts and "throw" it to the terminal speed of 7.6 km/s.

So yeah, why does it called as "Air augmented rocket" ? When in fact it is a ramjet/ ducted rocket as the 2nd stage ramjet propellant is solid, thus works in similar manner as SA-6 missile propulsion.

Thank you for any response given.
 
stealthflanker said:
So yeah, i think this one is quite famous. The Soviet era Gnom

Gnom

Gnom
www.astronautix.com www.astronautix.com

This ICBM use a propulsion system in one of the stage which if i'm reading correctly is a ramjet. So after 1st stage burnout, the rocket motor will be ejected/dropped and the Ramjet starts and will propel it to Mach 5.5 which then it will also be ejected and the 3rd stage rocket motor starts and "throw" it to the terminal speed of 7.6 km/s.

So yeah, why does it called as "Air augmented rocket" ? When in fact it is a ramjet/ ducted rocket as the 2nd stage ramjet propellant is solid, thus works in similar manner as SA-6 missile propulsion.

Thank you for any response given.
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It's not actually a 'ramjet' but a solid propellant rocket that burns 'fuel-rich' (so that the exhaust has excess fuel that can combust with the incoming air) but the shroud itself ingests air due to the ejector effect increasing the mass flow which in and of itself increases the thrust. Solid fuel ramjets are similar but the burning propellant doesn't add much to the thrust, (since it's far more fuel than oxidizer) whereas the AAR gets its 'main' propulsion from the thrust of the rocket with additional (augmented of course :) ) thrust due to the increased mass flow and some duct burning.

The neat thing about the Gnome is that it actually avoids the main shortcomings of most of the AAR design which were supposed to augment the takeoff rather than the supersonic acceleration phase. The "standard" AAR worked from take off to around Mach-1/2 before it started losing efficiency and had to be dropped. This was because, (for one reason that is) the idea was to boost the initial rocket performance with as little 'added' as possible. (Well a AAR duct is kinda bit but light :) )

Since a rocket isn't normally shaped to achieve significant air induction the shockwave of supersonic flight quickly moves to a position where the duct no longer ingests enough air to augment the rocket and begins to have more drag than thrust.

In this case the missile has a fairing over a specifically shaped set of upper stages, so when the fairing is jettisoned upon reaching almost Mach 2 the upper stages then help direct air into the duct where the increased mass flow greatly improves the ISP and thrust with no mass from the vehicle. Thus the portion of the flight from around Mach 2 to Mach 5.5 can use less propellant and therefor mass less.

It's a damn neat concept.

Randy
 
Could SABRE tech help the airbreathing? A tail-sitting vehicle where solid-insert sleeves are like Estes motors and support the weight-are sloughed off and and slides out the engine leaving everything else that returns lighter? Structural support IS the fuel. Reusability and Tsander autophage combined somehow. Ablation on ascent.
 
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publiusr said:
Could SABRE tech help the airbreathing? A tail-sitting vehicle where solid-insert sleeves are like Estes motors and support the weight-are sloughed off and and slides out the engine leaving everything else that returns lighter? Structural support IS the fuel. Reusability and Tsander autophage combined somehow. Ablation on ascent.
Click to expand...

Not really as SABRE is based on cooling the incoming air hence the need for the cooling system. The 'ablation' of the structure would carry the heat into the intake/engine which is the opposite of what you want.

There's other ways other than using an intercooler such as "Mass Injection Pre-Compressor Cooling" (in which water and LOX is injected into a jet engine in front of the compressor to cool and make the incoming air more dense) which greatly increases thrust at the cost of a lower isp, but it doesn't really do a lot for a rocket engine.

In the Gnom case (and many other solid based ramjet/rocket combinations) the incoming air was reacted to the burning solid fuel which had more fuel than actually needed for combustion which allowed it to be burned with the incoming air.

Randy
 
The air breathing bits would fly back and be part of a non-dead stick orbiter.

SSTO airframes typically are eggshells with no real payload. When fuel-fat, more stress is on the landing gear.

My suggestion is to have the fuel do more than burn, but add support. We saw this with balloon tanks that are filled out by propellant. The solids on STS bore the weight of the whole stack.

I envision a spaceplane that has some burn-away stiff inserts behind jet intakes used one way on ascent but another way on descent. No caissons or balloon tanks.

Where most spaceplanes try to eliminate LOX, I would embrace it as it feeds, maybe all solid fuel beneath?

It is a type of staging, yes, but even Starship throws its propellant out as thrust…meaning you have this unwieldy resonating eggshell on return.

The spacecraft I envision embraces LOX maybe even as cold has thrusters. GNOM augmentation of a type. What returns is more than capsule, less than Starship.

With SSTOs, you try to get the whole eggshell back. But if the fuel is self supporting, I don’t have to worry about bringing it back. The air breathing is as much about return with a small liquid fuel tank.
 
publiusr said:
The air breathing bits would fly back and be part of a non-dead stick orbiter.

SSTO airframes typically are eggshells with no real payload. When fuel-fat, more stress is on the landing gear.

My suggestion is to have the fuel do more than burn, but add support. We saw this with balloon tanks that are filled out by propellant. The solids on STS bore the weight of the whole stack.

I envision a spaceplane that has some burn-away stiff inserts behind jet intakes used one way on ascent but another way on descent. No caissons or balloon tanks.

Where most spaceplanes try to eliminate LOX, I would embrace it as it feeds, maybe all solid fuel beneath?

It is a type of staging, yes, but even Starship throws its propellant out as thrust…meaning you have this unwieldy resonating eggshell on return.

The spacecraft I envision embraces LOX maybe even as cold has thrusters. GNOM augmentation of a type. What returns is more than capsule, less than Starship.

With SSTOs, you try to get the whole eggshell back. But if the fuel is self supporting, I don’t have to worry about bringing it back. The air breathing is as much about return with a small liquid fuel tank.
Click to expand...

Drive-by posting as it's late and I got the notification late :)

Denser on reentry means higher heating and the need for a really robust heat shield. In theory "Starship" can get away with a lighter heatshield because it comes down mostly empty so it a lot less dense on reentry. Put a set of wings on it and it would have been vastly more likely to land intact at least once.

Randy
 
A "fluffy" airframe is good that way....but the SSTO would be payload free. I was thinking fuel cassettes that take the mass fraction hit. You would have a TAV type craft on return.
 

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