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So, in looking at Air-Augmented ("ducted") rockets recently, and considering nuclear propulsion,  this idea came to mind (I think I've read about it before- will post links for background when I have time)

Basically, it combines the features of a nuclear thermal rocket (aka. 'NERVA' aa the most famous example) or a nuclear thermal turbojet, with a ramrocket (itself the hybrid of a Ramjet and an Air-Augmented Rocket).

So, it looks something like this: air enters into intakes (and probably then a pre-cooler passing some heat to Liquid Hydrogen as a heat-sink: ala. "SABRE" intakes in real life) and enters a mixing chamber.

Separately, Liquid Hydrogen is passed over a nuclear reactor's heat-exchanger, just like in NERVA or any similar design.

The exhaust from the nuclear heat-exchanger then enters a mixing-chamber with the intake air, exactly like how any ducted rocket works (basically, ducted rockets mix the exhaust from a Combustion Chamber with intake air BEFORE ejecting it through a rocket nozzle- this is all there need be to such a design...  If the air is pre-cooled first, heat management becomes easier and you can use more heat-resistant materials or a lightweight heat-vulnerable Aerospike Nozzle, without them melting, but this is not usually done...)

However because there is Oxygen in the intake air, and the nuclear reactor exhaust is superheated Hydrogen, there is the possibility for Ramjet-style combustion.  This is how a ramrocket normally works (the ONLY difference here is that instead of Hydrogen-rich combustion products from a conventional rocket combustion chamber entering the mixing/ secondary combustion chamber, you have 100% Hydrogen from a nuclear reactor's heat exchanger entering it instead...)

This Hydrogen is afforded the opportunity to combust (this is also why you want pre-coolers: to allow compression and cooling of the intake airflow by Compressors to speeds/temperatures usable for a Ramjet even in very high speed/altitude flight), and you get additional energy from this Ramjet-style combustion, which gets you extra Thrust after you pass the exhaust through a rocket nozzle as with any ramrocket...

Basically, it's a nuclear thermal turbojet, but with the addition of an integral ramjet for extra Thrust and higher Exhaust Velocity (which also means the whole thing is useful at higher speeds than a normal nuclear turbojet).  The secondary combustion/mixing chamber could even be designed as a Scramjet: although that creates problems with no longer having any static thrust on the runway... (due to having low TWR, very high Effective ISP, and being optimal for high-speed atmospheric use: this is best used on a horizontal-takeoff spaceplane...)

Other notables:

- The airflow would be possible to close off at the point of the intake, or possibly also downstream, allowing for operation as a pure (but very heavy) nuclear thermal rocket once you leave the performance envelope for airbreathing propulsion.  Thos is similar to the Rocket-Based Combined Cycle ("RBCC"- basically a ducted rocket, ramrocket, and closed-cycle rocket all in one...) propulsion system, except that the initial heat source is a nuclear reactor rather than a primary rocket combustion chamber.

- This works best with lighter/more powerful next-gen nuclear reactors, like Molten Salt Reactors (not coincidentally, previous investigation into nuclear thermal turbojets looked at using MSR's for the reactor componemt...)

- Nuclear Reactors with TODAY's tech actually eject COLDER exhaust than a rocket combustion chamber.  The reason for their high ISP is due to using a pure exhaust of nothing but Hydrogen...  This means that, if you further diluted this already-lower heat with colder-still atmospheric air, you would have exhaust temperatures very usable for an Aerospike Nozzle: these nozzles normally having tendency to melt without a lot of extra weight for heat-managenent.

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2 hours ago, Northstar1989 said:

So, in looking at Air-Augmented ("ducted") rockets recently, and considering nuclear propulsion,  this idea came to mind (I think I've read about it before- will post links for background when I have time)

Basically, it combines the features of a nuclear thermal rocket (aka. 'NERVA' aa the most famous example) or a nuclear thermal turbojet, with a ramrocket (itself the hybrid of a Ramjet and an Air-Augmented Rocket).

So, it looks something like this: air enters into intakes (and probably then a pre-cooler passing some heat to Liquid Hydrogen as a heat-sink: ala. "SABRE" intakes in real life) and enters a mixing chamber.

Separately, Liquid Hydrogen is passed over a nuclear reactor's heat-exchanger, just like in NERVA or any similar design.

The exhaust from the nuclear heat-exchanger then enters a mixing-chamber with the intake air, exactly like how any ducted rocket works (basically, ducted rockets mix the exhaust from a Combustion Chamber with intake air BEFORE ejecting it through a rocket nozzle- this is all there need be to such a design...  If the air is pre-cooled first, heat management becomes easier and you can use more heat-resistant materials or a lightweight heat-vulnerable Aerospike Nozzle, without them melting, but this is not usually done...)

However because there is Oxygen in the intake air, and the nuclear reactor exhaust is superheated Hydrogen, there is the possibility for Ramjet-style combustion.  This is how a ramrocket normally works (the ONLY difference here is that instead of Hydrogen-rich combustion products from a conventional rocket combustion chamber entering the mixing/ secondary combustion chamber, you have 100% Hydrogen from a nuclear reactor's heat exchanger entering it instead...)

This Hydrogen is afforded the opportunity to combust (this is also why you want pre-coolers: to allow compression and cooling of the intake airflow by Compressors to speeds/temperatures usable for a Ramjet even in very high speed/altitude flight), and you get additional energy from this Ramjet-style combustion, which gets you extra Thrust after you pass the exhaust through a rocket nozzle as with any ramrocket...

Basically, it's a nuclear thermal turbojet, but with the addition of an integral ramjet for extra Thrust and higher Exhaust Velocity (which also means the whole thing is useful at higher speeds than a normal nuclear turbojet).  The secondary combustion/mixing chamber could even be designed as a Scramjet: although that creates problems with no longer having any static thrust on the runway... (due to having low TWR, very high Effective ISP, and being optimal for high-speed atmospheric use: this is best used on a horizontal-takeoff spaceplane...)

Other notables:

- The airflow would be possible to close off at the point of the intake, or possibly also downstream, allowing for operation as a pure (but very heavy) nuclear thermal rocket once you leave the performance envelope for airbreathing propulsion.  Thos is similar to the Rocket-Based Combined Cycle ("RBCC"- basically a ducted rocket, ramrocket, and closed-cycle rocket all in one...) propulsion system, except that the initial heat source is a nuclear reactor rather than a primary rocket combustion chamber.

- This works best with lighter/more powerful next-gen nuclear reactors, like Molten Salt Reactors (not coincidentally, previous investigation into nuclear thermal turbojets looked at using MSR's for the reactor componemt...)

- Nuclear Reactors with TODAY's tech actually eject COLDER exhaust than a rocket combustion chamber.  The reason for their high ISP is due to using a pure exhaust of nothing but Hydrogen...  This means that, if you further diluted this already-lower heat with colder-still atmospheric air, you would have exhaust temperatures very usable for an Aerospike Nozzle: these nozzles normally having tendency to melt without a lot of extra weight for heat-managenent.

 

I love it.

Yet being a ramjet it will either need boosters for VTOL or a boost assisted horizontal launch for the ramjets to work to assist the rocket.

 

In otherwords, this is NOT an SSTO. Since getting it up to speed for the ramjet requires disposable boosters or a turbojet.

Boosters being preferable as you can dump their weight.

 

What I think this is good for is perhaps more reusuable spacecraft?

 

A vessel like this could use the ramjet rocket on reentry to fly around project pluto style (only safer).

Without ANY propellant other than air of the speed is sufficiently high enough, assuming the airspeed won't ablate the vessel either.

 

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2 hours ago, Spacescifi said:

Yet being a ramjet it will either need boosters for VTOL or a boost assisted horizontal launch for the ramjets to work to assist the rocket.

Actually not.  The rocket part of a ramrocket generates Thrust even when stationary.  The rocket exhaust ignites the fuel-air mixture in the mixing chamber, so you get some (stationary Thrust from the ramjet part of this mutt of a rocket and a ramjet... (even with the scram-rocket version, the rocket itself will produce Thrust up until you reach the supersonic speeds necessary for the Scramjet part to ignite.  And, this can be combined: for instance the proposed RBCC cycle is an all-in-one Ducted Rocket, Ramrocket, and Scramrocket...)

The KSP ramjets actually perform much like ramrockets would IRL (substantial stationary Thrust, higher Thrust at speed) except that their ISP is much too high for a ramrocket, and they don't consume Oxidizer as a ramrocket would.

A similar, related concept is a turboramjet- which uses a small rocket to pull in additional air and sustain combustion in a ramjet even beyond speeds/altitudes where a ramjet would normally be capable of operation.  The rocket is placed a bit differently in such a design, though, and is much smaller relative to the ramjet.

The bigger problem is that it's nuclear, and hence radiation is going to be a real concern.  You probably wouldn't want to activate the reactor on the ground anyways (indeed not until you were already at a fairly high altitude).  This would thus be an engine for the speed-run of a spaceplane, or the second (seperable/decoupling) stage of a two-stage spaceplane.

2 hours ago, Spacescifi said:

In otherwords, this is NOT an SSTO. Since getting it up to speed for the ramjet requires disposable boosters or a turbojet.

Boosters being preferable as you can dump their weight.

You don't need to ignite all engines on the ground in a SSTO spaceplane.  Indeed many proposed designs don't (having rockets you don't use until altitude, plus maybe briefly at takeoff), or use multi--mode engines which switch operations in flight (RBCC has *THREE* modes, for instance: Ducted Rocket, Ramrocket, and Scramjet).

Re-read what I wrote (with the clarification here).  Any type of ramrocket design usually behaves as a Ducted Rocket at low speeds.  Ducted ("air augmented") Rockets produce Thrust and ISP slightly better than a rocket at first, increasing to the 700-800 second range by about Mach 3-4 (but a ramrocket will see ignition of the ramjet in the mixing zone long before this point...)

Two-Stage Spaceplanes are entirely feasible: with the upper stage spaceplane that actually achieves orbit riding piggyback on a larger spaceplane (technically only a plane, but to really get the most out of this it needs to be a much, much, much larger, faster, and more efficient plane than something like a 747) that then flies back to the runway independently.

This allows the upper stage to only be equipped with engines that work well at high speeds/altitudes, such as the nuclear ramrocket I refer to here (a CONVENTIONAL ramrocket doesn't actually need the booster to get off the ground: as the rockets within the ramrocket usually produce enough Thrust acting as air-augmented rockets without complete combustion yet occurring in the mixing chamber to reach speeds where the ramjets will operate efficiently.  And I repeat myself: the primary rocket produces a sufficiently hot/fast exhaust stream for the ramjet to start producing a little Thrust even on the runway...)

 

A diagram would be helpful, and maybe I'll produce one if you still don't understand.  But this is a textual illustration of how both ramrockets and some designs of ducted rocket work:

Primary Rocket --> Mixing Chamber --> Nozzle

- The mixing chamber is where the 'primary' rocket exhaust is mixed with air.  In a ramrocket, the rocket simply operates fuel-rich, and the mixing chamber is designed to encourage/allow for combustion of the air with the fuel-rich rocket exhaust.  But this ramjet combustion is not NECESSARY for the rocket to produce a fairly large Thrust through the Air-Augmentation and nozzle on its own (indeed most Thrust comes from the primary rocket EVEN WHEN the ramjet is operating...)

- The primary function of the mixing-chamber is to provide extra Working Mass for the rocket.  This roughly doubles the Thrust if you mix the rocket exhaust in a 3:1 ratio with air and no ramjet combustion occurs, for instance.  The ramjet combustion is actually a minor optimization to the design (typically providing around 10-20% extra Thrust in a conventional ramrocket design: although Nuclear ones would benefit more sue to their anemic base-Thrust levels)- ramjets don't produce that much Thrust at reasonable sizes in real life, unlike in KSP.

- The Nozzle, is s nozzle.  You can use a typical bell nozzle, or opt for an Aerospike.  Aerospikes should work very, very well here as ducted rocket exhaust is much cooler than in a conventional rocket (although you also have less unburnt fuel from the turbopump available for Regenerative Cooling) and the nozzle needs to be larger to accommodate the high Mass Flow Rate from all the extra Working Mass from the atmosphere (larger rockets are, paradoxically, EASIER to keep cool: due to effects resulting from the Square-Cube Law, which reduce the relative surface area exposed to hot gasses...  I *highly* recommend the Everyday Astronaut article on Aerospike Nozzles for more detail on precisely why...)

3 hours ago, Spacescifi said:

What I think this is good for is perhaps more reusuable spacecraft?

A HTHL spaceplane is a FULLY reusable spacecraft.

3 hours ago, Spacescifi said:

A vessel like this could use the ramjet rocket on reentry to fly around project pluto style (only safer).

Without ANY propellant other than air of the speed is sufficiently high enough, assuming the airspeed won't ablate the vessel either.

Earth isn't Kerbin.  You have to reach incredibly high speeds in the atmosphere (by Mach 4 or 5 your plane is already catching fire magnificently: orbital velocity on Earth is around Mach 20, I believe) to have any chance of reaching orbit with a spaceplane, due to the much larger radius of Earth.

A ramrocket isn't even designed for speeds that high.  We're talking a propulsion system that operates best between about Mach 2-5 (ramrockets have a much wider performance window than ramjets, as the rocket exhaust stabilizes ramjet combustion at low speeds or pressures), and operates mostly as a ducted rocket (with lower ISP) from stationary to about Mach 2 (although, as said, you still see a *little* combustion in the mixing chamber even at takeoff).  Its Thrust never drops to zero- or any less than the Thrust/ISP of the primary rocket.

This differs from the conventional (HydroLOX primary rocket) design in that the rocket is nuclear.  Once again, this means less Thrust (but higher ISP due to lighter exhaust gasses) when operating as a ducted rocket, but much, much more Hydrogen in the mixing chamber potentially subject to combustion (meaning instead of adding 10-20% Thrust, you might add 40-50% or more with a sufficiently large mixing chamber...)

Normally a ramjet would "choke" on this much Hydrogen in one place: but the nuclear reactor superheats the Hydrogen to a much higher temperature than compressive heating would normally pre-heat the intake air of a ramjet to, and as a result the ramjet should able to operate at much higher Mass Flow Rates across a much wider performance envelope... (even so, the need to dilute the Hydrogen a bit is why the mixing chamber should be designed larger than for a ducted rocket...)

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Posted (edited)

P.S.

And if you think 3-mode engines are insane, the Chinese recently opened a factory to assemble FOUR mode engines: turbofan, ramjet, scranjet, and (ducted) rocket all in one:

https://www.airuniversity.af.edu/CASI/Display/Article/1604494/chinas-opening-a-factory-to-build-engines-for-hypersonic-missiles-and-spaceplan/

What I suggested is actually simpler than this, in that it does away with the turbofan and Scramjet parts entirely (*OR* swaps the Ramjet for a Scramjet) and uses the ducted rocket to achieve ramjet speed (Mach 2) instead..

Only the heat source for the rocket is a nuclear reactor rather than combustion- and the nuclear rocket uses pure LH2 for propellant.  So some supplementary (conventional) ducted rockets might still be necessary to provide extra Thrust (still lighter/simpler than adding an integral turbofan, though!)

The Chinese engine is also designed to operate off LOX/RP-1 (Kerosene and Liquid Oxygen) rather than Liquid Hydrogen.  And is planned for use in the FIRST stage of a horizontal takeoff launch-system: with a reusable rocket launching off its back at the edge of the atmosphere (at speeds of at least Mach 7-8, likely, based on the engine capabilities) and propelling itself with rockets alone the rest of the way to orbit...

Edited by Northstar1989
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8 hours ago, Northstar1989 said:

P.S.

And if you think 3-mode engines are insane, the Chinese recently opened a factory to assemble FOUR mode engines: turbofan, ramjet, scranjet, and (ducted) rocket all in one:

How many of *any* (one) of those designs have China been able to develop and manufacture?  Looks like a combination of propaganda and trying to sucker rivals into an R&D rabbit hole.

Not that I don't think China would have all that much trouble doing one, but nobody is going to do all four at once.  Especially not someone whose never done even one.  China is great at going from crawl/walk/run at high speeds, but you still need to do them in order.

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40 minutes ago, wumpus said:

How many of *any* (one) of those designs have China been able to develop and manufacture?

It appears they've managed to ape off several Soviet ramjet designs - e.g. the Kh-31- but are behind the times when it comes to air-to-air ram-rockets (like the Meteor and late-model R-77s). They've also been known to have serious trouble with high-powered turbofans as recently as a few years back.

The Hyperhype is a pathway to many government grants some would consider 'misplaced'.

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59 minutes ago, wumpus said:
9 hours ago, Northstar1989 said:

And if you think 3-mode engines are insane, the Chinese recently opened a factory to assemble FOUR mode engines: turbofan, ramjet, scranjet, and (ducted) rocket all in one:

How many of *any* (one) of those designs have China been able to develop and manufacture? 

That's why they are going to give a try for all to see if any.

Upd.
If put it underwater it works like waterjet, so they should rename it into 5-mode.

Edited by kerbiloid
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9 hours ago, Northstar1989 said:

Actually not.  The rocket part of a ramrocket generates Thrust even when stationary.  The rocket exhaust ignites the fuel-air mixture in the mixing chamber, so you get some (stationary Thrust from the ramjet part of this mutt of a rocket and a ramjet... (even with the scram-rocket version, the rocket itself will produce Thrust up until you reach the supersonic speeds necessary for the Scramjet part to ignite.  And, this can be combined: for instance the proposed RBCC cycle is an all-in-one Ducted Rocket, Ramrocket, and Scramrocket...)

The KSP ramjets actually perform much like ramrockets would IRL (substantial stationary Thrust, higher Thrust at speed) except that their ISP is much too high for a ramrocket, and they don't consume Oxidizer as a ramrocket would.

A similar, related concept is a turboramjet- which uses a small rocket to pull in additional air and sustain combustion in a ramjet even beyond speeds/altitudes where a ramjet would normally be capable of operation.  The rocket is placed a bit differently in such a design, though, and is much smaller relative to the ramjet.

The bigger problem is that it's nuclear, and hence radiation is going to be a real concern.  You probably wouldn't want to activate the reactor on the ground anyways (indeed not until you were already at a fairly high altitude).  This would thus be an engine for the speed-run of a spaceplane, or the second (seperable/decoupling) stage of a two-stage spaceplane.

You don't need to ignite all engines on the ground in a SSTO spaceplane.  Indeed many proposed designs don't (having rockets you don't use until altitude, plus maybe briefly at takeoff), or use multi--mode engines which switch operations in flight (RBCC has *THREE* modes, for instance: Ducted Rocket, Ramrocket, and Scramjet).

Re-read what I wrote (with the clarification here).  Any type of ramrocket design usually behaves as a Ducted Rocket at low speeds.  Ducted ("air augmented") Rockets produce Thrust and ISP slightly better than a rocket at first, increasing to the 700-800 second range by about Mach 3-4 (but a ramrocket will see ignition of the ramjet in the mixing zone long before this point...)

Two-Stage Spaceplanes are entirely feasible: with the upper stage spaceplane that actually achieves orbit riding piggyback on a larger spaceplane (technically only a plane, but to really get the most out of this it needs to be a much, much, much larger, faster, and more efficient plane than something like a 747) that then flies back to the runway independently.

This allows the upper stage to only be equipped with engines that work well at high speeds/altitudes, such as the nuclear ramrocket I refer to here (a CONVENTIONAL ramrocket doesn't actually need the booster to get off the ground: as the rockets within the ramrocket usually produce enough Thrust acting as air-augmented rockets without complete combustion yet occurring in the mixing chamber to reach speeds where the ramjets will operate efficiently.  And I repeat myself: the primary rocket produces a sufficiently hot/fast exhaust stream for the ramjet to start producing a little Thrust even on the runway...)

 

A diagram would be helpful, and maybe I'll produce one if you still don't understand.  But this is a textual illustration of how both ramrockets and some designs of ducted rocket work:

Primary Rocket --> Mixing Chamber --> Nozzle

- The mixing chamber is where the 'primary' rocket exhaust is mixed with air.  In a ramrocket, the rocket simply operates fuel-rich, and the mixing chamber is designed to encourage/allow for combustion of the air with the fuel-rich rocket exhaust.  But this ramjet combustion is not NECESSARY for the rocket to produce a fairly large Thrust through the Air-Augmentation and nozzle on its own (indeed most Thrust comes from the primary rocket EVEN WHEN the ramjet is operating...)

- The primary function of the mixing-chamber is to provide extra Working Mass for the rocket.  This roughly doubles the Thrust if you mix the rocket exhaust in a 3:1 ratio with air and no ramjet combustion occurs, for instance.  The ramjet combustion is actually a minor optimization to the design (typically providing around 10-20% extra Thrust in a conventional ramrocket design: although Nuclear ones would benefit more sue to their anemic base-Thrust levels)- ramjets don't produce that much Thrust at reasonable sizes in real life, unlike in KSP.

- The Nozzle, is s nozzle.  You can use a typical bell nozzle, or opt for an Aerospike.  Aerospikes should work very, very well here as ducted rocket exhaust is much cooler than in a conventional rocket (although you also have less unburnt fuel from the turbopump available for Regenerative Cooling) and the nozzle needs to be larger to accommodate the high Mass Flow Rate from all the extra Working Mass from the atmosphere (larger rockets are, paradoxically, EASIER to keep cool: due to effects resulting from the Square-Cube Law, which reduce the relative surface area exposed to hot gasses...  I *highly* recommend the Everyday Astronaut article on Aerospike Nozzles for more detail on precisely why...)

A HTHL spaceplane is a FULLY reusable spacecraft.

Earth isn't Kerbin.  You have to reach incredibly high speeds in the atmosphere (by Mach 4 or 5 your plane is already catching fire magnificently: orbital velocity on Earth is around Mach 20, I believe) to have any chance of reaching orbit with a spaceplane, due to the much larger radius of Earth.

A ramrocket isn't even designed for speeds that high.  We're talking a propulsion system that operates best between about Mach 2-5 (ramrockets have a much wider performance window than ramjets, as the rocket exhaust stabilizes ramjet combustion at low speeds or pressures), and operates mostly as a ducted rocket (with lower ISP) from stationary to about Mach 2 (although, as said, you still see a *little* combustion in the mixing chamber even at takeoff).  Its Thrust never drops to zero- or any less than the Thrust/ISP of the primary rocket.

This differs from the conventional (HydroLOX primary rocket) design in that the rocket is nuclear.  Once again, this means less Thrust (but higher ISP due to lighter exhaust gasses) when operating as a ducted rocket, but much, much more Hydrogen in the mixing chamber potentially subject to combustion (meaning instead of adding 10-20% Thrust, you might add 40-50% or more with a sufficiently large mixing chamber...)

Normally a ramjet would "choke" on this much Hydrogen in one place: but the nuclear reactor superheats the Hydrogen to a much higher temperature than compressive heating would normally pre-heat the intake air of a ramjet to, and as a result the ramjet should able to operate at much higher Mass Flow Rates across a much wider performance envelope... (even so, the need to dilute the Hydrogen a bit is why the mixing chamber should be designed larger than for a ducted rocket...)

 

Hmmm... so how would this look?

Lemme guess:

Has some variation of shockcones, since you need them at high speeds.

 

SR-71_main.jpg

 

1200px-MiG-21_RB23.JPG

https://en.m.wikipedia.org/wiki/Inlet_cone

Or maybe this?

https://en.m.wikipedia.org/wiki/Diverterless_supersonic_inlet

 

250px-PLAAF_J-10B_with_PL-12_and_PL-8B_a

 

To quote the wiki:

A diverterless supersonic inlet (DSI) is a type of jet engine air intake used by some modern combat aircraft to control air flow into their engines. It consists of a "bump" and a forward-swept inlet cowl, which work together to divert boundary layer airflow away from the aircraft's engine. This eliminates the need for a splitter plate, while compressing the air to slow it down from supersonic to subsonic speeds. The DSI can be used to replace conventional methods of controlling supersonic and boundary-layer airflow.

DSIs can be used to replace the intake ramp and inlet cone, which are more complex, heavy and expensive.[1]

Technical backgroundEdit

When an aircraft is flying, the speed of the air relative to the engine is equal to the plane's flight speed. However, current turbine engines are unable to handle supersonic airflow. This is because shock waves associated with supersonic speeds can damage or cause dangerous vibrations in turbine blades, resulting in loss of thrust or engine failure. Consequently, in aircraft travelling at supersonic speeds, the air entering the inlet must be slowed down to subsonic speeds before reaching the compressor and turbine blades of the jet engine. Additionally, the airflow must also be at the optimal speed and volume so as to offer maximum thrust.[2]

InletsEdit

Modern combat aircraft accomplish this in a variety of ways, through design of the inlet. The inlet sits upstream of the compressor and has a strong influence on engine net thrust. A well-designed inlet straightens out the flow, and feeds the compressor with low-turbulence air at a relatively constant speed and volume. This is not difficult to achieve in subsonic aircraft such as passenger jets, which do not perform high-speed, high-G maneuvers that lead to turbulent airflow.[3]Inlets on subsonic aircraft are simple and shorter, and are basically an opening designed to minimize drag.[4]

On supersonic military jets, the inlets are usually much more complex and use shock waves to slow down the air, and movable internal vanes to shape and control the flow. Supersonic flight speeds form shock waves in the intake system and reduce the recovered pressure at the compressor, so some supersonic intakes use devices, such as a cone or ramp, to increase pressure recovery by making more efficient use of the shock waves. The complexity of these inlets increases with an increase in top speed. Planes with top speeds over Mach 2 require much more elaborate inlet designs. This limits most modern combat aircraft to top speeds of Mach 1.8-2.0.[citation needed]

Diverterless inletsEdit

The DSI bump functions as a compression surface and creates a pressure distribution that prevents the majority of the boundary layer air from entering the inlet at speeds up to Mach 2. In essence, the DSI does away with complex and heavy mechanical systems.

Weight and complexity reductionEdit

Traditional aircraft inlets contain many heavy moving parts. In comparison, DSI completely eliminates all moving parts, which makes it far less complex and more reliable than earlier diverter-plate inlets. The removal of moving parts also reduces the overall weight of the aircraft. [5]

Which is best for the air intake for this application?

I also think a big bell nozzle is better than aerospike as it is easier to cool.

 

What you think?

Edited by Spacescifi
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7 hours ago, wumpus said:

How many of *any* (one) of those designs have China been able to develop and manufacture?  Looks like a combination of propaganda and trying to sucker rivals into an R&D rabbit hole.

The publication I linked was not from the Chinese state media.  It was from a U.S. Air Force publication, 2 years ago.  No corrections have been required to these articles since.

These aren't multiple engines they are looking at designing.  This is a single, multi-stage engine they are ALREADY building the factory to manufacture.  The design work was apparently done years ago, in a highly secretive manner...

You would know all this if you read the publication.

EDIT: The engine in question (TBCC engine) has already been built and tested on test-stands, as of last year.  Next step is putting it on an aircraft:

https://m.economictimes.com/news/defence/china-successfully-completes-hypersonic-engine-test/articleshow/67435297.cms

Edited by Northstar1989
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This looks like an engine from the SR-71, just with an additional scramjet mode. Ramjet+scramjet is relatively straightforward, they work in a similar way, but have different geometry. For a turboramjet, you need variable geometry anyway. Keeping the ramjet burning while in scramjet mode is the biggest challenge here.

As for adding a rocket to the whole shebang, I don't see why not. A rocket engine discharging into the ramjet/afterburner part of the engine should be quite possible, though making it more efficient than a separate rocket would take some doing. 

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9 minutes ago, Northstar1989 said:

The publication I linked was not from the Chinese state media.  It was from a U.S. Air Force publication, 2 years ago.  No corrections have been required to these articles since.

These aren't multiple engines they are looking at designing.  This is a single, multi-stage engine they are ALREADY building the factory to manufacture.  The design work was apparently done years ago, in a highly secretive manner...

You would know all this if you read the publication.

EDIT: The engine in question (TBCC engine) has already been built and tested on test-stands, as of last year.  Next step is putting it on an aircraft:

https://m.economictimes.com/news/defence/china-successfully-completes-hypersonic-engine-test/articleshow/67435297.cms

Building a wind tunnel capable of testing a SCRAMJET is possibly as impressive as most of the feats needed to build this engine.

The variable nozzle is another breakthrough.  The shuttle's "works from sea level to vacuum" is impressive, but something efficient from sea level to vacuum would be far more so.  Presumably it would obsolete any aerospike...

Plenty of the hype listed seems overrated for such an exorbitant bit of technology.  Also I'd wait and see what type of mass ratio they need for the SSTO: this TBCC engine might have the Isp for SSTO, but it still in the wrong place (early in flight instead of late).  I suspect spacex's (use 2 stages and recover at least the more expensive one [you'll obviously need both to beat the SSTO]) method will be more effective for a long time.

I still suspect it is propaganda, but perhaps they took a page from the Russian/Soviet program and kept a massive leap forward secret until they fully leapfrogged their rival beyond any means of quickly catching up.

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I suspect that the secrecy is because the primary intended use for the tech is in missiles. The TBCC engine is great for missiles because it could allow them to use a single engine over the entire course of the flight. Same goes for high speed recon drones, which are essentially cruise missiles with the warhead replaced by a bunch of cameras. If they do build an SSTO using it, expect it to be a military program. Civilian space applications are in a distant third place, as far as this engine is concerned.

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59 minutes ago, wumpus said:

Plenty of the hype listed seems overrated for such an exorbitant bit of technology.  Also I'd wait and see what type of mass ratio they need for the SSTO: this TBCC engine might have the Isp for SSTO, but it still in the wrong place (early in flight instead of late).  I suspect spacex's (use 2 stages and recover at least the more expensive one [you'll obviously need both to beat the SSTO]) method will be more effective for a long time.

Let's not forget this thread was about nuclear ramrockets?

There are plenty of intelligent things to say about that: like I've been considering the TWR, and am concerned it would be abysmal without a much more powerful nuclear reactor (than what is currently possible with US reactor technology).

However talking about a TBCC engine (which the US has been working on its own versions of for a decade at least) as propaganda doesn't say anything about the possibilities for nuclear ramrockets.

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22 minutes ago, Northstar1989 said:

Let's not forget this thread was about nuclear ramrockets?

There are plenty of intelligent things to say about that: like I've been considering the TWR, and am concerned it would be abysmal without a much more powerful nuclear reactor (than what is currently possible with US reactor technology).

However talking about a TBCC engine (which the US has been working on its own versions of for a decade at least) as propaganda doesn't say anything about the possibilities for nuclear ramrockets.

 

Precisely.

A guy who claims to have worked at NASA for decades said rather bluntly that nuclear rocketry thrust *fails* big time.

He recomended nuclear for a second stage orbital insertion aince on paper it lasts twice as long as the shuttle orbiter's main engines.

The rest he said he would not know without actual testing and analysis.

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9 hours ago, Spacescifi said:

A guy who claims to have worked at NASA for decades said rather bluntly that nuclear rocketry thrust *fails* big time.

He recomended nuclear for a second stage orbital insertion aince on paper it lasts twice as long as the shuttle orbiter's main engines.

The rest he said he would not know without actual testing and analysis.

That applies to pure Nuclear Thermal Rocketry.

But this isn't a pure nuclear thermal rocket we are talking.

You take the power output of the reactor, and then you divide that among a MUCH larger Working Mass in a nuclear ramrocket- similar to how using heavier propellants gives you higher Thrust from a nuke.  But there is no Effective ISP cost to doing this here, as the extra Working Mass cones from the air intakes- so you actually INCREASE the Effective ISP while doing this.

The problem I was referring to is that a current-generation nuclear reactor weighs a lot, while not producing that much more (and often, less) Thermal Power than a chemical rocket's Combustion Chamber.  So TWR suffers.

But in terms of raw Thrust: when most of your Working Mass comes from the atmosphere, and the internal propellant merely acts as a means of transfer of heat to this air (similar to how a heat exchanger directly warms the air in a Nuclear Thermal Turbojet- except the bit of internal Hydrogen you add does give a little extra Thrust and Exhaust Velocity by slightly increasing the Working Mass *AND* provides the basis for a ramjet to operate in the Mixing Chamber at higher atmospheric speeds) the main determinant of Thrust is simply how much Thermal Power you can produce.  If you can produce more than an equivalent chemical rocket, your Thrust will actually be HIGHER when most of your Working Mass is atmospheric air...

The final iterations of NERVA (the -XE models) produced about 1140 MW of Thermal Power.  That was enough to produce 246.6 kN of Thrust at 841 seconds (8250 m/s Exhaust Velocity).

However if you split that same Thermal Power over enough Working Mass from air to bring Exhaust Velocity down to 2000 m/s (a little over 200 sec ISP, but due to use of atmospheric air, over 3400 sec *Effective ISP*) by dividing it over a bit more than 17x the Working Mass (given the relative densities of H2 and atmospheric air, this only requires a 1.10:1 ratio of atmospheric air volume to H2 volume: whereas ratios of up to 2:1 are easily achievable...) you get 4.125x the Thrust: or 1017.225 kN of Thrust.

That's more than the Thrust of a single Merlin engine (9 of which are used to lift a Falcon 9, at 854 kN of sea level Thrust each).  And if you used a 2:1 bypass ratio (easily feasible) you could get a little over 1.348 times the Thrust (sqrt of 1.818, which is 2/1.1) instead: or 1371.626 kN of Thrust.

At these #'s (note the high EFFECTIVE ISP massively reduces fuel requirements), you'd only need a cluster of 3 NERVA's converted into air-augmented rockets (at a 2:1 bypass ratio) to lift a rocket with a launch stage capable of propelling the Falcon 9 upper stage 7000 m/s, if most of that 7 km/s were provided in-atmosphere where the air-augmented rockets work (not feasible in reality, I know, but a useful thought-experiment).

More likely a single, larger reactor, as reactor Thermal Power scales much faster than mass when you scale an individual reactor up (meaning one large reactor is better than 3-4 small reactors).

And all this is with 1960's reactor technology.  More modern reactors should be able to obtain higher power density (more thermal power per kg of mass: NERVA-XE weighed 18.144 tons, nozzle and all, and included a 1140 MW reactor...)

Bottom Line: giving a nuclear reactor this much more Working Mass to play with MASSIVELY increases your Thrust (about 5.56- fold for a 2:1 bypass ratio, BEFORE you include any extra Thrust from an included ramjet/scramjet in the mixing chamber...)

Don't get me wrong though: chemical rockets can produce even more Thrust than this as ducted rockets for the same weight (about 4x more Thrust, in fact), at very respectable sea level ISP (up to about 700-1000 seconds Effective ISP, at a 4:1 bypass ratio).  But they aren't capable of then acting as a >800 sec ISP rocket once you leave the atmosphere (negating the need for separate, vacuum-specialized engines entirely: and allowing you to make all your staging just about losing/recovering bulky LH2 fuel tanks...)

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1 hour ago, Northstar1989 said:

That applies to pure Nuclear Thermal Rocketry.

But this isn't a pure nuclear thermal rocket we are talking.

You take the power output of the reactor, and then you divide that among a MUCH larger Working Mass in a nuclear ramrocket- similar to how using heavier propellants gives you higher Thrust from a nuke.  But there is no Effective ISP cost to doing this here, as the extra Working Mass cones from the air intakes- so you actually INCREASE the Effective ISP while doing this.

The problem I was referring to is that a current-generation nuclear reactor weighs a lot, while not producing that much more (and often, less) Thermal Power than a chemical rocket's Combustion Chamber.  So TWR suffers.

But in terms of raw Thrust: when most of your Working Mass comes from the atmosphere, and the internal propellant merely acts as a means of transfer of heat to this air (similar to how a heat exchanger directly warms the air in a Nuclear Thermal Turbojet- except the bit of internal Hydrogen you add does give a little extra Thrust and Exhaust Velocity by slightly increasing the Working Mass *AND* provides the basis for a ramjet to operate in the Mixing Chamber at higher atmospheric speeds) the main determinant of Thrust is simply how much Thermal Power you can produce.  If you can produce more than an equivalent chemical rocket, your Thrust will actually be HIGHER when most of your Working Mass is atmospheric air...

The final iterations of NERVA (the -XE models) produced about 1140 MW of Thermal Power.  That was enough to produce 246.6 kN of Thrust at 841 seconds (8250 m/s Exhaust Velocity).

However if you split that same Thermal Power over enough Working Mass from air to bring Exhaust Velocity down to 2000 m/s (a little over 200 sec ISP, but due to use of atmospheric air, over 3400 sec *Effective ISP*) by dividing it over a bit more than 17x the Working Mass (given the relative densities of H2 and atmospheric air, this only requires a 1.10:1 ratio of atmospheric air volume to H2 volume: whereas ratios of up to 2:1 are easily achievable...) you get 4.125x the Thrust: or 1017.225 kN of Thrust.

That's more than the Thrust of a single Merlin engine (9 of which are used to lift a Falcon 9, at 854 kN of sea level Thrust each).  And if you used a 2:1 bypass ratio (easily feasible) you could get a little over 1.348 times the Thrust (sqrt of 1.818, which is 2/1.1) instead: or 1371.626 kN of Thrust.

At these #'s (note the high EFFECTIVE ISP massively reduces fuel requirements), you'd only need a cluster of 3 NERVA's converted into air-augmented rockets (at a 2:1 bypass ratio) to lift a rocket with a launch stage capable of propelling the Falcon 9 upper stage 7000 m/s, if most of that 7 km/s were provided in-atmosphere where the air-augmented rockets work (not feasible in reality, I know, but a useful thought-experiment).

More likely a single, larger reactor, as reactor Thermal Power scales much faster than mass when you scale an individual reactor up (meaning one large reactor is better than 3-4 small reactors).

And all this is with 1960's reactor technology.  More modern reactors should be able to obtain higher power density (more thermal power per kg of mass: NERVA-XE weighed 18.144 tons, nozzle and all, and included a 1140 MW reactor...)

Bottom Line: giving a nuclear reactor this much more Working Mass to play with MASSIVELY increases your Thrust (about 5.56- fold for a 2:1 bypass ratio, BEFORE you include any extra Thrust from an included ramjet/scramjet in the mixing chamber...)

Don't get me wrong though: chemical rockets can produce even more Thrust than this as ducted rockets for the same weight, at only moderately lower sea level ISP.  But they aren't capable of then acting as a >800 sec ISP rocket once you leave the atmosphere (negating the need for separate, vacuum-specialized engines entirely: and allowing you to make all your staging just about losing/recovering bulky LH2 fuel tanks...)

 

Hmmm... why not use both?

Use chemical air augmented rockets for initial launch, and then use an NTR for orbital insertion?

Makes the nukes is dangerouscrowd happy and provides better thrust to for heavy launch.

If we want a really thrusty heavy launch, just scale up the old cold war sprint missiles which could do 100g acceleration as a firststage booster.

It won't be getting that with all the extra propellant weight, but the thrust will still be high enough for suborbital.

If chemical air augmented ram rockets beat nuclear for thrust we may as well go with those. Since anything worth shipping into orbit will be heavy and air augmented chemical ramjet rockets can loft more than a nuclear air augmented one.

Nuclear is best used for space or for missiles, since missiles weigh so much less than spacecraft that we can actuallly make them fly project pluto style using only a reactor and air.

 

 

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30 minutes ago, Spacescifi said:

Hmmm... why not use both?

Use chemical air augmented rockets for initial launch, and then use an NTR for orbital insertion?

Because then you need two seperate, both very heavy, engines.

A nuclear ramrocket might be lucky to clear a TWR of 15:1 or maybe 20:1 (with enough bypass, Thrust from the scram/ramjets, more modern materials than NERVA, and a more powerful reactor than NERVA) in atmospheric mode- but at least you don't need a seperate system for vacuum thrust.  A chemical ducted rocket gets maybe 30:1 TWR, but then you need an entire NTR for outside the atmosphere that weighs at least as much as the ducted rocket- and probably about 5-6x as much (NTR's only get a TWR of maybe 2:1 at best, NERVA only managed 1.38).

And your launch stage ends up being much heavier due to only having about 1/4th (or less) the Effective ISP in atmosphere (700-800 sec vs. 3400+ sec).

30 minutes ago, Spacescifi said:

Makes the nukes is dangerouscrowd happy and provides better thrust to for heavy launch.

Space Programs are expensive.  And haven't achieved but a fraction of what they're capable of.  With all the scientific benefits you'd reap (or money you'd save vs. the even more massive budgets necessary to achieve the same things with more conventional rocketry) you could save THOUSANDS of lives here on Earth...

For an example of just how many lives a little science can save, consider how many people have died worldwide of Covid-19 (numbering in the hundreds of thousands, and still growing).  Now imagine just how many lives could have been saved if we magically had a vaccine back in early March.  Ditto for a million other scientific breakthroughs.

You save far more lives pushing a space program forward at all costs (through discoveries that save lives here in Earth) than you could EVER possibly lose in nuclear rocketry accidents.  The cost:benefit analysis is MUCH more favorable than, say, nuclear power for electricity on Earth (which can give us something like Chernobyl, or Fukushima, and a cost:benefit analysis says we should HALT IMMEDIATELY, because we don't really spend THAT much money on generating electricity by more expensive alternatives...  Plus, we need ALL the nuclear fuel we can get for the next 3-5 centuries of space exploration...)

As far as I'm concerned, based on the costs and benefits, the anti-nuclear folks can suck it.

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5 hours ago, Northstar1989 said:

Because then you need two seperate, both very heavy, engines.

A nuclear ramrocket might be lucky to clear a TWR of 15:1 or maybe 20:1 (with enough bypass, Thrust from the scram/ramjets, more modern materials than NERVA, and a more powerful reactor than NERVA) in atmospheric mode- but at least you don't need a seperate system for vacuum thrust.  A chemical ducted rocket gets maybe 30:1 TWR, but then you need an entire NTR for outside the atmosphere that weighs at least as much as the ducted rocket- and probably about 5-6x as much (NTR's only get a TWR of maybe 2:1 at best, NERVA only managed 1.38).

And your launch stage ends up being much heavier due to only having about 1/4th (or less) the Effective ISP in atmosphere (700-800 sec vs. 3400+ sec).

Space Programs are expensive.  And haven't achieved but a fraction of what they're capable of.  With all the scientific benefits you'd reap (or money you'd save vs. the even more massive budgets necessary to achieve the same things with more conventional rocketry) you could save THOUSANDS of lives here on Earth...

For an example of just how many lives a little science can save, consider how many people have died worldwide of Covid-19 (numbering in the hundreds of thousands, and still growing).  Now imagine just how many lives could have been saved if we magically had a vaccine back in early March.  Ditto for a million other scientific breakthroughs.

You save far more lives pushing a space program forward at all costs (through discoveries that save lives here in Earth) than you could EVER possibly lose in nuclear rocketry accidents.  The cost:benefit analysis is MUCH more favorable than, say, nuclear power for electricity on Earth (which can give us something like Chernobyl, or Fukushima, and a cost:benefit analysis says we should HALT IMMEDIATELY, because we don't really spend THAT much money on generating electricity by more expensive alternatives...  Plus, we need ALL the nuclear fuel we can get for the next 3-5 centuries of space exploration...)

As far as I'm concerned, based on the costs and benefits, the anti-nuclear folks can suck it.

 

Hmmm.... have you considered reusuable air augmented nuclear solid booster rockets?

Nuclear reactors emit a lot of UV, quartz is transparent to that, and there should be a combustible solid propellant mix that could work off nuclear UV radiation.

 

It's an engineering challenge, but I also think it is the only way that nuclear can perform on the same level as chemical thrust.

If one wanted, they could use a mix of solid boosters for launch, and then keep the empty lighter tanks asthe heavier chemical tanks are burned for orbital insertion.

 

It's an engineering problem, not impossible.

 

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17 hours ago, Northstar1989 said:

That's more than the Thrust of a single Merlin engine (9 of which are used to lift a Falcon 9, at 854 kN of sea level Thrust each).  And if you used a 2:1 bypass ratio (easily feasible) you could get a little over 1.348 times the Thrust (sqrt of 1.818, which is 2/1.1) instead: or 1371.626 kN of Thrust.

So the big question is how much does the engine mass, and will you need some form of booster to get you off the ground...

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5 hours ago, wumpus said:

So the big question is how much does the engine mass, and will you need some form of booster to get you off the ground...

Generally the performance tends to be poor. The NK-14A turboprop was supposed to retain the jet fuel injection and ignition systems in addition to the reactor heat exchanger.

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20 hours ago, wumpus said:

So the big question is how much does the engine mass

A lot more than a comparable rocket (TWR is at least, 1:20 to maybe 1:24, with the mixing chamber ramjets also active).  But Effective ISP is much, much higher (in the range of a jet engine just for the ducted rocket performance, 3500-4200 sec Effective ISP, depending on mixing-ratios of LH2:air).

This is basically a type of Hybrid airbreathing/rocket engine, much like the SABRE, except that the TWR is actually much better than many jet engines (which typically range from TWR of about 1:6 to 1:12), and the airbreathing Effective ISP a bit lower than some high-end jet engines.  The Thrust per unit of cross-sectional area (important for spaceplane design) is also much higher than any jet...

The main advantage though (because none of that would nearly justify use of a nuclear reactor inside the atmosphere, from a PR/safety perspective) is that this doubles as a Nuclear Thermal Rocket when you reach the point where airbreathing propulsion is no longer viable (however with an internal Scramjet, rather than Ramjet, this wouldn't be until at least Mach 7-12).  So the NTR is actively producing a *HUGE* amount of Thrust (but TWR is still poor as it weighs so much) in the atmosphere when in airbreathing mode (at very low Exhaust Velocity: but since almost all the Working Mass is from the atmosphere, at high Effective ISP), rather than being deadweight all the way until rocket closed-cycle Thrust is desirable...

This unfortunately doesn't scale down well- nuclear reactors become less and less efficient in terms of power output per kg of mass the smaller they become, but DOES scale *UP* extremely well.

It would also require a rather large, to potentially HUGE airframe (with lots of wing-area, at very low Aspect Ratio due to the vast majority of the time spent in atmospheric being supersonic/hypersonic) if put on a spaceplane (which is where this really shines) both due to the lack of scalability of the engine (you have to build a really huge airframe around a really huge engine) and the need to reduce re-entry and ascent heating (you can fly higher for a given speed with larger wings, helping with heat issues) to reasonable levels...

If the payload capacity this design/airframe led to ended up being overkill, I would suggest NOT going the way of the Shuttle- and trying to find huge payloads to justify a huge spaceplane with more payload capacity than you actually need- nor of trying to shrink the whole thing down too far (which will kill the payload-fraction to little benefit, as reactors lose performance very quickly as you shrink them down), but instead suggest increasing the mass budget of the least reliable/reusable or most expensive parts of the design, so heavier/cheaper/more reliable parts with wider safety-margins (and built to higher tolerances of manufacturing error) and built of easier-to-machine materials (high-end Steel instead of Aluminum, for instance: which is far heavier, but more heat-tolerant and much cheaper to machine) can be substituted in instead (one of the reasons the Shuttle was so expensive- a lot of the parts were designed to INCREDIBLY strict margins, leading to a lot of parts that required excessive maintenance or had to be replaced after just a few flights...)

You can also add redundancies to the design, increasing mass but allowing use of less reliable (but cheaper) parts that are more likely to fail, to trade-off any excess payload-capacity for lower cost and higher overall vehicle reliability...

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