Is A Gimballed Aerospike Possible?

[Spacescifi]

 

I know about wedge shaped linear aerospikes, but I tend to think that the spikey aerospikes are better looking. Is it possible to build a gimballed aerospike? I want to know, since that would simplify aerial maneuvers without resorting to RCS thrusters while flying around in the atmosphere before reaching space.

 

Also, what is the best material we could build for a gimballed aerospike that is heat resistant? Tungsten/titanium alloy or something? Diamond tungsten alloy (if that is even possible LOL).

 

Thanks for your answers, have a great day.

[sevenperforce]

Wedge-shaped linear aerospikes can have thrust "vectoring" by differential throttling on the individual combustion chambers. On a linear aerospike like ARCA's (note, ARCA is a total scam, but their HAAS-2CA could be useful under different circumstances), there are eight chambers on either side of the aerospike. If they downthrottle the chambers on one side, they can pitch; if they downthrottle on opposite corners, they can roll. A combination of pitch and roll can produce whatever attitude control you need.

If you do a toroidal aerospike, you have two options. You can use a multichamber toroidal aerospike, in which you can use differential throttling of the individual combustion chambers to effect pitch and yaw (though not roll):

Or you can use an annular toroidal aerospike, which only has a single combustion chamber and accordingly cannot sustain any differential throttling:

The annular toroidal aerospike is the most similar to a standard rocket engine, in terms of operation. It has a single combustion chamber and only one throttle setting. There's no reason you cannot gimbal the entire engine in the same way you would gimbal a de Laval engine. Your gimbal mechanism will need to be a bit beefier, however. The engines in KSP only show nozzle gimbal, but in reality some engines have gimbaled nozzles and some have gimbaled engines. I believe that the F-1 and SSME had full-engine gimbal while the Merlin 1D only has nozzle gimbal, but I could be wrong.

[Barzon]

25 minutes ago, Spacescifi said:

Is it possible to build a gimballed aerospike?

Yes. By varying the thrust in each chamber, the thrust can be vectored.

 

26 minutes ago, Spacescifi said:

Diamond tungsten alloy (if that is even possible LOL).

Not possible.  Alloys require metals, and carbon is, well, not a metal.

[sevenperforce]

26 minutes ago, Spacescifi said:

Also, what is the best material we could build for a gimballed aerospike that is heat resistant? Tungsten/titanium alloy or something? Diamond tungsten alloy (if that is even possible LOL).

No material is heat-resistant enough to be the nozzle for any high-performance rocket engine. Not tungsten, not titanium alloy, not "diamond tungsten alloy" (which is impossible), not even tantalum halfnium carbide.

Any operational rocket engine requires either ablative cooling or active cooling.

[mikegarrison]

42 minutes ago, Barzon said:

Alloys require metals, and carbon is, well, not a metal.

This is not true, unless you take a very restrictive sense of the word "alloy".

Steel, for instance, is simply iron with some carbon atoms mixed in. (Of course there are more complex kinds of steel that include other kinds of atoms too.)

Edited September 20, 2019 by mikegarrison

[wumpus]

3 hours ago, mikegarrison said:

This is not true, unless you take a very restrictive sense of the word "alloy".

Steel, for instance, is simply iron with some carbon atoms mixed in. (Of course there are more complex kinds of steel that include other kinds of atoms too.)

While this is true, it wouldn't help at all to use diamond in a steel alloy.  Although if you absolutely want to try such a thing, look up cermet (ceramic with molten metal jammed inside).

[Spacescifi]

4 hours ago, sevenperforce said:

No material is heat-resistant enough to be the nozzle for any high-performance rocket engine. Not tungsten, not titanium alloy, not "diamond tungsten alloy" (which is impossible), not even tantalum halfnium carbide.

Any operational rocket engine requires either ablative cooling or active cooling.

 

So active cooling then... aww forget it

 By the time we add the cooling equpiment the extra weight offsets the thrust benefits of the aerospike, so we may as well stick with ordinary bell nozzles.

Aerospikes and all the many types of nuclear rocketry would work a lot better if we invented a way to block the effect of a planet's gravity.

Then you could pile on as much cooling equipment as you wanted and still launch without using up too much fuel in the process.

We could lift this off the planet for example if we could shut off gravity or toggle it on and off. With modern technology. All we need is a way to toggle gravity on/off.

Edited September 21, 2019 by Spacescifi

[mikegarrison]

2 hours ago, wumpus said:

While this is true, it wouldn't help at all to use diamond in a steel alloy.  Although if you absolutely want to try such a thing, look up cermet (ceramic with molten metal jammed inside).

Right. But not because carbon isn't a metal. It's because diamond is not just carbon -- it's carbon in a particular structure. With steel, the carbon atoms squeeze themselves one at a time into the iron's crystal structure.

[kerbiloid]

8 hours ago, sevenperforce said:

Any operational rocket engine requires either ablative cooling or active cooling.

And for me, the multichamber toroidal one, with its hollow nozzle, looks like it asks to place an active cooler inside.
Especially when the nozzle is several meters in diameter like in Nexus, and by defintion can't be not hollow.

***

Two questions, please.

1. In the multi-chamber design, what are the proper names of:

• the big nozzle (surrounded by the chambers), i.e. the nozzle itself,
• the small nozzle of every combustion chamber blowing at the big nozzle.

Are they all "nozzle"? Or there are more descriptive terms?

Say, here is 1 nozzle or 12+1 nozzles, or how this is called exactly?

 

2. If I got this right, at least one design of Nexus had an engine with single toroidal combustion chamber with 24 small nozzles, blowing at 1 big central nozzle.
Do I get this right, toroidal combustion chambers for liquid engines are normal?
If so, isn't it possible to fill the single toroidal chamber with hot inert fluid from a reactor, using no chemistry and single tank?
If so, can't such engine be used as both chemical and nuclear depending on rocket design?

if so, can't such engine be a tri-modal SSTO engine:
first it works as air+hydrogen rocket motor (maybe additionally warmed by reactor),
then as a hydrolox rocket (maybe additionally warmed by reactor),
then as a hydrogen-heating nuke, or so.

Also, maybe self-providing with hydrogen with the engine reactor in water electrolysis mode.

If put this into a lifting body spaceplane, the liquid oxygen can be stored in flight from the air.

Edited September 21, 2019 by kerbiloid

[DDE]

11 hours ago, Spacescifi said:

Also, what is the best material we could build for a gimballed aerospike that is heat resistant? Tungsten/titanium alloy or something? Diamond tungsten alloy (if that is even possible LOL).

Hafnium carbide, or even 'mundane' RCC for hydrolox engines without oxygen in the exhaust. TiCN-based cermet supposedly leads when it comes to exposure to hot oxygen, and apparently even iron aluminide (FeAl) has respectable properties.

[kerbiloid]

Why limit the fantasy with just HfC, when Ta₄HfC₅ is also possible.

And we should mine Ta and Hf on asteroids, that's a plan.

And Hf-C-N, too. 4161°C.

P.S.
As anyway we need a lot of Huffnium, and as wiki says, it doesn't have its own minerals, but always presents in zirconium ores, and the simplest zirconium ore is ZrO₂ known as Baddeleyite,
See that we need Baddeleyite resource in KSP for Zr for nuke reactors and engines, and for Hf for heat-proof ceramics, and just for nice-looking name.

So, we should mine asteroids with Spodumene for Lithium and Baddeleyite for Zirconium and Hafnium.

Edited September 21, 2019 by kerbiloid

[DDE]

2 hours ago, kerbiloid said:

As anyway we need a lot of Huffnium

I suggest processing the bones of Hufflepuffs.

[kerbiloid]

Spoiler

13 minutes ago, DDE said:

I suggest processing the bones of Hufflepuffs.

Probably, adopted by author from The Walking Dead, where Glenn and Maggie Maggie and Glenn are escaping from prison.
At least, I got this idea from there...

 

[magnemoe]

10 hours ago, Spacescifi said:

 

So active cooling then... aww forget it

 By the time we add the cooling equpiment the extra weight offsets the thrust benefits of the aerospike, so we may as well stick with ordinary bell nozzles.

Aerospikes and all the many types of nuclear rocketry would work a lot better if we invented a way to block the effect of a planet's gravity.

Then you could pile on as much cooling equipment as you wanted and still launch without using up too much fuel in the process.

We could lift this off the planet for example if we could shut off gravity or toggle it on and off. With modern technology. All we need is a way to toggle gravity on/off.

 

All high performance engines uses active cooling or ablative cooling. 
Now active cooling is not as bad as it sounds, pump fuel trough channels in the engine. You will do this in an aerospike too. 
Another tricks is to leak fuel along the wall of the nozzle create an protective film, this has the downside of leaking fuel. 

[sevenperforce]

11 hours ago, Spacescifi said:

So active cooling then... aww forget it

 By the time we add the cooling equpiment the extra weight offsets the thrust benefits of the aerospike, so we may as well stick with ordinary bell nozzles.

Nothing wrong with active cooling. Ordinary bell nozzles need active cooling too. All operational bell nozzle rockets are either actively cooled or ablatively cooled (or, in the case of vacuum engine bell extensions, radiatively cooled). The easiest way to do this is to pipe some of the chilled propellant through channels in the engine bell before injecting into the turbopump or combustion chamber or whatever. Aerospikes, due to their inside-out configuration, are actually quite amenable to active cooling in this way. 

9 hours ago, kerbiloid said:

And for me, the multichamber toroidal one, with its hollow nozzle, looks like it asks to place an active cooler inside.
Especially when the nozzle is several meters in diameter like in Nexus, and by defintion can't be not hollow.

Precisely.

One rarely-known fact about aerospikes is that the original term referred to a plug/truncated-spike nozzle, rather than a "pointy" spike nozzle. The "aero" in aerospike referred to the fact that gases would be entrained under the plug and provide a virtual spike extension, saving weight.

Quote

Two questions, please.

1. In the multi-chamber design, what are the proper names of:

• the big nozzle (surrounded by the chambers), i.e. the nozzle itself,
• the small nozzle of every combustion chamber blowing at the big nozzle.

Are they all "nozzle"? Or there are more descriptive terms?

Say, here is 1 nozzle or 12+1 nozzles, or how this is called exactly?

 

Good questions. An ordinary bell-nozzle engine has a combustion chamber, a throat (where the flow converges and then diverges to transition from subsonic to supersonic), and an expansion nozzle. You need that converging-diverging shape at the throat in order to create the Mach shock that produces the supersonic exhaust transition.

What you're seeing in the multichamber design is properly an extended throat coming off the combustion chambers. So it is a multichamber engine with 12 cylindrical chambers, 12 extended throats, and a single plug nozzle. I know the extended throats look like little nozzles because they are spread out, but it's really just a way to convert the cylindrical flow to a thin layer covering the actual nozzle, and the throats are not actually "diverging" in cross-sectional area until they open onto the nozzle.

Quote

2. If I got this right, at least one design of Nexus had an engine with single toroidal combustion chamber with 24 small nozzles, blowing at 1 big central nozzle.
Do I get this right, toroidal combustion chambers for liquid engines are normal?

Our understanding of flow and combustion in cylindrical combustion chambers and spherical combustion chambers is much, much more advanced than our understanding of flow and combustion in a toroidal chamber or annular cylindrical chamber. So it's easier to do a multichamber design, usually. But you can certainly have a single chamber with multiple throats. You just lose some of the advantages like differential throttling.

Quote

If so, isn't it possible to fill the single toroidal chamber with hot inert fluid from a reactor, using no chemistry and single tank?
If so, can't such engine be used as both chemical and nuclear depending on rocket design?

if so, can't such engine be a tri-modal SSTO engine:
first it works as air+hydrogen rocket motor (maybe additionally warmed by reactor),
then as a hydrolox rocket (maybe additionally warmed by reactor),
then as a hydrogen-heating nuke, or so.

Yes, you can absolutely do this. The trouble is in the heating cycle. The upper bounds on conventional bipropellant rocket engines come from the chemical potential energies of the propellants, while the upper bounds on a nuclear-thermal rocket come from the melting point of the reactor. You want the reactor to heat up the propellant as much as possible, almost to its own melting point, but not beyond.

Accordingly, you want the propellant to hit your reactor as cold as possible, and exit the reactor as hot as possible. It's an effectively infinite source of heat (unlike chemical potential energy); it's just got a maximum operating temperature. So it's not feasible to try and heat hydrolox exhaust after combustion. You'd be wasting the chemical potential energy since the reactor is going to get it to that temperature regardless.

What you can do, however, is to use hydrogen or methane in a nuclear-thermal rocket, and then inject liquid oxygen after it passes through the throat. This way you are adding energy after the maximum reactor temperature has already been reached. The resulting combustion is not as efficient as combustion in a dedicated combustion chamber (subsonic combustion is always better than supersonic combustion), but it definitely adds hella thrust.

Quote

Also, maybe self-providing with hydrogen with the engine reactor in water electrolysis mode.

Reactor can't possibly electrolyze water fast enough for these purposes.

Quote

If put this into a lifting body spaceplane, the liquid oxygen can be stored in flight from the air.

The problem with collecting oxygen from air in flight is that the air is REALLY really hot once you're moving at any appreciable speed, and so you end up needing to carry ridiculous amounts of liquid hydrogen to prechill the air, like SABRE. Additionally, there's a thrust problem. If you're trying to use propellant from the air, you have to collect it, which means speeding it up to your own speed. If you are flying at 2 km/s and collect one tonne of air every second, then burn it with hydrogen to push it out the back of the plane at 4.5 km/s, the actual effective thrust is as if you were only pushing that air out at 2.5 km/s. Once you accelerate to 3 km/s, then the effective exhaust velocity drops to 1.5 km/s. Once your airspeed exceeds your exhaust velocity, thrust becomes negative. 

Edited September 21, 2019 by sevenperforce

[kerbiloid]

@sevenperforce, thank you!
Your description is very informative!

[sevenperforce]

6 minutes ago, kerbiloid said:

@sevenperforce, thank you!
Your description is very informative!

Thanks!

Similar to a LOX-afterburning rocket, where the liquid oxygen is injected in the nozzle rather than in the chamber, I think the ideal design for any airbreather is to have an air inlet with injection/combination below the nozzle throat. The mixing problem is immense for any airbreather, and this injects the air where the propellant flow is already supersonic but at its highest density and greatest turbulence. Much better than trying to inject in the combustion chamber, and completely obviates the need for trying to solve supersonic combustion. 

[YNM]

16 hours ago, Spacescifi said:

Diamond tungsten alloy (if that is even possible LOL).

The "diamond" wouldn't be a diamond anymore, they'd just be individual carbon atoms dispersed in (or rather, breaking) the lattice.

 

Edited September 21, 2019 by YNM

[sevenperforce]

11 minutes ago, sevenperforce said:

I think the ideal design for any airbreather is to have an air inlet with injection/combination below the nozzle throat. The mixing problem is immense for any airbreather, and this injects the air where the propellant flow is already supersonic but at its highest density and greatest turbulence. Much better than trying to inject in the combustion chamber, and completely obviates the need for trying to solve supersonic combustion. 

Maybe something like this?

[DDE]

13 hours ago, kerbiloid said:

Say, here is 1 nozzle or 12+1 nozzles, or how this is called exactly?

Quote from Sutton:

Quote

It has been described as an inside-out nozzle with an annular combustion chamber. Alternatively the chamber consisted of a multiplicity of small thrust chambers (also called thrust cells) with low nozzle area ratios arranged in a ring.

The annular combustion chamber isn't even specific to aerospikes.

[kerbiloid]

*like*

Thank you for the reference!

[mikegarrison]

17 hours ago, sevenperforce said:

What you're seeing in the multichamber design is properly an extended throat coming off the combustion chambers. So it is a multichamber engine with 12 cylindrical chambers, 12 extended throats, and a single plug nozzle. I know the extended throats look like little nozzles because they are spread out, but it's really just a way to convert the cylindrical flow to a thin layer covering the actual nozzle, and the throats are not actually "diverging" in cross-sectional area until they open onto the nozzle.

This does not sound correct. Maybe it is, but usually it is very important to control exactly where the throat is (and therefore where the flow is choked). If you don't force the flow to choke at a particular spot than you can end up with a shock moving around as it pleases, which can have all sorts of bad effects.

[sevenperforce]

6 hours ago, mikegarrison said:

This does not sound correct. Maybe it is, but usually it is very important to control exactly where the throat is (and therefore where the flow is choked). If you don't force the flow to choke at a particular spot than you can end up with a shock moving around as it pleases, which can have all sorts of bad effects.

I mean, you're right -- the flow choking point is very important. I don't see any reason to think it is not controlled/designed here. There may be a very slight divergence to ensure that the choke point is firmly inside the extensions, but those individual "nozzles" are more throat and less nozzle.

Very accurate however that the flow is already supersonic (though wildly underexpanded) when it hits the main nozzle.