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A Cylindral Magnetic Nozzle... Would it Work Well?


Spacescifi
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According to Musk ideally you want a rocket nozzle to shoot as straight a flame backwards as possible, and that is what he endeavors to do with his Merlin engines.

Magnetic nozzles are designed as I understand it to protect the nozzle from ablation via hot plasma exhaust in vacuum.

But what if you made a cylindral scaffolding magnetic nozzle... long enough that the exhaust plasma beam went down it's length?

The plasma beam exhaust would be compressed via magnetic fields so that it would not expand until exiting the nozzle.

 

Would this help not waste thrust?

 

Secondary question: I know plasma rocketry is notorious for low thrust (plasma is a bunch of ionized particles anyway), but is it possible to have a high thrust one? Via antimatter injection?

 

Thanks for answers!

 

 

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Musk is correct that is the point of a nozzle (though that is immensely simplified, and not a new concept since it is rocket design 101). Basically a nozzle takes high temperature fluid and turns it into high speed fluid with large amounts of kinetic energy (see de Laval Nozzle). Temperature is random particle motion in every direction, while kinetic energy has a common velocity vector. In other words a nozzle is what forces the randomly moving particles to move (mostly) in the direction we want them to. A simple cylinder isn't going to do much in terms of shaping the direction of a fluid's velocity vectors, though you can certainly create magnetic fields with the convergent-divergent behavior you need, just with more complex shapes.

As far as high thrust is concerned, the answer is that you can have a higher thrust plasma thruster such as VASIMR, though even at max thrust it is only 5 Newtons. This is much higher than the 0.327 N of the NEXT ion thruster (itself a noticeable improvement over prior ion engines), but a long way from the 110 kN of an RL-10 hydrolox engine and a really long way from anything that will launch you from the sea-level on Earth. The high energy requirements of a high thrust plasma/ion engine are difficult to meet. You also have the usual problem of needing a lot of reaction mass for a high thrust engine which increases the mass you need to take with you. Plasma/ion engines are really good at accelerating exhausts to high velocity which makes them poorly optimized for high thrust operation. It is more energy efficient to get more thrust by throwing more reaction mass than by increasing velocity, but increasing the reaction mass means you have more mass to move so rockets are actually better off devoting energy to higher velocities. Plasma engines are doubly impacted when trying to increase thrust since you need to increase both reaction mass and energy generation/storage mass (chemical engines have the advantage that their reaction mass is also their energy storage mass).

Antimatter gives you really dense energy storage and a lot of energy to work with which does help a lot, though you still need to deal with waste heat and you still need reaction mass. You could do a higher thrust plasma engine using antimatter as an energy source, but the rocket equation still holds true and you would have an exponentially smaller spacecraft if you take the high exhaust velocity, low reaction mass, low thrust approach.

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35 minutes ago, satnet said:

Musk is correct that is the point of a nozzle (though that is immensely simplified, and not a new concept since it is rocket design 101). Basically a nozzle takes high temperature fluid and turns it into high speed fluid with large amounts of kinetic energy (see de Laval Nozzle). Temperature is random particle motion in every direction, while kinetic energy has a common velocity vector. In other words a nozzle is what forces the randomly moving particles to move (mostly) in the direction we want them to. A simple cylinder isn't going to do much in terms of shaping the direction of a fluid's velocity vectors, though you can certainly create magnetic fields with the convergent-divergent behavior you need, just with more complex shapes.

As far as high thrust is concerned, the answer is that you can have a higher thrust plasma thruster such as VASIMR, though even at max thrust it is only 5 Newtons. This is much higher than the 0.327 N of the NEXT ion thruster (itself a noticeable improvement over prior ion engines), but a long way from the 110 kN of an RL-10 hydrolox engine and a really long way from anything that will launch you from the sea-level on Earth. The high energy requirements of a high thrust plasma/ion engine are difficult to meet. You also have the usual problem of needing a lot of reaction mass for a high thrust engine which increases the mass you need to take with you. Plasma/ion engines are really good at accelerating exhausts to high velocity which makes them poorly optimized for high thrust operation. It is more energy efficient to get more thrust by throwing more reaction mass than by increasing velocity, but increasing the reaction mass means you have more mass to move so rockets are actually better off devoting energy to higher velocities. Plasma engines are doubly impacted when trying to increase thrust since you need to increase both reaction mass and energy generation/storage mass (chemical engines have the advantage that their reaction mass is also their energy storage mass).

Antimatter gives you really dense energy storage and a lot of energy to work with which does help a lot, though you still need to deal with waste heat and you still need reaction mass. You could do a higher thrust plasma engine using antimatter as an energy source, but the rocket equation still holds true and you would have an exponentially smaller spacecraft if you take the high exhaust velocity, low reaction mass, low thrust approach.

 

I see. Thank you.

High velocity exhaust acheves longer burns and higher top speeds at low thrust (since momentum transfer is less).

You can increase thrust by increasing the amount of energy into the propellant but that still requires extra mass for cooling with all of that heat. Even so there are limits to what we can cool and still lift.

 

So it seems as far as rocketry is concerned, promoting SSTO's is like beating a dead horse. It won't work. Even if you brought it back to life it would not work as well as a healthy horse (high thrust high mass flow rocket) since it has less mass to throw around.

 

I guess the best high thrust rocket would be a high mass flow liquid hydrogen (massive propellant tanks) powered with antimatter.

Which is ironic since even then a variant of project Orion or just plain project Orion could still outperform it in TWR.

 

Why? Antimatter thrust must be limited to avoid melting the engine 

Pulse detonation outside the engine solves that for an Orion pusher plate propelled vehicle.

 

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If TWR is all you care about, then Orion is a good bet. However, keep in mind that you need to calculate the average TWR, because thrust is not constant, this being a pulsed drive. Also, your overall dV will be lower than with an antimatter rocket. TWR is not all that important as long as you can keep it just above 1 for liftoff.

Atmospheric SSTOs work best with non-chemical propulsion and air augmentation. That way, you can make a rocket that uses no propellant for the initial phase of the flight, and has a higher thrust (air is heavier than hydrogen) in that regime, as well.

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2 hours ago, Dragon01 said:

If TWR is all you care about, then Orion is a good bet. However, keep in mind that you need to calculate the average TWR, because thrust is not constant, this being a pulsed drive. Also, your overall dV will be lower than with an antimatter rocket. TWR is not all that important as long as you can keep it just above 1 for liftoff.

Atmospheric SSTOs work best with non-chemical propulsion and air augmentation. That way, you can make a rocket that uses no propellant for the initial phase of the flight, and has a higher thrust (air is heavier than hydrogen) in that regime, as well.

Read me like a book. This one gets me guys and gals!

For a scifi setting high thrust is all I really need. Asofar readers are reading about people with cargo in space, not a spaceflight center managing space probes millions of kiometers away.

To make space a realistic people business in scifi, two things I find are needed.

Motive: Other intelligent alien life. Both profit and curiousity are involved. This is less about getting answers about origins as it is about pure profit, since in my scifi, there are entire races that agree on where they came from, even if they disagree about other stuff. While other more typical human behavior ones exist too (chaotic).

High thrust: How else they gonna get off that rock they call Earth/Terra/whatever? Air augmentation you mentioned and it is definitely the way, as we know that gravity losses will wreck any spacecraft's TWR until you are willing to do pulse detonation.

Air augmentation is also limited by heat tolerance, but scaling up the size helps with that.

So my idea for an air augmented SSTO would be an open air magnetic rail launch for the initial push. Fast enough to engage some kind of thermal ramjet, then switch to scram jet as the speed increases augmented with a few SRB's.

The alternative is some kind of MHD.

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

Personally I think the craft would still need propellant.... to get rid of waste heat if nothing else since MHD does not come free.

In other words... an MHD/ramjet/scramjet. Magnetohydrodynamics would get the vessel up to ramjet speed along with expending some chemical propellant for the initial launch from the ground. From then on the ramjet and scram jet would take over.

Whatever the craft, an SSTO by necessity needs to look like a spaceplane... unless it is powered by MHD. Even MHD airplanes still look like aircraft.

 

https://www.google.com/amp/s/northatlanticblog.wordpress.com/2015/03/30/what-is-the-russian-ayaks-aircraft/amp/

 

 

 

 

 

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1 hour ago, Spacescifi said:

High thrust: How else they gonna get off that rock they call Earth/Terra/whatever? Air augmentation you mentioned and it is definitely the way, as we know that gravity losses will wreck any spacecraft's TWR until you are willing to do pulse detonation.

Not really. What gravity loses do is kill delta-V. That requires you to carry a lot of propellant, which is what can kill your TWR, but doesn't have to. There are ways to balance it out.

Quote

Air augmentation is also limited by heat tolerance, but scaling up the size helps with that.

Note, with air augmentation the heat tolerance limits work completely differently from the normal thermal engine. Here, it's the air that you take in that's the problem. If your thermal engine is running hot, just give it more air. There's no real reason to run all that much hotter than the intake air temperature (which can be considerable).

Quote

So my idea for an air augmented SSTO would be an open air magnetic rail launch for the initial push. Fast enough to engage some kind of thermal ramjet, then switch to scram jet as the speed increases augmented with a few SRB's.

You can start with an airbreather from standstill, if you've got some kind of fan to give the air a push (like a nuclear turboramjet). Would also help landing. MHD is another option if you've got a lot of energy to spare.

Quote

Whatever the craft, an SSTO by necessity needs to look like a spaceplane... unless it is powered by MHD. Even MHD airplanes still look like aircraft.

Not necessarily. You can do vertical launch if you've got a power source which is strong and light enough. Waste heat is not a problem in atmosphere, and in fact, if you're not doing MHD, all you're doing is heating things up anyway. Air is far better at cooling than any sort of radiator, because it works via convection and not radiation. Heat is only a problem after you get to space (or high enough you can use your space engine, anyway).

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On 12/29/2019 at 8:07 AM, Dragon01 said:

Not really. What gravity loses do is kill delta-V. That requires you to carry a lot of propellant, which is what can kill your TWR, but doesn't have to. There are ways to balance it out.

Note, with air augmentation the heat tolerance limits work completely differently from the normal thermal engine. Here, it's the air that you take in that's the problem. If your thermal engine is running hot, just give it more air. There's no real reason to run all that much hotter than the intake air temperature (which can be considerable).

You can start with an airbreather from standstill, if you've got some kind of fan to give the air a push (like a nuclear turboramjet). Would also help landing. MHD is another option if you've got a lot of energy to spare.

Not necessarily. You can do vertical launch if you've got a power source which is strong and light enough. Waste heat is not a problem in atmosphere, and in fact, if you're not doing MHD, all you're doing is heating things up anyway. Air is far better at cooling than any sort of radiator, because it works via convection and not radiation. Heat is only a problem after you get to space (or high enough you can use your space engine, anyway).

 

So this how it would look... a rocket with a pair of big turbojets on the sides with rocket nozzles at their ends and nuclear reactors inside. The rocket would have chemical rocket engines for the main engine.

Sounds great but it is far from the scifi dream of an SSTO that can simply fly from Earth to the moon and back without using and leaving staging behind.

It has known issues that wikipedia cites:

 

Airbreathing SSTOEdit

350px-Skylon_colour.svg.png
Skylon spaceplane

Some designs for SSTO attempt to use airbreathing jet engines that collect oxidizer and reaction mass from the atmosphere to reduce the take-off weight of the vehicle.[citation needed]

Some of the issues with this approach:

  • No known air breathing engine is capable of operating at orbital speed within the atmosphere (for example hydrogen fueled scramjets seem to have a top speed of about Mach 17).[27] This means that rockets must be used for the final orbital insertion.
  • Rocket thrust needs the orbital mass to be as small as possible to minimize propellant weight.
  • Rocket thrust needs the orbital mass to be as small as possible to minimize propellant weight.
  • The thrust-to-weight ratio of rockets that rely on on-board oxygen increases dramatically as fuel is expended, because the oxidizer fuel tank has about 1% of the mass as the oxidizer it carries, whereas air-breathing engines traditionally have a poor thrust/weight ratio which is relatively fixed during the air-breathing ascent.
  •  
  • Very high speeds in the atmosphere necessitate very heavy thermal protection systems, which makes reaching orbit even harder.
  • While at lower speeds, air-breathing engines are very efficient, but the efficiency (Isp) and thrust levels of air-breathing jet engines drop considerably at high speed (above Mach 5–10 depending on the engine) and begin to approach that of rocket engines or worse.
  • Lift to drag ratios of vehicles at hypersonic speeds are poor, however the effective lift to drag ratios of rocket vehicles at high g is not dissimilar.

The biggest issue is probably this:

Similar issues occur with single-stage vehicles attempting to carry conventional jet engines to orbit—the weight of the jet engines is not compensated sufficiently by the reduction in propellant.[28]

 

However:

 

On the other hand, LACE-like precooled airbreathing designs such as the Skylon spaceplane (and ATREX) which transition to rocket thrust at rather lower speeds (Mach 5.5) do seem to give, on paper at least, an improved orbital mass fraction over pure rockets (even multistage rockets) sufficiently to hold out the possibility of full reusability with better payload fraction.[29]

It is important to note that mass fraction is an important concept in the engineering of a rocket. However, mass fraction may have little to do with the costs of a rocket, as the costs of fuel are very small when compared to the costs of the engineering program as a whole. As a result, a cheap rocket with a poor mass fraction may be able to deliver more payload to orbit with a given amount of money than a more complicated, more efficient rocket.[citation needed

So, I suppose one could combine a nuclear turboramjet with a precooler and try to pull off making an uber Skylon, even perhaps getting more payload up to orbit than multistage rockets. Yet with every reentry the craft will need to be repaired from reentry damage anyway, so I can see why SSTO's are a hard sell even though I like them for scifi.

The only currently known way that might provide man with an SSTO that can leave Earth and go to the moon on a round trip back would be some kind Project Orion. With both airbreathing and non-airbreathing shuttlecraft, since how else will anyone get to the moon? Landing an entire Orion on the moon will trade payload for propellant since landing witjh nuclear detonations seems like a nonstarter... even on the airless moon.

 

The good news is is that the nonairbreathing shuttles won't need a lot of propellant, since the Orion mothership has enough bombs to slow it's orbit and then release the shuttles to use their engines mostly for landing/take off.

 

Airbreathing shuttles would likely need some kind of active cooling like the sweating idea Musk favors, thus reducing thermal hull damage from repeated reentries.

An SSTO will likely be a shuttle, not the massive starships we see in scifi.

The only massive starship we currently theoretically can send up in one launch is an Orion.

 

Which will never land without trading cargo for lots of propellant, since landing via nuke detonation retropush is suicide.

 

 

 

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Actually, Skylon is only one way of doing that. TBH, I think airbreathers are a dead end, not to mention they're limited to Earth. By "air augmentation" I meant this:
gnome-image06.jpg

This is a cross-section of the proposed Gnom ICBM. That project died with its designer, but it's an ICBM the size of an IRBM (complete with being road-mobile), which should give you an idea of how much it could gain. Note the second stage rocket, which is surrounded by a large duct (this is not protective covering). Here's another design, exemplifying the same principle:
DlZk0R5W4AAjGUm.jpg

The best thing about it is that it works with any kind of thermal engine. So, you get your standard orbit-optimized nuclear rocket, add a big fat air duct around it, and you get a massive boost in Isp when at correct speed in atmosphere. It also makes a scramjet very easy to design, because you don't have to burn fuel in supersonic airstream - the rocket does all the combustion, and it doesn't care how fast the air is going. Also because of that, all you need is a reasonably thick atmosphere. It wouldn't work nearly as well on Mars, but it would work.

With a little extra hardware, it would even work for takeoff and landing. All you need is a fan of some sort, preferably with retractable blades so it can change into a ramjet. An even more advanced design could entirely replace propellant with air. You suck in air, heat it up and expel out of the nozzle. You wouldn't need propellant for the entire atmospheric flight

And no, it's not any kind of exotic, once-off principle. As a matter of fact, air-augmented rockets are a thing right now, MBDA Meteor missile that's been in service in several air forces since a few years is based on this technology. Now, you'd need to scale it up a bit to make it useful as SSTO, but it is definitely possible, as far as physics go.

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On 1/2/2020 at 5:47 PM, Dragon01 said:

Actually, Skylon is only one way of doing that. TBH, I think airbreathers are a dead end, not to mention they're limited to Earth. By "air augmentation" I meant this:
gnome-image06.jpg

This is a cross-section of the proposed Gnom ICBM. That project died with its designer, but it's an ICBM the size of an IRBM (complete with being road-mobile), which should give you an idea of how much it could gain. Note the second stage rocket, which is surrounded by a large duct (this is not protective covering). Here's another design, exemplifying the same principle:
DlZk0R5W4AAjGUm.jpg

The best thing about it is that it works with any kind of thermal engine. So, you get your standard orbit-optimized nuclear rocket, add a big fat air duct around it, and you get a massive boost in Isp when at correct speed in atmosphere. It also makes a scramjet very easy to design, because you don't have to burn fuel in supersonic airstream - the rocket does all the combustion, and it doesn't care how fast the air is going. Also because of that, all you need is a reasonably thick atmosphere. It wouldn't work nearly as well on Mars, but it would work.

With a little extra hardware, it would even work for takeoff and landing. All you need is a fan of some sort, preferably with retractable blades so it can change into a ramjet. An even more advanced design could entirely replace propellant with air. You suck in air, heat it up and expel out of the nozzle. You wouldn't need propellant for the entire atmospheric flight

And no, it's not any kind of exotic, once-off principle. As a matter of fact, air-augmented rockets are a thing right now, MBDA Meteor missile that's been in service in several air forces since a few years is based on this technology. Now, you'd need to scale it up a bit to make it useful as SSTO, but it is definitely possible, as far as physics go.

Some issues, first is that you only have fuel as in you are running an ramjet engine, you can add oxidizer and run fuel rich, you can also run an solid rocket engine fuel rich and have an afterburner effect with incoming air. 
They have even made artillery shells exploiting this. 
However you have some use scenarios: 
for an sea skimming missile or high speed cruise missile you are flying level so this makes perfect sense as the air density is set or constant, for short range missiles or artillery shells you have an pretty constant trajectory, you don't use this unless you want long range shots in any case. 

Gnom probably died because of the nuclear weapons reduction treaties. It restricted MIRV usage a lot and Soviet could easy put an singe warhead on an standard missile and have it road mobile, and add decoys in an world there ABM started to become an thing. 
And nuclear weapons was always an mind game, none wanted an nuclear war.
50 years earlier they had weapon restriction agreements on battleships, back then reason was economical as they was expensive however while battleships was still useful 50 years later they was not something who could end civilization. 
 

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Actually, in that case, the designer's death was the deciding factor. Gnom was a mid-60s project, so quite early in the nuclear arms race. It wasn't a matter of MIRV restrictions, because the first MIRVed missile was Minuteman III, introduced in 1968, three years after Gnom was canceled. In the USSR, technology development was intertwined with the political game, and it wasn't the only project that didn't survive the loss of its strongest proponent (it's hardly exclusive to Soviets, too, see Stratolaunch after its founder's death). In fact, road-mobile ICBMs were eventually made, in the 90s, by stacking a bunch of solid stages together. I also suspect that designing an optimal inlet duct wasn't easy before widespread and powerful computers, which would explain why the first air augmented missile entered service only four years ago, despite both Russians and NASA toying with the concept earlier.

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On 1/2/2020 at 8:47 AM, Dragon01 said:

Actually, Skylon is only one way of doing that. TBH, I think airbreathers are a dead end, not to mention they're limited to Earth. By "air augmentation" I meant this:
gnome-image06.jpg

This is a cross-section of the proposed Gnom ICBM. That project died with its designer, but it's an ICBM the size of an IRBM (complete with being road-mobile), which should give you an idea of how much it could gain. Note the second stage rocket, which is surrounded by a large duct (this is not protective covering). Here's another design, exemplifying the same principle:
DlZk0R5W4AAjGUm.jpg

The best thing about it is that it works with any kind of thermal engine. So, you get your standard orbit-optimized nuclear rocket, add a big fat air duct around it, and you get a massive boost in Isp when at correct speed in atmosphere. It also makes a scramjet very easy to design, because you don't have to burn fuel in supersonic airstream - the rocket does all the combustion, and it doesn't care how fast the air is going. Also because of that, all you need is a reasonably thick atmosphere. It wouldn't work nearly as well on Mars, but it would work.

With a little extra hardware, it would even work for takeoff and landing. All you need is a fan of some sort, preferably with retractable blades so it can change into a ramjet. An even more advanced design could entirely replace propellant with air. You suck in air, heat it up and expel out of the nozzle. You wouldn't need propellant for the entire atmospheric flight

And no, it's not any kind of exotic, once-off principle. As a matter of fact, air-augmented rockets are a thing right now, MBDA Meteor missile that's been in service in several air forces since a few years is based on this technology. Now, you'd need to scale it up a bit to make it useful as SSTO, but it is definitely possible, as far as physics go.

 

It sounds really good... so why is no one using it? Elon should be as aware of this as he was about aerospikes (which failed him during a test burn).

So as usual I went to wikpedia which said:

 

AdvantagesEdit

The effectiveness of this simple method can be dramatic. Typical solid rockets have a specific impulse of about 260 seconds (2.5 kN·s/kg), but using the same fuel in an air-augmented design can improve this to over 500 seconds (4.9 kN·s/kg), a figure even the best hydrogen/oxygen engines can't match. This design can even be slightly more efficient than a ramjet, as the exhaust from the rocket engine helps compress the air more than a ramjet normally would; this raises the combustion efficiency as a longer, more efficient nozzle can be employed. Another advantage is that the rocket works even at zero forward speed, whereas a ramjet requires forward motion to feed air into the engine.

 

DisadvantagesEdit

It might be envisaged that such an increase in performance would be widely deployed, but various issues frequently preclude this. The intakes of high-speed engines are difficult to design, and they can't simply be located anywhere on the airframe whilst getting reasonable performance – in general, the entire airframe needs to be built around the intake design. Another problem is that the air thins out as the rocket climbs, so the amount of additional thrust is limited by how fast the rocket climbs. Finally, the air ducting weighs about 5× to 10× more[citation needed] than an equivalent rocket that gives the same thrust. This slows the vehicle quite a bit towards the end of the burn.

 

So how would an SSTO using this technology really look?

Like a big intake fan with a rocket nozzle at the end, and the crew modules attached to the sides. Fuel tanks also attached to the sides for when it leaves the atmosphere.

Not like typical scifi fare, but reality seldom is, since reality is about optimization and conformity to reality.

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There's a ton of problems with air breathers in general, and GNOM and air-augmented rockets have almost all the issues and gain very little.

As mentioned "the entire airframe needs to be designed around the intakes".  Had Falcon 9 used this design, evolving to block 5 and nearly twice the mass to orbit  would have been impossible.

Even if you manage to increase Isp to "over 500s", this only works for the first stage.  You might save a bit of mass (which would certainly help the costs), but overall it wouldn't change rocket performance as much as you'd expect. Since you are lifting a fairly hefty second stage, fuel usage scales fairly linearly with Isp (once dry mass is reduced to just payload you will see exponential gains), so it isn't all that great.

Don't forget that the more delta-v you want out of this stage, the faster you will have to plough through the atmosphere: big gains are a chance to burn up your spacecraft.

Oddly enough, I'm a big fan of air breathers, especially the X-43.  The catch here is that you are optimizing the wrong problem, the cost of the fuel in the rocket simply is in the noise for a rocket launch.  SpaceX is currently attempting to re-use the Falcon 9's fairing (whether or not Mr. Thomas catches it).  The cost of the fairing is something like 10 times the cost of the entire fuel budget of a Falcon 9 launch.  I'm sure there are plenty more "low lying fruit" to discover and optimize before a huge and expensive project to shave maybe $50k off each flight.  Perhaps with Starship [booster] using considerably more fuel, there would be some justification for building some sort of air-breathing booster to launch it, but I doubt there are any plans for that in this decade.  I've noted that the crew Bezos hired for Blue Origin seems to have solved a ton of "the next low lying fruit" on an earlier project, perhaps after New Armstrong (assuming the ever build New Glenn) they might work on an air breather sooner.

There's an old (from the 1960s) saying in software that "premature optimization is the root of all evil".  Designing an air breather now would certainly qualify as premature optimization.  For sci-fi, it is quite reasonable that by the time that anybody can simply buy a ticket, go to a spacesport and be in space the next day to be flying by airbreather.   Just don't assume it will happen in the 2020s.

What would an SSTO look like?  Same as any other SSTO (from Earth): comically big, next to zero payload, and definitely single-use-only.  And definitely with liquid rockets, unless you want to either relight a solid rocket or have multiple solid rockets on your SSTO.  The X-43 has the potential to be an SSTO, but remember that it has almost no payload and barely gets anywhere near orbital velocity: it will still need other stages for pre and post-SCRAM flight (and the research "pre-SCRAM" booster was much bigger than the X-43 itself).

There's this great game that teaches things like orbital mechanics and the rocket equation so you don't fall for any pipe dreams like SSTO: it is called Kerbal Space Program and although it is no longer on sale for the Steam Winter Sale, it is still available to teach you these things (although you might need the Realism Overhaul mod to really understand the issues with SSTO.  Like the real Moon or Mars, Kerbol is a small planet and SSTO is possible on these bodies).

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15 minutes ago, wumpus said:

There's a ton of problems with air breathers in general, and GNOM and air-augmented rockets have almost all the issues and gain very little.

This isn't true. The Meteor missile has a maximum range of about 150km, 50km longer than an AIM-120C, despite being the same size. While AIM-120D is supposed to match its range, AFAIK it hasn't entered service yet, while Meteor is 4 years old by this point (I don't know how Slammer D gets its range boost). This technology is a reality right now. SpaceX doesn't do that because despite diminishing returns due to rocket equation, making a bigger rocket works well enough for what they are trying to do. 

If you want a reusable SSTO with decent payload and chemical propulsion, air augmentation is the way to go. It really shines when combined with nuclear engines, though. Since it gives you additional thrust, you can use a nuke engine that would otherwise not produce enough thrust for liftoff. Since nuclear engines have inferior TWR to chemical ones, a way to boost that would be particularly helpful. Of course, that would require someone to start building nuclear rockets.

1 hour ago, Spacescifi said:

So how would an SSTO using this technology really look?

Like a big intake fan with a rocket nozzle at the end, and the crew modules attached to the sides. Fuel tanks also attached to the sides for when it leaves the atmosphere.

Not like typical scifi fare, but reality seldom is, since reality is about optimization and conformity to reality.

It would look like a rocket with intakes:
meteor.jpg

That's all there's to it. It's not quite as restricting as Wikipedia makes it out to be. Anything using a scramjet needs to be designed around it to a degree, but that doesn't mean you don't have a rocket anymore, it just starts looking more like a cruise missile.

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34 minutes ago, Dragon01 said:

This isn't true. The Meteor missile has a maximum range of about 150km, 50km longer than an AIM-120C, despite being the same size. While AIM-120D is supposed to match its range, AFAIK it hasn't entered service yet, while Meteor is 4 years old by this point (I don't know how Slammer D gets its range boost). This technology is a reality right now. SpaceX doesn't do that because despite diminishing returns due to rocket equation, making a bigger rocket works well enough for what they are trying to do. 

If you want a reusable SSTO with decent payload and chemical propulsion, air augmentation is the way to go. It really shines when combined with nuclear engines, though. Since it gives you additional thrust, you can use a nuke engine that would otherwise not produce enough thrust for liftoff. Since nuclear engines have inferior TWR to chemical ones, a way to boost that would be particularly helpful. Of course, that would require someone to start building nuclear rockets.

It would look like a rocket with intakes:
meteor.jpg

That's all there's to it. It's not quite as restricting as Wikipedia makes it out to be. Anything using a scramjet needs to be designed around it to a degree, but that doesn't mean you don't have a rocket anymore, it just starts looking more like a cruise missile.

 

images?q=tbn:ANd9GcS4st7Jyv8O8qpX2pNpsuZ

It is still not built around the intake, and I suspect a space SSTO cargo carrier able to ship 500 tons, would need to scale up the intake and fan accordingly which adds to overall weight.

Perhaps it would look like vertical jet engine with a rocket nozzle at one end and fuel tanks and cargo pods attached to the sides?

 

If not why not?

Nuclear engines add shielding weight unless you simply don't care about cancer below (project pluto).

It could still work... still small payload though. I would use it along with staging. Use disposable boosters along with airaugmented rocket for launch, and then use air augmented rocket to land.

 

Not an SSTO but better since it increases the oayload which may be small otherwise.

 

 

 

 

Edited by Spacescifi
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3 hours ago, Dragon01 said:

This isn't true. The Meteor missile has a maximum range of about 150km, 50km longer than an AIM-120C, despite being the same size. While AIM-120D is supposed to match its range, AFAIK it hasn't entered service yet, while Meteor is 4 years old by this point (I don't know how Slammer D gets its range boost). This technology is a reality right now. SpaceX doesn't do that because despite diminishing returns due to rocket equation, making a bigger rocket works well enough for what they are trying to do.

A back of the envelope check says that Falcon 9 gets 3600m/s delta-v from its first stage (in expendable mode.  I just plugged mass and fuel into the rocket equation).  Scaling the Isp from 282 (sea level) to ~500 gives a first stage delta-v of 6300 m/s (assuming it doesn't burn up in the atmosphere).  This would be enough to take the "old" launchable mass and fling it to GTO.  Presumably they thought Falcon Heavy would be easier, because that's basically what Falcon Heavy does.  Or you could simply reduce the size of the rocket, but that wouldn't give you much of an advantage.

I'd also expect that the Meteor missile has the advantage of a narrow range of velocity (highly supersonic, but not trying to reach orbital velocity) and ceiling (roughly the ceiling of fighters and bombers).  Any rocket designer trying to use such a ducted engine would have more problems trying to get anywhere close to half orbital velocity.

3 hours ago, Dragon01 said:

If you want a reusable SSTO with decent payload and chemical propulsion, air augmentation is the way to go. It really shines when combined with nuclear engines, though. Since it gives you additional thrust, you can use a nuke engine that would otherwise not produce enough thrust for liftoff. Since nuclear engines have inferior TWR to chemical ones, a way to boost that would be particularly helpful. Of course, that would require someone to start building nuclear rockets.

If you want a reusable SSTO with decent payload and chemical propulsion you are on the wrong planet.  While you might get a high Isp through air-augmentation, you still are going to need to get the bulk of your delta-v outside the atmosphere, and the best you can do is hydrolox.  Consider an air augmented space shuttle (since it already lands and uses hydrolox to orbit, it is as close to an SSTO as we have seen).  You would have the "shuttle problem" (80 tons dry weight, 24 tons payload) only with the extra bonus of the fuel tank and [air-augmented] boosters.  Do you really think the boosters and fuel tank weigh less than 24 tons dry?  Otherwise you don't have *any* payload until you start adding (and carrying) bigger and bigger boosters (which because a worse and worse problem).  You might get close with a "real" SCRAMJET engine, but even that requires additional power to get up to speed and then to carry it all the way to orbital velocity (nevermind that the X-43 was thrust limited to ~11km/s, and that's the fastest ever made).

I strongly doubt that NTR (the only nuclear rockets* tested) would improve to positive TWR via air-augmentation.  But I won't ignore the possibility of a nuclear SSTO, just that chemical rockets won't have the Isp.

* ok, I can't include the rocket engine that allegedly exploded in Russia recently.  They aren't saying much about what it was and how it worked.

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Actually, the RD-0140 had a TWR of about 6.4, so the Russians were there already. Now, making one lift enough (on top of its own weight) to become useful as a launch engine is another story, but I think this is entirely within the realm of possibility. In fact, you could probably make a pure NTR lifter that'd work without any air augmentation, but it might end up fairly large.

1 hour ago, wumpus said:

While you might get a high Isp through air-augmentation, you still are going to need to get the bulk of your delta-v outside the atmosphere, and the best you can do is hydrolox.

Why are you assuming following a Shuttle-like trajectory? This definitely isn't true. An air-augmented lifter would follow a trajectory that takes the most advantage of the Isp gain. LEO rockets provide most of their dV outside atmosphere, because that's where their Isp is the highest. An air-augmented rocket would ideally ride its thermal limit curve instead, and be more similar to pure scramjet or Skylon launch. You're hauling a massive air intake, so you want to fly as to get all that you can out of it. I don't know if it could take you all the way to orbital speed, but it's a question of heat and drag, not the ability to sustain combustion, so it might.

Shuttle is a bad example, because most of its dry mass was for crew's sake, and it was a staged design in first place. Rather, I was thinking of something like a skinny Venture Star with intakes.

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36 minutes ago, Dragon01 said:

Actually, the RD-0140 had a TWR of about 6.4, so the Russians were there already. Now, making one lift enough (on top of its own weight) to become useful as a launch engine is another story, but I think this is entirely within the realm of possibility. In fact, you could probably make a pure NTR lifter that'd work without any air augmentation, but it might end up fairly large.

Why are you assuming following a Shuttle-like trajectory? This definitely isn't true. An air-augmented lifter would follow a trajectory that takes the most advantage of the Isp gain. LEO rockets provide most of their dV outside atmosphere, because that's where their Isp is the highest. An air-augmented rocket would ideally ride its thermal limit curve instead, and be more similar to pure scramjet or Skylon launch. You're hauling a massive air intake, so you want to fly as to get all that you can out of it. I don't know if it could take you all the way to orbital speed, but it's a question of heat and drag, not the ability to sustain combustion, so it might.

Shuttle is a bad example, because most of its dry mass was for crew's sake, and it was a staged design in first place. Rather, I was thinking of something like a skinny Venture Star with intakes.

 

It will have to be skinner. Venture star was Mc Chunky. And you do not want Mc Chunky trying to reach orbit against air. It slows the vessel down.

 

Vessel probably will look like a Concorde with rocket nozzles.

DSC_5894.jpg

Edited by Spacescifi
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What about an engine designed to pic up the smallest particles in space and convert them into thrust so you just need equipment and not fuel. Any sort of cosmic energy/microparticle even atoms. Waht exists in space constantly that we know of. Even if it's odd. Gravity? Radiations? Even if it's really small thrust. Make the equipment very small and use materials that naturally convert things with little weight. No mechanical parts. simpler probably last longer.

Make a space probe!! then figure out hwo to send data back quickly and use the same thing(s) driving it to power the data etc.

 

As for the concord idea:

What about removing the wings. Making a tube. And using gasses to remove air resistance. Or however you could minimize it. You only need the gas to keep the air away, enough fuel, which is reduced, and payload.

Use gas you can draw from the air at the launch site and fill the rocket with(or from water or something nearby.). Even if it takes a while. Time comes before the launch.

If such a rocket were limited by size you could make it an upper stage that helps the lower stages out. Or is fed by a lower stage and then uses the last of the fuel on the way up.

Say this:

https://en.wikipedia.org/wiki/Air-augmented_rocket

 

GTX-5880trefny-f2.jpg

 

The front part seperates and goes into orbit and helps with air resistance on the way up(using gas to reduce air resistance if needed and sufficient fuel) The back parts get a nose job and has a hidden nose cone underneath it flies back with. You could even launch this from a bomber like the B-52 to reduce delta V more, or save on fuel, or build a bigger rocket or get more payload up. You could do lots of them at once even. If not a lot of gas can be stored it can be used to help with the thinner upper air resistance to get a little extra delta V. Maybe the back could even glide back on no fuel depending on payload etc.

that or the entire thing is a rocket or the wings/pilot cockpit slide off and glide down with the entire inner fuselage being a seperate rocket slipped inside or some combination. I'm assuming that sqaure inside the front nose is a person. If not use a computer driven or even remote driving system with an option for pilot as cargo with the ability to drive to return for safety issues which can be used on the way up if needed. then you have auto pilot, manual pilot, and remote pilot for various stages and uses. Being able to fly it remotely from space could be useful as well as the ground in many situations. Including safetey ones in case of black out or other problems. Let alone things useful for missions. Maybe payloads have to be packed in a weird way. Who knows. More options the better though. Unless it has a downside somewhere. I would think modern computer systems might reduce those though now.

 

couldn't you compress some of that air out of the front nozzle to remove air resistance to the nose and other parts of the vehicle to reduce fuel etc? Can you separate that fast from the engine usage? Even collect and fill the tanks for the upper flight on the lower flight from the engines?

If needed you could partly fill from a bomber if more is needed for the flight. Also good in case you have to change the mission and need to adjust things as a precaution not to waste a flight. Various things could be done for versatility.

main-qimg-53da6ee152614b33c36a7eaa81e770

 

What if the nose had an engine also. This would give the ability for it to launch from various altitudes in various ways. This could seperate to get payload up. Maybe it doesn't need to at a high altitude but a slow one skimming through the air at specific altitudes to get as close to escape velocity as possible before using fuel or other propulsions like gas to lower the rocket stage fuel requirements. If you use the same gas as the fuel or part of the fuel would it save fuel if you release some out the front to remove air resistance. It might help if not to deal with all of the heat etc. Again, if it can make the fuel as the ram jets are combusting stuff you could have a small tank fill in flight to use for end rocket stages and the rest constantly coming out to lower thrust needs/flight times.

 

Each part of the aircraft could have intakes made for the different mass when together and separated. Then each can fly independently. But the back have might have a slower mode for return flights or something.

 

I had a cool rocket SSTO that used air bugs to float infinitely over Duna(Looked a fair bit like that GTX plane actually). And actual craft with gas or something added could hypothetically do the same and be cool for real world deliveries if it's possible. My rocket could float at a single altitude indefinitely and then float over to where ever you wanted it to. That could be good for getting payloads to places without having to be over it directly. Or allow different approaches and use the atmosphere more or something. Or just to get above and have a gentler drop for payloads. Obviously you can float around the planet also, but doing it in atmosphere might be useful too.

 

Some of those old bugs were fun. They allowed you to do stuff you can't currently from lack of correct parts in stock.

Edited by Arugela
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On 1/4/2020 at 11:04 PM, Arugela said:

What about an engine designed to pic up the smallest particles in space and convert them into thrust so you just need equipment and not fuel. Any sort of cosmic energy/microparticle even atoms. Waht exists in space constantly that we know of. Even if it's odd. Gravity? Radiations? Even if it's really small thrust. Make the equipment very small and use materials that naturally convert things with little weight. No mechanical parts. simpler probably last longer.

See:

https://en.wikipedia.org/wiki/Bussard_ramjet

Not really feasible unless you seed the expected trajectory with fuel before hand, as space is really really empty.

On 1/4/2020 at 11:04 PM, Arugela said:

As for the concord idea:

What about removing the wings. Making a tube. And using gasses to remove air resistance. Or however you could minimize it. You only need the gas to keep the air away, enough fuel, which is reduced, and payload.

you mean push gas out of the front of your vehicle so that the air does not drag against the skin of your vessel?

This just causes turbulence and even more air resistance

On 1/4/2020 at 11:04 PM, Arugela said:

Use gas you can draw from the air at the launch site and fill the rocket with(or from water or something nearby.). Even if it takes a while. Time comes before the launch.

You could even compress and purify the gasses so that you can fit more onto the vessel.

Congratulations, you designed a hydrolox rocket.

 

On 1/4/2020 at 11:04 PM, Arugela said:

Each part of the aircraft could have intakes made for the different mass when together and separated. Then each can fly independently. But the back have might have a slower mode for return flights or something.

The Concord flew at 56,000 feet(~17 miles)

The F-35 has a service ceiling of about 9 miles.

The Karman Line is at 100km(62 miles)

The Falcon 9 hits Mach 10 and drops the booster at 153 seconds(~2.6 min and 80km) and crosses the Karman line around 3.4 minute into it's flight.

 

The world record for jet powered aircraft(a scramjet) was  mach 9.6(3.3km/s) (this was an experimental engine that was initially accelerated by a rocket to above mach 5 and had zero payload)

 

Low earth orbit(200-2,000 km) is ~7-8km/s

So at best you could manage almost half of orbital velocity on air-breathing if it was your second stage and had no payload, as opposed to the Falcon 9 booster that tops mach 10 by itself in less than 3 minutes and also releases form the second stage at 80km.

Since the Falcon 9 booster does a better job and is fully reusable, why bother with something more complex and thus more prone to failure?

Perhaps once all rocket launches are fully reusable there will be pressure to reduce fuel costs, but for now, even a reusable booster is well ahead of the competition.

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On 1/6/2020 at 3:42 PM, Terwin said:

S

you mean push gas out of the front of your vehicle so that the air does not drag against the skin of your vessel?

This just causes turbulence and even more air resistance

You could even compress and purify the gasses so that you can fit more onto the vessel.

Congratulations, you designed a hydrolox rocket.

 

I'm referring to how those new russian rockets work by getting more speed by removing the air around them. I thought they pushed lighter than air gases in front to do so.

Or am I thinking of torpedos. I thought they did both.

Yea, I'm thinking of supercavitation torpedoes. I thought there was a rocket version of it that did the same with air effectively.

I assumed maybe you could push the air away like you can with water to remove resistance and fly faster.

https://physics.stackexchange.com/questions/351023/supercavitation-in-air

maybe it can be used for the lower parts of a flight to remove resistance?

Or something more complex to remove air and fly with less fuel etc.

 

https://www.quora.com/Can-the-concept-of-supercavitation-be-applied-to-hypersonic-travel-in-Earths-atmosphere

 

I wonder if it could be used to dissipate supersonic noise as well and get rid of booms. What if you keep it steady or disrupt the waves so they aren't as loud or make no noise somehow.

Edited by Arugela
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On 1/8/2020 at 11:01 AM, Arugela said:

Yea, I'm thinking of supercavitation torpedoes. I thought there was a rocket version of it that did the same with air effectively.

I assumed maybe you could push the air away like you can with water to remove resistance and fly faster.

Supercavitation cannot be used when traveling faster than the speed of sound.  Fortunately the speed of sound in water is faster than the speed of sound in air, so you can still approach Mach 1 with a supercavitating torpedo.

It does not work above the speed of sound as the speed of sound is the propagation speed of pressure waves in the medium, and supercavitation relies on pressure waves to work.

As per your link however, air resistance is no longer your biggest drag issue once super sonic, instead you have 'wave drag'  as a much more important factor then just air-friction.

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