The holy grail of cheap acesses to space & single-stage may have been found

[nec207]

Atomic metallic hydrogen, if metastable at ambient pressure and temperature could be used as the most powerful chemical rocket fuel, as the atoms recombine to form molecular hydrogen. This light-weight high-energy density material would revolutionize rocketry, allowing single-stage rockets to enter orbit and chemically fueled rockets to explore our solar system. To transform solid molecular hydrogen to metallic hydrogen requires extreme high pressures, but has not yet been accomplished in the laboratory. In the proposed new approach electrons will be injected into solid hydrogen with the objective of lowering the critical pressure for transformation. If successful the metastability properties of hydrogen will be studied. This new approach may scale down the pressures needed to produce this potentially revolutionary rocket propellant.

- Wigner and Huntington first predicted that pressures of order 25 GPa were required for the transition of solid molecular hydrogen to the atomic metallic phase. Later it was predicted that metallic hydrogen might be a metastable material so that it remains metallic when pressure is released. Experimental pressures achieved on hydrogen have been more than an order of magnitude higher than the predicted transition pressure and yet it remains an insulator. We discuss the applications of metastable metallic hydrogen to rocketry. Metastable metallic hydrogen would be a very light-weight, low volume, powerful rocket propellant. One of the characteristics of a propellant is its specific impulse, Isp . Liquid (molecular) hydrogen-oxygen used in modern rockets has an Isp of ~460s; metallic hydrogen has a theoretical Isp of 1700 s! Detailed analysis shows that such a fuel would allow single-stage rockets to enter into orbit or carry economical payloads to the moon. If pure metallic hydrogen is used as a propellant, the reaction chamber temperature is calculated to be greater than 6000 K, too high for currently known rocket engine materials. By diluting metallic hydrogen with liquid hydrogen or water, the reaction temperature can be reduced, yet there is still a significant performance improvement for the diluted mixture.


Read more here http://www.planettechnews.com/science/item945

[Eric Hedman]

Interesting, but I'll bet there are plenty of things to work out before this proves to be viable.  Definitely worth following.

[kkattula]

I think the title of this thread should end in 'has been wildly speculated about' instead of may have been found.

The only people to have actually made metallic hydrogen, found at room temperature it started transforming at 200 GPA but became fully metallic at 260-270 GPA. It then remained metallic back down to 200 GPA. That's your metastatic region.  http://www.nature.com/nmat/journal/v10/n12/full/nmat3175.html


Cooling doesn't help, it actually prevents metallization through at least 300 GPA.

So who want's to build a rocket with tanks pressurized to at least 2 million atmospheres (30 million PSI)? That may detonte like a small atomic bomb if a stray cosmic ray passes through?

[Moe Grills]

Atomic metallic hydrogen, if metastable at ambient pressure and temperature could be used as the most powerful chemical rocket fuel, as the atoms recombine to form molecular hydrogen. This light-weight high-energy density material would revolutionize rocketry, allowing single-stage rockets to enter orbit and chemically fueled rockets to explore our solar system. To transform solid molecular hydrogen to metallic hydrogen requires extreme high pressures, but has not yet been accomplished in the laboratory. In the proposed new approach electrons will be injected into solid hydrogen with the objective of lowering the critical pressure for transformation. If successful the metastability properties of hydrogen will be studied. This new approach may scale down the pressures needed to produce this potentially revolutionary rocket propellant.

- Wigner and Huntington first predicted that pressures of order 25 GPa were required for the transition of solid molecular hydrogen to the atomic metallic phase. Later it was predicted that metallic hydrogen might be a metastable material so that it remains metallic when pressure is released. Experimental pressures achieved on hydrogen have been more than an order of magnitude higher than the predicted transition pressure and yet it remains an insulator. We discuss the applications of metastable metallic hydrogen to rocketry. Metastable metallic hydrogen would be a very light-weight, low volume, powerful rocket propellant. One of the characteristics of a propellant is its specific impulse, Isp . Liquid (molecular) hydrogen-oxygen used in modern rockets has an Isp of ~460s; metallic hydrogen has a theoretical Isp of 1700 s! Detailed analysis shows that such a fuel would allow single-stage rockets to enter into orbit or carry economical payloads to the moon. If pure metallic hydrogen is used as a propellant, the reaction chamber temperature is calculated to be greater than 6000 K, too high for currently known rocket engine materials. By diluting metallic hydrogen with liquid hydrogen or water, the reaction temperature can be reduced, yet there is still a significant performance improvement for the diluted mixture.


Read more here http://www.planettechnews.com/science/item945

  It's probably easier to fuse hydrogen protons together with a device built in your garage to generate fusion energy than it is to compress
large numbers of hydrogen atoms to form a (questionably) stable solid form for hardware purposes.

[JohnFornaro]

NIAC just awarded a contract to a group studying this.

[Tass]

I think the title of this thread should end in 'has been wildly speculated about' instead of may have been found.

Yes.

And where is the news? It has been wildly speculated about for a long time, and it is no closer to being a reality.

[go4mars]

Polymeric nitrogen is just as close.  Not holding my breath.

[nec207]

From what I understand they found new type of hydrogen that is most powerful chemical rocket fuel ever found that will lower allow cheap acesses to space & single-stage .

Not sure what the mix up is over it here.

[go4mars]

From what I understand they found new type of hydrogen that is most powerful chemical rocket fuel ever found that will lower allow cheap acesses to space & single-stage .

Not sure what the mix up is over it here.

  Google how much pressure a GigaPascal is. 

It isn't like you can build a diamond anvil big enough.  And even if you could, dragging it to orbit through the controlled release of that pressure would more than offset its potency. 

Needs a light-weight method of containing the immense pressure.  That's the (main) problem.

[93143]

No, the main problem is that we're not sure if it can be metastable at pressures low enough for use in a rocket.  And if so, how much of a disturbance would be required to kick it out of the stability region.

200 GPa is a non-starter.

[go4mars]

No, the main problem is that we're not sure if it can be metastable at pressures low enough for use in a rocket.

No, we're pretty sure that it can't.  Hence the biggest problem is:

It isn't like you can build a diamond anvil big enough.

Though I would be happy to be educated to your point of view if you think I'm wrong.  I did a lot of reading related to the potential for metastability of polymeric nitrogen (nitrogen diamond) and a little reading about this hydrogen option a few years ago.  My impression then, which hasn't yet changed, is that we are pretty sure it can't be stable at low pressures (like carbon diamond).

And if so, how much of a disturbance would be required to kick it out of the stability region.

And even if you could, dragging it to orbit through the controlled release of that pressure would more than offset its potency. 

I think we are agreeing there (though I'll admit that your description is much more technically accurate). 

[93143]

No, the main problem is that we're not sure if it can be metastable at pressures low enough for use in a rocket.

No, we're pretty sure that it can't.

We're a lot more sure that we can't build a flight-weight pressure vessel to take 200 GPa.  Even hyperdiamond or multi-wall carbon nanotubes won't do it.

Just because one study found reversion at 200 GPa and 295 K doesn't mean there isn't a way to keep it metallic at ambient conditions.  Other studies have found different behaviour at different temperatures, and any path dependence is very poorly quantified at this time due to lack of observations.

[nec207]

From what I understand they found new type of hydrogen that is most powerful chemical rocket fuel ever found that will lower allow cheap acesses to space & single-stage .

Not sure what the mix up is over it here.

  Google how much pressure a GigaPascal is. 

It isn't like you can build a diamond anvil big enough.  And even if you could, dragging it to orbit through the controlled release of that pressure would more than offset its potency. 

Needs a light-weight method of containing the immense pressure.  That's the (main) problem.

What is problem with pressure ? Is this type of hydrogen under too much  pressure that it is a safety problem?

Have they done this in science lab ?


And how much cheaper with  this be than what they are using now ?

[e of pi]

The problem with pressure is the stresses it places on materials. Say you want to build the pressure vessel to contain this 200 GPa pressure out of carbon fiber that has a maximum stress of 6.3 GPa (just going off of a wikipedia table for the fiber only, the actual laid up material would be weaker). In order to keep material stresses below yield in a tank with a diameter of 5 m, you'd need a tank 6.25 cm thick. For a metal like steel or aluminum, the maximum stress is going to be an order of magnitude or so lower, and thus the walls another order of magnitude thicker.

And yeah, if that pressure vessel failed...it'd be a bad day all around.

[go4mars]

What is problem with pressure ? Is this type of hydrogen under too much  pressure that it is a safety problem?

200 GigaPascal's is 29 million pounds per square inch. 

Have they done this in science lab ?

Yes.  But the equipment is relatively heavy (and small scale), and controlled extraction of energy at those pressures (in this context) hasn't been done (to my knowledge).

[strangequark]

What is problem with pressure ? Is this type of hydrogen under too much  pressure that it is a safety problem?

Have they done this in science lab ?


And how much cheaper with  this be than what they are using now ?

There's no way of sustaining that large a pressure for any sizable amount of propellant. They can get something like a microliter of hydrogen to metallize when compressed between two smooth facets of a diamond under immensely concentrated force. This is the Diamond Anvil Cell that's been previously referenced.

It's not even that it's a safety problem. It's that there is nothing that can hold a substance at that pressure except a DAC.

If we had some super-tank that could handle this pressure, then pressurized water alone would get you an Isp of 2000 seconds.

[aquanaut99]

What is problem with pressure ? Is this type of hydrogen under too much  pressure that it is a safety problem?

To put it into perspective: 330 to 360 Gigapascals is the pressure inside Earth's Inner Core. That's the kind of pressure we are talking about here. We'd have to be able to contain that in a rocket fuel tank... And the resulting fuel would burn hotter than the surface of the sun...

This is way beyond our current and future technical ability to control. Also, I seriously doubt metallic hydrogen, even if feasible, could ever be produced in sufficient quantities and at a reasonable price. More likely, it is going to cost about as much to creat 1 mg of MH as it would cost to create 1 mg of anti-matter. And, in which case, we'd be better off going directly with anti-matter, which is only slightly more dangerous...

[Downix]

  It's probably easier to fuse hydrogen protons together with a device built in your garage to generate fusion energy than it is to compress
large numbers of hydrogen atoms to form a (questionably) stable solid form for hardware purposes.

Um, *pst*, it *is* easy to fuse hydrogen protons together with a device built in your garage:

http://www.fusor.net

[93143]

Say you want to build the pressure vessel to contain this 200 GPa pressure out of carbon fiber that has a maximum stress of 6.3 GPa (just going off of a wikipedia table for the fiber only, the actual laid up material would be weaker). In order to keep material stresses below yield in a tank with a diameter of 5 m, you'd need a tank 6.25 cm thick.

You've done that wrong.  For a 5 m spherical pressure vessel, using the thin-walled assumption, keeping the hoop stress below 6.3 GPa requires a wall thickness of 40 m.

Of course, that's not strictly accurate, since the calculation assumes that the wall thickness is much less than the tank radius...  but it gives you an idea.

[nec207]

What is problem with pressure ? Is this type of hydrogen under too much  pressure that it is a safety problem?

To put it into perspective: 330 to 360 Gigapascals is the pressure inside Earth's Inner Core. That's the kind of pressure we are talking about here. We'd have to be able to contain that in a rocket fuel tank... And the resulting fuel would burn hotter than the surface of the sun...

This is way beyond our current and future technical ability to control. Also, I seriously doubt metallic hydrogen, even if feasible, could ever be produced in sufficient quantities and at a reasonable price. More likely, it is going to cost about as much to creat 1 mg of MH as it would cost to create 1 mg of anti-matter. And, in which case, we'd be better off going directly with anti-matter, which is only slightly more dangerous...

Anti-matter is very costly to make and hard to control. That is why I think they are looking at this it is much cheaper.

But like other people here say on big scale it is hard to do .

[strangequark]

To put it into perspective: 330 to 360 Gigapascals is the pressure inside Earth's Inner Core. That's the kind of pressure we are talking about here. We'd have to be able to contain that in a rocket fuel tank... And the resulting fuel would burn hotter than the surface of the sun...

This is way beyond our current and future technical ability to control. Also, I seriously doubt metallic hydrogen, even if feasible, could ever be produced in sufficient quantities and at a reasonable price. More likely, it is going to cost about as much to creat 1 mg of MH as it would cost to create 1 mg of anti-matter. And, in which case, we'd be better off going directly with anti-matter, which is only slightly more dangerous...

Anti-matter is very costly to make and hard to control. That is why I think they are looking at this it is much cheaper.

But like other people here say on big scale it is hard to do .

His point was that metallic hydrogen would likely be as costly to make, and as hard to control.

My professional opinion is that it would be harder to control metallic hydrogen.

As for estimating cost at this juncture for either "technology":

At best, it's like Goddard debating the relative merits of using iridium-coated rhenium versus disilicide coated niobium for combustion chambers.

At worst, it's debating whether you can fit more dancing seraphims or cherabims on the surface of a pin.

[8900]

What is problem with pressure ? Is this type of hydrogen under too much  pressure that it is a safety problem?

200 GigaPascal's is 29 million pounds per square inch. 

Have they done this in science lab ?

Yes.  But the equipment is relatively heavy (and small scale), and controlled extraction of energy at those pressures (in this context) hasn't been done (to my knowledge).

How about laser confinement?

[kkattula]

To put things in perspective:

Pump-fed rocket tanks (light) = 50 to 100 PSI

Pressure-fed rocket tanks (heavy) = 300 to 1000 PSI

Rocket turbo pumps = 600 to 3000 PSI


Metallic Hydrogen tank (impossibly heavy) = 30000000 to 45000000 PSI

[aero]

To put things in perspective:

Pump-fed rocket tanks (light) = 50 to 100 PSI

Pressure-fed rocket tanks (heavy) = 300 to 1000 PSI

Rocket turbo pumps = 600 to 3000 PSI


Metallic Hydrogen tank (impossibly heavy) = 30000000 to 45000000 PSI

compare that to the theoritical maximum tensile strength of the strongest material known, multiwall carbon nanotubes, 43 511 321.402 pound/square inch. Current laboratory tests are a long way from reaching the theoritical maximum with the highest strength measured to date being 9 137 377.494 5 pound/square inch

[nec207]

To put it into perspective: 330 to 360 Gigapascals is the pressure inside Earth's Inner Core. That's the kind of pressure we are talking about here. We'd have to be able to contain that in a rocket fuel tank... And the resulting fuel would burn hotter than the surface of the sun...

This is way beyond our current and future technical ability to control. Also, I seriously doubt metallic hydrogen, even if feasible, could ever be produced in sufficient quantities and at a reasonable price. More likely, it is going to cost about as much to creat 1 mg of MH as it would cost to create 1 mg of anti-matter. And, in which case, we'd be better off going directly with anti-matter, which is only slightly more dangerous...

Anti-matter is very costly to make and hard to control. That is why I think they are looking at this it is much cheaper.

But like other people here say on big scale it is hard to do .

His point was that metallic hydrogen would likely be as costly to make, and as hard to control.

My professional opinion is that it would be harder to control metallic hydrogen.

As for estimating cost at this juncture for either "technology":

At best, it's like Goddard debating the relative merits of using iridium-coated rhenium versus disilicide coated niobium for combustion chambers.

At worst, it's debating whether you can fit more dancing seraphims or cherabims on the surface of a pin.

So in other words it is a sensational news article ( to give feel to public some thing found ) and the part saying bring space cost down is so very wrong..

It is the other way around not bring space cost down but make it very very very costly !!!

Thay need to say that than this sensational news article .

[93143]

It is the other way around not bring space cost down but make it very very very costly !!!

No.  This is something we can't do at all.  Cost doesn't factor into it.

If we eventually figure out how to use metallic hydrogen as propellant, it might turn out to be cheaper than modern chemical rockets, or whatever we're using by then.  Or it might not.

More importantly, we may not ever figure out how to do it - there may not be a way.

[JohnFornaro]

It is the other way around not bring space cost down but make it very very very costly !!!

No.  This is something we can't do at all.  Cost doesn't factor into it.

If we eventually figure out how to use metallic hydrogen as propellant, it might turn out to be cheaper than modern chemical rockets, or whatever we're using by then.  Or it might not.

More importantly, we may not ever figure out how to do it - there may not be a way.

+1

No holy grails of any near term utility have yet been found in this exotic propulsion technology. 

[Rugoz]

Seems like a team of researchers actually managed to create the stuff, although they're not 100% sure.

http://www.nature.com/news/metallic-hydrogen-hard-pressed-1.10817

For practical applications however (not only rocket fuel) it must prove to be metastable.

[simonbp]

For practical applications however (not only rocket fuel) it must prove to be metastable.

Which is the point that most of the commentators so far have missed. Noone is ever going to use metallic hydrogen if it doesn't prove to have a metastable state: a high-density phase of matter that is triggered by super-high pressure (the 200 GPa), but which is stable at lower pressures (>5 MPa).

Quantum theory predicts that it should be there, but it's been so far hard to experimentally prove it. It's important not simply for exotic propulsion, but also understanding the interior of Jupiter, which is mostly metallic hydrogen by mass. So, even if the metastable state does not exist, this is still good science to do.

[IRobot]

Considering the current testing process, I'm not sure they can make it cheap in large quantities, so achieving metastability might not be enough.

Quantum theory predicts that it should be there, but it's been so far hard to experimentally prove it.

Quantum theory is a tool, there are limits for what it can predict. It does not explain how the universe works, it just gives some results that fit some observations, just like Newtonian physics.

[grondilu]

Quantum theory predicts that it should be there, but it's been so far hard to experimentally prove it.

Quantum theory is a tool, there are limits for what it can predict. It does not explain how the universe works, it just gives some results that fit some observations, just like Newtonian physics.

What's your point exactly?

[KelvinZero]

compare that to the theoritical maximum tensile strength of the strongest material known, multiwall carbon nanotubes, 43 511 321.402 pound/square inch. Current laboratory tests are a long way from reaching the theoritical maximum with the highest strength measured to date being 9 137 377.494 5 pound/square inch

Disregarding whether the hydrogen actually becomes metallic or not yet, is there potentially a tank made of nanotubes that could hold significantly more energy in the form of pressurized hydrogen than the chemical energy in a similar mass of hydrogen and oxygen?

[meekGee]

Are we comparing the pressure in the gas to the stress in the tank walls?

These two numbers might have the same units, but are not to be equated.  The stress in the tank walls depends on wall thickness, and is generally a lot higher than the pressure in the tank.  (Unless the tank is VERY small and the walls are VERY thick....)

So in short, the allegedly solid Hydrogen had better be stable.

[IsaacKuo]

Disregarding whether the hydrogen actually becomes metallic or not yet, is there potentially a tank made of nanotubes that could hold significantly more energy in the form of pressurized hydrogen than the chemical energy in a similar mass of hydrogen and oxygen?

Please someone correct me if I'm wrong, but even if the tank has no mass at all, there's an inherent limit based on the temperature of the hydrogen, right?  I mean, when the gas escapes out of the exhaust nozzle there's just no way for the molecules to magically gain more kinetic energy per kg than before, right?

So, what is the upper temperature limit that nanotubes can handle?

[KelvinZero]

Disregarding whether the hydrogen actually becomes metallic or not yet, is there potentially a tank made of nanotubes that could hold significantly more energy in the form of pressurized hydrogen than the chemical energy in a similar mass of hydrogen and oxygen?

Please someone correct me if I'm wrong, but even if the tank has no mass at all, there's an inherent limit based on the temperature of the hydrogen, right?  I mean, when the gas escapes out of the exhaust nozzle there's just no way for the molecules to magically gain more kinetic energy per kg than before, right?

So, what is the upper temperature limit that nanotubes can handle?

Im a bit hazy of the physics. I guess you are talking about a compressed gas where the particles are not moving faster, there are just more of them. You couldnt get much ISP out of that because the velocity of the particles is not impressive, eg room temperature velocity.

But under these pressures im guessing you have gone past gas and possibly past liquid. The energy you are storing is in the atoms being closer than they would wish, or perhaps in the stretching of the carbon bonds.

[Tass]

Disregarding whether the hydrogen actually becomes metallic or not yet, is there potentially a tank made of nanotubes that could hold significantly more energy in the form of pressurized hydrogen than the chemical energy in a similar mass of hydrogen and oxygen?

Please someone correct me if I'm wrong, but even if the tank has no mass at all, there's an inherent limit based on the temperature of the hydrogen, right?  I mean, when the gas escapes out of the exhaust nozzle there's just no way for the molecules to magically gain more kinetic energy per kg than before, right?

So, what is the upper temperature limit that nanotubes can handle?

Im a bit hazy of the physics. I guess you are talking about a compressed gas where the particles are not moving faster, there are just more of them. You couldnt get much ISP out of that because the velocity of the particles is not impressive, eg room temperature velocity.

But under these pressures im guessing you have gone past gas and possibly past liquid. The energy you are storing is in the atoms being closer than they would wish, or perhaps in the stretching of the carbon bonds.

Yes. You won't gain anything besides density until you are pushing the atoms into each other. For an ideal gas it simply depends on temperature.

If you are using extreme pressures to carry more compression energy, I am not even sure hydrogen would give the best Isp.

[IsaacKuo]

Im a bit hazy of the physics. I guess you are talking about a compressed gas where the particles are not moving faster, there are just more of them. You couldnt get much ISP out of that because the velocity of the particles is not impressive, eg room temperature velocity.

I was actually thinking the opposite--that in principle, such a compressed gas rocket could be a good cheap SSTO.  If you could heat up the tank to about the same as a solid core nuclear thermal rocket, then you could have an exhaust velocity of 8km/s--pretty much the sweet spot for SSTO.

Assuming tank mass is minimal, of course.  And I'm guessing tank mass would not be anywhere near minimal.  But still, it's a fun thought.

So let's pretend for the moment that this magical tank exists and doesn't have much mass.

Then, our SSTO could be a simple compressed gas rocket with no cryogenic support equipment--unless it's more convenient to fill up the tank with LH2.  But even then, you could centralize the LH2 handling hardware just to fill up the tank and then let it warm up in storage/transit.  (Make sure to keep the tanks in the sort of open pits used for fireworks storage.)

Then on the launchpad, the tank is heated up to the desired operating temperature, before letting loose with the release valve!  Whoosh!  Hmm...conveniently, tank pressure goes down as the remaining propellant mass goes down, so I think the acceleration won't blow up out of control.

[JohnFornaro]

"Fully functional" in this article does not mean that the scientist is selling fusion generated electricity to the grid.  It means that he has built a "fully functional" experimental fusion device.

[Tass]

I was actually thinking the opposite--that in principle, such a compressed gas rocket could be a good cheap SSTO.  If you could heat up the tank to about the same as a solid core nuclear thermal rocket, then you could have an exhaust velocity of 8km/s--pretty much the sweet spot for SSTO.

Yes, sure. With magic SSTO is easy.

[KelvinZero]

Yes, sure. With magic SSTO is easy.

NASA's anti-pagen bias could be seriously hampering our space program. Someone start a petition.

[Robotbeat]

Im a bit hazy of the physics. I guess you are talking about a compressed gas where the particles are not moving faster, there are just more of them. You couldnt get much ISP out of that because the velocity of the particles is not impressive, eg room temperature velocity.

I was actually thinking the opposite--that in principle, such a compressed gas rocket could be a good cheap SSTO.  If you could heat up the tank to about the same as a solid core nuclear thermal rocket, then you could have an exhaust velocity of 8km/s--pretty much the sweet spot for SSTO.

Assuming tank mass is minimal, of course.  And I'm guessing tank mass would not be anywhere near minimal.  But still, it's a fun thought.

So let's pretend for the moment that this magical tank exists and doesn't have much mass.

Then, our SSTO could be a simple compressed gas rocket with no cryogenic support equipment--unless it's more convenient to fill up the tank with LH2.  But even then, you could centralize the LH2 handling hardware just to fill up the tank and then let it warm up in storage/transit.  (Make sure to keep the tanks in the sort of open pits used for fireworks storage.)

Then on the launchpad, the tank is heated up to the desired operating temperature, before letting loose with the release valve!  Whoosh!  Hmm...conveniently, tank pressure goes down as the remaining propellant mass goes down, so I think the acceleration won't blow up out of control.

You're a fine specimen of someone who I think understands math quite well but who has somehow an ENORMOUS gap in their physics knowledge...

[IsaacKuo]

I was actually thinking the opposite--that in principle, such a compressed gas rocket could be a good cheap SSTO.  If you could heat up the tank to about the same as a solid core nuclear thermal rocket, then you could have an exhaust velocity of 8km/s--pretty much the sweet spot for SSTO.

Yes, sure. With magic SSTO is easy.

Well, the part quoted above isn't the hard part.  The temperature of a solid core nuclear thermal rocket is pretty low--it has to be below the melting point of the reactor pipes, after all.

The magical part is where the tank doesn't have much mass.  But I don't know how magical that part is, really.  Carbon nanotube is some counterintuitively strong stuff.

[Robotbeat]

The density of a gas at a certain pressure is inversely proportional to the temperature, thus if tanks are heavy for compressed hydrogen at regular pressures, they're far worse at high temperatures.

P*V=n*k*T

[IsaacKuo]

The density of a gas at a certain pressure is inversely proportional to the temperature, thus if tanks are heavy for compressed hydrogen at regular pressures, they're far worse at high temperatures.

P*V=n*k*T

That only matters if you care about storing as much hydrogen as possible--for example, for a fuel cell car or chemical powered rocket.

But in this case, what we care about is the impulse stored.  For that, it actually evens out.  Storing half the gas at twice the pressure provides the same amount of impulse...it's actually better that way since there's less mass in the gas itself.  The specific impulse is higher--slightly higher if the tank mass dominates.  In theory, much higher if gas mass dominates (I seriously doubt it).

[KelvinZero]

Hi Robotbeat,
I dont think anyone was pushing this too hard anyway, just talking about the absurdly high pressures apparently possible with nanotubes and buckyballs and such.

I don't have it quite clear in my head what energy can be stored this way. For example, is the energy simply equal to how much a carbon bond can be stretched before breaking? If so, how does this energy compare to that of typical rocket fuel combustion?

[Robotbeat]

And you can get wonderful Isp with a battery powering an ion thruster.

[Robotbeat]

Also, don't forget that as you start releasing pressure, the temperature of the gas that's still in the tank starts to decrease as well. This makes it impossible to get to orbit this way (at least in a single stage), even with space-elevator materials.

(And yes, I did sit down and do the relevant equations.... spherical pressure vessel, ideal gas law, Isp vs temp for a hydrogen rocket, and the rocket equation.)

[tnphysics]

Unfortunately, if the only way to make metallic hydrogen is with a diamond anvil cell, using it as a propellant - even if it can be metastable - would be far too expensive.

Not to mention the explosive hazard.

[john smith 19]

Read more here http://www.planettechnews.com/science/item945

AS impressive now as it was in 1970, when an AFRL report on advanced future chemical propellants was written by Robert L Forward.

Note the original properties were calculated70 years ago and still no mH has been mfg (Robert Heinlein used it as the propellant of choice in his early 50's novel Space Family Stone).

It's one of those things that if it worked it would be brilliant.

Hopefully the new project will do something practical rather than another study.

The question is not what it's properties are it's why have all efforts failed.

[RanulfC]

Read more here http://www.planettechnews.com/science/item945

Note the original properties were calculated70 years ago and still no mH has been mfg (Robert Heinlein used it as the propellant of choice in his early 50's novel Space Family Stone).

Actually I think you're thinking "Space Cadet" and it was Single-H (Monoatomic Hycrogen) rather than metallic hydrogen.

Randy

[R7]

Seems like a team of researchers actually managed to create the stuff, although they're not 100% sure.

http://www.nature.com/news/metallic-hydrogen-hard-pressed-1.10817

For practical applications however (not only rocket fuel) it must prove to be metastable.

If it were metastable, shouldn't they find teeny weeny spec of it on culet surfaces?

In any case, if made in 160μm³ chunks takes 6.25e12 cycles per liter. Large scale manufacturing appears to be quite a challenge.

[grondilu]

Seems like a team of researchers actually managed to create the stuff, although they're not 100% sure.

http://www.nature.com/news/metallic-hydrogen-hard-pressed-1.10817

For practical applications however (not only rocket fuel) it must prove to be metastable.

If it were metastable, shouldn't they find teeny weeny spec of it on culet surfaces?

In any case, if made in 160μm³ chunks takes 6.25e12 cycles per liter. Large scale manufacturing appears to be quite a challenge.

Are you sure about this number?  160µm^3 is 0.16mm^3, 0.16e-3cm^3, thus 0.16e-6 liter.   And 1/0.16e-6 is 6,250,000.   Not 6.25e12.

[R7]

Are you sure about this number?  160µm^3 is 0.16mm^3

Pretty. Your µm³ to mm³ conversion is off by a factor of million. The article speaks of cubic micrometers. The way I see it it's a cube with sides one micrometer long.

(0.000001m)³ = 0,000000000000000001m³ (17 zeroes after decimal  )

edit: See http://www.aqua-calc.com/what-is/volume/cubic-micrometer

[grondilu]

Are you sure about this number?  160µm^3 is 0.16mm^3

Pretty. Your µm³ to mm³ conversion is off by a factor of million. The article speaks of cubic micrometers. The way I see it it's a cube with sides one micrometer long.

(0.000001m)³ = 0,000000000000000001m³ (17 zeroes after decimal  )

edit: See http://www.aqua-calc.com/what-is/volume/cubic-micrometer

Oh yeah.  My bad.

[R7]

Oh yeah.  My bad.

No worries. I too had difficulties believing the figure at first. Checked many times.

Gotta keep in mind that when stepping between metric prefixes the respective step size is squared or cubed too if measuring area or volume.

[john smith 19]

Actually I think you're thinking "Space Cadet" and it was Single-H (Monoatomic Hycrogen) rather than metallic hydrogen.

I've never been quite clear if metalic Hydrogen was monotomic or not. I was definitely thinking Space Family Stone but Space Cadet (I never realized it was a TV show) was set in the same universe. IIRC the engines are a nuclear system as well, which the (theoretical) performance of metalic H thrashes.

Do you know if anyone's had any more luck with making monatomic Hydrogen?

[IsaacKuo]

Also, don't forget that as you start releasing pressure, the temperature of the gas that's still in the tank starts to decrease as well. This makes it impossible to get to orbit this way (at least in a single stage), even with space-elevator materials.

(And yes, I did sit down and do the relevant equations.... spherical pressure vessel, ideal gas law, Isp vs temp for a hydrogen rocket, and the rocket equation.)

Just for fun, I decided to calculate it out:

Let's suppose we have a nanotube material with a tensile strength of 60GPa.  Let's assume a 1m radius sphere, with a 1cm wall thickness.

A cross section gives a wall area of 0.0628m^2, and a tank area of 3.14m^2, so a wall strength of 300GPa translates to a tank pressure of 1.2GPa.

Let's assume a temperature of 3000K, which corresponds to an exhaust velocity of 10km/s.  So...

PV = nRT

n = PV/(RT) = 1.2GPa * 4.19m^3 / [(8.314J/K/mol) * 3000K]
= 202,000 mol = 404kg of hydrogen gas

Assuming a density of 1.3g/cc, The mass of the tank is 163kg...

Umm...okay.  That's actually not bad at all.  This is not the result I was expecting.

The easiest way to use the rocket equation is if we assume there are a hundred little tanks rather than one big tank.  Each little tank only holds 4.04kg of hydrogen, and has a tank mass of 1.63kg.  The tanks are simply released into the nozzle, one at a time; each one provides an impulse of 40.4kg*km/s.  Assuming a payload of 50kg, we would get:

delta-v = 10km/s * ln ( (50+404+163)/(50+163)) = 10.64km/s

That is actually enough to get to orbit!

If you have a smaller number of larger tanks, the efficiency is lower, but you have less complex plumbing.

Now, do I actually think this is a practical concept?  NO.

Obvious deal killers are:

1) 60GPa is an optimistic tensile strength for this carbon nanotube tank.  It corresponds to the strength demonstrated for small samples in the lab.

2) Hot 3000K hydrogen gas is plausibly not going to play nice with carbon nanotube tank.

3) Even if the above were solved, carbon nanotube is really expensive stuff.

But it's a fun thought experiment.

[Robotbeat]

Again, you forgot to mention that the temperature of the gas inside the tank goes down as you decrease its pressure.

P*V=n*k*T

If we say the first volume expanded adiabatically into an additional other volume so that the contained pressure was half as much:
P1*V1^gamma = P2*V2^gamma

P1/2=P2, so 2*P2=P1, so: 2*P2*V1^gamma= P2*V2^gamma

which becomes 2*V1^gamma=V2^gamma

log(2*V1^gamma) =log(V2^gamma)
log(2)+gamma*log(V1)=gamma*log(V2)
log(2)=gamma*(log(V2)-log(V1))
log(2)/gamma=log(V2/V1)
2^(1/gamma)=V2/V1

V1*2^(1/gamma)=V2


P1*V1/(P2*V2)=(n*k*T1)/(n*k*T2)=T1/T2
becomes:
P1*V1/(P2*V2)=2*P2*V1/(P2*V2)=2*V1/V2=2/(2^(1/gamma))

2^(1-1/gamma)=T1/T2



So:

T2=T1*2^((1/gamma) - 1)

For hydrogen, gamma is about 1.3 at high temperatures, so when T1=3000K:
2^((1/1.3) - 1)=0.85218039642

T2=3000K*0.85=2550K

So when you've used up half of your propellant (when your pressure is half as much), your temperature is already down significantly. As you use up more propellant, your temperature gets yet lower. Your Isp goes down the more you use up. This is why I said you can't get to orbit.

[IsaacKuo]

Again, you forgot to mention that the temperature of the gas inside the tank goes down as you decrease its pressure.

With a bunch of little tanks, this doesn't actually matter.  The decrease in temperature is simply a consequence of expansion ratio as it zooms out the nozzle.

[Robotbeat]

Again, you forgot to mention that the temperature of the gas inside the tank goes down as you decrease its pressure.

With a bunch of little tanks, this doesn't actually matter.  The decrease in temperature is simply a consequence of expansion ratio as it zooms out the nozzle.

Nope! It still matters. Even with a bunch of smaller tanks. You decrease the pressure in the tank (even if you do it carefully so as not to increase the entropy too much), and that causes the temperature to decrease in the tank. I just did a similar problem for my Master's comprehensive exam (which I passed, by the way).

[IsaacKuo]

Again, you forgot to mention that the temperature of the gas inside the tank goes down as you decrease its pressure.

With a bunch of little tanks, this doesn't actually matter.  The decrease in temperature is simply a consequence of expansion ratio as it zooms out the nozzle.

Nope! It still matters. Even with a bunch of smaller tanks. You decrease the pressure in the tank (even if you do it carefully so as not to increase the entropy too much), and that causes the temperature to decrease in the tank. I just did a similar problem for my Master's comprehensive exam (which I passed, by the way).

Please, consider what happen if a tank starts off with a volume of, say, 1cc, and then it is released into an open tube which is 100cc in volume.  It will expand by a 100:1 ratio, right?  In the process, it will cool down, but it will trade this for velocity.  This is just the way a pulsed rocket works.

Now, consider what happened to all of the other little tanks while this was going on.  Do any of them cool down just because the first little tank of gas cooled on its way out the nozzle?  No, of course not.

[Robotbeat]

Except, the gas in BOTH tanks cools down!!!

[Robotbeat]

<a href="http://www.youtube.com/v/6vxHkAQRQUQ&rel=1" target="_blank">http://www.youtube.com/v/6vxHkAQRQUQ&rel=1</a>

[IsaacKuo]

Except, the gas in BOTH tanks cools down!!!

Huh?  Do you mean the gas in both the tank and the nozzle cools down?  Sure thing.  But so what?  My point was that it doesn't matter.  What matters is that you get efficient thrust.  In the extreme example I gave, the thrust efficiency is defined by the 100:1 expansion ratio.

[Robotbeat]

Except, the gas in BOTH tanks cools down!!!

Huh?  Do you mean the gas in both the tank and the nozzle cools down?  Sure thing.  But so what?  My point was that it doesn't matter.  What matters is that you get efficient thrust.  In the extreme example I gave, the thrust efficiency is defined by the 100:1 expansion ratio.

It ABSOLUTELY matters!

When you're halfway through expending your propellant (in a single tank or halfway through expending your propellant in one of many tanks), your temperature /in the tank/ decreases by ~15%.

[IsaacKuo]

Except, the gas in BOTH tanks cools down!!!

Huh?  Do you mean the gas in both the tank and the nozzle cools down?  Sure thing.  But so what?  My point was that it doesn't matter.  What matters is that you get efficient thrust.  In the extreme example I gave, the thrust efficiency is defined by the 100:1 expansion ratio.

It ABSOLUTELY matters!

When you're halfway through expending your propellant (in a single tank or halfway through expending your propellant in one of many tanks), your temperature /in the tank/ decreases by ~15%.

So what?  In the example I gave of a 1cc tank expanding into a 100cc exhaust tube, cooling by 15% is merely an arbitrary point along the way to cooling by 99% as it expands.  This 1cc tank is merely the tip of an iceberg known as the exhaust nozzle.

The system doesn't gain any bonus points for retaining a high temperature in the exhaust.  All it cares about is the impulse provided.

To be clear, the geometry starts off as a gas confined to a small 1cc closed cylinder.  Then, the "bottom" is opened up, so the geometry is now an open tube 100cc in volume.  The gas starts off compressed and hot at the top.  As it expands, it does indeed cool, but it also gains bulk velocity.  That's where the impulse comes from.

[Robotbeat]

Calculate the specific heat of hydrogen. Can't be constant pressure, though! Because your pressure is decreasing. You have to use the lower value (10kJ/(kg*degree)). This means you don't have enough stored heat energy at 3000K to expend the propellant at 10km/s.

[Robotbeat]

Again, you can't beat the physics. Take a thermo class.

[Tass]

Robotbeat, please consider that you may be wrong. You make a wrong assumption in that it expands adiabatically.

No one said you can beat physics, there is simply disagreement about what physics is correct.

Since you pulled argument from authority with your masters, let me say that I hold a phd in physics, most of which was about thermodynamics. That doesn't mean I am right, put I hope it will make you consider that I might be and consider my argument.

At 3000K at least five degrees of freedom (translation and rotation) of the hydrogen molecule is not frozen out and thus contain kB*T of energy each. This translates to 125kJ/mol = 62 kJ/g which is enough for an exhaust speed of 11km/s if it is all converted into translational motion. 

Where do you suppose this energy goes if not the exhaust?

Take a tiny tank, put it into an engine and blow it open, all the hot gas expands, cooling as the bell nozzle converts the thermal energy into motion. There is never a half full tank in this scenario, this was what IssacKuo was getting at. Sure the gas gets colder. It is supposed to.   

What about the slightly more realistic scenario of one big tank? Expanding gas cools right? Yes, if it is adiabaticallly. Adibatically means without producing entropy and without heat flow in or out. Adiabatic expansion means doing work on the surroundings. What does the gas do work on here? Only itself. If you extract no work from the gas you do not cool it down. If you allow gas to slowly leak from the tank then you are not extracting work. The remainder gas will take up more volume but will not have cooled, it thus has more entropy. As long as the pressure remains high enough that you can get a good expansion ratio of the nozzle this entropy is no problem. The only thing which extracts work from the gas is the nozzle which allows it to expand adiabatically and gets a lot of work in the form of motion from it.

http://en.wikipedia.org/wiki/Free_expansion

Of course we cannot assume hydrogen acts as an ideal gas under this extreme pressure. At the density calculated the molecules will overlap. Thus there will be stored a lot of energy in the steric repulsion of the molecules and temperature would actually rise on expansion at first.

It is this energy as far as I understood that KelvinZero was originally getting at with his question about carbon nanotube compressed hydrogen. I don't know how big it would be, but it might well be big enough that preheating of the hydrogen would be unnecessary. (If of course this ridiculous strength tank could be made)   

[Robotbeat]

The heat capacity of hydrogen is 10-12kJ/(kg*degree) for constant volume (because you aren't squeezing the tanks as you go up, pressure doesn't stay the same). There's not enough energy.

[Robotbeat]

Tass: If I get this right, you're assuming no thermodynamic equilibrium? All the gas is expended at once to prevent equilibrium? I do not believe rocket engines work efficiently in this regime, since they can't convert the other degrees of freedom into translation.

[Tass]

Sorry. You are right. The heat per degree of freedom is 1/2*kB*T, I forgot the factor 1/2. That cuts the energy calculated in half and gives an exhaust speed of maximally 8km/s.

Or as you say: Constant pressure heat capacity for a gas weighing 2g/mol and having 5 degrees of freedom available is

5/2 R / (2g/mol) = 10.4 kJ/(kg*K)

But 8 km/s is still not bad.

[Robotbeat]

It's just a factor of 1/2. That's close enough.

But it does still leave us ~1km/s short of orbit.

Also, I'm sorry, IsaacKuo, for me getting excited about this.

"But someone is /wrong/ on the Internet!"

[Tass]

Tass: If I get this right, you're assuming no thermodynamic equilibrium? All the gas is expended at once to prevent equilibrium? I do not believe rocket engines work efficiently in this regime, since they can't convert the other degrees of freedom into translation.

Never mind that it was issacKuos idea as a thought experiment having hundreds of small tanks.

You are right, there is not enough energy for 11km/s exhaust. If you do let it expand adiabatically so that the hydrogen in the tank does work on the hydrogen on its way out then you can get 11km/s initially, but as you say then the remainder expends energy and cools so you cant keep it up.

[Tass]

"But someone is /wrong/ on the Internet!"

Haha. Exactly

It's just a factor of 1/2. That's close enough.

But it does still leave us ~1km/s short of orbit.

Well that is exhaust speed. Along with mass ratio it should do fine.

And then there is the thing I am most excited about, KelvinZeros original question: How much energy would be stored in the steric repulsion? Could it make significant Isp even without being hot? 

[Robotbeat]

I know, but our mass ratio is so bad that it turns out the exhaust velocity is pretty close to the produced delta-v (see IsaacKuo's post a couple pages back).

[Tass]

I know, but our mass ratio is so bad that it turns out the exhaust velocity is pretty close to the produced delta-v (see IsaacKuo's post a couple pages back).

Right.

And even assuming the 60GPa nanotube tether I don't buy his calculation for the pressure the tank can hold. The 60GPa is tensile strength along the length, a spherical tank would have to be a mesh reducing the strength in any one direction. 

[Robotbeat]

Yeah, carbon nanotubes aren't exactly isotropic.

[KelvinZero]

And then there is the thing I am most excited about, KelvinZeros original question: How much energy would be stored in the steric repulsion? Could it make significant Isp even without being hot? 

I had to look that word 'steric' up to figure out the clever thing I said

btw, I tried to figure out how much energy you could store by stretching carbon bonds to breaking point. I don't have any great confidence in my logic but I got a figure of about 3 or 4 times the energy from the same mass of hydrogen/oxygen burnt to form water. This was based on the "bond dissociation" energy of C-C, and assuming twice as many bonds as atoms in a purely carbon material. Is that the right value to use?

If this is true I guess you still dont get a great performance increase unless you are throwing the carbon material itself out the back for thrust, rather than carrying it all the way to orbit.

[scienceguy]

If you had pure carbon nanotubes, wouldn't it be better to build a space elevator?

[KelvinZero]

Don't trust em, never will.

Some people swear black and blue by space elevators. Other people come up with the same list of objections that occur to me. Definitely something to discuss on a space elevator thread and not here..

..but yeah there might be a list of better things to do with nanotubes if we had them.

[jongoff]

Guys could you take the remedial thermodynamics lessons (and the discussion of hydrogen cold gas thrusters) somewhere else? It seems a bit off topic.

~Jon

[RanulfC]

Actually I think you're thinking "Space Cadet" and it was Single-H (Monoatomic Hycrogen) rather than metallic hydrogen.

I've never been quite clear if metalic Hydrogen was monotomic or not. I was definitely thinking Space Family Stone but Space Cadet (I never realized it was a TV show) was set in the same universe. IIRC the engines are a nuclear system as well, which the (theoretical) performance of metalic H thrashes.

Do you know if anyone's had any more luck with making monatomic Hydrogen?

In SC it was mentioned that the "jeeps" (SSTO shuttlecraft) used single-h while the big ships used atomic pile motors. IIRC the same set up was mentioned in RS/SFS.

As for making Single-H, I recall some work on high-temp seperation but nothing on making it stable enough to store for any length of time.

Randy

[R7]

[possibly stupid question warning]: If the metallic hydrogen would somehow be metastable at pressures practical for rocketry, would it be a solid, dense liquid with metallic properties, or something else? In other words, what would we be pumping?

OT observation: the military applications of this stuff might be very impressive, like TNT on steroids that turns into secondary aerosol bomb. Edit: On the second thought, this property could also make launch mishaps very nasty 

[Lee Jay]

Let's assume a temperature of 3000K, which corresponds to an exhaust velocity of 10km/s.  So...

PV = nRT

n = PV/(RT) = 1.2GPa * 4.19m^3 / [(8.314J/K/mol) * 3000K]
= 202,000 mol = 404kg of hydrogen gas

Are you aware of the fact that Hydrogen is NOT an ideal gas?

[Robotbeat]

Let's assume a temperature of 3000K, which corresponds to an exhaust velocity of 10km/s.  So...

PV = nRT

n = PV/(RT) = 1.2GPa * 4.19m^3 / [(8.314J/K/mol) * 3000K]
= 202,000 mol = 404kg of hydrogen gas

Are you aware of the fact that Hydrogen is NOT an ideal gas?

Of course it isn't, but the equations are good enough for napkin-work. Also, we've pretty much resolved this question and don't need to rehash it. There's not quite enough delta-v to get to orbit.

[simonbp]

Chris, have you actually read any of the several papers about using metallic hydrogen as a propellant? Specially the fact that all of them use a small trickle of hot hydrogen from the small metallatic hydrogen tank to heat a working fluid (water on first stages, LH2 on upper stages) which then provides the actual thrust.

With water as the working fluid, they could easily make an SSTO with considerable margin, as it has NTR-type Isp (600-700 sec). A two stage vehicle not much taller than an Atlas V, with LH2 as the working fluid on the second stage, could land on the moon and return. In all these cases, the metallic hydrogen is stored in ~2 m diameter spherical tanks at 5 MBar. That's hard, but not impossible.

Again, the difficult hill to climb is proving that the metastable state exisits. If we can get that far, the engineering will follow.

[Tass]

Chris, have you actually read any of the several papers about using metallic hydrogen as a propellant? Specially the fact that all of them use a small trickle of hot hydrogen from the small metallatic hydrogen tank to heat a working fluid (water on first stages, LH2 on upper stages) which then provides the actual thrust.

With water as the working fluid, they could easily make an SSTO with considerable margin, as it has NTR-type Isp (600-700 sec). A two stage vehicle not much taller than an Atlas V, with LH2 as the working fluid on the second stage, could land on the moon and return. In all these cases, the metallic hydrogen is stored in ~2 m diameter spherical tanks at 5 MBar. That's hard, but not impossible.

Again, the difficult hill to climb is proving that the metastable state exisits. If we can get that far, the engineering will follow.

The post you comment on was part of our off topic discussion about high pressure non-metalic hydrogen.

[R7]

In all these cases, the metallic hydrogen is stored in ~2 m diameter spherical tanks at 5 MBar. That's hard, but not impossible.

Five million bars??

[Tass]

In all these cases, the metallic hydrogen is stored in ~2 m diameter spherical tanks at 5 MBar. That's hard, but not impossible.

Five million bars??

Yeah, something is off there. Thats 500GPa, that is beyond even theoretical nanotubes.

[Robotbeat]

Chris, have you actually read any of the several papers about using metallic hydrogen as a propellant? Specially the fact that all of them use a small trickle of hot hydrogen from the small metallatic hydrogen tank to heat a working fluid (water on first stages, LH2 on upper stages) which then provides the actual thrust.

With water as the working fluid, they could easily make an SSTO with considerable margin, as it has NTR-type Isp (600-700 sec). A two stage vehicle not much taller than an Atlas V, with LH2 as the working fluid on the second stage, could land on the moon and return. In all these cases, the metallic hydrogen is stored in ~2 m diameter spherical tanks at 5 MBar. That's hard, but not impossible.

Again, the difficult hill to climb is proving that the metastable state exisits. If we can get that far, the engineering will follow.

My comments were referring to the (admittedly off-topic) discussion about storing hot hydrogen gas in a carbon nanotube tank.

As far as metallic hydrogen...

In all these cases, the metallic hydrogen is stored in ~2 m diameter spherical tanks at 5 MBar. That's hard, but not impossible.

Five million bars??

Yeah, something is off there. Thats 500GPa, that is beyond even theoretical nanotubes.

It's not off, it really /does/ take something around that much pressure to get metallic hydrogen.

It's not practical. In fact, it may be even less practical than antimatter. At least we've /definitely/ produced some of that!

[john smith 19]

In SC it was mentioned that the "jeeps" (SSTO shuttlecraft) used single-h while the big ships used atomic pile motors. IIRC the same set up was mentioned in RS/SFS.

It's been a while. I'll go with that.

As for making Single-H, I recall some work on high-temp seperation but nothing on making it stable enough to store for any length of time.

You mean someone has actually made some?

By the standards of metallic Hydrogen that's practically off the shelf 

[Tass]

It's not off, it really /does/ take something around that much pressure to get metallic hydrogen.

It's not practical. In fact, it may be even less practical than antimatter. At least we've /definitely/ produced some of that!

I know but he talked about keeping it stored in spherical tanks.

Making it in a diamond anvil is one thing. Storing it if it is found not to be metastable is quite another.

Now if it was found to be metastable at something like one GPa but not at 1bar, then high pressure tanks might make sense.