Author Topic: Compressed hydrogen and oxygen instead of liquid for storage  (Read 21809 times)

Offline DarkenedOne

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Much of the discussion regarding fuel storage in space involves liquid hydrogen and oxygen.  What I have been wondering is why not simply store the hydrogen an oxygen in compressed form.  Doing so completely eliminates the problem of long time storage as extremely low temperatures do not need to be maintained.  Now at 700 bar the density of hydrogen at room temperature is only half that of its liquid state, so you would need bigger tanks. 

Now that is just for storage.  For use the gases can be liquified again, and used in a traditional LH2/LO engine.  Another possibility would be to keep it in gas form and just build rocket engines that run on the gas.  Such a engine would not be as powerful, but it should in theory produce the same specific impulse. 

Offline peter-b

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Much of the discussion regarding fuel storage in space involves liquid hydrogen and oxygen.  What I have been wondering is why not simply store the hydrogen an oxygen in compressed form.  Doing so completely eliminates the problem of long time storage as extremely low temperatures do not need to be maintained.  Now at 700 bar the density of hydrogen at room temperature is only half that of its liquid state, so you would need bigger tanks. 

Firstly, recall that LH2 has such an awkwardly low density that it makes LH2 challenging to use as a first stage fuel because the tanks need to be so large.

A tank capable of coping with 700 bar will be much (much much) stronger than one the same size capable of handling ~80 bar (LH2 tank pressure, IIRC), with concomitant necessary increase in mass. If it needs to be much larger (due to lower density of compressed H2 than LH2) and much stronger, then you're looking at paying a very high mass penalty for launching the thing, surely? Also, gaseous hydrogen has a horrible tendency to diffuse through things.
Research Scientist (Sensors), Sharp Laboratories of Europe, UK

Offline Robotbeat

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The tank would be heavier than the hydrogen it holds.
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Offline DarkenedOne

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Guys remember we are talking about a depot here.  Its not going anywhere so it will only cost you on getting it up there.  Once it is built hopefully we can expect a reasonable long lifespan of like 15-20 years, which is the typical lifespan of most satellites.

Secondly that is 700 bar at room temperature.  Assuming you use a sun shield you can probably maintain the tanks at a temperature at -100 C, which would decrease the pressure proportionately according to the ideal gas law. 

Lastly for comparison you have to factor in the insulation and boil off of cryogenic tanks. 

Offline Jim

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Guys remember we are talking about a depot here.  Its not going anywhere so it will only cost you on getting it up there.  Once it is built hopefully we can expect a reasonable long lifespan of like 15-20 years, which is the typical lifespan of most satellites.

Secondly that is 700 bar at room temperature.  Assuming you use a sun shield you can probably maintain the tanks at a temperature at -100 C, which would decrease the pressure proportionately according to the ideal gas law. 

Lastly for comparison you have to factor in the insulation and boil off of cryogenic tanks. 

and a compressors and power supplies for them on the depot, along with the extra mass of the tanks on the receiving vehicles makes this unfeasible.

The extra insulation pales compared to the extra mass of high pressure tanks.  Boil off will be used for station keeping and attitude control and can be used for power production.

Offline RocketmanUS

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As tank mass increases so would the amount of propellent needed for station keeping.

ACES depots concept are to make the depot cheap enough to be able to dispose of them. They don't have to last for long periods of time. This has an advantage to upgrade them over time as practical. Life span also has to do with how many time the tanks are designed to be refueled. Longer life span could mean greater tank mass and design, and the tanks no longer in common with the ACES upper stage for manufacturing ( higher over all costs ).

The amount of energy that might be needed to liquify and cool down GH2 to LH2, you might as well just add a recooler for the H2 boil off. However that GH2 is used for station keeping.

Guys remember we are talking about a depot here.  Its not going anywhere so it will only cost you on getting it up there.  Once it is built hopefully we can expect a reasonable long lifespan of like 15-20 years, which is the typical lifespan of most satellites.

Secondly that is 700 bar at room temperature.  Assuming you use a sun shield you can probably maintain the tanks at a temperature at -100 C, which would decrease the pressure proportionately according to the ideal gas law. 

Lastly for comparison you have to factor in the insulation and boil off of cryogenic tanks. 

and a compressors and power supplies for them on the depot, along with the extra mass of the tanks on the receiving vehicles makes this unfeasible.

The extra insulation pales compared to the extra mass of high pressure tanks.  Boil off will be used for station keeping and attitude control and can be used for power production.
As I was typing my post , Jim posted.

To add, greater size tanks also mean greater size in Sun shield too.

For LEO or EML1/2 depots , power will most likely be by solar panels.

Offline Lee Jay

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Have a look here:

http://www.qtww.com/assets/u/129LTankBrochure.pdf

Note the mass of the tank and the mass of hydrogen it stores, as well as the service life.
« Last Edit: 11/08/2012 01:14 am by Lee Jay »

Offline RocketmanUS

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Have a look here:

http://www.qtww.com/assets/u/129LTankBrochure.pdf

Note the mass of the tank and the mass of hydrogen it stores, as well as the service life.

What would it's mass be to store 52,881.61 cu ft?

Five years of life! How many refills is it rated for?

At 70MPa , what is the leak rate of the hydrogen per week, per month?

Offline DarkenedOne

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I suppose it all comes down to the boil off.  The problem is that many of you are assuming small storage times.  For a big mission especially a Mars mission it could take several heavy lift launch vehicles to provide the propellant.  Launching them would likely take several months. 
« Last Edit: 11/08/2012 01:27 am by DarkenedOne »

Offline Lee Jay

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I suppose it all comes down to the boil off.  The problem is that many of you are assuming small storage times.  For a big mission especially a Mars mission it could take several heavy lift launch vehicles to provide the propellant.  Launching them would likely take several months. 

You are assuming the leak rate from a compressed H2 tank is zero.  I don't think that's a good assumption.

Offline Jim

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I suppose it all comes down to the boil off.  The problem is that many of you are assuming small storage times.  For a big mission especially a Mars mission it could take several heavy lift launch vehicles to provide the propellant.  Launching them would likely take several months. 

wrong, that is still "small storage times"  Anyways, if you are talking that amount of H2, then high pressure storage is even less viable.  The mass of the tanks is even worse.  Also, you still haven't addressed the compressor.

Offline DarkenedOne

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I suppose it all comes down to the boil off.  The problem is that many of you are assuming small storage times.  For a big mission especially a Mars mission it could take several heavy lift launch vehicles to provide the propellant.  Launching them would likely take several months. 

You are assuming the leak rate from a compressed H2 tank is zero.  I don't think that's a good assumption.

Well maybe not, but some estimate the boil off rates of liquid hydro to be as much as 3.8% per month.  I do not think that the compressed H2 leakage is that high, but I could be wrong. 

Offline kkattula

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I suppose it all comes down to the boil off.  The problem is that many of you are assuming small storage times.  For a big mission especially a Mars mission it could take several heavy lift launch vehicles to provide the propellant.  Launching them would likely take several months. 

Please.  Do the math.
 
A GH2 tank is going to mass at least 10 times the hydrogen it holds.
 
A LH2 tank is going to mass about 1/10 of the hydrogen it holds.
 
So if you need 500 tons of LH2 for e.g. a Mars mission, would you rather launch a 5000 ton depot, a massive liquifier plant, and 500 tons of GH2?
 
Or a less than 100 ton depot, 1000 tons of LH2, and let half of it boil-off? Or a slightly heavier depot that can reduce boil-off to say 100 tons?

Offline DarkenedOne

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I suppose it all comes down to the boil off.  The problem is that many of you are assuming small storage times.  For a big mission especially a Mars mission it could take several heavy lift launch vehicles to provide the propellant.  Launching them would likely take several months. 

wrong, that is still "small storage times"  Anyways, if you are talking that amount of H2, then high pressure storage is even less viable.  The mass of the tanks is even worse.  Also, you still haven't addressed the compressor.

Compressor is not needed.  Assuming the hydrogen is shipped to the depot as a liquid which would make the most sense, then the liquid will pressurize the tank as it boils to reach equilibrium.   

Offline Jim

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Compressor is not needed.  Assuming the hydrogen is shipped to the depot as a liquid which would make the most sense, then the liquid will pressurize the tank as it boils to reach equilibrium.   

So, after the first shipment of H2 is in the depot at pressure, how does the LH2 in the second shipment get from the delivery vehicle into the depot?
« Last Edit: 11/08/2012 01:54 am by Jim »

Offline RocketmanUS

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I suppose it all comes down to the boil off.  The problem is that many of you are assuming small storage times.  For a big mission especially a Mars mission it could take several heavy lift launch vehicles to provide the propellant.  Launching them would likely take several months. 

You are assuming the leak rate from a compressed H2 tank is zero.  I don't think that's a good assumption.

Well maybe not, but some estimate the boil off rates of liquid hydro to be as much as 3.8% per month.  I do not think that the compressed H2 leakage is that high, but I could be wrong. 

Boil off and leakage are two different issues.

I suppose it all comes down to the boil off.  The problem is that many of you are assuming small storage times.  For a big mission especially a Mars mission it could take several heavy lift launch vehicles to provide the propellant.  Launching them would likely take several months. 

wrong, that is still "small storage times"  Anyways, if you are talking that amount of H2, then high pressure storage is even less viable.  The mass of the tanks is even worse.  Also, you still haven't addressed the compressor.

Compressor is not needed.  Assuming the hydrogen is shipped to the depot as a liquid which would make the most sense, then the liquid will pressurize the tank as it boils to reach equilibrium.   
Compressor needed to make LH2 from the GH2 for the EDS.
And how big of a power system is that going to be? ( more added mass )

Offline Lee Jay

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I suppose it all comes down to the boil off.  The problem is that many of you are assuming small storage times.  For a big mission especially a Mars mission it could take several heavy lift launch vehicles to provide the propellant.  Launching them would likely take several months. 

You are assuming the leak rate from a compressed H2 tank is zero.  I don't think that's a good assumption.

Well maybe not, but some estimate the boil off rates of liquid hydro to be as much as 3.8% per month.  I do not think that the compressed H2 leakage is that high, but I could be wrong. 


If you need a long-term depot, you have to reduce the boiloff.  That can be done, if necessary (see JWST).

Offline DarkenedOne

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I suppose it all comes down to the boil off.  The problem is that many of you are assuming small storage times.  For a big mission especially a Mars mission it could take several heavy lift launch vehicles to provide the propellant.  Launching them would likely take several months. 

Please.  Do the math.
 
A GH2 tank is going to mass at least 10 times the hydrogen it holds.
 
A LH2 tank is going to mass about 1/10 of the hydrogen it holds.
 
So if you need 500 tons of LH2 for e.g. a Mars mission, would you rather launch a 5000 ton depot, a massive liquifier plant, and 500 tons of GH2?
 
Or a less than 100 ton depot, 1000 tons of LH2, and let half of it boil-off? Or a slightly heavier depot that can reduce boil-off to say 100 tons?

You should do the math first before you ask someone else to, instead of using wild guesses. 

The tank mass to hydrogen mass depends on the size of the tank.  The tanks mass scales proportionally to its surface area, where as the mass of the hydrogen it contains scales proportionally to the tank's volume.  For a tank of any reasonable shape the volume of the tank will increase faster than the surface area. 

Lets take a look at the hydrogen tank Lee made a link to.   It has a tank mass to hydrogen mass ratio of about 18.4:1, and it is only 1.6 meters long.  Lets suppose the radius and diameter were increase by 10 times.  Then its surface area would increase by 100 times, and thus the weight of the tank would increase by 100 times.  However the tanks volume would increase 1000 times, thus the hydrogen's mass would increase 1000 times.  The ratio of the tank mass to hydrogen mass would then be  1.84:1. 

So there I did "the math." 

Offline DarkenedOne

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Compressor is not needed.  Assuming the hydrogen is shipped to the depot as a liquid which would make the most sense, then the liquid will pressurize the tank as it boils to reach equilibrium.   

So, after the first shipment of H2 is in the depot at pressure, how does the LH2 in the second shipment get from the delivery vehicle into the depot?

Such a depot would need multiple tanks.  Unless the tank was launched by a rocket substantially bigger than the ones that launch the delivery vehicles than you are pretty much going to have a one to one ratio.  Remember the LH2 in the delivery vehicle will expand two times when it boils.  One tank will be able to hold the contains of one only delivery vehicle. 

Of course there is no issue with a depot with multiple tanks. 

Offline RocketmanUS

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Compressor is not needed.  Assuming the hydrogen is shipped to the depot as a liquid which would make the most sense, then the liquid will pressurize the tank as it boils to reach equilibrium.   

So, after the first shipment of H2 is in the depot at pressure, how does the LH2 in the second shipment get from the delivery vehicle into the depot?

Such a depot would need multiple tanks.  Unless the tank was launched by a rocket substantially bigger than the ones that launch the delivery vehicles than you are pretty much going to have a one to one ratio.  Remember the LH2 in the delivery vehicle will expand two times when it boils.  One tank will be able to hold the contains of one only delivery vehicle. 

Of course there is no issue with a depot with multiple tanks. 
multiply tanks = greater mass, greater surface area for H2 leakage, added plumbing, and added cost.

Offline A_M_Swallow

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The Mars Transfer Vehicle also has to handle boil off.  For a 1000 day trip the boil off has to be less than 0.01% per day of the full tank if 90% of the fuel is needed for the return burn.

Offline Lee Jay

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The tanks mass scales proportionally to its surface area,

No, it doesn't.  The hoop stress goes with radius.  Therefore the wall thickness goes with radius.  You assumed the thickness was constant above.

Offline pippin

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So there I did "the math." 
OK, you did the maths but you did not do the physics.
The force on the tank hull increases with the tank size which means the wall thickness (assuming constant pressure as you do) also grows linearly and all of a sudden your tank weight grows to the 3rd order like your volume does. No gain in making the tank bigger.

Oops. Lee Jay beat me to it.

Edit 2: Let's start with the basics: https://en.wikipedia.org/wiki/Barlow%27s_formula
« Last Edit: 11/08/2012 02:52 am by pippin »

Offline RocketmanUS

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The tanks mass scales proportionally to its surface area,

No, it doesn't.  The hoop stress goes with radius.  Therefore the wall thickness goes with radius.  You assumed the thickness was constant above.
Using the info from this link that was given before
http://www.qtww.com/assets/u/129LTankBrochure.pdf

What would the mass be using that material to make a tank the size of the shuttles ET? Lets see how it compares to the material used to make the SLWT.

Offline strangequark

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The tanks mass scales proportionally to its surface area,

No, it doesn't.  The hoop stress goes with radius.  Therefore the wall thickness goes with radius.  You assumed the thickness was constant above.
Using the info from this link that was given before
http://www.qtww.com/assets/u/129LTankBrochure.pdf

What would the mass be using that material to make a tank the size of the shuttles ET? Lets see how it compares to the material used to make the SLWT.

Tank factor for this is:

P*V/(m*g0)=(70 MPa*129 L)/(92 kg * 9.81 m/s^2)=10km, pretty typical, if a little conservative, for COPV

Tank factor for the SLWT hydrogen tank is:

(230 kPa*1497 m^3)/(~19000kg*9.81 m/s^2)=1.8km

ET has more demands on it though, and that includes its proportional share of interstage mass.
« Last Edit: 11/08/2012 03:25 am by strangequark »

Offline RocketmanUS

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Another option would be to launch water and store it at a LEO depot.
Only one type of tanker needed ( water ).
Split the water into H2 and O2 then convert it into LH2 and LOX.

Now that would keep the storage tank at a similar size to using the LH2 and LOX tanks.

However there would be the need of all that extra equipment in space.
It would take time to convert the water into propellent and the EDS would need to be in orbit to store the newly made propellent or additional tanks would need to be at the depot.

Then there is the need to convert some of the water into propellent for station keeping.

So the ACES concept is the better way to go.
Launch it when we need it.
Low enough cost to dispose of it if it is not needed for a given period of time ( might be less cost to dispose than to launch more LH2 for station keeping ).
Has upgrade possibilities, and is common with the ACES upper stage.

The tanks mass scales proportionally to its surface area,

No, it doesn't.  The hoop stress goes with radius.  Therefore the wall thickness goes with radius.  You assumed the thickness was constant above.
Using the info from this link that was given before
http://www.qtww.com/assets/u/129LTankBrochure.pdf

What would the mass be using that material to make a tank the size of the shuttles ET? Lets see how it compares to the material used to make the SLWT.

Tank factor for this is:

P*V/(m*g0)=(70 MPa*129 L)/(92 kg * 9.81 m/s^2)=10km, pretty typical, if a little conservative, for COPV

Tank factor for the SLWT hydrogen tank is:

(230 kPa*1497 m^3)/(~19000kg*9.81 m/s^2)=1.8km

ET has more demands on it though, and that includes its proportional share of interstage mass.
What did you calculate for?

I was asking what the mass would be if a tank was to be made the size of the shuttle ET out of the same material as that tank in the link, just scaled up in size ( no added figuring in extra strength for it's larger size )?

Offline john smith 19

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Have a look here:

http://www.qtww.com/assets/u/129LTankBrochure.pdf

Thanks for that. It's good to put numbers on these sorts of ideas.

I recall the big GHe purge tanks on the SSME weighed 270lbs and carried 30lb of GHe,IE about 11% of tank mass (but at somewhere around 3-4Ksi IIRC). But those were aerospace grade spherical and this is built to survive a car crash (I presume) as its for automotive use.

Note also that the USAF (and AFAIK NASA) classify high pressure tanks by their TNT equivalent mass. IE if it fails what is the equivalent mass of TNT that would simulate it. This applies to *any* tank, even ones with inert gasses like N2 OR He.

So they'd be viewed as heavy, expensive, difficult to build in LV tank sizes and a very big explosion hazard if you did.

Bottom line. Not a good idea *unless* you need to drive some pneumatic powered machinery for a *very* long time or you want to build the solar systems biggest pressure fed rocket.

I think a propellent depot in SS301 (what Centaur tanks are made of and 1/10 the thermal conductivity of Aluminum alloy) wins hands down.
« Last Edit: 11/08/2012 07:22 am by john smith 19 »
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Offline DarkenedOne

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Compressor is not needed.  Assuming the hydrogen is shipped to the depot as a liquid which would make the most sense, then the liquid will pressurize the tank as it boils to reach equilibrium.   

So, after the first shipment of H2 is in the depot at pressure, how does the LH2 in the second shipment get from the delivery vehicle into the depot?

Such a depot would need multiple tanks.  Unless the tank was launched by a rocket substantially bigger than the ones that launch the delivery vehicles than you are pretty much going to have a one to one ratio.  Remember the LH2 in the delivery vehicle will expand two times when it boils.  One tank will be able to hold the contains of one only delivery vehicle. 

Of course there is no issue with a depot with multiple tanks. 
multiply tanks = greater mass, greater surface area for H2 leakage, added plumbing, and added cost.

Your right.  That problem exists with liquid hydrogen storage as well.  You might get sightly more than a one to one ratio.  You might get something like a 1.5 to 1 ratio, but the problem is the same.  Hydrogen and even liquid hydrogen has very low density.  The trouble is building and deploying large tanks in space.

Perhaps we should design and build a very large rocket for a few tens of billions that we will use for this one purpose.  Oh wait that is what they are doing for SLS, and what they did for Apollo.  In both projects the cost of the rocket is by far the largest expensive of the program.

Yes having a single depot with multiple tanks, or having multiple depots flying in the same orbit will cost more than a single depot with one massive tank launched by a massive rocket when you fail to take into account the cost of developing such a rocket.

Offline Jim

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Such a depot would need multiple tanks.  Unless the tank was launched by a rocket substantially bigger than the ones that launch the delivery vehicles than you are pretty much going to have a one to one ratio.  Remember the LH2 in the delivery vehicle will expand two times when it boils.  One tank will be able to hold the contains of one only delivery vehicle. 
 

wrong and False assumptions in your scenario in reqarding H2 transfer and storage.  A compressor will be required, period.  No ifs, ands or buts about it.
The movement of GH2 will require a pressure differential.  For tanks near the same size with one full and one empty, the gas will move from the one to the other until the pressure is equal.  So using your 700 bar baseline, either the depot would have to be at 1400 bar to get 700 bar in the receiving tank or the other is case is 700 and 350. 

So then you say that the depot will have larger tank volume.  Ok, then what happens when it does get down to the same pressure as the receiving tank.  How are you going to get LH2 into it to replenish it?  The depot tanks are still going to be at a high pressure (the same pressure as the receiving tanks were at)

This idea is not unworkable as described.  Once it is made it workable, it becomes unfeasible.

« Last Edit: 11/08/2012 11:50 am by Jim »

Offline Jim

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The trouble is building and deploying large tanks in space.

That is not a problem.  It is easy.  Empty tanks don't weight much.  Delta and Atlas could launch tanks as large or even larger than their existing large fairings.  These tanks would be many times larger than their upperstages. 

Offline kevin-rf

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Another option would be to launch water and store it at a LEO depot.
Only one type of tanker needed ( water ).
Split the water into H2 and O2 then convert it into LH2 and LOX.

Only problem with that approach is Rocket engines burn fuel rich, so you will need more LH than would be generated by cracking water and using all the heavier O2. You either are mass inefficient and launch more O2 (locked in the H2O) or you launch extra LH.
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Offline Lee Jay

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Another option would be to launch water and store it at a LEO depot.
Only one type of tanker needed ( water ).
Split the water into H2 and O2 then convert it into LH2 and LOX.

Only problem with that approach is Rocket engines burn fuel rich, so you will need more LH than would be generated by cracking water and using all the heavier O2. You either are mass inefficient and launch more O2 (locked in the H2O) or you launch extra LH.

What if you also had some liquid ammonia.  You could electrochemically reform that into hydrogen and nitrogen.  Now you've got more H2, a smaller amount of excess O2 and some excess N2 as well.  The humans on board might enjoy that combination.

Offline wolfpack

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Another option would be to launch water and store it at a LEO depot.
Only one type of tanker needed ( water ).
Split the water into H2 and O2 then convert it into LH2 and LOX.

Assuming you use solar power to electrochemically decompose the liquid water into GH2 and GO2, how do you liquify those into LH2 and LO2? Don't you need compressors and heat exchangers?

Offline JohnFornaro

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I suppose it all comes down to the boil off.   
Also, you still haven't addressed the compressor.

A GH2 tank is going to mass at least 10 times the hydrogen it holds.

Address the mass of the compressor, and the mass of the tanks.


Compressor is not needed.  Assuming the hydrogen is shipped to the depot as a liquid which would make the most sense, then the liquid will pressurize the tank as it boils to reach equilibrium.   

So, after the first shipment of H2 is in the depot at pressure, how does the LH2 in the second shipment get from the delivery vehicle into the depot?

Again, address the compressor.

However the tanks volume would increase 1000 times, thus the hydrogen's mass would increase 1000 times.  The ratio of the tank mass to hydrogen mass would then be  1.84:1. 

Address the structure of the tank, which is not just a hollow structure.  Address porosity and leakage.

The tanks mass scales proportionally to its surface area,

No, it doesn't.  The hoop stress goes with radius.  Therefore the wall thickness goes with radius.  You assumed the thickness was constant above.

Address the structure of the tank.
Sometimes I just flat out don't get it.

Offline Lee Jay

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The tanks mass scales proportionally to its surface area,

No, it doesn't.  The hoop stress goes with radius.  Therefore the wall thickness goes with radius.  You assumed the thickness was constant above.

Address the structure of the tank.

The wall is the structure.

Offline Robotbeat

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Guys, the mass ratio of a pressure vessel, to first order, doesn't depend on the scale. For compressed hydrogen, it's going to suck no matter what. Why is this conversation still going on?
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

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Offline kkattula

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The tanks mass scales proportionally to its surface area,

No, it doesn't.  The hoop stress goes with radius.  Therefore the wall thickness goes with radius.  You assumed the thickness was constant above.

So there I did "the math." 
OK, you did the maths but you did not do the physics.
The force on the tank hull increases with the tank size which means the wall thickness (assuming constant pressure as you do) also grows linearly and all of a sudden your tank weight grows to the 3rd order like your volume does. No gain in making the tank bigger.

Oops. Lee Jay beat me to it.
...

What they said. :)

To a first approximation, at the same pressure, tank mass scales with volume.

Look at it this way:  You have a tank with 300 times the pressure, holding a propellant with half the density. How much heavier do you think the GH2 tank would have to be for the same mass of H2?

Offline kkattula

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Guys, the mass ratio of a pressure vessel, to first order, doesn't depend on the scale. For compressed hydrogen, it's going to suck no matter what. Why is this conversation still going on?

Educating the 'masses'.  ;)   
« Last Edit: 11/08/2012 02:35 pm by kkattula »

Offline cambrianera

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There is an interesting tidbit using Barlow's formula (see pippin's post)
P=2*s*t/D
where P=internal pressure s=strenght of wall material t=thickness of the wall D=diameter of the cylindrical section

Mass of tank is
m1=L*2*pi*D*t*d1
where L=lenght of the cylindrical section d1=density of wall material

Mass of fluid is
m2=L*pi*D^2*d2/4
where d12=density of the fluid

Solving Barlow's formula for t:
t=P*D/(2*s)

substituting in mass of tank:
m1=L*pi*D^2*d1*P/s

Ratio of masses is:
m1/m2= 4*(d1/d2)*(P/s)

This is adimensional (you can use metric or imperial, once you use same unit before and after the / sign)
No dimension effect (diameter of the tank doesn't remain in the equation)
Another curiosity is compressing gases isn't an advantage on tank mass: increasing d2 you proportionally increase P and m1/m2 remains unchanged. It's an advantage on tank volume only.
Clearly this math is simplified, (true for cylindrical sections without domes) but the results are nonetheless valid for the general situation.
 
« Last Edit: 11/09/2012 06:01 pm by cambrianera »
Oh to be young again. . .

Offline Robotbeat

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Precisely.
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

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Offline DarkenedOne

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Another option would be to launch water and store it at a LEO depot.
Only one type of tanker needed ( water ).
Split the water into H2 and O2 then convert it into LH2 and LOX.

Only problem with that approach is Rocket engines burn fuel rich, so you will need more LH than would be generated by cracking water and using all the heavier O2. You either are mass inefficient and launch more O2 (locked in the H2O) or you launch extra LH.

What if you also had some liquid ammonia.  You could electrochemically reform that into hydrogen and nitrogen.  Now you've got more H2, a smaller amount of excess O2 and some excess N2 as well.  The humans on board might enjoy that combination.

Have you people bothered to compute the energy it would take to drive the reactions you are talking about?  "The enthalpy of combustion for hydrogen is −286 kJ/mol."  Thus by the laws of energy conservation breaking the bond will take at least that much energy.  That comes out to 16MJ per kg. 

Not saying its not doable, but the energy required to compress hydrogen pails in comparison to the energy required to break these chemical bonds.   

Offline Lee Jay

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Another option would be to launch water and store it at a LEO depot.
Only one type of tanker needed ( water ).
Split the water into H2 and O2 then convert it into LH2 and LOX.

Only problem with that approach is Rocket engines burn fuel rich, so you will need more LH than would be generated by cracking water and using all the heavier O2. You either are mass inefficient and launch more O2 (locked in the H2O) or you launch extra LH.

What if you also had some liquid ammonia.  You could electrochemically reform that into hydrogen and nitrogen.  Now you've got more H2, a smaller amount of excess O2 and some excess N2 as well.  The humans on board might enjoy that combination.

Have you people bothered to compute the energy it would take to drive the reactions you are talking about?

Absolutely, I have.  In great detail, in fact.  It's fun topic on which to do thought experiments.

Offline JohnFornaro

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The tanks mass scales proportionally to its surface area,

No, it doesn't.  The hoop stress goes with radius.  Therefore the wall thickness goes with radius.  You assumed the thickness was constant above.

Address the structure of the tank.

The wall is the structure.

A simple one layer structure is not sufficient. 

but the energy required to compress hydrogen [pales] in comparison to the energy required to break these chemical bonds.

Goal post relocation alert.
Sometimes I just flat out don't get it.

Offline Warren Platts

Even if you have a compressed gas depot, you still need a cryocooling system to make LH2/LO2 for whatever rocket in question that takes delivery of the fuel.

Q: How much energy does it take, practically, to liquify a kg of H2?
"When once you have tasted flight, you will forever walk the earth with your eyes turned skyward, for there you have been, and there you will always long to return."--Leonardo Da Vinci

Online guckyfan

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Even if you have a compressed gas depot, you still need a cryocooling system to make LH2/LO2 for whatever rocket in question that takes delivery of the fuel.

Q: How much energy does it take, practically, to liquify a kg of H2?

And if you have a cryocooling system you can store LH2 and recool the boiloff only. Should be easier.


Offline DarkenedOne

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but the energy required to compress hydrogen [pales] in comparison to the energy required to break these chemical bonds.

Goal post relocation alert.

Just pointing things into perspective.  I ran the numbers, and I do not see the power for compression being a big issue, but I am not going to argue with Jim on the subject because he probably know more about it than I.   

However if people believe that the power to compress hydrogen would make a compressed hydrogen satellite unfeasible than they should not then start talking about methods of storing hydrogen that require even more power.

Offline RocketmanUS

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but the energy required to compress hydrogen [pales] in comparison to the energy required to break these chemical bonds.

Goal post relocation alert.

Just pointing things into perspective.  I ran the numbers, and I do not see the power for compression being a big issue, but I am not going to argue with Jim on the subject because he probably know more about it than I.   

However if people believe that the power to compress hydrogen would make a compressed hydrogen satellite unfeasible than they should not then start talking about methods of storing hydrogen that require even more power.
What methods are you referring to that would require more power to store hydrogen?

Offline Warren Platts

Much of the discussion regarding fuel storage in space involves liquid hydrogen and oxygen.  What I have been wondering is why not simply store the hydrogen an oxygen in compressed form.  Doing so completely eliminates the problem of long time storage as extremely low temperatures do not need to be maintained.  Now at 700 bar the density of hydrogen at room temperature is only half that of its liquid state, so you would need bigger tanks. 

Now that is just for storage.  For use the gases can be liquified again, and used in a traditional LH2/LO engine.  Another possibility would be to keep it in gas form and just build rocket engines that run on the gas.  Such a engine would not be as powerful, but it should in theory produce the same specific impulse. 

Actually, now that I think about it, this concept could actually be useful at a place like the Lunar surface in the context of an ISRU program. After all, after cracking dihydrogen monoxide, the resultant products are in gaseous form, and so have to be stored for at least a little while before they are converted to liquid form.

If the tanks were made from Lunar steel, the mass wouldn't be a problem. But in the initial stages of a Lunar base, the capability to store gases might be so important so as to be worth it to import a tank or two from Earth.

Thus, a useful tidbit of information would be the storage capability and volume of a 25 mT tank that could store gases at 2000 psi....
"When once you have tasted flight, you will forever walk the earth with your eyes turned skyward, for there you have been, and there you will always long to return."--Leonardo Da Vinci

Offline HMXHMX

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Much of the discussion regarding fuel storage in space involves liquid hydrogen and oxygen.  What I have been wondering is why not simply store the hydrogen an oxygen in compressed form.  Doing so completely eliminates the problem of long time storage as extremely low temperatures do not need to be maintained.  Now at 700 bar the density of hydrogen at room temperature is only half that of its liquid state, so you would need bigger tanks. 

Now that is just for storage.  For use the gases can be liquified again, and used in a traditional LH2/LO engine.  Another possibility would be to keep it in gas form and just build rocket engines that run on the gas.  Such a engine would not be as powerful, but it should in theory produce the same specific impulse. 

Actually, now that I think about it, this concept could actually be useful at a place like the Lunar surface in the context of an ISRU program. After all, after cracking dihydrogen monoxide, the resultant products are in gaseous form, and so have to be stored for at least a little while before they are converted to liquid form.

If the tanks were made from Lunar steel, the mass wouldn't be a problem. But in the initial stages of a Lunar base, the capability to store gases might be so important so as to be worth it to import a tank or two from Earth.

Thus, a useful tidbit of information would be the storage capability and volume of a 25 mT tank that could store gases at 2000 psi....

At PV/W of about 2 million (in english units), with a safety factor of 2, using composites, the tank should be able to hold around 450 cubic meters or about 16K cubic feet of fluid.

Offline rklaehn

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I think the idea of gaseous H2/O2 storage has merit for ISRU on asteroids or phobos/deimos. While the mass ratio including the tank mass is not enough for large maneuvers like entering or leaving mars orbit, it is more than enough for "moving around".

One way to improve the mass ratio would be to cool the gases a bit (to whatever temperature you can reach with passive cooling without too much effort)

An initial application might be a secondary payload spacecraft that has to be inert during launch, but can make H2/O2 from water after it has separated from the main payload.

There is a company called orbitec that is working on an engine that burns gaseous H2/O2 at stoechiometric ratio.
http://www.orbitec.com/documents/SCORE_2006.pdf

Addition: for a secondary spacecraft in GTO that wants to go to the moon or mars it might make sense to use solar power to produce hydrogen for the duration of one orbit, and then expend it all at perigee to take maximum advantage of the oberth effect. This is a form of electric propulsion that needs less power than ion engines (less solar cell mass) and can use ISRU water, which is by definition available in most interesting locations.
« Last Edit: 11/11/2012 07:02 pm by rklaehn »

Offline vulture4

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A well insulated tank with a small cryocooler to remove leaking heat will have zero loss. There are space-rated cryocoolers for several cryogenic gasses and work is in progress to develop the technology for LH2. They usually use a separate helium loop for cooling rather then the working gas. Power requirement depends on the quality of insulation and sunshielding but can be quite manageable.
« Last Edit: 11/15/2012 10:56 pm by vulture4 »

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