High strength fibers for hydrogen storage on the VentureStar.

On Aug 9, 7:32 pm, Robert Clark wrote:
...

Another possible solution to having so many tubes release the
hydrogen in unison might be to have them bound together with one end
closed and the other end left open but with a cap over the open end of
all of them made of a high strength material to which would be
connected the controlling valve. Since the end cap would have a much
smaller size than the full tank you could afford to have it be thicker
so as to withstand the pressure of the fuel without it taking up too
much weight. You would need though to have a strong bond between the
material of the end cap and the material composing the separate
microtubes.


This article claims a solution to the composite tank problem for the
Venture Star/X-33 :

New Composite Hydrogen Fuel Tank For RLVs Successfully Tested.
Fuel tank problems on the X-33 Venture Star project were crtitical to
ending what was the last major new space transportation R&D program at
NASA.
Huntsville - Dec 22, 2003
http://www.space-travel.com/reports/...ly_Tested.html

This is after the 2001 program cancellation that was due to a
failure of those tanks so I assume this addressed the debonding
problems that weren't solved then.


Bob Clark

In article
,
wrote:

Hoop stresses of a tube under pressure increase with the diameter but
volume increases with the square of diameter. ?High volume/weight
pressurised gas storage would, therefore, favor a bigger cylinder.

. . .

Container weight scales with area times thickness, and
thickness scales with hoop stress,

But the area and volume increase with the diameter _squared_.

Assuming you are not talking about a squat cylinder with length much
less than diameter, no.

For a long cylinder, ignoring the endcaps and keeping the length the
same, the area is proportional to the diameter and the volume to the
diameter squared. Letting the length be proportional to the diameter
gives an area of diameter squared and a volume of diameter cubed.

Looking just at spherical endcaps, their volume goes as diameter cubed
and area as diameter squared.

--
David M. Palmer (formerly @clark.net, @ematic.com)

For a given volume the area is larger with a thin tube but the
thickness is greater with a larger dia tube at the same pressure.
These cancel so the diameter doesn't matter as far as weight/volume is
concerned.


Bret Cahill

On Jul 29, 12:59 pm, Robert Clark wrote:
Nice articles here on the problems that led to the cancellation of the
VentureStar/X-33, a single-stage to orbit vehicle:

Lockheed Martin X-33.http://en.wikipedia.org/wiki/Lockheed_Martin_X-33

X-33/VentureStar - What really happened.http://www.nasaspaceflight.com/content/?id=4180

Interestingly the main problem was making the liquid hydrogen tanks
light enough, certainly not ahightech problem. I wonder if
lightweight storage could be achieved by storing the hydrogen in very
many micron-scale hollow fibers. See the table of tensile strengths
listed he

Tensilestrength.http://en.wikipedia.org/wiki/Tensile_strength

The solutions investigated for the hydrogen tanks for VentureStar
included usinghighstrengthaluminum alloys or composite fiber tanks.
The composite tanks were lighter but had a problem of debonding underhighpressure. Note in the table of tensile strengths carbon fiber has
a betterstrengthto weight ratio than the aluminum alloy listed by a
factor of 19 to 1. And thehighstrengthglass fibers known as S-glass
is better than the aluminum alloy by 10 to 1. There is also a special
steel fiber known as scifer steel not listed in the table that has a
tensilestrengthof 5500 MPa at a density of 7.8 g/cc. That is better
than aluminum alloy by a factor of 4 to 1. It might even be for the
carbon fibers and the S-glass fibers theirstrengthto weight ratios
are sohighyou wouldn't need to store the hydrogen in liquid form.
You could store it ashighdensity gas. That would eliminate the
weight of the cryogenic systems for the hydrogen.
However, a key question here is whether thisstrengthwill be
maintained in the radial direction. All the strengths listed for the
fibers are for pulling along their lengths, i.e, their longitudinal
tensilestrength. But to use the fibers as thin hollow pressure tubes
will require theirstrengthto hold in the radial direction. After
investigating this question before for hydrogen storage, I know that S-
glass and scifer steel fibers do retain thatstrengthin the radial
directions. I'm not sure if this is true for the carbon fiber. (BTW,
thehighstrengthpolymer fibers listed in the table such as Kevlar,
Dyneema, or Spectra are unsuitable because theirstrengthonly holds
in the longitudinal direction, not radially.)
Another key problem for usinghighstrengthfibers as hollow tubes is
that they are only about 10 microns wide. So millions to billions of
them would be needed to form sizable storage tanks. You would need a
method of opening and closing these microscopically thin tubes at the
same time for a throttleable engine. Perhaps one solution would be to
have only a small portion of them being used at any one time and
letting those completely empty out, then open another portion, and so
on until all the fuel is used up. This would be an easier solution
than having so many precisely controlled valves at the micro-scale
that operated all in unison.

Bob Clark

Another solution for releasing the hydrogen in unison comes from the
method of storing hydrogen in glass microspheres:

A future for glass in a hydrogen economy?
Researchers envision tiny spheres storing the gas in cars.
http://www.msnbc.msn.com/id/5343023/

These glass microspheres, about 50 microns across, can store hydrogen
at high pressure. They can be made to release the hydrogen on demand
by exposure to high intensity light. It might be the method of using
very many of the microspheres can itself be used for the hydrogen
tanks on the VentureStar. However, I prefer the method of many glass
microtubes since it would be easier to release the hydrogen in one
direction by illuminating just the front ends of the tubes that are
connected to the fuel lines that are connected to the engine.
This paper shows the possible strength of the microspheres:

Advancing the Hydrogen Infrastructure Using Stronger Glass.
http://www.gmic.org/Student%20Contes...er%20Glass.doc

This page gives the dimensions of the hydrogen and LOX tanks on the
X-33:

X-33 Program in the Midst of Final Testing and Validation of Key
Components.
http://www.xs4all.nl/~carlkop/x33.html

The twin hydrogen tanks weigh 4,600 pounds each and the single LOX
tank weighs 6,000 pounds. Since the X-33 is a 1/2-scale version of the
VentureStar, the VentureStar tank dimensions would be twice as large
so their mass would be 8 times as great, so 73,800 pounds total for
the two liquid hydrogen tanks and 48,000 pounds for the liquid oxygen
tank. That's a mass of 121,600 pounds for the empty tanks alone. Using
the S-glass fibers that has a 10 to 1 better strength to weight ratio
for the tanks, the weight would be reduced to 12,000 pounds. That's a
more than 100,000 pound saving in weight. That saving in weight could
go to extra payload. The stated payload for VentureStar was 45,000
pounds. Then with these lighter tanks its payload could be increased
to 145,000 pounds.
However, the estimate I gave for the weight of the VentureStar tanks
(I wasn't able to find the exact values) was based on their thickness
increasing in the same proportion as the other dimensions over those
of the X-33, i.e., by a factor of 2. This would mean the pressure the
VentureStar tanks would be able to withstand would be the same as
those of the X-33. However, the weight being increased by a factor of
8 and the surface area being increased by a factor of 4 means the
pressures involved would actually be greater than those of the X-33 by
a factor of 2. Then an additional factor of 2 in thickness may be
required. Still this would only give a total mass of the tanks with
the stronger S-glass material of 24,000 pounds. Then the payload could
still be increased to be more than 130,000 pounds.


Bob Clark

On Aug 17, 7:42 pm, Robert Clark wrote:

Another solution for releasing the hydrogen in unison comes from the
method of storing hydrogen in glass microspheres:

A future for glass in a hydrogen economy?
Researchers envision tiny spheres storing the gas in cars.http://www.msnbc.msn.com/id/5343023/

These glass microspheres, about 50 microns across, can store hydrogen
at high pressure. They can be made to release the hydrogen on demand
by exposure to high intensity light. It might be the method of using
very many of the microspheres can itself be used for the hydrogen
tanks on the VentureStar. However, I prefer the method of many glass
microtubes since it would be easier to release the hydrogen in one
direction by illuminating just the front ends of the tubes that are
connected to the fuel lines that are connected to the engine.
This paper shows the possible strength of the microspheres:

Advancing the Hydrogen Infrastructure Using Stronger Glass.http://www.gmic.org/Student%20Contes...Contest%20Entr...

This page gives the dimensions of the hydrogen and LOX tanks on the
X-33:

X-33 Program in the Midst of Final Testing and Validation of Key
Components.http://www.xs4all.nl/~carlkop/x33.html

The twin hydrogen tanks weigh 4,600 pounds each and the single LOX
tank weighs 6,000 pounds. Since the X-33 is a 1/2-scale version of the
VentureStar, the VentureStar tank dimensions would be twice as large
so their mass would be 8 times as great, so 73,800 pounds total for
the two liquid hydrogen tanks and 48,000 pounds for the liquid oxygen
tank. That's a mass of 121,600 pounds for the empty tanks alone. Using
the S-glass fibers that has a 10 to 1 better strength to weight ratio
for the tanks, the weight would be reduced to 12,000 pounds. That's a
more than 100,000 pound saving in weight. That saving in weight could
go to extra payload. The stated payload for VentureStar was 45,000
pounds. Then with these lighter tanks its payload could be increased
to 145,000 pounds.
However, the estimate I gave for the weight of the VentureStar tanks
(I wasn't able to find the exact values) was based on their thickness
increasing in the same proportion as the other dimensions over those
of the X-33, i.e., by a factor of 2. This would mean the pressure the
VentureStar tanks would be able to withstand would be the same as
those of the X-33. However, the weight being increased by a factor of
8 and the surface area being increased by a factor of 4 means the
pressures involved would actually be greater than those of the X-33 by
a factor of 2. Then an additional factor of 2 in thickness may be
required. Still this would only give a total mass of the tanks with
the stronger S-glass material of 24,000 pounds. Then the payload could
still be increased to be more than 130,000 pounds.

Bob Clark

I don't like the estimate of the empty weight of the tanks for the
VentureStar of 121,600 lbs. This page compares the specifications of
the X-33 and the VentureStar:

MILNET: X-33 Aerospace Test Bed for VentureStar.
http://www.milnet.com/x-33.htm

It gives the fully fueled weight of the VentureStar as 2,186,000 lbs.
and the weight of the fuel alone as 1,929,000 lbs. So the empty weight
of the vehicle would be 257,000 lbs. This only a factor of 4 greater
than the empty weight of the X-33.
If the VentureStar tanks are 4 times as heavy as those of the X-33,
that would give them a total empty weight of 60,000 lbs. So if they
could be made 1/10th as heavy, the payload could be increased by
54,000 lbs. to about 100,000 lbs. If the tank thickness had to be
increased by an additional factor of 2, then the payload could still
be increased to about 90,000 lbs. Note also that lighter tanks would
mean lighter support structures for them so the increase in payload
might be more than this.


Bob Clark

On Aug 10, 9:15 am, Bret Cahill wrote:
Hoop stresses of a tube under pressure increase with the diameter but
volume increases with the square of diameter. High volume/weight
pressurised gas storage would, therefore, favor a bigger cylinder.

Bret Cahill

At the 1e-21 bar vacuum of our Selene/moon L1, the volume and/or
tonnage of that hydrogen gas storage is unlimited.

~ Brad Guth Brad_Guth Brad.Guth BradGuth

Hoop stresses of a tube under pressure increase with the diameter but
volume increases with the square of diameter. �High volume/weight
pressurised gas storage would, therefore, favor a bigger cylinder.

At the 1e-21 bar vacuum of our Selene/moon L1, the volume and/or
tonnage of that hydrogen gas storage is unlimited.

Several times I tried to design a lighter than air vacuum structure --
a _really_ worthless project -- but no material was strong/light
enough except maybe C nanotubes. All three times I determined that
there was no advantage either in scaling up or down. I somehow forgot
my own conclusion. Again.


Bret Cahill

On Aug 19, 10:23 am, Robert Clark wrote:
...
I don't like the estimate of the empty weight of the tanks for the
VentureStar of 121,600 lbs. This page compares the specifications of
the X-33 and the VentureStar:

MILNET: X-33 Aerospace Test Bed for VentureStar.http://www.milnet.com/x-33.htm

It gives the fully fueled weight of the VentureStar as 2,186,000 lbs.
and the weight of the fuel alone as 1,929,000 lbs. So the empty weight
of the vehicle would be 257,000 lbs. This only a factor of 4 greater
than the empty weight of the X-33.
If the VentureStar tanks are 4 times as heavy as those of the X-33,
that would give them a total empty weight of 60,000 lbs. So if they
could be made 1/10th as heavy, the payload could be increased by
54,000 lbs. to about 100,000 lbs. If the tank thickness had to be
increased by an additional factor of 2, then the payload could still
be increased to about 90,000 lbs. Note also that lighter tanks would
mean lighter support structures for them so the increase in payload
might be more than this.

Bob Clark

At the bottom of this page are given some images for the 3 competing
proposals for NASA's reusable launch vehicle:

NASA Dryden X-33 Advanced Technology Demonstrator Photo Collection.
http://www.dfrc.nasa.gov/gallery/photo/X-33/

The Rockwell proposal was quite similar to the Space Shuttle without
the external tank and solid rocket boosters. The McDonnell Douglas
proposal was the DC-X. And the Lockheed proposal was the VentureStar
which won the competition.
It is quite likely that for all the proposals the mass of the tanks
alone was a significant portion of the mass of the empty vehicle,
about 1/4 for the Space Shuttle and also for the half-scale Lockheed
X-33 suborbital test vehicle.
Then decreasing the weight of the tanks by 1/10th might make all three
proposals feasible.


Bob Clark

On Aug 19, 9:21 am, wrote:
Hoop stresses of a tube under pressure increase with the diameter but
volume increases with the square of diameter. High volume/weight
pressurised gas storage would, therefore, favor a bigger cylinder.
At the 1e-21 bar vacuum of our Selene/moon L1, the volume and/or
tonnage of that hydrogen gas storage is unlimited.

Several times I tried to design a lighter than air vacuum structure --
a _really_ worthless project -- but no material was strong/light
enough except maybe C nanotubes. All three times I determined that
there was no advantage either in scaling up or down. I somehow forgot
my own conclusion. Again.

Bret Cahill

Would you care to try again, on behalf of creating a composite rigid
airship intended for safely cruising about Venus?

Either a vacuum and/or a hydrogen displaced composite hull interior
would do rather nicely. A series of rigid spheres forming an airship
would become truly impressive, especially since the volumetric size
and mass are not the least bit significant factors.

Even that of a 99% hydrogen and 1% O2 cabin interior would become
entirely human survivable while parked near or on the surface of
Venus. A terrestrial application of 4% O2 and 96% H2 is perfectly
safe and sane, as having been more than proven to sustain human life
while under terrific pressure as is. France has for decades had a 68
bar (1000 psi) habitat chamber for further testing of such humanly
survivable environments.

Don’t forget that Venus also offers roughly 10% less gravity, and
there’s unlimited local energy to burn (so to speak), as well as
countless local minerals that are continually getting geothermally
contributed to that toasty surface and robust atmospheric environment.

btw, there’s already a complex tarmac of absolutely terrific size,
along with a substantial township of highrise structures and multiple
nearby reservoirs, plus a downright nifty bridge, not to mention that
nearby rigid airship and of its mostly underground facility, and
otherwise that rather nifty looking fluid arch that’ll knock your
socks off.

Would you care to review and deductively interpret the radar obtained
image, on behalf of any of this?

~ Brad Guth Brad_Guth Brad.Guth BradGuth

On Aug 17, 7:42 pm, Robert Clark wrote:
On Jul 29, 12:59 pm, Robert Clark wrote:



Nice articles here on the problems that led to the cancellation of the
VentureStar/X-33, a single-stage to orbit vehicle:

Lockheed Martin X-33.http://en.wikipedia.org/wiki/Lockheed_Martin_X-33

X-33/VentureStar- What really happened.http://www.nasaspaceflight.com/content/?id=4180

Interestingly the main problem was making the liquid hydrogen tanks
light enough, certainly not ahightech problem. I wonder if
lightweight storage could be achieved by storing the hydrogen in very
many micron-scale hollow fibers. See the table of tensile strengths
listed he

Tensilestrength.http://en.wikipedia.org/wiki/Tensile_strength

The solutions investigated for the hydrogen tanks forVentureStar
included usinghighstrengthaluminum alloys or composite fiber tanks.
The composite tanks were lighter but had a problem of debonding underhighpressure. Note in the table of tensile strengths carbon fiber has
a betterstrengthto weight ratio than the aluminum alloy listed by a
factor of 19 to 1. And thehighstrengthglass fibers known as S-glass
is better than the aluminum alloy by 10 to 1. There is also a special
steel fiber known as scifer steel not listed in the table that has a
tensilestrengthof 5500 MPa at a density of 7.8 g/cc. That is better
than aluminum alloy by a factor of 4 to 1. It might even be for the
carbon fibers and the S-glass fibers theirstrengthto weight ratios
are sohighyou wouldn't need to store the hydrogen in liquid form.
You could store it ashighdensity gas. That would eliminate the
weight of the cryogenic systems for the hydrogen.
However, a key question here is whether thisstrengthwill be
maintained in the radial direction. All the strengths listed for the
fibers are for pulling along their lengths, i.e, their longitudinal
tensilestrength. But to use the fibers as thin hollow pressure tubes
will require theirstrengthto hold in the radial direction. After
investigating this question before for hydrogen storage, I know that S-
glass and scifer steel fibers do retain thatstrengthin the radial
directions. I'm not sure if this is true for the carbon fiber. (BTW,
thehighstrengthpolymer fibers listed in the table such as Kevlar,
Dyneema, or Spectra are unsuitable because theirstrengthonly holds
in the longitudinal direction, not radially.)
Another key problem for usinghighstrengthfibers as hollow tubes is
that they are only about 10 microns wide. So millions to billions of
them would be needed to form sizable storage tanks. You would need a
method of opening and closing these microscopically thin tubes at the
same time for a throttleable engine. Perhaps one solution would be to
have only a small portion of them being used at any one time and
letting those completely empty out, then open another portion, and so
on until all the fuel is used up. This would be an easier solution
than having so many precisely controlled valves at the micro-scale
that operated all in unison.

Bob Clark

Another solution for releasing the hydrogen in unison comes from the
method of storing hydrogen in glass microspheres:

A future for glass in a hydrogen economy?
Researchers envision tiny spheres storing the gas in cars.http://www.msnbc.msn.com/id/5343023/

These glass microspheres, about 50 microns across, can store hydrogen
at high pressure. They can be made to release the hydrogen on demand
by exposure to high intensity light. It might be the method of using
very many of the microspheres can itself be used for the hydrogen
tanks on theVentureStar. However, I prefer the method of many glass
microtubes since it would be easier to release the hydrogen in one
direction by illuminating just the front ends of the tubes that are
connected to the fuel lines that are connected to the engine.
This paper shows the possible strength of the microspheres:

Advancing the Hydrogen Infrastructure Using Stronger Glass.http://www.gmic.org/Student%20Contes...Contest%20Entr...

This page gives the dimensions of the hydrogen and LOX tanks on the
X-33:

X-33 Program in the Midst of Final Testing and Validation of Key
Components.http://www.xs4all.nl/~carlkop/x33.html

The twin hydrogen tanks weigh 4,600 pounds each and the single LOX
tank weighs 6,000 pounds. Since the X-33 is a 1/2-scale version of theVentureStar, theVentureStartank dimensions would be twice as large
so their mass would be 8 times as great, so 73,800 pounds total for
the two liquid hydrogen tanks and 48,000 pounds for the liquid oxygen
tank. That's a mass of 121,600 pounds for the empty tanks alone. Using
the S-glass fibers that has a 10 to 1 better strength to weight ratio
for the tanks, the weight would be reduced to 12,000 pounds. That's a
more than 100,000 pound saving in weight. That saving in weight could
go to extra payload. The stated payload forVentureStarwas 45,000
pounds. Then with these lighter tanks its payload could be increased
to 145,000 pounds.
However, the estimate I gave for the weight of theVentureStartanks
(I wasn't able to find the exact values) was based on their thickness
increasing in the same proportion as the other dimensions over those
of the X-33, i.e., by a factor of 2. This would mean the pressure theVentureStartanks would be able to withstand would be the same as
those of the X-33. However, the weight being increased by a factor of
8 and the surface area being increased by a factor of 4 means the
pressures involved would actually be greater than those of the X-33 by
a factor of 2. Then an additional factor of 2 in thickness may be
required. Still this would only give a total mass of the tanks with
the stronger S-glass material of 24,000 pounds. Then the payload could
still be increased to be more than 130,000 pounds.

Bob Clark

New synthetic diamond particles might also be a good choice as
microspheres:

Brief Communications
Nature 421, 599-600 (6 February 2003)
Materials: Ultrahard polycrystalline diamond from graphite.
"Polycrystalline diamonds are harder and tougher than single-crystal
diamonds and are therefore valuable for cutting and polishing other
hard materials, but naturally occurring polycrystalline diamond is
unusual and its production is slow. Here we describe the rapid
synthesis of pure sintered polycrystalline diamond by direct
conversion of graphite under static high pressure and temperature.
Surprisingly, this synthesized diamond is ultrahard and so could be
useful in the manufacture of scientific and industrial tools."
http://www.nature.com/nature/journal...l/421599b.html

Since the hardness is superior to natural diamond, the tensile
strength likely would be higher as well, which has been measured to be
up to 60 GPa for natural diamond. These would also be an excellent
choice to investigate for storing hydrogen for the proposed "hydrogen
economy".
And silicon nitride and silicon carbide whiskers have been found to
have tensile strength up to 50 GPa and 20 GPa respectively. In the
case of silicon nitride this remarkable strength extends almost to the
macroscale since they have been found to have this strength at
centimeters lengths though still only at micron wide widths:

A synthesis of mono-crystalline silicon nitride filaments.
Journal of Materials Science.
Volume 29, Number 11 / June, 1994
http://www.springerlink.com/content/t7u643052q1865q6/


Bob Clark