Telescoping habitat modules

I have been thinking a bit about how to make kitset habitat modules
requiring minimal payload size and orbital assembly.

One thought that occurred is that it is quite straight forward to
construct a telescoping pressure vessel much like a portable radio
antenna. A set of large diameter nested cylinders with appropriate seals
can be quickly pressurised and extended in orbit. While diameter is
limited, the walls are very thin and it should be possible to nest many
cylinders enabling many times the original length and volume. As rigid
materials can be used this should be lighter and cheaper than the
transhab inflatable module. If need be, the lighter weight sections
might be launched individually and nested in orbit.

A related approach is that it should also be possible to take very large
diameter flexible thin wall cylindrical sections, with the appropriate
locking shoulders at each end, and fold them in on themselves to a much
smaller diameter for launching. In this fashion very large diameter
telescopic habitat modules might be quickly assembled. The end caps
might still be a problem though conical sections could be used at each
end. Double wall techniques are possible and if need be the section
joints could be permanently fixed from within after initial
pressurisation.

Pete.

"Pete Lynn" wrote in message
...
One thought that occurred is that it is quite straight forward to
construct a telescoping pressure vessel much like a portable radio
antenna. A set of large diameter nested cylinders with appropriate seals
can be quickly pressurised and extended in orbit. While diameter is
limited, the walls are very thin and it should be possible to nest many
cylinders enabling many times the original length and volume. As rigid
materials can be used this should be lighter and cheaper than the
transhab inflatable module.

What basis do you have for the assertion that this should be lighter and
cheaper than an inflatable module?

Jeff
--
Remove icky phrase from email address to get a valid address.

"Jeff Findley" wrote in message
...

"Pete Lynn" wrote in message
...
One thought that occurred is that it is quite straight
forward to construct a telescoping pressure vessel much
like a portable radio antenna. A set of large diameter
nested cylinders with appropriate seals can be quickly
pressurised and extended in orbit. While diameter is
limited, the walls are very thin and it should be possible
to nest many cylinders enabling many times the original
length and volume. As rigid materials can be used this
should be lighter and cheaper than the transhab
inflatable module.

What basis do you have for the assertion that this should
be lighter and cheaper than an inflatable module?

A good question to which I do not have a good answer. Direct experience
would infer that the soft high strength fabrics are more expensive, less
available and much harder to use.

In theory they should be similar weight and cost - they are basically
the same or similar materials manufactured in similar fashions.
However, the softer composites are not well developed compared to the
rigid carbon fibre lay-up systems. Of course metals while heavier may
have other advantages.

With rigid carbon fibre shells one would probably expect better adhesion
by the matrix between fibres, repairs should be much easier as would the
reinforcement of various points, they also tend to be more resistant to
wear and tear.

Pete.

On Fri, 22 Jul 2005 02:19:59 GMT, in a place far, far away, "Pete
Lynn" made the phosphor on my monitor glow
in such a way as to indicate that:

What basis do you have for the assertion that this should
be lighter and cheaper than an inflatable module?

A good question to which I do not have a good answer. Direct experience
would infer that the soft high strength fabrics are more expensive, less
available and much harder to use.

In theory they should be similar weight and cost - they are basically
the same or similar materials manufactured in similar fashions.
However, the softer composites are not well developed compared to the
rigid carbon fibre lay-up systems. Of course metals while heavier may
have other advantages.

With rigid carbon fibre shells one would probably expect better adhesion
by the matrix between fibres, repairs should be much easier as would the
reinforcement of various points, they also tend to be more resistant to
wear and tear.

In other words, you have no basis at all for your assertion.

You could have saved a lot of bandwidth and keystrokes by simply
admitting that, instead of conjuring up nonsense to try to defend it.

"Rand Simberg" wrote in message
.. .
On Fri, 22 Jul 2005 02:19:59 GMT, in a place far, far away, "Pete
Lynn" made the phosphor on my monitor glow
in such a way as to indicate that:

What basis do you have for the assertion that this
should be lighter and cheaper than an inflatable
module?

A good question to which I do not have a good answer.
Direct experience would infer that the soft high strength
fabrics are more expensive, less available and much
harder to use.

In theory they should be similar weight and cost - they
are basically the same or similar materials manufactured
in similar fashions. However, the softer composites are
not well developed compared to the rigid carbon fibre
lay-up systems. Of course metals while heavier may
have other advantages.

With rigid carbon fibre shells one would probably
expect better adhesion by the matrix between fibres,
repairs should be much easier as would the
reinforcement of various points, they also tend to be
more resistant to wear and tear.

In other words, you have no basis at all for your assertion.

Assuming such inflatable vessels are cheaper and lighter, why are they
not used for generic pressure vessel applications? Why are they not
used for say, aircraft drop tanks? What about propellant tanks for
space transports? Are such things on the drawing boards?

I get the impression that the inflatable habitat module is being sold
primarily on its volume expansion capacity, is this true? If so, how
does it compare to say, a telescoping rigid expansion module?

Pete.

"Pete Lynn" wrote in message
...
Assuming such inflatable vessels are cheaper and lighter, why are they
not used for generic pressure vessel applications? Why are they not
used for say, aircraft drop tanks? What about propellant tanks for
space transports? Are such things on the drawing boards?

You're comparing apples and oranges here. "generic pressure vessels" don't
have to deal with extremely high velocity debris impacts (i.e. also called
micrometeorite protection).

One of the advantages over an inflatable pressurized module in space is that
it makes orbital debris protection easier. On an infaltable, you've got
nearly unlimited (inflated) volume potential, which allows you to put a lot
of space between the layers which make up the debris shield. On a rigid
structure, you're limited to the diameter of the payload bay or aerodynamic
shroud of the launch vehicle.

I get the impression that the inflatable habitat module is being sold
primarily on its volume expansion capacity, is this true? If so, how
does it compare to say, a telescoping rigid expansion module?

Maybe you should do some math.

Remember that the best shape to maximize your volume while minimizing
surface area is a sphere. Next up, considering the shape of the shuttle
payload bay and the shape of ELV's payload shrouds), would likely be shapes
that are roughly cylindrical. Your telescoping module doesn't help much,
since it only increases the length of the module, not the diameter.

Think of it this way. Compare a single cylindrical (rigid) module to a
telescoping module who's extended length is 2x the length of a single,
monolithic, module. What mass is saved by the telescoping module? Even
assuming that things like seals and structural reinforcement of the joint
weighs nothing and costs you nothing, you've only saved the mass and the
cost of two of the end caps. If your payload bay has a diameter to length
ratio of 4 (i.e. like the shuttle payload bay), most of the mass of the
module is in the barrel section, not the end caps. Whether the barrel
section or the end caps cost more depends on the details of the design...

However, an inflatable module with a rigid core would typically extend in
the radial direction (i.e. the radial direction relative to the payload bay
cylinder volume limits). As such, you get a much more volume to surface
area out of such a module than you ever could out of a telescoping module.

One thing to consider would be an inflatable module with a telescoping rigid
core, so that you could not only inflate in the radial direction, but also
along the axis as well. That way, you've still got a rigid core, but the
inflated length can exceed the length of your payload bay or launch shroud.

Of course, even the above thought experiment doesn't get into cost of the
inflatable structure versus the cost of a rigid structure. It also doesn't
consider if an inflatable sphere would be cheaper to manufacture than an
inflatable cylinder (with some other variables remaining constant like
deployed internal volume and the same fixed launch volume).

The devil is in the details. You'd have to do a detailed cost/engineering
analysis of all the above proposed designs in order to find out the "best
design". And even then, the "best design" depends entirely on how the high
level requirements are written. If they're over specified, as NASA tends to
do on big projects, the "best design" is the one that the writers of the
specs had already chosen before the specs were even written...

Jeff
--
Remove icky phrase from email address to get a valid address.

"Jeff Findley" wrote in message
...
If your payload bay has a diameter to length
ratio of 4 (i.e. like the shuttle payload bay), most of the mass of the

I got this backwards. The length to diameter ratio is 4:

60 feet (long) / 15 feet (diameter) = 4

Still, anyone familiar with the shuttle knows that its payload bay is a lot
longer than it is wide.

Jeff
--
Remove icky phrase from email address to get a valid address.

"Jeff Findley" wrote in message
...

"Pete Lynn" wrote in message
...
Assuming such inflatable vessels are cheaper and lighter,
why are they not used for generic pressure vessel
applications? Why are they not used for say, aircraft
drop tanks? What about propellant tanks for space
transports? Are such things on the drawing boards?

You're comparing apples and oranges here. "generic
pressure vessels" don't have to deal with extremely high
velocity debris impacts (i.e. also called micrometeorite
protection).

Another solution might be to cover the entire module in a much larger
tent - spacing being the critical factor in such protection. This could
be applied to both soft or hard habitat designs.

One of the advantages over an inflatable pressurized
module in space is that it makes orbital debris protection
easier. On an infaltable, you've got nearly unlimited
(inflated) volume potential, which allows you to put a lot
of space between the layers which make up the debris
shield. On a rigid structure, you're limited to the diameter
of the payload bay or aerodynamic shroud of the launch
vehicle.

The telescoping structure does have a larger surface area to volume
ratio with regard to micrometeors and heat transfer. I am not sure but
this last might actually be a benefit, waste heat rejection could be
useful.

I get the impression that the inflatable habitat module is
being sold primarily on its volume expansion capacity, is
this true? If so, how does it compare to say, a
telescoping rigid expansion module?

Maybe you should do some math.

On what?

Remember that the best shape to maximize your volume
while minimizing surface area is a sphere. Next up,
considering the shape of the shuttle payload bay and the
shape of ELV's payload shrouds), would likely be shapes
that are roughly cylindrical. Your telescoping module
doesn't help much, since it only increases the length of the
module, not the diameter.

Why is minimising surface area so critical? I did suggest another
method of increasing diameter, basically folding thin wall cylindrical
sections in on themselves, though assembly is far more involved. This
is also raises the possibility of an access system suitable for very
large objects, (space transports, etcetera).

Think of it this way. Compare a single cylindrical (rigid)
module to a telescoping module who's extended length is
2x the length of a single, monolithic, module. What mass
is saved by the telescoping module? Even assuming that
things like seals and structural reinforcement of the joint
weighs nothing and costs you nothing, you've only saved
the mass and the cost of two of the end caps. If your
payload bay has a diameter to length ratio of 4 (i.e. like
the shuttle payload bay), most of the mass of the
module is in the barrel section, not the end caps. Whether
the barrel section or the end caps cost more depends on
the details of the design...

Pressure vessel mass is roughly proportional to volume, pressure and
specific strength. Beyond minimum gauge constraints, such that wall
thickness is not fixed, it is independent of length.

However, an inflatable module with a rigid core would
typically extend in the radial direction (i.e. the radial
direction relative to the payload bay cylinder volume
limits). As such, you get a much more volume to surface
area out of such a module than you ever could out of a
telescoping module.

One thing to consider would be an inflatable module with
a telescoping rigid core, so that you could not only inflate
in the radial direction, but also along the axis as well. That
way, you've still got a rigid core, but the inflated length can
exceed the length of your payload bay or launch shroud.

I never really understood the need for a rigid core. It just seemed
like extra payload weight and complexity to me, just for the sake of a
pre-furnished habitat. Without it one could launch a much larger
habitat module.

Of course, even the above thought experiment doesn't get
into cost of the inflatable structure versus the cost of a
rigid structure. It also doesn't consider if an inflatable
sphere would be cheaper to manufacture than an
inflatable cylinder (with some other variables remaining
constant like deployed internal volume and the same fixed
launch volume).

The construction method and cost thereof of an inflated habitat is a
difficult question - composites are perhaps more known in this regard.
I had originally assumed a 3DL process - basically filament winding the
material in place over a male mould. This is expensive. On further
investigation it seems this is not entirely necessary, though it could
be lighter and stronger, (no seams).

The devil is in the details. You'd have to do a detailed
cost/engineering analysis of all the above proposed
designs in order to find out the "best design". And even
then, the "best design" depends entirely on how the high
level requirements are written. If they're over specified, as
NASA tends to do on big projects, the "best design" is
the one that the writers of the specs had already chosen
before the specs were even written...

Indeed, on the weight question I did a little revision. The soft high
specific strength materials and construction methods have improved
somewhat. It depends on specifics, however a very high strength carbon
fibre lay-up might have similar weight to the Vectran shell currently
favoured by Bigelow. Direct and development cost comparison?

Cuban fibre, (spectra), would be significantly lighter again, though the
construction of such a pressure vessel could be very challenging.
Alternatively a direct 3DL process might be used with raw spectra
filaments. Spectra is very difficult to adhere to or join, it also has
some distressing failure tendencies. I am not sure how this one would
eventually pan out, though would probably favour avoiding it for now.

Another interesting piece of information I came across was that the
Vectra polymer is as strong at LOX temperatures as it is at room
temperature. The Vectran fibre has only been tested to around minus 60C
and found to be slightly stronger than at room temperature. This raises
the possibility of external Vectran inflatable LOX tanks, (in addition
to hydrocarbon tanks), with tank mass fractions of less than 1%. This
could make for some very interesting space transport designs.

Pete.

"Pete Lynn" wrote in message
news
"Jeff Findley" wrote in message
...

"Pete Lynn" wrote in message
...
Assuming such inflatable vessels are cheaper and lighter,
why are they not used for generic pressure vessel
applications? Why are they not used for say, aircraft
drop tanks? What about propellant tanks for space
transports? Are such things on the drawing boards?

You're comparing apples and oranges here. "generic
pressure vessels" don't have to deal with extremely high
velocity debris impacts (i.e. also called micrometeorite
protection).

Another solution might be to cover the entire module in a much larger
tent - spacing being the critical factor in such protection. This could
be applied to both soft or hard habitat designs.

Far easier said than done. For adequate protection, you need many layers,
all with space between them. This is so when a micrometorite hits the first
layer and shatters into many smaller objects still at high velocity, they
will spread out before hitting the next layer. You should read up on
micrometeorite protection for spacecraft. It's an interesting topic.

Think of it this way. Compare a single cylindrical (rigid)
module to a telescoping module who's extended length is
2x the length of a single, monolithic, module. What mass
is saved by the telescoping module? Even assuming that
things like seals and structural reinforcement of the joint
weighs nothing and costs you nothing, you've only saved
the mass and the cost of two of the end caps. If your
payload bay has a diameter to length ratio of 4 (i.e. like
the shuttle payload bay), most of the mass of the
module is in the barrel section, not the end caps. Whether
the barrel section or the end caps cost more depends on
the details of the design...

Pressure vessel mass is roughly proportional to volume, pressure and
specific strength. Beyond minimum gauge constraints, such that wall
thickness is not fixed, it is independent of length.

The shape of the vessel does matter. A sphere gives you a minimum mass for
a given pressure, volume, material density, and material strength.

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

I assumed you'd want to launch your telescoping, rigid, or inflatable
pressure vessel in one launch. Being able to maximize the available
pressurized volume for a single launch seems like a good thing to do, but
clearly, this ignores price. It would be better to maximize your
pressurized volume in LEO for the dollars you spent to build and launch the
module.

However, an inflatable module with a rigid core would
typically extend in the radial direction (i.e. the radial
direction relative to the payload bay cylinder volume
limits). As such, you get a much more volume to surface
area out of such a module than you ever could out of a
telescoping module.

One thing to consider would be an inflatable module with
a telescoping rigid core, so that you could not only inflate
in the radial direction, but also along the axis as well. That
way, you've still got a rigid core, but the inflated length can
exceed the length of your payload bay or launch shroud.

I never really understood the need for a rigid core. It just seemed
like extra payload weight and complexity to me, just for the sake of a
pre-furnished habitat. Without it one could launch a much larger
habitat module.

Again, this comes down to cost. It depends if its cheaper to configure the
core on the ground or if it's cheaper to outfit a completely empty module in
LEO. At today's launch costs, it's generally cheaper to do as much work on
the ground as possible, because astronauts in LEO are few and their cost is
high.

Of course, even the above thought experiment doesn't get
into cost of the inflatable structure versus the cost of a
rigid structure. It also doesn't consider if an inflatable
sphere would be cheaper to manufacture than an
inflatable cylinder (with some other variables remaining
constant like deployed internal volume and the same fixed
launch volume).

The construction method and cost thereof of an inflated habitat is a
difficult question - composites are perhaps more known in this regard.
I had originally assumed a 3DL process - basically filament winding the
material in place over a male mould. This is expensive. On further
investigation it seems this is not entirely necessary, though it could
be lighter and stronger, (no seams).

That's not what is meant by inflatable. Have you read about Transhab? If
not, you should. The concept involves a flexible, inflatable vessel. There
is no solid composite outer structure. To deploy Transhab, you'd simply
inflate it to 14.7 psi and you're done. That's the type of module I think
about when someone says inflatable.

Jeff
--
Remove icky phrase from email address to get a valid address.

"Jeff Findley" wrote in message
...

"Pete Lynn" wrote in message
news

Another solution might be to cover the entire module in
a much larger tent - spacing being the critical factor in
such protection. This could be applied to both soft or
hard habitat designs.

Far easier said than done. For adequate protection, you
need many layers, all with space between them. This is so
when a micrometorite hits the first layer and shatters into
many smaller objects still at high velocity, they will spread
out before hitting the next layer. You should read up on
micrometeorite protection for spacecraft. It's an
interesting topic.

The Transhab of old used a soft foam to separate the three or four, (I
forget), micrometeor protection layers. I remember doing the numbers
and figuring they must have cut large holes in the foam to try to get
the weight down to sensible levels. This type of foam in this context
is not noted for its high compressive strength. It was also very
problematic to pack.

A tent can similarly be multi-layered and self erecting in this context.
A few poles at each end are far lighter than the foam and pack far far
better. The poles might be positioned in a spoked arrangement at each
end, pointing out at say a 45 degree angle over the end cap. Multiple
layers of far greater spacing can be easily suspended from these poles
and it will be self erecting. This was one of my primary objections,
(along with the rigid core), to the Transhab design. I have discussed
this previously.

Pressure vessel mass is roughly proportional to volume,
pressure and specific strength. Beyond minimum gauge
constraints, such that wall thickness is not fixed, it is
independent of length.

The shape of the vessel does matter. A sphere gives you
a minimum mass for a given pressure, volume, material
density, and material strength.

Only if one assumes an isentropic material like most metals. Composite
and inflatable tanks use fibres distributed in an anisotropic fashion.
Fibre distribution is optimised in accordance with axial and hoop
stresses. This has been discussed many times.

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

I assumed you'd want to launch your telescoping, rigid, or
inflatable pressure vessel in one launch. Being able to
maximize the available pressurized volume for a single
launch seems like a good thing to do, but clearly, this
ignores price. It would be better to maximize your
pressurized volume in LEO for the dollars you spent to
build and launch the module.

The degree of assembly and size of the telescoping habitat at launch
would depend on the launch constraints, orbital assembly capabilities
and orbital volume needs. Remember that the pressure vessel of the
Transhab module is but a very small proportion of its overall mass -
most of which is the rigid core. Such pressurised volume limits are
still a long way off.

I never really understood the need for a rigid core. It
just seemed like extra payload weight and complexity to
me, just for the sake of a pre-furnished habitat. Without
it one could launch a much larger habitat module.

Again, this comes down to cost. It depends if its cheaper
to configure the core on the ground or if it's cheaper to
outfit a completely empty module in LEO. At today's
launch costs, it's generally cheaper to do as much work on
the ground as possible, because astronauts in LEO are
few and their cost is high.

This is the part that I have issues with. In both circumstances the
core would be configured on the ground. In the kitset version
furnishings would be moved in after and Velcroed into the pre-planned
places, or whatever. Even with an air conditioning system, I do not see
why this should take more than a few hours. It would be far more
flexible and allow for a much larger habitat.

Designing a rigid core for both launch and habitation is a major
compromise requiring significant extra mass and design effort. It is
also very constraining with regard to room layout and size. It is
effectively a conforming tank design, but conforming to what?

The construction method and cost thereof of an inflated
habitat is a difficult question - composites are perhaps
more known in this regard. I had originally assumed a
3DL process - basically filament winding the material in
place over a male mould. This is expensive. On further
investigation it seems this is not entirely necessary,
though it could be lighter and stronger, (no seams).

That's not what is meant by inflatable. Have you read
about Transhab? If not, you should. The concept
involves a flexible, inflatable vessel. There is no solid
composite outer structure. To deploy Transhab, you'd
simply inflate it to 14.7 psi and you're done. That's the
type of module I think about when someone says
inflatable.

Sorry I was unclear. The 3DL process is sometimes used in sail making.
An example - an adhesive mylar layer is laid down face up over an exact
mould. High strength fibres, (carbon, spectra, Kevlar, etcetera), are
then laid down in a precise fashion exactly where they are desired. A
second mylar layer is then placed over top. The result is a close to
ideal sail shape with fibre strength exactly where it is wanted - no
seams or panel distortions. As far as I can tell the inflated Bigelow
modules are not made this way, they use Vectran fabric panels joined by
seams.

Pete.