If a Buckminster Fuller Sky city were constructed in space,..

What altitude & what lift capacity would it have if vacuum, i.e.,
'no air' were used instead of hot air?

What savings if a payload could be hoisted to it by CNT cable before
launch ?

RKH

Hi RKH,

Current balloons tend to have virtually the same gas pressure inside as
outside the envelope. It's only the average density of the lifting gas -
got by using either "hot air" or "a gas whose molecules are lighter than
air" - which provides the lift.

You're suggesting making a shell and evacuating the contents to get the
perfect lifting gas: one of no density! ;-)

That said, this shell would have to be immensely strong. At ground
level, it would have to be able to support around 10 tonnes per square
metre of atmospheric pressure, and yet mass as little as possible in
order to provide any useful lift.

Maybe some CNT fabric is possible, draped over the necessary struts and
bracing, but if the material technologists can crack that, then a
Beanstalk or usable tether would be presumably far easier to achieve?

Regards,

Andy

Andy,

You said:

"You're suggesting making a shell and evacuating the
contents to get the perfect lifting gas: one of no density!
1. I am not suggesting "evacuating the contents" - If the sphere is
constructed in space, there will be no "contents".

2. "perfect lifting gas"

Vacuum is a [virtual] absence of gas, perfect or otherwise.

You said:
"this shell would have to be immensely strong. At ground
level,...

3. There is no need for the sphere ever to approach "ground level",
-it only needs to be lowered to the point where it will 'float'
on or in the atmosphere.

As you said:

"Current balloons tend to have virtually the same gas pressure
inside as outside the envelope."

You said:
"Maybe some CNT fabric is possible, draped over the necessary
struts and bracing,"

4. I never suggested any kind of "fabric" to be used in covering the
sphere. -And CNT fabric would be overkill.

You said:
"a Beanstalk or usable tether would be presumably far easier
to achieve?"

5. If you are referring to a space elevator, I strongly disagree as to
cost and difficulty of construction.

A geodesic sphere could be constructed [in space] today with
yesterday's methods.

I do agree however, that a space elevator is a much preferable way
of getting into space, but there is currently no assurance that this
can even be accomplished.

A geodesic sphere, if it could be used as I suggested [a big IF] would
simply help to cut lift costs as we currently know them. [A very 'weak
sister' to the Space Elevator... -but possibly worth considering]

RKH

P.S. -For more info on Geodesic Spheres see:

http://www.cjfearnley.com/fuller-faq-5.html#ss5.2

I believe there may be a questionable statement or 2 but I assume
they can be attributed to poor editing.

.

> You said:
> "Maybe some CNT fabric is possible, draped over the necessary
> struts and bracing,"
>
> 4. I never suggested any kind of "fabric" to be used in covering the
> sphere. -And CNT fabric would be overkill.

Any structure that has a vacuum inside and pressure outside needs to ensure
that it can resist the forces of implosion......how would one do this
without a rigid structure?

Hi Bob!

Please accept my apologies relating to my somewhat lighthearted tone
regarding "perfect lifting gas" and other comments. I was simply
intrigued by your idea, and wanted to look into some of the potential
technologies and engineering that would lie behind it. Thinking beyond
the envelope of what we are told is realistic and achievable is always a
good attitude to take, I believe.

I misinterpreted your suggestion (to make vacuum-balloons in space and
lower them to float in the atmosphere) as the url'd proposal was to do
things the other way around: fly up materials from Earth and launch them
to orbit from floating platforms.

That said, there are serious issues here. Assuming a CNT structure -
presumably some form of latticework along the lines of a
geodesic-dome-meeting-zeppelin-bracing - that structure would need to be
extraordinarily resilient to inward pressure forces, whether from very
thin air in the upper atmosphere, or while the structure was being
deorbited from 7km/s to float in upper atmosphere winds.

As I understand it, even at 400km the density of the atmosphere changes
markedly in relation to the solar cycle. The impact on dense orbiting
objects - shuttle, ISS - is a concern today, but it would be far more
noticeable on large, light structures such as the vacuum-balloon, which,
presumably, would need many stable orbits of low decelerative
aero-braking in order to de-orbit to a (very high) floating altitude
without damage.

Regards,

Andy Goddard

Re Digest 1074

Message: 3 From: "Alan Patrick"

A.P.: "Any structure that has a vacuum inside and pressure outside
needs to ensure that it can resist the forces of implosion..."
Patrick,

1. "Implosion" is a bit strong, "Collapse" might be better..

-But as Andy said ""Current balloons tend to have virtually the
same gas pressure inside as outside the envelope."

-At sufficiently high altitudes air pressure is not much greater
than the so-called vacuum of space.

Besides: when I suggested construction take place in space I
had other considerations in mind, most importantly,
-ground level weather.

There is still the problem of high altitude winds and
temperature variance. Perhaps the answer would be to seek an
"optimal" altitude with some atmosphere let in rather than
just the greatest altitude achievable.

-This would allow buoyancy control thru heat management.

In the original B.Fuller design buoyancy was dependant upon air
temperature. The claim was that heat from every day activities,
..even body heat would be sufficient to maintain buoyancy.

A.P.: "..how would one do this without a rigid structure?"

2. The structure need not be absolutely rigid.

Rem: "The oak breaks, the reed bends."

[as Thor Heyerdahl discovered when designing transatlantic reed
boats :-]

Also geodesic structure is surprisingly strong. Just this week
I saw [on TV] a couple of kids who constructed a geodesic dome
in just a few minutes, about 2.5 +/- feet high out of not very
neatly rolled newspaper. When done, the dome was capable of
supporting the weight of one of the kids.

Also, I would assume that the internal structures, living
quarters, flight deck, etc. would be supported more or less
centrally by some sort of "tensegrity" arrangement of cables
with multiple points of attachment, which might actually
strengthen the "balloon's" overall structural integrity .

See:
http://www.google.com/search?sourceid=mozclient&ie
=utf-8&oe=utf-8&q=tensegrity

or, http://tinyurl.com/67qux [which is the same thing reduced]

Re message: 5 From: "Andrew Goddard"

A.G: "I misinterpreted your suggestion ... as the url'd proposal was
to do things the other way around: fly up materials from Earth
and launch them to orbit from floating platforms."

1. There was nothing in the URL which proposed "flying" things up..
nor was there anything in it related to "space" or "launching".
"Cloud 9" was simply a floating city at no great altitude.

2. But most importantly:

To "fly" materials up would defeat the whole purpose !!!!

3. My 'take' was that materials could be lifted up in much the same
manner as they would be by the Space Elevator.

4. -This would no doubt require suitable tethering, probably by
CNT cables.

A.G:"a geodesic-dome-meeting-zeppelin-bracing - that structure would
need to be extraordinarily resilient to inward pressure forces,
whether from very thin air in the upper atmosphere,..."

5. I have no reason to believe that a properly designed geodesic
structure would not be sufficiently resilient. This would pose
a problem however with regard to a cable supported infrastucture.
There would have to be some equivalent to spring loaded cables
or some other kind of "shock absorber".

-As regards "zeppelin-bracing", see "tensegrity" above.

6. Also, as I suggested above, there would be no objection, and in
fact there would be a benefit from allowing air in to balance
pressure until optimum altitude was reached.

A.G."..or while the structure was being deorbited from 7km/s to float
in upper atmosphere winds."

7. Structural materials would have to be brought to a geostationary
orbit before construction could begin.

A.G.:"As I understand it, even at 400km the density of the atmosphere
changes markedly in relation to the solar cycle."

8. The questions are:

a. How rapidly do these changes take place, and can they be dealt
with by heat management protocols?

-If by "solar cycle" you mean normal daily and seasonal changes,
then the answer is probably "Yes".

-and,

b. What would be the nature of unpredictable events at a given
altitude?

[i.e., unusual weather events..., sunspots...,other ?]

RKH

> 1. "Implosion" is a bit strong, "Collapse" might be better..

Semantics......you must have done the experiment at school or uni where you
evacuate a tin can and watch it collapse....

> -But as Andy said ""Current balloons tend to have virtually the
> same gas pressure inside as outside the envelope."

Well obviously, as they stay inflated - but they aren't supporting
vacuums......If pressure outside is greater than a vacuum, the forces will
be inward......and if the structure cannot support that it will collapse
(well it did when I studied Engineering anyway)

> -At sufficiently high altitudes air pressure is not much greater
> than the so-called vacuum of space.

It is still greater, ergo your balloon structure must resist those forces,
and a floppy one will not without some rigididity in the structure somewhere

> Besides: when I suggested construction take place in space I
> had other considerations in mind, most importantly,
> -ground level weather.

How does this stop the pressure differential acting across the balloon
surface?

> A.P.: "..how would one do this without a rigid structure?"
>
> 2. The structure need not be absolutely rigid.

No, but somewhere there will need to be a rigid frame or something...c'mon,
thats semantics, you know what I'm saying. I would be interested is seeing
your proposed non-rigid structure to hold a vacuum against an outside
pressure....somewhere you are going to have to brace or support something.

Alan

Message: 2

From: "Alan Patrick"

AP: "Well obviously, as they stay inflated - but they aren't
supporting vacuums......If pressure outside is greater than
a vacuum, the forces will be inward."...

RKH: I believe its the gradient of inward forces which account for
buoyancy, but read on..

AP: "I would be interested in seeing your proposed non-rigid
structure hold a vacuum against an outside pressure...
somewhere you are going to have to brace or support something."

RKH: I suspect that a properly constructed geodesic sphere could
survive and be strengthened [made more rigid] by slightly
negative internal pressure so long as there are no seriously
unbalanced external forces. However, if you will refer to my
previous msg. you will see that the point is moot as I point out
the advantages of admitting 'some' air.
Of course, the less you admit the higher the balloon will float,
but the object would be to find the optimal,not necessarily the
greatest, altitude.

Also,If the balloon contains sufficient air, and if buoyancy is
made a function of heat, then we may assume that the pressure
inside is greater than outside.

In any case, if construction takes place in space you will
necessarily begin with a vacuum,[altho moderate pre-pressuriza-
tion is an option] and then hold at the greatest altitude con-
sistent with stability/manageability. CNT tethers will help.

[Note that at sufficient altitude the outside pressure might be
considered a [relative] 'vacuum' at sea level. :-]

>> When I suggested construction take place in space I had other
>> considerations in mind, most importantly, -ground level
>> weather.

As you may imagine there would be serious problems trying to
construct a sphere a mile or more in diameter on the ground.
And while those problems are likely soluble, weather
permitting, -I believe construction in space would be compara-
tively straightforward.
Its a question of considerable engineering and physical
bother vs the expense of sending up astronauts and/or robots
to perform a task which is essentially the same as working
with a giant erector set.

RKH

P.S. -Sorry about my "Tensegrity" link. #:-/

Here are some URLs about "Cloud Nine", although googling

-Buckminster Fuller domes- [which are common]

would give a clearer understanding of geodesic construction.

http://www.cjfearnley.com/fuller-faq-5.html#ss5.2

see also May 29 at:

http://www.duntemann.com/may2004.htm

.

> RKH: I believe its the gradient of inward forces which account for
> buoyancy, but read on..

Strictly speaking, pressure increases with depth so there will always be a
slightly larger force pushing up than down on an object. When its mass
equals the force differential it is in equilibrium. A fast way of
calculating it is to calculate relative densities - but the intrinsic
assumption is always that the foating object must withstand the pressure of
the outside environment, either by having a higher pressure (eg of a less
dense gas in a balloon at higher prssure) or having structural rigidity (eg
a ship in water) or intrinsic rigidity (eg wood in water).

>RKH: I suspect that a properly constructed geodesic sphere could
survive and be strengthened [made more rigid] by slightly
negative internal pressure so long as there are no seriously
unbalanced external forces.

Yes, but it is then by definition a rigid structure, as I pointed out,
albeit rigid in compression rather than tension.

> However, if you will refer to my
previous msg. you will see that the point is moot as I point out
the advantages of admitting 'some' air.

A Vacuum has no pressure, so the structure must resist all the pressure of
the outside environment. A slight amount of gas in the balloon here will not
help unless it is at a pressure that prevents collapse...and to achieve this
pressure one needs a certain concentration of gas....so one can't choose to
put in "some" gas. Agreed, the pressure is less as it rises (which is why
weather balloons swell as they rise as the internal pressure increases vs
the outside )

Rgds

Alan

> Here are some URLs about "Cloud Nine", although googling
>
> -Buckminster Fuller domes- [which are common]
>
> would give a clearer understanding of geodesic construction.

I actually built a geodesic dome, as part of our university buildings - it
was the canteen & bar - out of thin fibreglass. The point of them is that
they have thin, rigid pieces that fit together and once in the spherical
frame are strong (some footballs are made in a similar way).

Cloud 9 merely uses the effect that the mass increase of the thin surface
becomes a reducing % of the total mass of the sphere, and if the rest is air
it eventually becomes negligibly different to the surrounding
environment....put a few warm bodies in it and you have sustained
floatability....but you can't do this with a non rigid structure! B-F
proposed geodesic frame draped in thin material.

I recall my brother and I reading about this yonks ago as a teenager and we
wound up building a 1m cube (easier to build - and lighter btw - than the
Fuller geodesic would be at that scale) out of wire and aeromodeller's
tissue paper and putting a small burner underneath it on the open face, it
worked very well as a rigid hot-air balloon

Rgds

Alan

Re: Digest 1076 Msg. 2
From: "Alan Patrick"

Alan,
Apparently we are now in agreement, aside from matters of
semantics.

Not acceptable where science is concerned, but after all isn't this
clarifying type of discussion the chief function of sites like this?

1. There was a misunderstanding on my part regarding "flexibility".

One "strong" point of a geodesic sphere is its ability to distribute a
"point" load over a wide area.

I had assumed that absolute rigidity was both unlikely and unwise.

It also occurs to me that I may have been influenced by having seen,
[on TV] but forgotten, those "collapsing" sculptures which are rather
similar in appearance.
[I am approaching senility after all ... :-]

[I had also forgotten that my brother recently made one of these..]

-He's an engineer(*) a "doer" [and a model maker], while I'm just a
dreamer.

*My brother, by the way, was involved in the design of the "Manhattan"
ice breaker, a project ultimately abandoned in favor of the Alaska
Pipeline.

2. And a misunderstanding on your part regarding my use of the word
"vacuum". It was only meant to be a starting point [a convenient
result of assembly in space] on a gradient leading [compromisingly]
to the highest practical altitude.

3.You said:

"A slight amount of gas in the balloon here will not help unless it
is at a pressure that prevents collapse"

-I agree.

4.You then said:

"and to achieve this pressure one needs a certain concentration of
gas....so one can't choose to put in "some" gas."

By the use of "some" I merely meant the minimum amount necessary.

Less gas = less mass = greater altitude.

5. There was also my reference to "negative pressure". The statement
was not incorrect per se (you agree that compressive rigidity would
result) ... -It was simply irrelevant and out of context.

I had in the back of my mind that stability would require tethering
which would hold the balloon lower than its point of neutral buoyancy
thus increasing upward force [pressure] and providing stabilizing
tension in the tethers.

I should have kept in mind that buoyancy is a function of total body
mass and has little to do with the internal pressure which provides
rigidity.

====================================================================
-That said, the question remains:

Is this type of balloon a useful and viable means of cutting launch
costs?

P.S. I could have sworn I once saw an illustration of this idea in
which the balloon was used as a way station for launch via
Electromagnetic Linear Accelerator.

i.e., Use a CNT elevator for all or most of the trip up, then switch
to the ELA.

-The much reduced atmosphere might make this an attractive option.

RKH