Can we now build the "space tower"?

Pat Flannery wrote:

Remus Shepherd wrote:
You're robbing it from the Earth, which barely notices.

You climb up the tower by exerting a force on it downward. The tower
transmits that downward force to the Earth. The Earth pushes back up,
which pushes the tower back up, which lifts you.

That's for a rigid structure though; in the case of a cable type space
elevator, you are pulling on the cable, not pushing on the Earth.

The cable is in tension when there's no payload on it. It has to be in
order for it to be stable, otherwise the slightest downward tug would
start a runaway collapse. When a payload starts going up the tension on
the cable's anchor point is reduced slightly. That's equivalent to
pushing downward.

Think of it in terms of center of mass if you prefer. Moving mass up the
elevator is going to move the center of mass of the combined
Earth-elevator system in the same direction, causing Earth to "drop"
minutely.

The problem of the rigid type space elevator (or space tower) concept is
that it's going to have a very large diameter at its base just to take
the weight of the upper part, and that base part is going to have to
deal with winds close to the surface, then go through the jet stream as
it ascends into space.
Even small shifts in the base due to winds are going to act like a
bullwhip as they ascend its leangh, so that a shift of a few inches near
the base could equal the top of the tower lashing back and forth by a
mile or so given its 22,000 mile height.

I suspect a rigid compressional tower 22,000 miles tall is going to have
a base that's wider than the troposphere is deep. I doubt it'll be doing
much shifting due to wind.

Not that it's particularly plausible either way, though.

On Dec 9, 8:32 pm, Bryan Derksen wrote:
Pat Flannery wrote:

Remus Shepherd wrote:
You're robbing it from the Earth, which barely notices.

You climb up the tower by exerting a force on it downward. The tower
transmits that downward force to the Earth. The Earth pushes back up,
which pushes the tower back up, which lifts you.

That's for a rigid structure though; in the case of a cable type space
elevator, you are pulling on the cable, not pushing on the Earth.

The cable is in tension when there's no payload on it. It has to be in
order for it to be stable, otherwise the slightest downward tug would
start a runaway collapse. When a payload starts going up the tension on
the cable's anchor point is reduced slightly. That's equivalent to
pushing downward.

Think of it in terms of center of mass if you prefer. Moving mass up the
elevator is going to move the center of mass of the combined
Earth-elevator system in the same direction, causing Earth to "drop"
minutely.

The problem of the rigid type space elevator (or space tower) concept is
that it's going to have a very large diameter at its base just to take
the weight of the upper part, and that base part is going to have to
deal with winds close to the surface, then go through the jet stream as
it ascends into space.
Even small shifts in the base due to winds are going to act like a
bullwhip as they ascend its leangh, so that a shift of a few inches near
the base could equal the top of the tower lashing back and forth by a
mile or so given its 22,000 mile height.

I suspect a rigid compressional tower 22,000 miles tall is going to have
a base that's wider than the troposphere is deep. I doubt it'll be doing
much shifting due to wind.

Not that it's particularly plausible either way, though.

22,000 miles worth of tower is simply not a viable project.

A 100 mile tower (free standing) of substantial mass is perhaps as far
out as you'd dare go.

~ BG

On Dec 9, 3:34*pm, Pat Flannery wrote:

That does bring up a problem for the space elevator cable though. This
thing is going to be going all the way from the Earth's surface clean
out through the Van Allen belts. There is going to be a terrific electrical
potential along its length, far more than fused the tethered satellite cable.

First and foremost, no. You build up potential along the tether due to
it being a conductor moving in a magnetic field. An orbital elevator
(at least a "classical" one, from a fix surface point to geosync and
beyond) doesn't move with respect to the Earth's magnetic field*.

Secondly, a "terrific electrical potential" is just what you need
(honestly, it's too bad such a tower wouldn't have more of one) - it's
called a power source. You just have to make sure your electrical
system can handle the load you want to put through it. For the test
tether, that wasn't the case.

--
Brian Davis

On Dec 9, 3:22*pm, Pat Flannery wrote:

N:dlzc D:aol T:com (dlzc) wrote:

On the way up, the "lift cable" is pulled westwards, drawing the
needed energy / momentum from both the Earth and the anchor.

I suspect one of the things being misunderstood here is that the cable
does not remain radial. As a mass moves along it, the cable is
deflected east or west, which results in a component of the tension (a
small component) to accelerate the mass west or east. What is changing
the tangential velocity of the payload mass is the tangential
component of the cable tension...

*The anchor can have the rockets.

And the rockets need fuel, which has to go up the space elevator, which
will pull it to the west, which means the anchor will need to fire its
rockets, which means they will need fuel... :-D

First, no: while the mass is ascending, it would indeed be "pulling
back" on the upper portion of the tower, that's not a static
situation, any more than a plucked string on a violin is. Second, with
the ascending payload mass either removed or stopped, you have a
situation where the cable as a whole has been deflected westward,
yes... which means the earth tether point must be to the east of the
cable, and therefore there's (again) a tangential component to the
tether tension that is accelerating the cable as a whole eastward,
speeding it back up.

I'm not sure why this is so surprising; I've given it to my P200
students as an exercise and had them get the right result (to be fair,
I let them use a non-tapered cable, as that wasn't a problem I wanted
to get them entangled in). Pearson put this all together very well in
his paper (I think in the 70's?) on orbital elevators - perhaps you
should acquaint yourself with the literature? It goes back further
than that even. Here's a start:

http://www.star-tech-inc.com/id4.html

Note that the paper by Isaacs et. al., in 1966, is written by a bunch
of folks who were oceanographers at the time. Seems only they had a
lot of experience with very long cables hanging under their own weight
(go figure ).

--
Brian Davis

On Dec 9, 2:57*pm, Pat Flannery wrote:

In other words:
Velocity of a object on the Earth's equator due to rotation
is around 725 mph.
Velocity of a object in GEO at around 22,250 miles up is
around 17,000 mph.
So where does the extra 16,275 mph velocity come from?

Tension in the cable. As has been pointing out (several times) the
cable is not static or vertical when moving mass in or out. Deflection
of the cable results in acceleration of the mass... that's essentially
how a bow and arrow works as well. Except here the tension is supplied
by orbital dynamics & angular momentum transfers, not a bent bow.

--
Brian Davis

On Dec 9, 9:52*pm, Orval Fairbairn
wrote:

I am fully aware of the physics of orbital mechanics and,
unlike most of the posters here, have worked the problems
for many years.

Actually, I suspect some of us *may* be of a similar level of
education and experience to you in this. At least that's what I
maintained when I defended my PhD in physics .

More seriously, it seem you doubt rational arguments on USENET.
Perhaps you should try doing an old-fashioned literature search and
read up on the subject? Or even just Google it (the new-fashioned
literature search). For instance, here's a nice collection of links
from one of the folks who has (professionally) worked on this topic:

http://www.star-tech-inc.com/id4.html

--
Brian Davis

On Dec 10, 7:05 am, Brian Davis wrote:
On Dec 9, 9:52 pm, Orval Fairbairn
wrote:

I am fully aware of the physics of orbital mechanics and,
unlike most of the posters here, have worked the problems
for many years.

Actually, I suspect some of us *may* be of a similar level of
education and experience to you in this. At least that's what I
maintained when I defended my PhD in physics .

More seriously, it seem you doubt rational arguments on USENET.
Perhaps you should try doing an old-fashioned literature search and
read up on the subject? Or even just Google it (the new-fashioned
literature search). For instance, here's a nice collection of links
from one of the folks who has (professionally) worked on this topic:

http://www.star-tech-inc.com/id4.html

--
Brian Davis

Technically the space elevator is doable, and roughly 36 fold more
doable with that of my lunar space elevator (LSE-CM/ISS).

~ Brad Guth Brad_Guth Brad.Guth BradGuth BG / “Guth Usenet”

Dear Brian Davis:

On Dec 10, 7:56*am, Brian Davis wrote:
On Dec 9, 3:22*pm, Pat Flannery wrote:

N:dlzcD:aol T:com (dlzc) wrote:

On the way up, the "lift cable" is pulled westwards,
drawing the needed energy / momentum from both
the Earth and the anchor.

I suspect one of the things being misunderstood here
is that the cable does not remain radial. As a mass
moves along it, the cable is deflected east or west,
which results in a component of the tension (a small
component) to accelerate the mass west or east.
What is changing the tangential velocity of the
payload mass is the tangential component of the
cable tension...

Yes. Would look much like a pulled bowstring...

David A. Smith

On Dec 10, 12:46*am, BradGuth wrote:
On Dec 9, 5:18 am, gabydewilde wrote:



On Dec 8, 6:44 pm, Robert Clark wrote:

*Very interesting article here reporting on researchers who had
previously announced a rapid means of producing synthetic gem sized
diamonds, now believe their methods will work to produce diamonds of
arbitrary size:

Artificial diamonds - now available in extra large.
18:11 13 November 2008 by Catherine Brahic.
"A team in the US has brought the world one step closer to cheap,
mass-
produced, perfect diamonds. The improvement also means there is no
theoretical limit on the size of diamonds that can be grown in the
lab.
"A team led by Russell Hemley, of the Carnegie Institute of
Washington, makes diamonds by chemical vapour deposition (CVD), where
carbon atoms in a gas are deposited on a surface to produce diamond
crystals.
"The CVD process produces rapid diamond growth, but impurities from
the gas are absorbed and the diamonds take on a brownish tint.
"These defects can be purged by a costly high-pressure, high-
temperature treatment called annealing. However, only relatively small
diamonds can be produced this way: the largest so far being a 34-carat
yellow diamond about 1 centimetre wide.
Microwaved gems
"Now Hemley and his team have got around the size limit by using
microwaves to "cook" their diamonds in a hydrogen plasma at 2200 °C
but at low pressure. Diamond size is now limited only by the size of
the microwave chamber used.
"The most exciting aspect of this new annealing process is the
unlimited size of the crystals that can be treated. The breakthrough
will allow us to push to kilocarat diamonds of high optical quality,"
says Hemley's Carnegie Institute colleague Ho-kwang Mao."http://www.newscientist.com/article/dn16036

*Original research article:

Enhanced optical properties of chemical vapor deposited single crystal
diamond by low-pressure/high-temperature annealing.
Yu-fei Meng, Chih-shiue Yan, Joseph Lai, Szczesny Krasnicki, Haiyun
Shu, Thomas Yu, Qi Liang, Ho-kwang Mao, and Russell J. Hemley
Published online before print November 12, 2008, doi: 10.1073/pnas.
0808230105
PNAS *November 18, 2008 * vol. 105 *no. 46 *17620-17625http://www.pnas.org/content/105/46/17620[abstract]

*The team's earlier research had showed they could make
synthetic diamonds of perhaps 50% greater hardness than natural
diamond. *This should correspond to 50% greater compressive strength
as well.
*Most discussion on the space elevator has centered on ultra strong
materials for a cable in tension. However, according to this recent
report,
synthetic diamond production can now be scaled up to arbitrarily
large sizes. So a compressive structure to space made of diamond might
be
feasible earlier, as diamond is much stronger in compression than in
tension.
*I've seen various estimates for the compressive strength of natural
diamond. If we take it as 400 GPa, then a space tower of diamond would
have
characteristic length of 400x10^9 Pa/(9.8m/s^2 x 3600 kg/m^3) =
1.13x10^7
meters, *or 11,300 km. If this new synthetic diamond method really
does create
diamond of 50% higher compressive strength than natural diamond, then
this
length would be 17,000 km.
*And these are lengths without taper. Considering also that this
maximal
height for an untapered *tower assumes constant gravity where in
actuality
the gravity is 1/16th as strong at 17,000 km altitude, it is possible
that a
tower made of diamond could reach all the way to geosynchronous
altitude
without taper.
*There aren't many references on the net available that do the
calculations for
a space tower in compression as opposed to a space elevator cable in
tension.
*Here's one that gives the equations and some sample calculations:

Optimal Solid Space Tower.http://arxiv.org/abs/physics/0701093

* *Bob Clark

Shall we say "Alchemy vindicated!" ?

It's easy actually. The only problem is in the size of things. All
that is required is a hot air, hydrogen or helium balloon with walls
of steel or rubbery plastics or a mix of both. Sure it seems way to
heavy but if you make it a few KM in diameter each floor will have
less than zero weight. Do the math. Flying cities are an oxymoron.
NASA already build solid state weather balloons that can stay in
"orbit" for years.

Academic Bookwurms can absorb gigantic amounts of information. It's
quite an amazing skill. It does however go at the expense of basic
imagination.

You know? The stuff dreamers live on? That 1% every project starts
with?

Space travel is only a dream, just like eternal life is.

*_* closing hailing frequency *_*

The 100+ km tower (free standing) is technically doable, as long as
you think equally big in all dimensions and do not otherwise restrict
intellectual talent and expertise.

Keeping the whole thing from sinking out of sight, such as falling
through Earth's crust, is not insurmountable. *Keeping investors happy
for what only their next generations will ever get to use, as such may
impose the most risk.

*~ Brad Guth Brad_Guth Brad.Guth BradGuth BG / “Guth Usenet”

Falling though the crust - thats funny.

I guess we could pump air into a continent and make it rise out of the
sea.

Could stick Alaska up there, no one seems to be using that anyway.

If we use hot air we could fly a continent around the planet.

It's not space travel but I reckon it the next best thing.



__________
http://blog.360.yahoo.com/factuurexpress

On Dec 10, 4:36 pm, gabydewilde wrote:
On Dec 10, 12:46 am, BradGuth wrote:



On Dec 9, 5:18 am, gabydewilde wrote:

On Dec 8, 6:44 pm, Robert Clark wrote:

Very interesting article here reporting on researchers who had
previously announced a rapid means of producing synthetic gem sized
diamonds, now believe their methods will work to produce diamonds of
arbitrary size:

Artificial diamonds - now available in extra large.
18:11 13 November 2008 by Catherine Brahic.
"A team in the US has brought the world one step closer to cheap,
mass-
produced, perfect diamonds. The improvement also means there is no
theoretical limit on the size of diamonds that can be grown in the
lab.
"A team led by Russell Hemley, of the Carnegie Institute of
Washington, makes diamonds by chemical vapour deposition (CVD), where
carbon atoms in a gas are deposited on a surface to produce diamond
crystals.
"The CVD process produces rapid diamond growth, but impurities from
the gas are absorbed and the diamonds take on a brownish tint.
"These defects can be purged by a costly high-pressure, high-
temperature treatment called annealing. However, only relatively small
diamonds can be produced this way: the largest so far being a 34-carat
yellow diamond about 1 centimetre wide.
Microwaved gems
"Now Hemley and his team have got around the size limit by using
microwaves to "cook" their diamonds in a hydrogen plasma at 2200 °C
but at low pressure. Diamond size is now limited only by the size of
the microwave chamber used.
"The most exciting aspect of this new annealing process is the
unlimited size of the crystals that can be treated. The breakthrough
will allow us to push to kilocarat diamonds of high optical quality,"
says Hemley's Carnegie Institute colleague Ho-kwang Mao."http://www..newscientist.com/article/dn16036

Original research article:

Enhanced optical properties of chemical vapor deposited single crystal
diamond by low-pressure/high-temperature annealing.
Yu-fei Meng, Chih-shiue Yan, Joseph Lai, Szczesny Krasnicki, Haiyun
Shu, Thomas Yu, Qi Liang, Ho-kwang Mao, and Russell J. Hemley
Published online before print November 12, 2008, doi: 10.1073/pnas.
0808230105
PNAS November 18, 2008 vol. 105 no. 46 17620-17625http://www.pnas.org/content/105/46/17620[abstract]

The team's earlier research had showed they could make
synthetic diamonds of perhaps 50% greater hardness than natural
diamond. This should correspond to 50% greater compressive strength
as well.
Most discussion on the space elevator has centered on ultra strong
materials for a cable in tension. However, according to this recent
report,
synthetic diamond production can now be scaled up to arbitrarily
large sizes. So a compressive structure to space made of diamond might
be
feasible earlier, as diamond is much stronger in compression than in
tension.
I've seen various estimates for the compressive strength of natural
diamond. If we take it as 400 GPa, then a space tower of diamond would
have
characteristic length of 400x10^9 Pa/(9.8m/s^2 x 3600 kg/m^3) =
1.13x10^7
meters, or 11,300 km. If this new synthetic diamond method really
does create
diamond of 50% higher compressive strength than natural diamond, then
this
length would be 17,000 km.
And these are lengths without taper. Considering also that this
maximal
height for an untapered tower assumes constant gravity where in
actuality
the gravity is 1/16th as strong at 17,000 km altitude, it is possible
that a
tower made of diamond could reach all the way to geosynchronous
altitude
without taper.
There aren't many references on the net available that do the
calculations for
a space tower in compression as opposed to a space elevator cable in
tension.
Here's one that gives the equations and some sample calculations:

Optimal Solid Space Tower.http://arxiv.org/abs/physics/0701093

Bob Clark

Shall we say "Alchemy vindicated!" ?

It's easy actually. The only problem is in the size of things. All
that is required is a hot air, hydrogen or helium balloon with walls
of steel or rubbery plastics or a mix of both. Sure it seems way to
heavy but if you make it a few KM in diameter each floor will have
less than zero weight. Do the math. Flying cities are an oxymoron.
NASA already build solid state weather balloons that can stay in
"orbit" for years.

Academic Bookwurms can absorb gigantic amounts of information. It's
quite an amazing skill. It does however go at the expense of basic
imagination.

You know? The stuff dreamers live on? That 1% every project starts
with?

Space travel is only a dream, just like eternal life is.

*_* closing hailing frequency *_*

The 100+ km tower (free standing) is technically doable, as long as
you think equally big in all dimensions and do not otherwise restrict
intellectual talent and expertise.

Keeping the whole thing from sinking out of sight, such as falling
through Earth's crust, is not insurmountable. Keeping investors happy
for what only their next generations will ever get to use, as such may
impose the most risk.

~ Brad Guth Brad_Guth Brad.Guth BradGuth BG / “Guth Usenet”

Falling though the crust - thats funny.

I guess we could pump air into a continent and make it rise out of the
sea.

Our crust is somewhat buoyant. Antarctica offers up to 35 km of
crust, more if you'd include them antipode mountains.

~ BG


Could stick Alaska up there, no one seems to be using that anyway.

If we use hot air we could fly a continent around the planet.

It's not space travel but I reckon it the next best thing.

__________http://blog.360.yahoo.com/factuurexpress