Can we now build the "space tower"?

On Dec 16, 7:06 am, Bryan Derksen wrote:
Yousuf Khan wrote:
BradGuth wrote:
On Dec 15, 12:24 pm, Yousuf Khan wrote:
BradGuth wrote:
A 150 km tower of compression is not the same application as your
50,000 km of tension.
Aren't they both for space elevator purposes?
Not at all. One would offer access to orbital space, and the other
would offer access to space that's 150 km above the surface of Earth.

They are both a form of orbit.

The top of a 150km tower is not in any useful sense "in orbit". If you
drop something off of it, it will simply plummet to the ground.

To be in orbit one must not only be at the proper altitude, one must
also be at the proper velocity. I suppose you could put an
electromagnetic launcher at the top of the 150 km tower, but that makes
the already-hard engineering vastly harder.

Exactly, not that having a km2 platform at 150 km wouldn't otherwise
come in real handy.

~ BG

On Dec 16, 8:57 am, Puppet_Sock wrote:
On Dec 15, 4:55 pm, BradGuth wrote:

On Dec 15, 10:06 am, Puppet_Sock wrote:
[snip]
Maybe you have not been paying attention. But a 100 km
high tower has nothing to do with an orbital tower.
Socks

Correct, as it never did. So, what's your point?

Well, again, maybe you have not been paying attention,
but the OP talked about a17,000 km tower, not 100 km.
So, maybe *you* think that 100 km is a "space tower"
but the OP was talking about a beanstalk.

So, my point was, your remarks about a 100 km tower
were not relevant.
Socks

17,000 km is silly, as that's why I've suggested the 100 km or 150 km
as technically doable.

A 58,000 km beanstalk as a tether that's starting off from our Selene/
moon to its L1, and than onto reaching its dipole element to within 2r
of Earth, is however doable.

~ BG

On Dec 16, 11:42 am, Brian Davis wrote:
On Dec 15, 8:20 pm, Yousuf Khan wrote:

At around 10-15 km up, they will be contending against
the Jet Stream, sometimes reaching upto 400 km/h.

I always find it humorous that when talking about very tall, space-
elevator-style constructions, the terrifying jet stream always seems
to pop up. For a structure in compression 150 km high, any minor force
exerted by the wind below 10 km is literally going to be like a high-
velocity wind directed at my ankles: locally something to be concerned
about, but not a factor for the tower. And for tensional
(conventional) space elevators, it's even sillier: you build them at
the equator, and their minimum cross-section is down in the "turbulent
ten" lowest kilometers. Besides which, there is no jet stream at the
equator. Sigh... invoking non-applicable threats into situations where
they wouldn't matter much anyway really doesn't inspire confidence in
the line of reasoning.

--
Brian Davis

The status quo norm of Usenet/newsgroups is to continually and
perpetually topic/author stalk and bash for all it's worth, and then
some. It's kind of a Zionist/Nazi blood-sport that they like to play,
but only as long as they are publicly funded and/or as having been
faith-based funded.

Think of it as the modern way of killing off any messenger that rocks
their mainstream good ship LOLLIPOP.

~ BG

On Dec 16, 10:06*am, Bryan Derksen wrote:
Yousuf Khan wrote:
BradGuth wrote:
On Dec 15, 12:24 pm, Yousuf Khan wrote:
BradGuth wrote:
A 150 km tower of compression is not the same application as your
50,000 km of tension.
Aren't they both for space elevator purposes?
Not at all. *One would offer access to orbital space, and the other
would offer access to space that's 150 km above the surface of Earth.

They are both a form of orbit.

The top of a 150km tower is not in any useful sense "in orbit". If you
drop something off of it, it will simply plummet to the ground.

To be in orbit one must not only be at the proper altitude, one must
also be at the proper velocity. I suppose you could put an
electromagnetic launcher at the top of the 150 km tower, but that makes
the already-hard engineering vastly harder.

A similar idea is proposed he

The Space Pier
A hybrid Space-launch Tower concept.
http://autogeny.org/tower/tower.html

This proposes structures 100 km high and 300 km long that would allow
electromagnetic launchers to launch large payloads including manned
craft along a horizontal track at the top to orbital velocities. The
problem is the great horizontal length and the numerous 100 km high
support structures underneath increase the cost and complexity by
orders of magnitude.
It would be nice if could do this instead along a single vertical
tower. The problem is you need the 8 km/sec orbital velocity to be in
the horizontal direction to achieve orbit. What might work for
unmanned cargo would be to have the high g's required to get to 8 km/
sec over 100 km distance operate along the vertical tower then at the
top have a short ramp that curved over horizontally to translate that
vertical velocity into a horizontal velocity.
The acceleration, a, required for a straight distance, d, needed to
get to a speed, v, is: a = v^2/(2*d). So to reach 8,000 m/s over a
100,000 m distance would require a 320 m/s^2 acceleration, about 32
g's. This is *probably* too high for humans. But what really stops the
idea for manned craft is the curved ramp at the top to turn the craft
horizontally.
The acceleration along a circular path is: a = v^2/r. To get the
acceleration down to even 32 g's would require the radius to be 200
km, and you have the same problem of a long horizontal distance that
would have to have multiple towers beneath it supporting it. However,
unmanned cargo can be strengthened to withstand 10's of thousands of
g's of acceleration. So the curved ramp would only have to be a few
10's of meters wide in this case, and it could be supported by a
single vertical tower.
What might work instead for manned craft would be to get to the high
orbital speed in the vertical direction along the vertical tower as
before but then to use aerodynamic surfaces, i.e. lift, to curve the
path to turn the vertical velocity into the horizontal velocity needed
for orbit. The problem now is you would *probably* need 200 to 300 km
vertical distance to keep the acceleration low enough for humans while
attaining the 8,000 m/s velocity needed for orbit. But the air is
quite thin at such altitudes so you would need quite large aerodynamic
surfaces to effect the required lift force. Additionally the drag for
such large surfaces at such high speeds might cause you to lose most
of the velocity you had already attained traveling up the tower.
However, possibly some hypersonic aerodynamic shapes could have a
sufficiently large lift/drag ratios, say close to 8, that not much
velocity would be lost while achieving the required lift force. See
for example the first graph he

Hypersonic Vehicle Design.
http://www.aerospaceweb.org/design/w...r/design.shtml

Above, I said only *probably* 32 g's would be too high for humans.
This is because there were experiments that human subjects could
withstand markedly higher accelerations using water immersion. See for
example the table at the bottom of this page:

Adventuring hazards.
http://hiddenway.tripod.com/hero/hazards.html


Bob Clark

In rec.arts.sf.science Brian Davis wrote:
On Dec 15, 8:20?pm, Yousuf Khan wrote:

At around 10-15 km up, they will be contending against
the Jet Stream, sometimes reaching upto 400 km/h.

I always find it humorous that when talking about very tall, space-
elevator-style constructions, the terrifying jet stream always seems
to pop up. For a structure in compression 150 km high, any minor force
exerted by the wind below 10 km is literally going to be like a high-
velocity wind directed at my ankles: locally something to be concerned
about, but not a factor for the tower. And for tensional
(conventional) space elevators, it's even sillier: you build them at
the equator, and their minimum cross-section is down in the "turbulent
ten" lowest kilometers. Besides which, there is no jet stream at the
equator. Sigh... invoking non-applicable threats into situations where
they wouldn't matter much anyway really doesn't inspire confidence in
the line of reasoning.

I think people also forget about the effect of atmospheric density. Jet
streams are fast but they aren't all *that* strong. They're very high and
therefore are in very thin air, which substantially reduces the force that
they will impart to anything they encounter.

Typical skyscrapers are built to withstand hurricane-force winds, which
happen at sea level and are therefore more forceful. Those winds also act
along the entire height of the skyscraper instead of just some small
portion, which as you point out makes them even less significant.

--
Mike Ash
Radio Free Earth
Broadcasting from our climate-controlled studios deep inside the Moon

On Dec 16, 12:37 pm, Michael Ash wrote:
In rec.arts.sf.science Brian Davis wrote:



On Dec 15, 8:20?pm, Yousuf Khan wrote:

At around 10-15 km up, they will be contending against
the Jet Stream, sometimes reaching upto 400 km/h.

I always find it humorous that when talking about very tall, space-
elevator-style constructions, the terrifying jet stream always seems
to pop up. For a structure in compression 150 km high, any minor force
exerted by the wind below 10 km is literally going to be like a high-
velocity wind directed at my ankles: locally something to be concerned
about, but not a factor for the tower. And for tensional
(conventional) space elevators, it's even sillier: you build them at
the equator, and their minimum cross-section is down in the "turbulent
ten" lowest kilometers. Besides which, there is no jet stream at the
equator. Sigh... invoking non-applicable threats into situations where
they wouldn't matter much anyway really doesn't inspire confidence in
the line of reasoning.

I think people also forget about the effect of atmospheric density. Jet
streams are fast but they aren't all *that* strong. They're very high and
therefore are in very thin air, which substantially reduces the force that
they will impart to anything they encounter.

Typical skyscrapers are built to withstand hurricane-force winds, which
happen at sea level and are therefore more forceful. Those winds also act
along the entire height of the skyscraper instead of just some small
portion, which as you point out makes them even less significant.

--
Mike Ash
Radio Free Earth
Broadcasting from our climate-controlled studios deep inside the Moon

Spooks, moles and MIB of the mainstream status quo have license to
kill.

~ BG

BradGuth wrote:

Spooks, moles and MIB of the mainstream status quo have
license to kill.

Now that you gave up the secret, you have to kill everybody.
Turkey.

--
"From each according to his ability, to each according to his
need."
--Karl Marx, on "the ideal state of communism"
"You may have to give up a piece of your pie so that someone
else can have more."
--Obama, explicitly endorsing "the ideal state of communism"

On Dec 16, 9:22 am, Robert Clark wrote:

Diamond is valuable because of its rarity.

Only partly. Diamond is valuable mostly because De Beers invented the
engagement ring and persuaded people they needed it, in order to raise
the price of certain (now called gem) diamonds. Before that, diamond
wasn't so valuable, even though it was still rare.

Yousuf Khan wrote:

There is no reason why anyone should worship this worthless shiny stone.
This stone whose most useful purpose is as a material for cutting and
abrading equipment.

So it's not worthless, then?

Until we can find ways of harnessing degenerate
matter from dwarf stars or neutron stars, it's our hardest known material.

Since as you say such matter is degenerate, that means that it isn't
harnessable. White dwarf and neutron star matter is not stable in
substellar lumps.

--
Erik Max Francis && && http://www.alcyone.com/max/
San Jose, CA, USA && 37 18 N 121 57 W && AIM, Y!M erikmaxfrancis
Walking in space, man has never looked more puny or insignificant.
-- Alexander Chase

In rec.arts.sf.science BradGuth wrote:
On Dec 16, 12:37 pm, Michael Ash wrote:
In rec.arts.sf.science Brian Davis wrote:
On Dec 15, 8:20?pm, Yousuf Khan wrote:

At around 10-15 km up, they will be contending against
the Jet Stream, sometimes reaching upto 400 km/h.

I always find it humorous that when talking about very tall, space-
elevator-style constructions, the terrifying jet stream always seems
to pop up. For a structure in compression 150 km high, any minor force
exerted by the wind below 10 km is literally going to be like a high-
velocity wind directed at my ankles: locally something to be concerned
about, but not a factor for the tower. And for tensional
(conventional) space elevators, it's even sillier: you build them at
the equator, and their minimum cross-section is down in the "turbulent
ten" lowest kilometers. Besides which, there is no jet stream at the
equator. Sigh... invoking non-applicable threats into situations where
they wouldn't matter much anyway really doesn't inspire confidence in
the line of reasoning.

I think people also forget about the effect of atmospheric density. Jet
streams are fast but they aren't all *that* strong. They're very high and
therefore are in very thin air, which substantially reduces the force that
they will impart to anything they encounter.

Typical skyscrapers are built to withstand hurricane-force winds, which
happen at sea level and are therefore more forceful. Those winds also act
along the entire height of the skyscraper instead of just some small
portion, which as you point out makes them even less significant.

Spooks, moles and MIB of the mainstream status quo have license to
kill.

That's, er, fascinating, but what's it got to do with jet streams or space
towers or, well, *anything*?

--
Mike Ash
Radio Free Earth
Broadcasting from our climate-controlled studios deep inside the Moon