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Space Elevator by 2019?



 
 
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  #1  
Old June 27th 04, 07:55 AM
Steve Dufour
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Default Space Elevator by 2019?

Space elevator eyed as possible by 2019



ASSOCIATED PRESS
President Bush wants to return to the moon and put a man on Mars.
But scientist Bradley C. Edwards has an idea that's really out of this
world: an elevator that climbs 62,000 miles into space.

Mr. Edwards thinks an initial version could be operating in 15
years, a year earlier than Mr. Bush's 2020 timetable for a return to
the moon. He pegs the cost at $10 billion, a pittance compared with
other space endeavors.
"It's not new physics — nothing new has to be discovered, nothing
new has to be invented from scratch," he said. "If there are delays in
budget or delays in whatever, it could stretch, but 15 years is a
realistic estimate for when we could have one up."
Mr. Edwards is not just some guy with an idea. He's head of the
space elevator project at the Institute for Scientific Research in
Fairmont, W.Va. NASA already has given it more than $500,000 to study
the idea, and Congress has earmarked $2.5 million more.
"A lot of people at NASA are excited about the idea," said Robert
Casanova, director of the NASA Institute of Advanced Concepts in
Atlanta.
Mr. Edwards believes a space elevator offers a cheaper, safer form
of space travel that eventually could be used to carry explorers to
the planets.
Mr. Edwards' elevator would climb on a cable made of nanotubes —
tiny bundles of carbon atoms many times stronger than steel. The cable
would be about 3 feet wide and thinner than a piece of paper, but
capable of supporting a payload up to 13 tons.
The cable would be attached to a platform on the equator, off the
Pacific coast of South America where winds are calm, weather is good
and commercial airplane flights are few. The platform would be mobile
so the cable could be moved to get out of the path of orbiting
satellites.
David Brin, a science-fiction writer who formerly taught physics
at San Diego State University, believes the concept is solid but
doubts such an elevator could be operating by 2019.
"I have no doubt that our great-grandchildren will routinely use
space elevators," he said. "But it will take another generation to
gather the technologies needed."
Mr. Edwards' institute is holding a third annual conference on
space elevators in Washington starting tomorrow. A keynote speaker at
the three-day meeting will be John Mankins, NASA's manager of human
and robotics technology. Organizers say it will discuss technical
challenges and solutions and the economic feasibility of the elevator
proposal.
The space elevator is not a new idea. A Russian scientist,
Konstantin Tsiolkovsky, envisioned it a century ago. And Arthur C.
Clarke's novel "The Fountains of Paradise," published in 1979, talks
of a space elevator 24,000 miles high, and permanent colonies on the
moon, Mercury and Mars.
The difference now, Mr. Edwards said, is "we have a material that
we can use to actually build it."
He envisions launching sections of cable into space on rockets. A
"climber" — his version of an elevator car — would then be attached to
the cable and used to add more lengths of cable until eventually it
stretches down to the Earth.
  #2  
Old June 27th 04, 02:33 PM
Vincent Cate
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Default Space Elevator by 2019?

(Steve Dufour) wrote in message . com...
"It's not new physics ? nothing new has to be discovered, nothing
new has to be invented from scratch," he said. "If there are delays in
budget or delays in whatever, it could stretch, but 15 years is a
realistic estimate for when we could have one up."


Edwards is making it sound like we know how to make the rope when
the truth is we can not even make a rope of 1/10th the needed
strength/weight. We can make strong molecules, but we are not
able to bind these together into a really strong rope. The
space elevator needs a rope with tensile strength higher than
40 GPa and we have never made a rope with even 4 GPa. People
trying to get money from politicians have found they sometimes
get more by making things sound better than they are. Remember
how NASA lied about how good the shuttle was going to be in order
to get money from congress? Edwards may be doing a similar
thing here.

The rope is still a research problem. We had 20 GPa "carbon
whiskers", which are very similar to carbon-nanotubes, 48
years ago and we still don't know how to make a 4 GPa rope out
of these yet. To talk about a 15 year timetable for development
when the research for the rope is not finished yet is either
foolish or dishonest.

I think that 5 years ago Edwards was also estimating 15 years. And
I expect that 5 years from now he will still be estimating
15 years more.

--- Vince
  #3  
Old June 27th 04, 02:55 PM
Peter Fairbrother
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Default Space Elevator by 2019?

The thing I don't understand about a space elevator is how they are going to
get the first thread in place.

I read somewhere that they wanted to start at GSO and unreel it both
downwards and upwards simultaneously, but that won't work - the bits will
move sideways. Does anyone know?

Another is, why do they want to put it on the equator? It can touch down
anywhere on Earth. Near-space above the equator should be reserved for
orbits.

--
Peter Fairbrother

  #4  
Old June 27th 04, 04:02 PM
e7
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Default Space Elevator by 2019?

Peter Fairbrother wrote:

The thing I don't understand about a space elevator is how they are going
to get the first thread in place.


Give it to a cat.

A. They can thread anything through anywhere first time, second time, third
time,... I think u get the picture

B. They always land on their feet right side up.

C. They are cute.


  #5  
Old June 27th 04, 05:55 PM
Peter Fairbrother
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Default Space Elevator by 2019?

Joann Evans wrote:

Peter Fairbrother wrote:

The thing I don't understand about a space elevator is how they are going to
get the first thread in place.

I read somewhere that they wanted to start at GSO and unreel it both
downwards and upwards simultaneously, but that won't work - the bits will
move sideways. Does anyone know?


No. I agree the engineering is far off, but there's no physical
reason one could not do exactly as you say. Space elevators are
essentially long, thin orbiting objects that happen to be long enough to
reach the surface.


Consider an element at the Earthward end of the rope. It is moving
horizontally at a velocity v, and is kept in a circular path by the forces
of gravity and tension which give it a resultant vertical acceleration in
the direction of Earth.

Now decrease the tension, in order to extend the rope, and the acceleration
increases. The horizontal velocity component remains the same though, and as
the length of the element's orbit decreases, the period decreases too,
causing the rope to bend.



Another way to look at it is to consider the half-extended rope. It is
rotating at one revolution per second. Extend it and it slows like a
spinning ballerina opening her arms unless some extra angular momentum can
be gotten from somewhere.

As far as I can tell that cannot come from the interaction with the earth's
gravity, and certainly not sufficiently evenly over the entire length of the
rope to keep it straight, but perhaps I missed something?

I expect the people who fly tethers know a bit about doing this sort of
thing, but I haven't heard how the Elevator people plan to do it.



Another is, why do they want to put it on the equator? It can touch down
anywhere on Earth. Near-space above the equator should be reserved for
orbits.


Because, just like the big satcoms, that's the only place you can be
stationary with respect to Earth's surface.


I do not understand. Surely once it reaches equilibrium the rope does not
move relative to the spinning Earth, no matter the latitude at which the end
is attached?

It would certainly be possible to arrange for the rope to pass through the
GEO circle, with the Earth end attached at say 20 degrees North.

Think of a dangling chain. It goes almost vertically at the top, but may go
at an angle at the bottom.

Any other inclination (at
the same altitude) will trace out a figure-8 pattern on the ground.


Why would that be important?

Lower orbits will be even messier. You don't want to drag the end of
this thing through the atmosphere.


I'm afraid I cannot make head nor tail of that.




--
Peter Fairbrother

  #6  
Old June 27th 04, 05:57 PM
Peter Fairbrother
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Default Space Elevator by 2019?

Peter Fairbrother wrote:

Another way to look at it is to consider the half-extended rope. It is
rotating at one revolution per second.


per DAY.

Ooops.


--
Peter Fairbrother

  #7  
Old June 27th 04, 06:09 PM
Christopher James Huff
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Default Space Elevator by 2019?

In article ,
Peter Fairbrother wrote:

I read somewhere that they wanted to start at GSO and unreel it both
downwards and upwards simultaneously, but that won't work - the bits will
move sideways. Does anyone know?


The ends won't move sideways. Even if they tried to send them out that
way, small irregularities would throw them off...that position is
unstable. The portion extending past GEO will be drawn outward by
centrifugal force, the portion below it will be pulled inward by
gravity. It's basically tidal forces.

However, at the very beginning, they may use small rockets or thrown
weights to get the ends traveling in the right directions. Otherwise,
they might end up with both ends going one way and the center going the
other way, which could lead to a tangled cable when the satellite
attempted to climb to the "far" end.


Another is, why do they want to put it on the equator? It can touch down
anywhere on Earth. Near-space above the equator should be reserved for
orbits.


It can't touch anywhere on Earth. Gravitational force remains pointing
toward the center of the earth, while centrifugal force points
perpendicular to the axis of rotation. As you move from the equator, the
lower portion of the elevator will be pulled closer to parallel to the
earth's surface. This means more elevator in the atmosphere, a slightly
longer elevator, and some north-south tension on the anchor. It doesn't
have to be exactly equatorial, but it is easier the closer you are.

--
Christopher James Huff
http://home.earthlink.net/~cjameshuff/
POV-Ray TAG:
http://tag.povray.org/
  #8  
Old June 27th 04, 06:38 PM
Peter Fairbrother
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Default Space Elevator by 2019?

Christopher James Huff wrote:

In article ,
Peter Fairbrother wrote:

I read somewhere that they wanted to start at GSO and unreel it both
downwards and upwards simultaneously, but that won't work - the bits will
move sideways. Does anyone know?


The ends won't move sideways. Even if they tried to send them out that
way, small irregularities would throw them off...that position is
unstable.


Agreed

The portion extending past GEO will be drawn outward by
centrifugal force, the portion below it will be pulled inward by
gravity.


Agreed. But is a dynamically extending straight line stable? A simple
vertical one doesn't appear to be, but perhaps an angled one is? Is there a
stable solution (taking into account that the rope is extending)?

It's basically tidal forces.


Not that I don't believe you, but that is not an explanation. For instance,
how is the angular momentum fed to the rope? What slows the Earth end's
horizontal motion as it nears the earth?

Where's the friction?


Another is, why do they want to put it on the equator? It can touch down
anywhere on Earth. Near-space above the equator should be reserved for
orbits.


It can't touch anywhere on Earth.


As far as staying up it can touch anywhere, even the poles - but it also
wants to take momentum from the Earth, slightly lengthening the day, to give
to it's cargoes, and it can't be too near the poles and still do that.

But certainly 20 or 30 degrees North or South latitiude would be possible.
If it goes up at 45 degrees to start with, well why not?


--
Peter Fairbrother


  #9  
Old June 27th 04, 07:18 PM
Jorge R. Frank
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Default Space Elevator by 2019?

Peter Fairbrother wrote in
:

The thing I don't understand about a space elevator is how they are
going to get the first thread in place.

I read somewhere that they wanted to start at GSO and unreel it both
downwards and upwards simultaneously,


That is correct.

but that won't work - the bits
will move sideways. Does anyone know?


Only during deployment. Considering the tether stationary in its rotating
frame-of-reference, there are two apparent forces acting on it, a tidal
force that tends to pull the Earthward side Earthward and the anti-
Earthward side anti-Earthward (in other words, keeps the tether vertical
and in tension), and a Coriolis force that tends to pull the Earthward side
eastward (in the direction of orbital motion) and the anti-Earthward side
westward (opposite orbital motion) (in other words, tries to pull the
tether diagonally in the orbital plane). Once the tether is fully deployed
and is no longer unreeling, the Coriolis force goes to zero and the tidal
force pulls the tether vertical. The Earthward end can then be anchored to
the ground.

Another is, why do they want to put it on the equator? It can touch
down anywhere on Earth.


Not stably. A tether at non-zero latitude will have a side force acting on
it due to the tidal force no longer being perfectly vertical, which will
tend to make the upper end oscillate. That's assuming the lower end is
still anchored to the ground - if the lower end isn't anchored, you get the
figure-eight orbit Joann described. The whole point of a space elevator is
to turn space travel into a statics problem. Introducing dynamics is an
unnecessary complication to what is already a challenging statics problem.

You *can* anchor a space elevator at a non-zero latitude by making the
tether Y-shaped with the double end Earthward, and anchoring it at plus-
and-minus latitude. But the center of mass still needs to be over the
equator for stability. It's also more complicated to deploy.
--
JRF

Reply-to address spam-proofed - to reply by E-mail,
check "Organization" (I am not assimilated) and
think one step ahead of IBM.
  #10  
Old June 27th 04, 09:08 PM
Peter Fairbrother
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Default Space Elevator by 2019?

Jorge R. Frank wrote:

Peter Fairbrother wrote in
:

The thing I don't understand about a space elevator is how they are
going to get the first thread in place.

I read somewhere that they wanted to start at GSO and unreel it both
downwards and upwards simultaneously,


That is correct.

but that won't work - the bits
will move sideways. Does anyone know?


Only during deployment.


Yes.

At last, someone who agree that it will go sideways! Do you know any details
of how the deployment actually works?


Another is, why do they want to put it on the equator? It can touch
down anywhere on Earth.


Not stably. A tether at non-zero latitude will have a side force acting on
it due to the tidal force no longer being perfectly vertical, which will
tend to make the upper end oscillate.


Could you explain that please. Why should the side force make the upper end
oscillate? Can't any oscillation be damped? Is there no stable position?

That's assuming the lower end is
still anchored to the ground - if the lower end isn't anchored, you get the
figure-eight orbit Joann described.


If the lower end is not anchored then the end is going to whip around the
Earth's surface if you have a figure-8 orbit (if I understand you correctly
- CoM? not on the GEO plane?). Not advisable!

The whole point of a space elevator is
to turn space travel into a statics problem. Introducing dynamics is an
unnecessary complication to what is already a challenging statics problem.



Even if you are correct about the oscillation of an anchored tether, what
difference would it make? I mean, who cares if it oscillates a little bit
once a day? It is flexible after all. It's going to bend, move and flex
because of the cars going up and down anyway.



Don't get me started on the taper ...


--
Peter Fairbrother



 




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