Cost of launch and laws of physics

Alain Fournier wrote in message ...
....snip...

From what I have read building an elevator from steel is not practical
but unlimited financial resources can make not practical possible.
On the other hand, in an other post gbaikie wrote :

Well according to NASA:
"But possible is not the same as practical. A steel cable 1 millimetre
across at ground level would have to be 40 billion kilometres in
diameter at geostationary orbit-equivalent to building an upside-down
mountain bigger than the Solar System."
http://plastics.about.com/library/PR/2001/blnasa2.htm

He also wrote more showing how that 40 billion km could be reduced.
But still if that is correct it might be true that it really is
impossible to do it with steel. I think that the NASA calculation
was done using low grade steel but maybe my memories of what I have
read about the possibility of doing it with steel are wrong. The
author of my readings on that was Henry Spencer, so it is not
possible that the author made a mistake :-) but it is possible
that my memories aren't accurate. I don't think this is interesting
enough to actually look up the best tensile strength of steel
and redo the calculations myself since I don't think anyone with
unlimited financial resources will come along and want to build
an elevator so I will leave it to this.

Alain Fournier

I remember getting very excited about the possibility
of lifting things from the surface via a cable suspended
from GEO--about fifty years ago. And then I did the math.

Best regards,
Len (Cormier)
PanAero, Inc. and Third Millennium Aerospace, Inc.
( http://www.tour2space.com )

gbaikie wrote:
Ian Stirling wrote in message ...
Alain Fournier wrote:
Michael Walsh wrote:
Christopher James Huff wrote:
In article ,
(John Ordover) wrote:

Putting the thing in the middle of the ocean makes building the thing
in the first place and using it for space access problematic.

Because nobody ever builds anything in the ocean, and even if they did,
nobody would ever launch anything into space from the ocean...
snip
If your financial resources were unlimited you could build a space
elevator out of steel.

No, you can't.
Steel isn't strong enough, and it ends up too heavy.
(A sizable fraction of the weight of the earth)

Well according to NASA:
"But possible is not the same as practical. A steel cable 1 millimetre
across at ground level would have to be 40 billion kilometres in
diameter at geostationary orbit-equivalent to building an upside-down
mountain bigger than the Solar System."
http://plastics.about.com/library/PR/2001/blnasa2.htm

But I don't know what they talking about. My guess is NASA is simply
wrong. It wouldn't be the first time. First the gravity of steel
40,000 billion kilometres in diameter in itself would be quite
significant and second I don't see any reason to hang the cable to the
It would, that's just based on the strength of materials, neglecting
other factors that make it impossible.

ground. It seems like they simply didn't want to think, but simply
plugged in some numbers. Hanging a cable from the "ground" to first 5
miles from surface would be problematic, but you could build a

The problem isn't the first 5, or even 500 miles, it's the rest.

A steel cable can only support a certain length without breaking.

Let's call it 20Km.
So, if you have a cable 400Km long, then 20Km up it, you need to double
the cable to make it not break.
At 60Km, it's eight times.
At 80Km, 16 times.
At 100Km 32 times, ...
At 400Km, it's a million times its original thickness, or if a millimeter
at the base, a meter across.

And you'r only 1% of the way there.

It doesn't really matter if you start a few hundred miles up, the
numbers are almost as bad.

--
http://inquisitor.i.am/ | | Ian Stirling.
---------------------------+-------------------------+--------------------------
Money is a powerful aphrodisiac, but flowers work almost as well.
-- Robert A Heinlein.

Len wrote:
Alain Fournier wrote in message ...
...snip...

From what I have read building an elevator from steel is not practical
but unlimited financial resources can make not practical possible.
On the other hand, in an other post gbaikie wrote :

Well according to NASA:
"But possible is not the same as practical. A steel cable 1 millimetre
across at ground level would have to be 40 billion kilometres in
diameter at geostationary orbit-equivalent to building an upside-down
mountain bigger than the Solar System."
http://plastics.about.com/library/PR/2001/blnasa2.htm

He also wrote more showing how that 40 billion km could be reduced.
But still if that is correct it might be true that it really is
impossible to do it with steel. I think that the NASA calculation
snip

I remember getting very excited about the possibility
of lifting things from the surface via a cable suspended
from GEO--about fifty years ago. And then I did the math.

It'll happen sometime soon.
Maybe a hundred years, maybe 20.

In the lab, ropes of nanotubes a few microns long have been made
that are strong enough, made from tubes much shorter than the
ropes length.

The thesis I've quoted in the past got results of 54Gpa, for a short
rope, which is plenty.

Once you get above a certain threshold (IIRC it's around density/strength
1.5*10^9) then you get to the more interesting category of space elevators -
those that can carry their own mass in payload in a year or two.
This brings up the possibility of bootstrapping from very small cables.

--
http://inquisitor.i.am/ | | Ian Stirling.
---------------------------+-------------------------+--------------------------
Windows 2000, software for next millenia. latin pun alert - Ian Stirling.

(Len) wrote in message . com...
Alain Fournier wrote in message ...
...snip...

From what I have read building an elevator from steel is not practical
but unlimited financial resources can make not practical possible.
On the other hand, in an other post gbaikie wrote :

Well according to NASA:
"But possible is not the same as practical. A steel cable 1 millimetre
across at ground level would have to be 40 billion kilometres in
diameter at geostationary orbit-equivalent to building an upside-down
mountain bigger than the Solar System."
http://plastics.about.com/library/PR/2001/blnasa2.htm

He also wrote more showing how that 40 billion km could be reduced.
But still if that is correct it might be true that it really is
impossible to do it with steel. I think that the NASA calculation
was done using low grade steel but maybe my memories of what I have
read about the possibility of doing it with steel are wrong. The
author of my readings on that was Henry Spencer, so it is not
possible that the author made a mistake :-) but it is possible
that my memories aren't accurate. I don't think this is interesting
enough to actually look up the best tensile strength of steel
and redo the calculations myself since I don't think anyone with
unlimited financial resources will come along and want to build
an elevator so I will leave it to this.

Alain Fournier

I remember getting very excited about the possibility
of lifting things from the surface via a cable suspended
from GEO--about fifty years ago. And then I did the math.

Oops. I did the math wrong. Only about forty years ago.

Len

Best regards,
Len (Cormier)
PanAero, Inc. and Third Millennium Aerospace, Inc.
( http://www.tour2space.com )

(gbaikie) wrote in message . com...

But I don't know what they talking about. My guess is NASA is simply
wrong. It wouldn't be the first time. First the gravity of steel
40,000 billion kilometres in diameter in itself would be quite
significant and second I don't see any reason to hang the cable to the
ground.

The gravity of the cable is irrelevant, because there's no way to get
enough material to make it. The cable does have to be thicker around
the geosynchronous point, because that part has to hold up the weight
of the elevator. Steel isn't strong enough to support its weight. You
get those ridiculous numbers that obviously can't work, because it
won't work. As far as I know, carbon nanotubes are the only material
with sufficient tensile strength to build a space elevator from.


It seems like they simply didn't want to think, but simply
plugged in some numbers. Hanging a cable from the "ground" to first 5
miles from surface would be problematic, but you could build a
structure up 5 mile & then start "hanging your cable".

I'm not real sure what you're suggesting, but removing the lowest 5
miles would make very little difference...geosynchronous orbit, which
would be slightly under the center of mass of the elevator, is over
22,000 miles out. Almost unnoticeable change in cable length.


Now, I wouldn't
limit your structure to only 5 miles- but if a "stupid mountain" can
get 5 miles above sea level, then it seems pretty obvious that you
"could" build a structure up this high, or *simply* build on top of a
mountain which on equator and is +20,000 feet high and make up
difference in building structure.

Mountains, and most other ground-based structures, are in a state of
compression. The elevator is in tension, if you tried to build a tower
5 miles tall it would probably collapse under its own weight. Even
mountains are limited in height by their weight. Plus, this giant
tower could cause a lot of damage if it falls.


But I would not choose a mountain,
rather build it in the ocean. I think you could make a structure 5
miles tall cheaper than adding a mile to some mountain site. But
either of these options would be expensive. And one might ask, why
build the rest of the Elevator- a structure which is 5 mile tall could
be used to support a mass driver.

A mass driver would put even more stress on the tower, and has several
disadvantages compared to an elevator. And you seem to be talking
about shooting straight up...you won't get into Earth orbit that way.


Or suppose you used a balloon. Say
the balloon floats at 100,000' (*around* 20 miles). Of course, this
balloon would monsterously huge- like mile plus in diameter volume.
And of course, you might think just the balloon was enough- why not
launch rocket from the Balloon & forget about the rest of the
elevator.

A balloon could get you above most of the atmosphere, but it is
otherwise of little help. It can't get you into orbit significantly
easier.


Or add in the structure of 5 mile, and connect this to the
huge balloon and have some mass driver. Or make your whole structure
"balloon-like" - a big diameter pipe which is made material which has
higher strength to weight as it got higher and make it be the support
of a mass driver or if you still want elevator at hanging your cable
at 20 miles up.

20 miles would still make no difference in elevator weight. You might
as well go all the way to the ground.


Or if you accelerate at a gee over gravity for 20
miles straight up, then at whatever speed this is you will go at least
another 20 miles straight up "coasting" and at around the point you
would normally stop, have the cable which takes you the rest of the
way up to GEO. Or you could have a continuous connection, but not put
any significant load from payload on the cable in area of 20 to 40
miles above Earth's surface.

If you accellerated straight up, you'd miss the low end of an elevator
directly above the tower. The idea of an elevator that stays outside
of the atmosphere has some uses, but would not be a direct substitute
for a full elevator, and a rotating tether design would probably work
better. In fact, you would probably have difficulty keeping a
stationary tether vertical.


Anyways, I'm just trying to show that there are many ways this could
be done. And actually I think the way to CATS is not Space elevator,
but rather I think plain old rockets will do, but maybe someday
something that sort of looks like a space elevator will be built
[After we get CATS using "normal" chemical rockets].

"Plain old rockets" are noisy, expensive, and failure-prone, as well
as causing potential damage to the atmosphere. An elevator would be
far superior.

It's always interesting to me how quickly threads on this group
descend into what we could do if we had technology we don't have and
that isn't on the horizon. Even if we had the right materials to
build a space elevator, we probably wouldn't - after all, we have the
tech right now to build a moonbase, and we don't do that, either.

Christopher James Huff wrote:

It seems like they simply didn't want to think, but simply
plugged in some numbers. Hanging a cable from the "ground" to first 5
miles from surface would be problematic, but you could build a
structure up 5 mile & then start "hanging your cable".


I'm not real sure what you're suggesting, but removing the lowest 5
miles would make very little difference...geosynchronous orbit, which
would be slightly under the center of mass of the elevator, is over
22,000 miles out. Almost unnoticeable change in cable length.

The currents of the lower atmosphere would exert substantial force on
the cable. Also I believe the lower part would need to be coated to
prevent chemical corrossion. It seems to me you would want it dipping in
as little atmosphere as possible.

Hop
http://clowder.net/hop/index.html

ground. It seems like they simply didn't want to think, but simply
plugged in some numbers. Hanging a cable from the "ground" to first 5
miles from surface would be problematic, but you could build a

The problem isn't the first 5, or even 500 miles, it's the rest.

"I would think the problem is the first 500 miles up, because above
this the orbital speed of the cable would reduce it's weight and you
are getting significantly further from earth thereby reducing gravity.
I mention 5 miles because if you had a structure this high and you
planning on lifting thing up this high using the structure, "I see" a
vertical track in which you accelerate payload, ie, if you were only
accelerating the payload at a modest 10' per sec you would reach the 5
mile point in 72 seconds and reach a speed of 726' per sec (495 mph
going straight up). If you made the structure robust enough to handle
large payload, this would be good for assisting a rocket launch- you
probably reduce the first stage of a typical rocket by say 1/2 of it's
mass and getting as much more payload into orbit- rather than spending
billions more to extend it up to GEO

"Plain old rockets" are noisy, expensive, and failure-prone, as well
as causing potential damage to the atmosphere.

Damage the atmosphere? How?

At most, the rockets will number in the tens any given year. Jet engines use
similar chemistry (at least to a LOX rocket) and number in the tens of
thousands, yet we have no atmospheric catastrophe.

An elevator would be
far superior.

No argument there. It's a *shame* that most of us will already have left the
Earth, without our bodies, before the thing is financed let alone operating.

Anyways, I'm just trying to show that there are many ways this could
be done. And actually I think the way to CATS is not Space elevator,
but rather I think plain old rockets will do, but maybe someday
something that sort of looks like a space elevator will be built
[After we get CATS using "normal" chemical rockets].

I'm interested in why you think so.

I think a Space elevator would need a high volume of traffic to
economically have a chance of working. A higher volume of traffic
would also "solve" the problem with the high cost of rockets- and I
think you need significantly less volume is needed with rockets. And
even a space elevator made of long nano carbon would need lots of mass
in space which could done at lower cost if you already had significant
infrastructure in space. Plus their would be significantly more
political will for doing this elevator.
Finally, the market for this new stronger material which makes a space
elevator "seem possible" would have much higher demand currently for
things like bridges. You could sell this stuff tomorrow to some bridge
project, whereas you would need to wait for the elevator to begin
construction- and if NASA or some govt was doing it could take a
decade or more before plans were finalized.
And finally I wonder about the gravity losses- the slower to orbit the
more significant this becomes- the faster you accelerate and the
higher speeds you attain on a Space elevator the more problematic it
becomes. I think that if you could wave a magic wand and have a space
elevator magically appear, that rockets could still out compete it-
assuming now no laws were passed preventing this competition.