Micro Gravity and A Space Elevator?

On Jun/11/2020 at 18:09, JF Mezei wrote :
On 2020-06-11 13:37, David Spain wrote:

Actually, have read articles that suggest rocket propulsion for this
purpose.


The space elevators I have seen used mag lev engine to cause it to rise
along the spine. (for instance, when Neelix and Tuvok use on in S03E19
of Star Trek Voyager :-)

Hydro Québec has a 450kv DC power line from James Bay to Boston which is
nearly 1500kim long. (it is +450kv and -=450km so really 900kV line). It
is nearly uninterrupted eccept for one station near St-Lawrence river
(Nicollet) where they draw some power from it to feed the QUébec grid,
with the rest going to USA.

That 1500 km line is *very* heavy. You want to use the best strength to
weight ratio, you don't want to add the constraint that the material is
also a good electrical conductor.


Alain Fournier

On Jun/10/2020 at 14:58, Jeff Findley wrote :
In article , says...

I haven't done any research in this area. Does anyone know of any
studies of micro-gravity inside the cab of a space elevator?

Remember to work, the entire system has to be under elastic tension. The
designs I've seen discussed use a big counter-mass at the far space end
of the cable to hold the system in place above the anchorpoint on
Earth's equator.

The trivial case is when the cab is down on the Earth side. Obviously
we're at 1G on the surface. I've presumed as the cab rises the effect of
Earth's gravity goes down as inverse square (Universal Gravitation):

https://en.wikipedia.org/wiki/Newton's_law_of_universal_gravitation

Are objects inside the cab of the space elevator near the "space" end
undergoing any form of microgravity? The system really isn't in free
fall because of the counter-mass suspended above it and the cable
running below. Does the tensive forces provide any form of microgravity
inside the cabin or are the occupants fully in 'free fall'? That doesn't
seem quite correct either. Only if the cabin were in orbit without any
connective cable. The counter-mass *is* appling force to the system to
hold it stable. Maybe the effect of any 'artificial gravity' are too
small to be consequential? If you were to suspend a cabin above the
counter-mass would you end up with an artificial gravity in the vector
direction of 180 degrees opposite the Earth's surface? i.e. the 'floor'
of the cabin becomes the surface of the cabin opposite the Earth,
alongside empty space?

I haven't studied this question at all. Any cites to any studies on this
appreciated.

See "Apparent gravitational field" he

https://en.wikipedia.org/wiki/Space_elevator

A rough approximation is that there is one point on the length of the
space elevator where the cabin crawling up the elevator is in "free
fall". This altitude is the geostationary orbital altitude. Anything
below that, and the earth's gravity is greater than centripetal force.
Anything above that, and the centripetal force is greater the earth's
gravity (so "down" is away from the earth!).

This also has a huge impact on what happens to any mass released from
the elevator. From the Wikipedia entry:

Any object released from the cable below that level would initially
accelerate downward along the cable. Then gradually it would
deflect eastward from the cable. On the cable above the level of
stationary orbit, upward centrifugal force would be greater than
downward gravity, so the apparent gravity would pull objects
attached to the cable upward. Any object released from the cable
above the geosynchronous level would initially accelerate upward
along the cable. Then gradually it would deflect westward from
the cable.

I think that what happens above geostationary altitude on an elevator is
often overlooked. People talk about putting a counter weight to keep the
cable taught. I think you want to have 30,000 km of cable above
geostationary altitude and you don't need to put a big massive object at
the end of those 30,000 km. What you put at the end of the cable is
another cable, this one spinning. All those cables are your counter
weight, but you can also use them to go away in the solar system. Just
going to 30,000 km above geostationary gives you enough angular momentum
to escape Earth. The spinning cable gives you more umpf, but it also
lets you go outside of Earth's equatorial plane.

That said, I'm not really a beleiver in an Earth space elevator. You
have to compare the cost of such an elevator not to the cost of a launch
on a Falcon 9. Not even to the cost of a launch on a soon to exist
Starship. But to the cost of a future generation of cheaper rockets. You
know rockets that can launch 100 times in a month before you need to
keep them grounded for a day for inspection and maintenance. Yeah, I
know I'm day dreaming about that kind of rocket, but weren't we already
day dreaming about space elevators?


Alain Fournier

On 2020-06-11 7:21 PM, Alain Fournier wrote:

That 1500 km line is *very* heavy. You want to use the best strength to
weight ratio, you don't want to add the constraint that the material is
also a good electrical conductor.


Alain Fournier

Ahh but for the near-miraculous carbon nanotube in the 'armchair'
configuration (acting as a metallic nanotube) it is! From Wikipedia:

"In theory, metallic nanotubes can carry an electric current density of
4 × 10**9 A/cm2, which is more than 1,000 times greater than those of
metals such as copper..."

Dave


Ref cites:

https://en.wikipedia.org/wiki/Carbon...e#cite_note-55

https://doi.org/10.1103%2FPhysRevLett.68.631

http://resolver.tudelft.nl/uuid:4e58...2-aabcc9eaad35

https://doi.org/10.1038%2Fnnano.2007.89

On 2020-06-11 7:41 PM, Alain Fournier wrote:
but weren't we already
day dreaming about space elevators?

Yeah until they got bombarded by a Starlink cluster f**k.

oh well.....

Dave

On 2020-06-11 7:45 PM, David Spain wrote:

Ref cites:

https://en.wikipedia.org/wiki/Carbon...ube#Electrical

On Jun/11/2020 at 19:45, David Spain wrote :
On 2020-06-11 7:21 PM, Alain Fournier wrote:

That 1500 km line is *very* heavy. You want to use the best strength
to weight ratio, you don't want to add the constraint that the
material is also a good electrical conductor.


Alain Fournier

Ahh but for the near-miraculous carbon nanotube in the 'armchair'
configuration (acting as a metallic nanotube) it is! From Wikipedia:

"In theory, metallic nanotubes can carry an electric current density of
4 × 10**9 A/cm2, which is more than 1,000 times greater than those of
metals such as copper..."

Dave


Ref cites:

https://en.wikipedia.org/wiki/Carbon...e#cite_note-55

https://doi.org/10.1103%2FPhysRevLett.68.631

http://resolver.tudelft.nl/uuid:4e58...2-aabcc9eaad35

https://doi.org/10.1038%2Fnnano.2007.89

Yes but carbon nanotube aren't a material. Until someone figures out how
to make a useable material out of them, you can't make a cable with
them. Just aligning lots of nanotubes one next to the other doesn't make
a strong cable. You need to get the nanotubes to hold together. And
if/when someone does figure out how to make a useable material out of
nanotubes, it isn't sure that such a material will still be highly
conductive. It might be, in which case yes running electricity in the
cable might make sense.


Alain Fournier

Le Jun/11/2020 Ã* 19:41, Alain Fournier a écritÂ*:
On Jun/10/2020 at 14:58, Jeff Findley wrote :
In article , says...

I haven't done any research in this area. Does anyone know of any
studies of micro-gravity inside the cab of a space elevator?

Remember to work, the entire system has to be under elastic tension. The
designs I've seen discussed use a big counter-mass at the far space end
of the cable to hold the system in place above the anchorpoint on
Earth's equator.

The trivial case is when the cab is down on the Earth side. Obviously
we're at 1G on the surface. I've presumed as the cab rises the effect of
Earth's gravity goes down as inverse square (Universal Gravitation):

https://en.wikipedia.org/wiki/Newton's_law_of_universal_gravitation

Are objects inside the cab of the space elevator near the "space" end
undergoing any form of microgravity? The system really isn't in free
fall because of the counter-mass suspended above it and the cable
running below. Does the tensive forces provide any form of microgravity
inside the cabin or are the occupants fully in 'free fall'? That doesn't
seem quite correct either. Only if the cabin were in orbit without any
connective cable. The counter-mass *is* appling force to the system to
hold it stable. Maybe the effect of any 'artificial gravity' are too
small to be consequential? If you were to suspend a cabin above the
counter-mass would you end up with an artificial gravity in the vector
direction of 180 degrees opposite the Earth's surface? i.e. the 'floor'
of the cabin becomes the surface of the cabin opposite the Earth,
alongside empty space?

I haven't studied this question at all. Any cites to any studies on this
appreciated.

See "Apparent gravitational field" he

https://en.wikipedia.org/wiki/Space_elevator

A rough approximation is that there is one point on the length of the
space elevator where the cabin crawling up the elevator is in "free
fall".Â* This altitude is the geostationary orbital altitude.Â* Anything
below that, and the earth's gravity is greater than centripetal force.
Anything above that, and the centripetal force is greater the earth's
gravity (so "down" is away from the earth!).

This also has a huge impact on what happens to any mass released from
the elevator.Â* From the Wikipedia entry:

Â*Â*Â* Any object released from the cable below that level would initially
Â*Â*Â* accelerate downward along the cable. Then gradually it would
Â*Â*Â* deflect eastward from the cable. On the cable above the level of
Â*Â*Â* stationary orbit, upward centrifugal force would be greater than
Â*Â*Â* downward gravity, so the apparent gravity would pull objects
Â*Â*Â* attached to the cable upward. Any object released from the cable
Â*Â*Â* above the geosynchronous level would initially accelerate upward
Â*Â*Â* along the cable. Then gradually it would deflect westward from
Â*Â*Â* the cable.

I think that what happens above geostationary altitude on an elevator is
often overlooked. People talk about putting a counter weight to keep the
cable taught. I think you want to have 30,000 km of cable above
geostationary altitude and you don't need to put a big massive object at
the end of those 30,000 km. What you put at the end of the cable is
another cable, this one spinning. All those cables are your counter
weight, but you can also use them to go away in the solar system. Just
going to 30,000 km above geostationary gives you enough angular momentum
to escape Earth. The spinning cable gives you more umpf, but it also
lets you go outside of Earth's equatorial plane.

I forgot to mention also that once you are past geostationary altitude,
you no longer have to figure out how to power your cabin. The cabin is
pulled out by the centrifugal force. Now you have to figure out what you
are going to do with the electricity you generate while controlling your
speed and/or slowing down. So using the cable after geostationary
altitude to go out in the solar system is really a free ride.


Alain Fournier

On 2020-06-11 8:01 PM, Alain Fournier wrote:
Yes but carbon nanotube aren't a material. Until someone figures out how
to make a useable material out of them, you can't make a cable with
them. Just aligning lots of nanotubes one next to the other doesn't make
a strong cable. You need to get the nanotubes to hold together. And
if/when someone does figure out how to make a useable material out of
nanotubes, it isn't sure that such a material will still be highly
conductive. It might be, in which case yes running electricity in the
cable might make sense.

Gee, weren't you just saying a few hours ago this was totally feasible
with today's technology? Or am I imagining things?

Did you not have carbon nanotubes in mind when you wrote that?

Dave

Allow me to refresh your memory:

On 2020-06-10 7:46 PM, Alain Fournier wrote:
On Jun/10/2020 at 18:35, Scott Kozel wrote :
On Wednesday, June 10, 2020 at 2:28:39 PM UTC-4, David Spain wrote:
On 2020-06-10 2:16 PM, Scott Kozel wrote:

It would be possible for the Moon today, given its much lower
gravity.Â* Given
its very slow rotation, a geosynchronous anchor would not work, but
they could
use one of the Moon's LaGrange points.

You're thinking a fuel depot? Water pumped up from the surface to the
anchored depot at L1 or L2? Micro-gravity available when docked?

I wasn't advocating or opposing a Moon space elevator, just saying
that it is
technologically feasible with today's materials.

I read somewhere that a Mars space elevator is technologically
feasible with
today's materials, but I am not sure about that.

An Earth space elevator is technologically feasible with today's ---- emphasis mine
material. See for instance
space.nss.org/wp-content/uploads/2000-Space-Elevator-NIAC-phase1.pdf
that's a little old, but materials available 20 years ago should be
available now. It would be too expensive, but technically, it is doable.
Costs estimates in that report are of $40B (page 11.4), but I would say
the author is a little optimistic, not ridiculously so, but a little
optimistic.

On Mars, I'm not sure how one would solve the problem caused by the low
orbiting moons but I think it would be doable. Anyway, for the time
being, the traffic from Mars surface to Mars orbit is too low to justify
the cost, whatever that cost would be :-)


Alain Fournier

On Jun/11/2020 at 20:26, David Spain wrote :
On 2020-06-11 8:01 PM, Alain Fournier wrote:
Yes but carbon nanotube aren't a material. Until someone figures out
how to make a useable material out of them, you can't make a cable
with them. Just aligning lots of nanotubes one next to the other
doesn't make a strong cable. You need to get the nanotubes to hold
together. And if/when someone does figure out how to make a useable
material out of nanotubes, it isn't sure that such a material will
still be highly conductive. It might be, in which case yes running
electricity in the cable might make sense.

Gee, weren't you just saying a few hours ago this was totally feasible
with today's technology? Or am I imagining things?

Did you not have carbon nanotubes in mind when you wrote that?

No I did not have carbon nanotubes in mind when I wrote that. I wrote
that using faulty memory. I thought that Edwards paper was about
building a space elevator with materials that actually existed when he
wrote his paper.

It is theoretically possible to build a space elevator using materials
that do exist today, but the taper ratio calls for an outrageously big
cable near geostationary altitude. The cost would be staggering.


Alain Fournier