Micro Gravity and A Space Elevator?

On Jun/12/2020 at 13:27, Greg (Strider) Moore wrote :
"Scott Kozel"Â* wrote in message

Something that I read in the literature a few years ago, what happens
if the
cable breaks?

It would depend on where it breaks, as to what part falls to the ground,
what part heads out into space, and what part might just wave around
at high
altitude and not fall.

Also the expense of rebuilding part or all of the elevator cable.

I saw someone do the math once. Ignoring any payloads, the cable itself
is so light that it "falling" on pretty much anyone or anything most
likely wouldn't do much kinetic damage. As for other problems (say falls
against a road, truck runs into it) that's another issue.

What happens is a complex issue. I wouldn't trust it to gently lay
itself on the ground. If the cable breaks, I would get out of its path.

Imagine if the cable breaks near the top. The broken off part just flies
off, we can ignore that part. The top of the cable still anchored to the
ground is still pulling the bottom part up but the bottom part is
pulling down harder than the top part, so the cable is slowly coming
down vertically. At first the cable is still taut, but it is gaining
vertical speed downward. This puts some slack in the top of the cable,
not the bottom where the pull is stronger. The bottom part of the cable
is accumulating on the ground near the anchor point. After a while, the
top part has too much angular speed for its lower altitude and starts to
pull the cable eastward. As the cable gets lower, this eastward pull
becomes stronger and the cable that was on the ground near the anchor
point starts being pulled eastward. When all the slack of the grounded
cable is taken up, the cable now has significant eastward speed and you
have a huge mass with significant speed pulling eastward. SNAP. Not pretty.

Now imagine that instead of breaking near the top, the cable breaks near
geosynchronous altitude. Much the same as above happens again, even if
the top part at geosynchronous altitude is not pulling up, it wants to
stay at its altitude but is pulled down by the bottom part. Things go
along much as in the case where the initial break was much higher up, it
only happens in a different time frame.

Imagine this time that the cable breaks at an altitude of 10,000. This
time ignore the bottom part which hits the ground. A little more
surprisingly, the top part will do much as the two examples above. The
cable first goes up vertically, then the bottom part loses angular
momentum. It starts pulling the cable westwardly, this westwardly pull
accelerates, but mostly in the bottom, while the top is accumulating
some slack. After a while, the top part receives the cue that there is a
big westwardly pull. Again SNAP.

In reality, all of the above can happen together. Different parts of the
cable will be pulling in different directions there will be some slack
accumulating here and there and the the cable becoming taut again and
snapping here and there.

The pieces falling to the ground might not be taut. Who knows, you could
have some big balls of cable that have curled up. And even if you don't
have big balls of cable, you can have some cable fall lightly to the
ground and then be dragged eastward pulling anything with it.

The physical properties of the material used to make the cable would
also have an effect on what happens.

Just a simple cable breaking could have a mostly unpredictable chaotic
outcome. One could put in some apparatus here and there on the cable to
keep it somewhat under control. If you roll in the cable where some
slack accumulates, you don't end up having wide speed differences for
different parts of the cable.

It certainly would be fairly spectacular to see though!

Yes. :-(


Alain Fournier

On Saturday, June 13, 2020 at 12:01:34 PM UTC-4, Alain Fournier wrote:

[. . . .]

Just a simple cable breaking could have a mostly unpredictable chaotic
outcome. One could put in some apparatus here and there on the cable to
keep it somewhat under control. If you roll in the cable where some
slack accumulates, you don't end up having wide speed differences for
different parts of the cable.

Part of the reason for having the Earth anchor being on a platform well out
in the ocean.

Still, the various outcomes could affect shipping and aviation over a wide
area.

On Jun/14/2020 at 01:43, JF Mezei wrote :
On 2020-06-13 12:01, Alain Fournier wrote:

What happens is a complex issue. I wouldn't trust it to gently lay
itself on the ground. If the cable breaks, I would get out of its path.

Following assumes a cut just below geosynchronous altitude and a tether
of equal mass from sea level to cut.


The way I see it, a mass exerts upward force when its orbital speed is
higher than needed at that altitude and it isn't allowed to rise.

With the 0 point being geosyncrhonous altitude, when the cut happens,
the position of cable at -1m is pretty close to having orbital speed. So
it weights less than the same lenght of cable at sea level, not only
because gravity is less, but also because it is nearly at orbital speed
where its weight (strict definition) would be near 0.

So with cable at sea level wanting to accelerate down at 9.8m/s2, the
portion at the top wants to go down at only 0.1 m/s2 (pr whatever low
value). The lower end wanting to accelerate more than the top would
create tension in cable, keeping it straight.


So far correct?

Not really. At very first, yes that is what will happen. The bottom part
will pull the cable down under some tension. This will cause parts
higher up to go eastward. Pieces higher up will start going eastward
slower than pieces in the middle, but with time the pieces higher up
will get more eastward speed than those in the middle. You get a chaotic
result, the cable breaks at multiple places.

Since the tip of cable had enough energy to almost be in orbit, as it is
pulled down, it will reach an altitude where its energy is above what is
necessary to be in orbit, below which, the cable will have upward force
and want to slow down the fall.

So, when the tip of cable is pulled down, its orbital instinct will be
to try to increase its forward speed. Won't that result in part of the
force pulling upwards since the cable will end up diagonal? Won't that
also slow down the fall?

Yes it will, but this phenomenon will happen all along the cable with
different intensities and different speeds at different heights.

Big picture, will the cable trying to move eastward during its fall give
back to the planet the eastward spin that the planet gave up when it
accelerated the cable?

The cable will give some negligeable amount of eastward spin to the
planet when it falls. I'm not quite sure what you mean by "the spin the
planet gave up when it accelerated the cable". When the cable is put in
place, it is put there at orbital speed at geosynchronous orbit. The
planet does not lose angular momentum when you anchor the cable to the
ground. The planet does lose some momentum when a payload goes up the
elevator. The amount of angular momentum the cable will give the planet
uppon falling to the ground has nothing to do with the amount the planet
lost while payloads were going up.

More imkportantly, will a 36,000km cable end up almostly circling the
equator (40,000) as it falls, or will there be significant amounts of
cable that will be piulot onto itself, greatly reducing the distance
covered as the cable falls back down?

Sorry, I can't parse piulot.

Now, changing cable to "structure". If it breaks at geostationary AND
ground levels, are there scenarios where distribution of mass and energy
might result in the structure going horizontal and at half geostationary
orbit ? (aka: top part lowering from geo to half and bottom part dragged
up to half geo?

No. A cable in orbit will always take a vertical orientation because of
tidal forces. The cable might break up in several pieces and some pieces
might go kind of horizontal momentarily (while spinning). But the pieces
that stay in orbit will stabilize in a vertical orientation.


Alain Fournier

You can look at the simulations of broken space elevator cables at
https://gassend.net/spaceelevator/breaks/index.html

I don't know that guy and I haven't validated his simulations but I have
no reasons to believe that his simulations are not accurate.


Alain Fournier


On Jun/15/2020 at 04:34, JF Mezei wrote :
On 2020-06-14 06:51, Alain Fournier wrote:

Not really. At very first, yes that is what will happen. The bottom part
will pull the cable down under some tension. This will cause parts
higher up to go eastward.

In wanting to go eastward, won't the cable also end up pulling up
because wanting to go faster will only work for so long until the slack
is gone and the increased speed is decelerated back to geosynch speed of
one orbit per 24 hours?




Pieces higher up will start going eastward
slower than pieces in the middle, but with time the pieces higher up
will get more eastward speed than those in the middle. You get a chaotic
result, the cable breaks at multiple places.

So if the cable between LEO and Geo breaks up, won't each individual
segment just drop till they are at an orbital speed that matches their
altitude?

For pieces low enough, they won't have enough altitude to convert a
droip in altitude into horizontal speed enough to stay in orbit, so they
will hit atmosphere and drop to sea level.

So assuming such a tether has separateion mechanism, not all of it would
fall down since pieces high enough to achieve orbital speed as they drop.

And if it breaks up into seperate segments, it also means that the
"heavy" segments near ground stop pulling down thosesegments near geo.

The cable will give some negligeable amount of eastward spin to the
planet when it falls. I'm not quite sure what you mean by "the spin the
planet gave up

I was thinking about the spin the Earth woudl give up when it
accelerates the elevators as they rise. But you're right in that the
cable itself is more likely to be assembled with rocket engines
accelerating it.





More imkportantly, will a 36,000km cable end up almostly circling the
equator (40,000) as it falls, or will there be significant amounts of
cable that will be piulot onto itself, greatly reducing the distance
covered as the cable falls back down?

Sorry, I can't parse piulot.

Sorry, pile up. Assuming the cable doesn't break, would it fall down
drawing a stright line towards the east that almost goes around all the
globe? Or woulf there be periods where the cable piles up onto itself,
then perhaps moves some, pules up again (at which point the whole
36,000km of cable make span perhaps just 1000km, with piles containing
36km of cable left every 10km.

No. A cable in orbit will always take a vertical orientation because of
tidal forces.

Sorry for basic orbital mechanic quaestion: say you have a 1000km cable
which is vertical, and the top at 36,000km altitude. (lets say for sake
of discussion geostationary is 36,001)

So a piece at 36,000 altitude is going at 9424km/h when on tether.
The piece at 35,000 altitiude is going ay 9162km/h. Both have sale
360°/24 hours angular speed.

Now, say the whole segment drops 1000km. How will the speeds of each
end accelerate relative to each other? Will the top end up with more
angular speed than the bottom? Or vice versa? Or would it remain
strictly the same?

If either side wants to accelerate horizontally more than the other,
won't the cable end up near horizontal eventually?