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Towards routine, reusable space launch.



 
 
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  #91  
Old June 21st 18, 03:02 AM posted to sci.space.policy
Scott M. Kozel[_2_]
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Posts: 141
Default Towards routine, reusable space launch.

On Wednesday, June 20, 2018 at 8:21:31 PM UTC-4, Alain Fournier wrote:

The cable is tapered, so it is stronger at geostationary altitude.
The most likely reason for the cable to break is if it is hit by
something. The cable being very big at geostationary altitude (and most
likely multi-stranded) it is probably more likely to survive a hit there.


Sooner or later an aircraft will blunder into the area and hit the
cable and break it. Is there any way to prevent that?
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  #93  
Old June 21st 18, 11:26 AM posted to sci.space.policy,sci.physics,rec.arts.sf.science
Jeff Findley[_6_]
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Posts: 1,577
Default Towards routine, reusable space launch.

In article ,
says...

Alain Fournier wrote on Tue, 19 Jun 2018
19:45:53 -0400:

On Jun/18/2018 at 11:00 PM, Fred J. McCall wrote :
Alain Fournier wrote on Mon, 18 Jun 2018
21:06:46 -0400:


You put the cable on an east coast.


Uh, do you mean west coast? If the thing falls isn't it going to lay
out along the direction of spin, which means it falls to the west.


Uh, no I meant east coast.

At least one of the two of us is making a very silly mistake here.


That would be me, although the 'obvious things' you mentioned were no
help at all.

For some reason known only to my tiny mind it was thinking of the
tether structure as having zero tangential velocity. That meant that
as it fell the Earth would rotate out from under it, leading to a fall
to anti-spinward.

Of course, that's absolutely wrong, since the further up the cable you
go the higher the tangential velocity has to be for the thing to stay
radially 'still'. That means as it falls the upper portions of the
cable will 'outrun' the surface of the Earth and it will fall to
spinward (to the East), which is what you said.

DOH!


It's kind of terrifying what the thing does. And where it breaks has a
huge impact on what it does as it falls.

http://gassend.net/spaceelevator/breaks/index.html

Jeff
--
All opinions posted by me on Usenet News are mine, and mine alone.
These posts do not reflect the opinions of my family, friends,
employer, or any organization that I am a member of.
  #94  
Old June 21st 18, 12:23 PM posted to sci.space.policy
Scott M. Kozel[_2_]
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Posts: 141
Default Towards routine, reusable space launch.

On Thursday, June 21, 2018 at 6:26:58 AM UTC-4, Jeff Findley wrote:

It's kind of terrifying what the thing does. And where it breaks has a
huge impact on what it does as it falls.

http://gassend.net/spaceelevator/breaks/index.html


Plus having to rebuild the whole thing, that would be expensive.
  #95  
Old June 21st 18, 02:16 PM posted to sci.space.policy
Greg \(Strider\) Moore
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Posts: 595
Default Towards routine, reusable space launch.

"Jeff Findley" wrote in message
...

In article ,
says...

On Wednesday, June 20, 2018 at 8:21:31 PM UTC-4, Alain Fournier wrote:

The cable is tapered, so it is stronger at geostationary altitude.
The most likely reason for the cable to break is if it is hit by
something. The cable being very big at geostationary altitude (and most
likely multi-stranded) it is probably more likely to survive a hit
there.


Sooner or later an aircraft will blunder into the area and hit the
cable and break it. Is there any way to prevent that?


Also orbital debris. ISS maneuvers to avoid large bits. Not sure how
you could do that with the space elevator.

Jeff


The answer I've seen is you intentionally cause a "wave" to occur in the
cable to that the peak of the wave moves the cable out of the way of the
debris.
I find that... questionable....

I love the idea of a space elevator, but I sure do question the details.



--
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CEO QuiCR: Quick, Crowdsourced Responses. http://www.quicr.net
IT Disaster Response -
https://www.amazon.com/Disaster-Resp...dp/1484221834/

  #96  
Old Yesterday, 01:57 AM posted to sci.space.policy,sci.physics,rec.arts.sf.science
Alain Fournier[_3_]
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Posts: 312
Default Towards routine, reusable space launch.

On Jun/21/2018 at 1:35 PM, JF Mezei wrote :
On 2018-06-21 06:26, Jeff Findley wrote:

http://gassend.net/spaceelevator/breaks/index.html



Looked at "breaks at counter weight" (longest section of cable that
falls down with only counter weight going away)

Why would the falling cable become "loose" and snake ?

Since the top most portions, when being pulled down, would accelerate
more that portions below it, wouldn't the cable remain raughts and thus
no slack that allows snaking ?


Because of elasticity. I don't know how they chose a value for the
elasticity of the cable. It is very difficult to know how elastic a
cable will be if you don't know how the cable will be built. But I would
expect that a space elevator cable would become loose after snapping.

Why would it break up in space as it falls?


Take a strand of spaghetti (not fresh spaghetti, the dried variety you
will find in a grocery store) hold one end in your left hand the other
end in your right hand and bend until it snaps. You should do this over
a counter with a wall behind. After the spaghetti snaps you will have
one piece in your right hand, another piece in your left hand. But look,
you will see there is a third piece that went flying into the wall and
is now on the counter. Take another strand try again, you will get the
same result. If you repeat several times you might get a different
result once or twice, but almost every time it will break in three pieces.

When you bend a strand of spaghetti until is snaps, it will snap into
two pieces, then the whiplash will break it once more. A space elevator
cable would have much a more complex whiplash than a strand of
spaghetti. So breaking into multiple pieces isn't impossible.

Once again that will depend on the physical properties of the cable. If
instead of breaking spaghetti you tried doing the same with pieces of
wood, you wouldn't get three pieces. But if you don't use fresh pasta
and you didn't get three pieces while breaking your spaghetti, remind me
to bring my own pasta if I ever go dining at your place.

If you did multiple spaghetti breaking tests, let me propose that you
pick up all the pieces. Boil them until al dente. Strain them. Do not
rinse in cold water. Then either mix them with pesto verde or put
St-Jacques sauce over it. Delicious. If you need a recipe for the pesto
verde or the St-Jacques sauce you can send me a private e-mail.


Alain Fournier
  #97  
Old Yesterday, 05:22 AM posted to sci.space.policy,sci.physics,rec.arts.sf.science
Sergio
external usenet poster
 
Posts: 35
Default Towards routine, reusable space launch.

On 6/21/2018 7:57 PM, Alain Fournier wrote:
On Jun/21/2018 at 1:35 PM, JF Mezei wrote :
On 2018-06-21 06:26, Jeff Findley wrote:

http://gassend.net/spaceelevator/breaks/index.html



Looked at "breaks at counter weight" (longest section of cable that
falls down with only counter weight going away)

Why would the falling cable become "loose" and snake ?

Since the top most portions, when being pulled down, would accelerate
more that portions below it, wouldn't the cable remain raughts and thus
no slack that allows snaking ?


Because of elasticity. I don't know how they chose a value for the
elasticity of the cable. It is very difficult to know how elastic a
cable will be if you don't know how the cable will be built. But I would
expect that a space elevator cable would become loose after snapping.

Why would it break up in space as it falls?


Take a strand of spaghetti (not fresh spaghetti, the dried variety you
will find in a grocery store) hold one end in your left hand the other
end in your right hand and bend until it snaps. You should do this over
a counter with a wall behind. After the spaghetti snaps you will have
one piece in your right hand, another piece in your left hand. But look,
you will see there is a third piece that went flying into the wall and
is now on the counter. Take another strand try again, you will get the
same result. If you repeat several times you might get a different
result once or twice, but almost every time it will break in three pieces.

When you bend a strand of spaghetti until is snaps, it will snap into
two pieces, then the whiplash will break it once more. A space elevator
cable would have much a more complex whiplash than a strand of
spaghetti. So breaking into multiple pieces isn't impossible.

Once again that will depend on the physical properties of the cable. If
instead of breaking spaghetti you tried doing the same with pieces of
wood, you wouldn't get three pieces. But if you don't use fresh pasta
and you didn't get three pieces while breaking your spaghetti, remind me
to bring my own pasta if I ever go dining at your place.

If you did multiple spaghetti breaking tests, let me propose that you
pick up all the pieces. Boil them until al dente. Strain them. Do not
rinse in cold water. Then either mix them with pesto verde or put
St-Jacques sauce over it. Delicious. If you need a recipe for the pesto
verde or the St-Jacques sauce you can send me a private e-mail.


Alain Fournier


Alains idea to make a "space elevator" out of al dente spehetti is an
amazing idea. Who bring the meat ball ?
  #98  
Old Yesterday, 05:24 AM posted to sci.space.policy,sci.physics,rec.arts.sf.science
Sergio
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Posts: 35
Default Towards routine, reusable space launch.

On 6/20/2018 7:07 PM, Fred J. McCall wrote:
Sergio wrote on Wed, 20 Jun 2018 15:42:56 -0500:

On 6/19/2018 4:38 PM, Fred J. McCall wrote:
Sergio wrote on Tue, 19 Jun 2018 15:58:10 -0500:

On 6/19/2018 2:45 AM, Fred J. McCall wrote:
Sergio wrote on Mon, 18 Jun 2018 22:17:21 -0500:

On 6/18/2018 8:06 PM, Alain Fournier wrote:
On Jun/18/2018 at 2:45 PM, Sergio wrote :
On 6/16/2018 8:54 AM, Alain Fournier wrote:
On Jun/15/2018 at 11:34 PM, Fred J. McCall wrote :
JF Mezei wrote on Fri, 15 Jun 2018
22:13:01 -0400:

On 2018-06-15 19:21, Alain Fournier wrote:

Yes. But I think I am a little less optimistic than you about it
becoming practical in the future. If we have fantastic materials
in the
future, maybe an elevator will become more practical,


Apart from lifting geostationary satellites to just below orbit and
then
let them use their own thrusters to position to their assigned
slot/longitude, what other use would a space elevator have ?


You go above the GEO point on the cable and get flung on
interplanetary trajectories.

Yes!

You would also likely put at least one cable above GEO rotating in a
plane perpendicular to the main cable. So you can give an extra push for
interplanetary trajectories and to fine tune in which direction you
depart for said trajectories.

You can also jump off at an altitude of about 15000 km (that figure is
from the top of my head, it might be more or might be less). From there
after a few passes of aero-braking you can reach LEO with very small
thrusters.

For polar orbits, you use the rotating cable above GEO mentioned above.
But instead of using it for extra push you get off while it is
subtracting some speed but not quite in the direction of rotation of the
cable. So you subtract some speed in the direction of rotation of the
cable and give some speed in the north-south axis. You then use
aero-braking again to lower apogee, and a small thruster to raise
perigee. Note however that using the elevator to reach polar orbits in
this way isn't obvious. You would want a long and fast rotating cable
and you would want it far above GEO, it might not be practical to do so.

Building an elevator, with current technologies, is outrageously
expensive. But if you have one, it can be very useful.


we don't have one, and never will.* It is a joke among Engineers.

What would is the monthly insurance payment for it?* if it fell over ?

You put the cable on an east coast. You also put a system to cut the
cable at something like 10000 km high. If the cable breaks below that
10000 km the upper part doesn't fall it goes up, the bottom part falls
in the ocean, where it isn't likely to cause damage. If the cable breaks
higher than 10000 km, you cut it at 10000 km, the bottom 10000 km falls
once again in the ocean. The two other parts won't fall to the ground,
the lower part will probably be in an elliptical orbit, the higher part
might be in an escape trajectory. So the damage from a cable breaking
doesn't have to be high. It might be a little difficult to explain that
to an insurance company, but if you can pay for the cable, you should be
able to cover the damages.


how much does 10,000 of cable weigh? 100,000 #
the center of gravity is directly over the support, so you have 100,000#
of steel cable crashing onto it.


Nope. The Earth spins, you know. And STEEL? That's cute.


earth spin is red herring, do the math.


You do the math.


you gave up.


On you? Yes, I certainly did. You're far too adamantly stupid.



no worries! I'll do it for you, since you are new to math and materials.
  #99  
Old Yesterday, 05:38 AM posted to sci.space.policy,sci.physics,rec.arts.sf.science
Fred J. McCall[_3_]
external usenet poster
 
Posts: 9,638
Default Towards routine, reusable space launch.

Sergio wrote on Thu, 21 Jun 2018 23:24:53 -0500:

On 6/20/2018 7:07 PM, Fred J. McCall wrote:
Sergio wrote on Wed, 20 Jun 2018 15:42:56 -0500:

On 6/19/2018 4:38 PM, Fred J. McCall wrote:
Sergio wrote on Tue, 19 Jun 2018 15:58:10 -0500:

On 6/19/2018 2:45 AM, Fred J. McCall wrote:
Sergio wrote on Mon, 18 Jun 2018 22:17:21 -0500:

On 6/18/2018 8:06 PM, Alain Fournier wrote:
On Jun/18/2018 at 2:45 PM, Sergio wrote :
On 6/16/2018 8:54 AM, Alain Fournier wrote:
On Jun/15/2018 at 11:34 PM, Fred J. McCall wrote :
JF Mezei wrote on Fri, 15 Jun 2018
22:13:01 -0400:

On 2018-06-15 19:21, Alain Fournier wrote:

Yes. But I think I am a little less optimistic than you about it
becoming practical in the future. If we have fantastic materials
in the
future, maybe an elevator will become more practical,


Apart from lifting geostationary satellites to just below orbit and
then
let them use their own thrusters to position to their assigned
slot/longitude, what other use would a space elevator have ?


You go above the GEO point on the cable and get flung on
interplanetary trajectories.

Yes!

You would also likely put at least one cable above GEO rotating in a
plane perpendicular to the main cable. So you can give an extra push for
interplanetary trajectories and to fine tune in which direction you
depart for said trajectories.

You can also jump off at an altitude of about 15000 km (that figure is
from the top of my head, it might be more or might be less). From there
after a few passes of aero-braking you can reach LEO with very small
thrusters.

For polar orbits, you use the rotating cable above GEO mentioned above.
But instead of using it for extra push you get off while it is
subtracting some speed but not quite in the direction of rotation of the
cable. So you subtract some speed in the direction of rotation of the
cable and give some speed in the north-south axis. You then use
aero-braking again to lower apogee, and a small thruster to raise
perigee. Note however that using the elevator to reach polar orbits in
this way isn't obvious. You would want a long and fast rotating cable
and you would want it far above GEO, it might not be practical to do so.

Building an elevator, with current technologies, is outrageously
expensive. But if you have one, it can be very useful.


we don't have one, and never will.* It is a joke among Engineers.

What would is the monthly insurance payment for it?* if it fell over ?

You put the cable on an east coast. You also put a system to cut the
cable at something like 10000 km high. If the cable breaks below that
10000 km the upper part doesn't fall it goes up, the bottom part falls
in the ocean, where it isn't likely to cause damage. If the cable breaks
higher than 10000 km, you cut it at 10000 km, the bottom 10000 km falls
once again in the ocean. The two other parts won't fall to the ground,
the lower part will probably be in an elliptical orbit, the higher part
might be in an escape trajectory. So the damage from a cable breaking
doesn't have to be high. It might be a little difficult to explain that
to an insurance company, but if you can pay for the cable, you should be
able to cover the damages.


how much does 10,000 of cable weigh? 100,000 #
the center of gravity is directly over the support, so you have 100,000#
of steel cable crashing onto it.


Nope. The Earth spins, you know. And STEEL? That's cute.


earth spin is red herring, do the math.


You do the math.


you gave up.


On you? Yes, I certainly did. You're far too adamantly stupid.


no worries! I'll do it for you, since you are new to math and materials.


Gee, let's not tell the university. They might ask for my degree in
mathematics back. And certainly let's not tell Texas Instruments or
Raytheon, as they might want some of that salary back that they paid
me for being an engineer all those years.


--
"Ignorance is preferable to error, and he is less remote from the
truth who believes nothing than he who believes what is wrong."
-- Thomas Jefferson
  #100  
Old Yesterday, 12:18 PM posted to sci.space.policy,sci.physics,rec.arts.sf.science
Jeff Findley[_6_]
external usenet poster
 
Posts: 1,577
Default Towards routine, reusable space launch.

In article ,
says...

On 2018-06-21 06:26, Jeff Findley wrote:

http://gassend.net/spaceelevator/breaks/index.html


Looked at "breaks at counter weight" (longest section of cable that
falls down with only counter weight going away)

Why would the falling cable become "loose" and snake ?


Because it's flexible, duh. Imagine that you took 10 meters of fishing
line with a weight at the bottom then cut it in the middle. Would it
stay straight as it fell? Try it!

I majored in dynamics and control at Purdue. This stuff is *not*
intuitive, but it can be simulated and verified experimentally.

Since the top most portions, when being pulled down, would accelerate
more that portions below it, wouldn't the cable remain raughts and thus
no slack that allows snaking ?

Why would it break up in space as it falls?


To put it simply, it breaks when the stress at a point exceeds the
material strength. Again, the dynamics of the falling tether is not
intuitive. That's why we perform simulations like this.

Why did the Tacoma Narrows Bridge break up due to *wind*?

https://en.wikipedia.org/wiki/Tacoma...s_Bridge_(1940)

https://www.youtube.com/watch?v=j-zczJXSxnw

Again, this stuff isn't intuitive. The bridge designers, at the time,
simply didn't take into account the dynamics of the bridge in a strong
wind.

Jeff
--
All opinions posted by me on Usenet News are mine, and mine alone.
These posts do not reflect the opinions of my family, friends,
employer, or any organization that I am a member of.
 




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