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Old June 22nd 18, 05:38 AM posted to sci.space.policy,sci.physics,rec.arts.sf.science
Fred J. McCall[_3_]
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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