Japanese company plans space elevator by 2050

On Monday, October 13, 2014 9:08:43 PM UTC-4, Orval Fairbairn wrote:
In article ,

David Spain wrote:

The rockets are there to add/remove velocity on ascent/descent, thereby

removing one of the arguments for the space elevator in the first place.


No. Not required. My bad memory. IIRC rockets were to used to position the countermass during construction, in a design study that had the cable being extruded Earthward from spools on the countermass. For normal operation (post Earth anchoring) see Jeff's reference. The key to making this work is this salient point (from Wikipedia article):

/quote
As a payload is lifted up a space elevator, it gains not only altitude, but horizontal speed (angular momentum) as well. The angular momentum is taken from the Earth's rotation. As the climber ascends, it is initially moving slower than each successive part of cable it is moving on to. This is the coriolis force: the climber "drags" (Westward) on the cable, as it climbs, and slightly decreases the Earth's rotation speed. The opposite process occurs for descending payloads: the cable is tilted eastwards, thus slightly increasing Earth's rotation speed.

The overall effect of the centrifugal force acting on the cable causes it to constantly try to return to the energetically favorable vertical orientation, so after an object has been lifted on the cable the counterweight will swing back towards the vertical like an inverted pendulum.[39] Space elevators and their loads will be designed so that the center of mass is always well-enough above the level of geostationary orbit[43] to hold up the whole system. Lift and descent operations must be carefully planned so as to keep the pendulum-like motion of the counterweight around the tether point under control.[44]
/end-quote

Quoted sources a

[39] Lang, David D. Space Elevator Dynamic Response to In-Transit Climbers.
[43] "Why the Space Elevator's Center of Mass is not at GEO" by Blaise Gassend. Gassend.net. Retrieved on September 30, 2011.
[44] Cohen, Stephen S.; Misra, Arun K. (2009). "The effect of climber transit on the space elevator dynamics". Acta Astronautica 64 (5-6): 538-553. doi:10.1016/j.actaastro.2008.10.003.

Ascent to orbit must maintain conservation of energy -- altitude plus
velocity. The space elevator concept accounts for altitude only.

Cable "tilts" off vertical axis to address this issue, but (for any "reasonable" climber mass) only very very slightly and with countermass beyond GEO and center of mass always maintained to be above GEO, the system will self correct back to vertical.

Dave

On Wednesday, October 15, 2014 4:05:42 AM UTC-4, snidely wrote:
After serious thinking David Spain wrote :

On Thursday, October 9, 2014 7:18:44 AM UTC-4, Jeff Findley wrote:

This is bleeding-edge tech. Absolutely no doubt about it.



I'd say right now, as it stands, it's over the edge.


Maybe a reachable edge. One candidate has turned up already:
stiffest material ever discovered.

/dps

Good article, thanks for link. However, IMO it'll be a "reasonable edge" when they can extrude this stuff by the kilometer. Not a few centimeters.

Dave

Another factor is the radiation shielding you'll need if people are going to ride the climbers through the Van Allen Belts. Transiting these is not going to be quick in a space elevator. Today, that would translate into more climber mass to provide shielding and that means issues.

Dave

In article ,
David Spain wrote:

On Monday, October 13, 2014 9:08:43 PM UTC-4, Orval Fairbairn wrote:
In article ,

David Spain wrote:

The rockets are there to add/remove velocity on ascent/descent, thereby

removing one of the arguments for the space elevator in the first place.


No. Not required. My bad memory. IIRC rockets were to used to position the
countermass during construction, in a design study that had the cable being
extruded Earthward from spools on the countermass. For normal operation (post
Earth anchoring) see Jeff's reference. The key to making this work is this
salient point (from Wikipedia article):

/quote
As a payload is lifted up a space elevator, it gains not only altitude, but
horizontal speed (angular momentum) as well. The angular momentum is taken
from the Earth's rotation. As the climber ascends, it is initially moving
slower than each successive part of cable it is moving on to. This is the
coriolis force: the climber "drags" (Westward) on the cable, as it climbs,
and slightly decreases the Earth's rotation speed. The opposite process
occurs for descending payloads: the cable is tilted eastwards, thus slightly
increasing Earth's rotation speed.


The overall effect of the centrifugal force acting on the cable causes it to
constantly try to return to the energetically favorable vertical orientation,
so after an object has been lifted on the cable the counterweight will swing
back towards the vertical like an inverted pendulum.[39] Space elevators and
their loads will be designed so that the center of mass is always well-enough
above the level of geostationary orbit[43] to hold up the whole system. Lift
and descent operations must be carefully planned so as to keep the
pendulum-like motion of the counterweight around the tether point under
control.[44]
/end-quote

Quoted sources a

[39] Lang, David D. Space Elevator Dynamic Response to In-Transit Climbers.
[43] "Why the Space Elevator's Center of Mass is not at GEO" by Blaise
Gassend. Gassend.net. Retrieved on September 30, 2011.
[44] Cohen, Stephen S.; Misra, Arun K. (2009). "The effect of climber transit
on the space elevator dynamics". Acta Astronautica 64 (5-6): 538-553.
doi:10.1016/j.actaastro.2008.10.003.

Ascent to orbit must maintain conservation of energy -- altitude plus
velocity. The space elevator concept accounts for altitude only.

Cable "tilts" off vertical axis to address this issue, but (for any
"reasonable" climber mass) only very very slightly and with countermass
beyond GEO and center of mass always maintained to be above GEO, the system
will self correct back to vertical.

Dave

It pulls energy away from the counter mass.

In article ,
says...
Cable "tilts" off vertical axis to address this issue, but (for any
"reasonable" climber mass) only very very slightly and with countermass
beyond GEO and center of mass always maintained to be above GEO, the system
will self correct back to vertical.

Dave

It pulls energy away from the counter mass.

If the cable was not anchored to the earth, then yes, you would need
rockets on the counter mass or the cable would no longer be stationary
above the earth after a mass ascended the cable.

But no one would do that. A sanely designed space elevator is anchored
to the earth at a fixed point. So, the counter mass slows its orbital
speed only for a relatively short time and only for a very small amount.
Since the elevator is anchored to the earth, both the earth and the
counterweight lose a bit of rotational speed.

But, the mass of the ascender is far less than the mass of the elevator
plus counterweight. Also, the mass of the earth is far greater than the
mass of the counterweight. Taking all of this into account, the change
in rotational speed of the system (earth plus cable) is very, very
negligible.

Jeff
--
"the perennial claim that hypersonic airbreathing propulsion would
magically make space launch cheaper is nonsense -- LOX is much cheaper
than advanced airbreathing engines, and so are the tanks to put it in
and the extra thrust to carry it." - Henry Spencer

In sci.space.policy message LsidnecFmpgwcKDJnZ2dnUU7-T2dnZ2d@earthlink.
com, Tue, 14 Oct 2014 23:44:44, "Greg (Strider) Moore" mooregr@deletet
hisgreenms.com posted:


I'd recommend anyone who doesn't fully grok this read Fountains of
Paradise by ACClarke. This is a great story and goes into some of the
physics (especially how if you're below GEO and stepped "off the cable"
you'd still plummet to Earth. BUT, even with that, you gain huge
advantages even for LEO sats.)

The first parenthetic statement "sentence tail" is obviously false. If
one gently steps off *at* GEO, one clearly remains at GEO. If one
gently steps off at a metre below GEO, the result will be
insignificantly different (consider ACC's "Jupiter Five").

If one steps off at **about** two-thirds of GEO height, the perigee of
one's orbit is tangential to Earth's surface. I forget the actual
figure, but the calculation can be found easily enough on my Web site.
One never quite plummets to Earth, but one virtually plummets by
stepping off low enough.

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