Post by Quadibloc Post by Quadibloc
I came across this video on YouTube
which appears to claim that it has become practical to produce
graphene at such a cost, and in such sizes, so that it can be used in
Post by Quadibloc
However, it isn't until 2:52 that they get to the point; what this is
about is about concrete that is 30% stronger because some graphene has
been mixed in. So that isn't quite close to the theoretical strength of
pure graphene on a large scale.
For a Space Elevator and high skyscrapes the relevant figure is AFAIK
how strong it is in compression. They seem to only talk about tensile
strength which is rarely the limiting factor issue for these kind of
constructions which makes the cynic in me think there's little or no
improvement on that aspect or they would have mentioned it given that
it's basically a SALES PITCH.
Increasing the tensile strength does help with some thing though IF my
understand is right that's mostly in reducing or eliminating the need
for rebar (steel) reinforcement. Which is valuable because usually
most of the time is spent on that and time is money but is less
helpful for this.
They do mention reduced cracking which CAN help these kind of projects
but given that it's a sales pitch I wouldn't trust that it's better at
that than various already existing advanced concrete formulations.
Post by Quadibloc
We need a lot more experience with tall buildings before building a
space elevator. Just building the space elevator structure will be
difficult. Then adding the elevators will be tricky as air and power
will be needed. Probably toilet facilities too as the elevator will
take hours ??? to get to LEO ? And part of that trip will be at zero
Doesn't one space elevator design have an asteroid maneuvered into place
in GEO with the elevator suspended from it ?
No, for a Space Elevator the "mid-point" is at GEO or corresponding
(stationary) altitude for other planets/moons, with the counterweight
much further out (you can balance weight vs how much further out).
Going further out with the counterweight increases the speed boost the
Space Elevator can provide by "flinging" crafts! If you extend the
outer structure far enough out it IS the counterweight but it would
need to be very long, it's hard to imagine a case where they don't end
up with a substantial counterweight part added at the end.
Any kind of non-magic-tech (IE not scrith) Space Elevator on Earth
will use significant taper, IE it's much thicker/heavier far away from
the mid-point to reduce the material strength requirement.
I don't think we've reached the point where we can build one for Earth
yet, but one on the moon is relatively easy but still require taper
and IIRC Mars is doable but require significant larger but doable
However, we CAN build a Space Fountain *TODAY*, complete plans for
one were drawn up back in the early to mid 1990's and it would be
significantly cheaper to do today due to much better power handling
electronics and better magnets.
A Space Fountain is an example of a dynamic structure, thus it's
sufficient that it gets up above the atmosphere though higher has some
benefits (but also costs more).
The dynamic nature worries some which is why the plan that was drawn
up used multiple redundant "stream pairs" and was able to handle
complete power loss (it would gradually contract down to a stable
state). It doesn't need to be on or near the equator either, though it
does get more useful (lower extra delta-V required) if it is.
It's still vulnerable to sabotage/terrorism but that's just as much
the case for Space Elevators too, and they would make a MUCH bigger
mess on Earth if that happens.
For more information I can recommend the relevant chapter in Robert L.
Forward's _Indistinguishable From Magic_, and if you want more he
provides several references. The entire book is well worth reading.
Skyhooks, Rotovators and Bolos are also possible for Earth already
but for Earth they all require something else to get up above almost
all of the atmosphere. On the moon OTOH they could be really useful as
The delivery to these on Earth could in theory be some kind of
sub-orbital craft but my feeling is that these consctructs probably
only make sense for Earth if you've first built one or more Space
Fountain (to 70-100km) and launch so much that you want to reduce
launch costs even further.