Micro Gravity and A Space Elevator?

On Jun/10/2020 at 18:35, Scott Kozel wrote :
On Wednesday, June 10, 2020 at 2:28:39 PM UTC-4, David Spain wrote:
On 2020-06-10 2:16 PM, Scott Kozel wrote:

It would be possible for the Moon today, given its much lower gravity. Given
its very slow rotation, a geosynchronous anchor would not work, but they could
use one of the Moon's LaGrange points.

You're thinking a fuel depot? Water pumped up from the surface to the
anchored depot at L1 or L2? Micro-gravity available when docked?

I wasn't advocating or opposing a Moon space elevator, just saying that it is
technologically feasible with today's materials.

I read somewhere that a Mars space elevator is technologically feasible with
today's materials, but I am not sure about that.

An Earth space elevator is technologically feasible with today's
material. See for instance
space.nss.org/wp-content/uploads/2000-Space-Elevator-NIAC-phase1.pdf
that's a little old, but materials available 20 years ago should be
available now. It would be too expensive, but technically, it is doable.
Costs estimates in that report are of $40B (page 11.4), but I would say
the author is a little optimistic, not ridiculously so, but a little
optimistic.

On Mars, I'm not sure how one would solve the problem caused by the low
orbiting moons but I think it would be doable. Anyway, for the time
being, the traffic from Mars surface to Mars orbit is too low to justify
the cost, whatever that cost would be :-)


Alain Fournier

On 2020-06-10 2:58 PM, Jeff Findley wrote:

This also has a huge impact on what happens to any mass released from
the elevator. From the Wikipedia entry:

....

That actually makes sense to me. I can see that.

Dave

So while I'm still on the subject, seems likely if you have gone to all
the trouble and expense to build a space elevator you'd design it so
that the masses are attached to the cable in such a way that
here are both anchor cable and transport cable. So the 'elevator' can
pass by the 'station platforms' on the way up. At the counter-weight
mass you might also have the cable to extend beyond with a slightly
smaller counter-weight to give you negative g. Perhaps on a separate
elevator with an 'upside-down' orientation!

So the 'elevator' would be designed more like a vertical train. In fact
it is probably wise to have multiple transport cable 'tracks'. Then you
can simultaneously have trains going up and down. There could be
separate cars on the train that could be unloaded at various
drop-off/platform stops along the cable. Thus you could have stops at
300miles, 500miles, 1000miles (oops! Van Allen Belt!!) etc. up to and
beyond geosynchronous orbit. The 'train' would need to travel fairly
fast if you want to get to anywhere above the Earth's atmosphere in any
'reasonable' amount of time. But the 'elevator' could travel at
different speeds at different points along its journey. With less air
resistance the higher up it is the faster it can go. I'm thinking
something along rail gun technology. Of course if you're willing to wait
months to get to your destination, you can go more slowly. So the cabs
have to be more like living habitats that move (imperceptibly).

Another feature not to be discounted are stops along the cable that
remain in the atmosphere. You could have observation stations in both
lower and upper troposphere, stratosphere and ionosphere. Something that
is exceedingly difficult to do today, even with balloons.

Dave

On 2020-06-11 1:24 PM, David Spain wrote:
But the 'elevator' could travel at
different speeds at different points along its journey. With less air
resistance the higher up it is the faster it can go. I'm thinking
something along rail gun technology. Of course if you're willing to wait
months to get to your destination, you can go more slowly. So the cabs
have to be more like living habitats that move (imperceptibly).

Actually, have read articles that suggest rocket propulsion for this
purpose. To save on carry along oxidizer, maybe another use for a
SABRE[1] engine? Like the old water powered steam engines or even modern
locomotives, you'd make way stops to refuel. Thus there may also be
required a 'cargo' train/elevator or cargo cars. I'm going to coin a new
noun for these things. The Space Trelevator or just Trelevator for
short. All Aboard! :-)

Fun to imagine how such tech would be managed/implemented.

Dave

[1] https://en.wikipedia.org/wiki/SABRE_(rocket_engine)

On 2020-06-10 7:46 PM, Alain Fournier wrote:

An Earth space elevator is technologically feasible with today's
material. See for instance
space.nss.org/wp-content/uploads/2000-Space-Elevator-NIAC-phase1.pdf

Interesting, will take a look, thanks. Reformatted for one-click...

https://space.nss.org/wp-content/upl...IAC-phase1.pdf

Dave

On Thursday, June 11, 2020 at 1:24:46 PM UTC-4, David Spain wrote:

Another feature not to be discounted are stops along the cable that
remain in the atmosphere. You could have observation stations in both
lower and upper troposphere, stratosphere and ionosphere. Something that
is exceedingly difficult to do today, even with balloons.

Something that I haven't heard addressed, is how to protect the cable from
aircraft collisions. No matter how well marked and lighted, sooner or later an
aircraft will hit it, resulting in the severing of the cable and the crashing of
the aircraft.

On 2020-06-11 1:44 PM, David Spain wrote:
On 2020-06-10 7:46 PM, Alain Fournier wrote:

An Earth space elevator is technologically feasible with today's
material. See for instance
http://space.nss.org/wp-content/uplo...IAC-phase1.pdf

OK I've read through Chapter 2. There are a lot of if's here. I would
judge this as written as currently feasible without further study. The
good news is that at the time of writing of this paper in 2000 where
lengths of carbon nanotubes were only in a few centimeters, such results
have been subsumed by newer research ([1], 2013) that have produced a
length of 50 centimeters. So work is progressing, but to say it's
feasible is still a "stretch", pun intended.

There have been more recent papers published on the NSS website he

https://space.nss.org/space-elevator-library/

I'll have to take a look and see what progress has been made since 2000.
The 2000 Edwards paper shows promise and consideration but in and of
itself is not convincing.

Also I take some issue with the need to use a ground laser / climber
solar arrays to power climbers if the cable itself has unique electrical
conductivity. Save some effort here?

Dave

[1] https://pubs.acs.org/doi/10.1021/nn401995z

On 2020-06-11 2:25 PM, David Spain wrote:
There are a lot of if's here. I would
judge this as written as [not] currently feasible without further study.
Sorry bad typo.

Dave

On 2020-06-11 2:16 PM, Scott Kozel wrote:
On Thursday, June 11, 2020 at 1:24:46 PM UTC-4, David Spain wrote:

Another feature not to be discounted are stops along the cable that
remain in the atmosphere. You could have observation stations in both
lower and upper troposphere, stratosphere and ionosphere. Something that
is exceedingly difficult to do today, even with balloons.

Something that I haven't heard addressed, is how to protect the cable from
aircraft collisions. No matter how well marked and lighted, sooner or later an
aircraft will hit it, resulting in the severing of the cable and the crashing of
the aircraft.


As well as bad weather, high shearing winds, lightning strikes etc.
which would be all too common a problem no matter how well you sited the
ground station.

As far as stray aircraft is concerned: Well one of the schemes to power
the cable climber, uses ground based lasers to power it.

Just sayin'.... :-)

Dave

PS: On a serious note, doesn't look to me where the proposed ground site
would be, right along the equator and possibly out at sea to the west of
South America, near the Galapagos Islands, is a highly traversed area of
air transit. Obviously this would need to be an air travel exclusion
zone. But there is also terrorism to consider...

The 'nail' in the Space Elevator coffin might not have actually ANYTHING
to do with the technical feasibility of building one, but that the
environment that it would operate within has become too hostile!

Scott Kozel posted about the hazards of aircraft hitting the cable, but
a far more likely scenario will be a member of a LEO satellite
constellation, such as Starlink or one of it many competitors that may
be launched.

Having an entire constellation of thousands of low Earth orbiting
satellites may very well present too much of a challenge to have one
stable ribbon cable extending vertically across the orbital planes of
these constellations at the Earth's Equator. The orbital pathways of
Starlink look far more like a weave than a circle. Requiring frequent
and potentially costly moves of an Earth-side anchor even if it were
designed to be mobile from the get go. A further design complication.
This may render the entire concept moot. Like setting up a lemonade
stand in the middle of an eight lane superhighway!

So if this ever happens, maybe Moon or Mars will be the first, even if
technically doable on Earth!

Dave