
Optimal Sunshade Configurations for Geoengineering Near Sun-Earth L1 Point - ezequiel-garzon
http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0136648
======
eggy
I used to belong to the L5 Society in NYC back in 1985, which was a group of
space enthusiasts. We would meet at the Intrepid Sea, Air and Space museum in
New York City. Scientists, poets, sci-fi geeks, artists, musicians, and even
NASA employees and astronauts. Ideas like this for using the other Lagrange
equilibrium points were always being discussed. The Lagrange points allow for
insertion of objects that while at those equilibrium points, require minimal
energy to maintain that position or orbit. AFAIK, there are 5. L5 was a choice
for a space colony hence the L5 Society. The L5 Society became absorbed along
with the National Space Instititute into the National Space Society. I believe
Carl Sagan was President.

------
clord
The biggest problem I see with this is that we will lose the incentive to dial
down extraction of fossil energy. The non-warming side-effects of oil and
other deposits such as carbonic acid in the oceans would become just as severe
if not moreso.

------
dreamcompiler
Although this would be a major engineering feat, it could be done. It would
stop global warming almost immediately. What it won't do is reduce the CO2 in
the atmosphere, so ocean acidification and the resulting dieoff of aquatic
life would still happen. Perhaps even worse, it would enable the continued
"business as usual" burning of fossil fuels and likely cause CO2 levels to
rise even higher than they would have otherwise.

------
cromwellian
This also makes for a somewhat spooky dystopian science fiction. Society
engineers a gigantic sunshade. Something goes wrong and they lose contact with
the shade unable to adjust it. Leading to crop failures, ecosystem collapse,
and a global ice age. Frantically, the world governments race to launch a
mission to repair or destroy the shade before life on earth is plunged into a
permanent ice age from which a collapsed technological civilization could
never hope to avert.

That is, this thing should have a dead man's switch on it, and if it isn't
renewed every few years, it will self destruct, alter course, stop station
keeping, etc Of course, this is probably an implausible scenario but it would
make for a great TV movie.

~~~
sbierwagen
Radiation pressure will push it out of the L1 point pretty quickly (months?)
without active stationkeeping. Tidal forces will want to rotate it edge-on to
the Earth, and the tug of the Moon's gravity will want to pull it out of
alignment between the Sun and the Earth.

"Causing a ice age" is pretty rich, too. It can only block 1.7% of the light
the Earth gets. If it gets any closer to the Earth, then it ends up in a non-
geosynchronous orbit, (Well, not strictly geosynchronous. You know what I
mean) and stops blocking the Sun. All the failure modes of a L1 sunshade are
pretty benign.

~~~
emiliobumachar
I believe gp was talking about a failure mode in which station-keeping goes on
automatically when communication fails, as we learn that we massively overdone
it because climate science is hard.

~~~
cromwellian
Right, I was talking about a sci-fi failure mode where the onboard program
goes haywire and it ends up actively station keeping and maintaining the block
for hundreds of years. Is 1.7% not something to worry about? IIRC, Solar
variance of 0.1% has correlated with a 0.32F temperature variance. If that
relation were linear, that would amount to almost a 5.5F variance.

I'm not proposing this as a 'hard scifi' model for a story, but you could
tweak the scenario to get suitably scary failures (multiple shades)

------
gnarbarian
Mr. Burns tried this:

[http://www.extremetech.com/wp-
content/uploads/2012/09/simpso...](http://www.extremetech.com/wp-
content/uploads/2012/09/simpsons-mr-burns-blocks-out-the-sun1-640x353.jpg)

------
sbierwagen

      The estimated mass of the deployed structure is in the 
      order of 10^7–10^8 tonnes.
    

Ouch.

~~~
fernly
Quoting further, "the mass and scale of the sunshades will also be similar to
current terrestrial civil engineering projects such as the Chinese Three
Gorges Dam [20], and require a mass production of coated thin material
equivalent to the current world decadal production of aluminium foil."

They continue with "Nevertheless, scholarly work has yet to identify a
scientific showstopper for its implementation". To me, the idea of designing a
practical support framework for a disc of aluminium foil having a diameter of
one thousand four hundred kilometers -- a framework that has to be shipped
from earth one rocket-load at a time and assembled in space -- would be at
least a show slower-downer.

~~~
mrec
There's a substantial amount of aluminium on the Moon, as well as in some
asteroids. Extracting and turning it into sunshade won't be _easy_ ,
obviously, but when budgets in the tens or hundreds of trillions are being
talked about, the options widen a bit.

~~~
JoeAltmaier
Wow you're right! Its apparently a huge thing on the moon:

    
    
       "Aluminum composes 10% of the atoms and 13% of the mass of lunar highland regolith, being the third most abundant element. In the mare basins, aluminum makes up only 4.5% of the atoms and 5% of the weight, strongly suggesting the use of highland feedstocks for aluminum extraction."
    

Pretty much a little solar energy and a crucible and you'd turn out aluminum
like mad. Absolutely the right choice for a lunar civilization, instead of
lifting structures from Earth's gravity well.

~~~
fernly
Right! So all we have to do is establish a base on the moon, build a mining
and smelting facility, build a fabrication plant, build a rail-gun launcher,
operate all three long enough to fling at least 10e7 tonnes [1] of finished
aluminum parts toward L1, where we catch them and assemble them.

The rail-gun is not likely to be the pinch-point in the process, but suppose
that the mining, smelting, fabrication, packaging and transport process can
deliver a shipping unit to the rail head every minute, around the clock [2].
That's 10e7 minutes, pretty close to 20 years of continuous operation.

This stream of 1-tonne bundles of finished rods and other parts has to cross
space to L1. I have no idea what the orbital feasibility of Luna-to-L1 is; I'm
just assuming that a rail-gun can impart enough energy to get it there. But,
one, if a bundle requires any guidance or course corrections en route, that
would mean every bundle would have to be equipped with at least a computer,
gyros and some type of propulsion units; and two if it approaches L1 with any
significant relative velocity, it needs all that and a serious rocket engine
to slow down [3]. So we are not merely flinging passive bales of aluminum
parts from the rail-gun, we are launching little one-tonne spacecraft. One per
minute. For 20 years. [4]

So supposing all that is in place, then you need to have sufficient personnel
(plus a swarm of quite intelligent robots) at L1 to receive them, unbundle
them, and distribute the parts across a disc that even in the earliest stages
is hundreds of fucking kilometers in diameter, and assemble them. For 20
years.

There is nothing in this scenario that is inherently impossible. On the other
hand, given it currently takes us a decade to design and transport a 1/2-tonne
robot to Mars, how many decades would it take to design and build the proposed
Lunar infrastructure? On time alone, never mind the costs, wouldn't it be
simpler, quicker and cheaper to just stop burning petroleum?

[1] the article says 10e7 - 10e8, so we're giving them the low side of a power
of 10 here.

[2] something like a factory that builds a new economy car every 2 minutes. On
the moon, in a vacuum.

[3] or it has an ion engine like the Dawn craft and does continuous thrust,
yadda yadda, same basic problem.

[4] you might say we could recycle the computer and ion engine from each bale,
but then you need to figure out how to fire about 10e6 bundles of used engines
from L1 back to the moon and soft-land them there next to the factory.

~~~
JoeAltmaier
Here's some help: regolith is broken rock and dust on the ground. So no mining
necessary - just earth movers (luna movers?) and a conveyor belt.

Probably the first thing you'd build would be - more mining equipment. Let the
thing bootstrap itself, including the fabrication plant, the rail-gun and more
mining equipment.

In 20 years you'd be ready to begin doing the rest of the project, but it
would be much easier with the orders-of-magnitude larger infrastructure you'd
bootstrapped.

~~~
sbierwagen
Incidentally, NASA commissioned a study back in 1980 about self-replicating
factories harvesting lunar regolith. It's quite good, and goes into excellent
detail:

[http://www.nss.org/settlement/moon/library/1982-SelfReplicat...](http://www.nss.org/settlement/moon/library/1982-SelfReplicatingLunarFactory.pdf)

(Edited by Robert A. Freitas, who went on to write Kinematic Self-Replicating
Machines)

------
mirimir
What about the impact of reduced insolation on photosynthesis? Wouldn't crop
yields be lower? And what about reduced carbon sequestration via buried
biomass? Not to mention ecosystem-wide impacts of reduced photosynthesis.

But as long as it's under control, I suppose that shading could be adjusted as
appropriate.

~~~
marcosdumay
Adjusted by whom? Will it be the same party suffering must of the effects of
lower plants grow?

~~~
mirimir
Probably not :(

------
kylek
This sounds like something a supervillain would build o_O

------
mrfusion
Would this be useful for terraforming Venus as well?

------
codecamper
One possibly overlooked problem with this is that alien races / robots may be
able to see this sun shield from a vast distance. They will know that we are
primitive people who have not yet figured out quantum dot solar and who still
die from cancer.

No wait... if we put it up then we'll still have 50 or so years before this
information reaches such alien planet. So we should be OK if we can figure
those things out soon.

Sorry for the alarm.

~~~
pavel_lishin
Given our current telescope technology, and assuming that others in the galaxy
have the same thing, they could probably easily figure out that we're here -
in the same amount of time. (Limit of light speed, and all that.)

And unless they've got FTL, it'll take awhile for them to do anything about
it, anyway.

