Article Summary: This is a highly speculative article about possible defenses against a major solar event (if everything we know about solar long term stability turns out to be wrong.) Or to defend against a hypothetical point source of light and heat event of presently unknown nature that could fry the unprotected Earth. It discusses a band of reflective material in one scenario deployed at geostationary orbit to function as a skyshade. The need for this is unjustifiable on a cost accounting basis, (until the Sun ages far in the future) but as an exercise in engineering against existential risk it may have interest. But if humanity's waste heat reaches some writer's projections, we may be building it within 300--2000 years.
Hi, everybody, this is Joseph Friedlander in
If our ideas of solar stability are right the the bell by Wikipedia’s reckoning tolls for thee a mere 600 million years in the future.
The Sun's increasing luminosity begins to disrupt the carbonate-silicate cycle; higher luminosity increases weathering of surface rocks, which traps carbon dioxide in the ground as carbonate. As water evaporates from the Earth's surface, rocks harden, causing plate tectonics to slow and eventually stop. Without volcanoes to recycle carbon into the Earth's atmosphere, carbon dioxide levels begin to fall. By this time, they will fall to the point at which C3 photosynthesis is no longer possible. All plants that utilize C3 photosynthesis (~99 percent of present-day species) will die.
Carbon dioxide levels fall to the point at which C4 photosynthesis is no longer possibleMulticellular life dies out.
The Sun's luminosity has increased by 10 percent, causing Earth's surface temperatures to reach an average of 47°C. The atmosphere will become a "moist greenhouse", resulting in a runaway evaporation of the oceans. Pockets of water may still be present at the poles, allowing abodes for simple life.
Eukaryotic life dies out due to carbon dioxide starvation. Only prokaryotes remain.
Earth's surface temperature, even at the poles, reaches an average of 147°C. At this point life, now reduced to unicellular colonies in isolated, scattered microenvironments such as high-altitude lakes or subsurface caves, will completely die out.
Surface conditions on Earth are comparable to those on Venus today
And if our ideas about the future risks from the Sun or unknown point source events are wrong even worse scenarios are possible and far sooner.
There is also the hot prospect of civilization frying in its' own waste heat.
Unless you own a We Are The World Barbecue Set, the outlook seems grim.
This being Next Big Future, we have a plan to get out of it though.
Consider the idea of a thin membrane shield (sort of a Dyson sphere for Earth, but aluminized on the outside) at geostationary distances (to avoid lunar tidal problems and conserve on material)
This is a huge amount of material, (~teraton range if built robustly) but further out material demanded (obviously) is even worse because of the bigger area.
But is it even structurally possible at all with ordinary strength of materials?
There is kind of a delicate dance between material strength, tidal flexing, and differential orbital speed (another reason for not putting it in the lower, faster LEO) that would want to tear the thing apart.
A sun-centered Dyson sphere with ordinary materials is dynamically impossible partly because of the ~30 km/sec orbital speeds even at the Earth's distance. Wiki gives GEO orbital speed as about a tenth of that:
Orbital speed is calculated by multiplying the angular speed by the orbital radius:
Lower speed, less speed differential between different latitudes of the Dyson sphere, less stress on materials. But a thin shell GEO band would only need to go up to the tropics of Cancer and Capricorn and a bit more to completely block the sun. (Obviously stowed during non-event times, then unfurled during flare sequences) when we get the signal from say a Venus orbit SV L-4 observation and warning satellite. Although the signal would only travel at the speed of light itself, it would give us a pre-computed value for the intensity of the flare that could automatically trigger a pre-worked out deployment sequence. This could save vital seconds in case of a major heat pulse-- like ducking and covering in case of a nearby thermonuclear flash. Which in astronomical terms, a flare star is.
The strength of material calculations are key to this and I frankly am not comfortable that it is possible. We could cheat of course and postulate AB Matter construction http://nextbigfuture.com/2011/11/starbase-jupiter-and-other-femtotech.html
but that is the easy way out.
Is a geostationary solar shield possible with present day materials such as aerospace aluminum and glass fiber?
From Wiki-- A geostationary orbit (GEO) is a circular geosynchronous orbit in the plane of the Earth's equator with a radius of approximately 42,164 km (26,199 mi) (measured from the center of the Earth). A satellite in such an orbit is at an altitude of approximately 35,786 km (22,236 mi) above mean sea level.
Even if you could build a skyshade up to nearly the Earth-Moon null point, that would generate tidal stresses as the Moon orbited flexing the whole structure as it passed by. I am guessing that 100000 km radius would be doable but love to be proved that GEO is possible. Solar tides are not to be neglected either.
Now on a rhetorical level, some level of sunshading certainly is possible. There is no question that a GEO ring is possible; Arthur Clarke actually had most people living in GEO in his novel 3001 The Final Odyssey if I recall correctly. The idea is a (very large) number of GEO satellites, literally less than a meter apart, then they join hands.
The fact that there are drag forces stresses it, and it seems it may need orbital maintenance. But how much and at what cost? The best case would be Drexler-design thin film solar sails with tethers tugging where needed.
But the further out north and south from equatorial orbit you unfurl Skyshade material, the bigger the stress on the equatorial chain.
It is not clear to me that a Dyson Sphere wouldn't work on a smaller planet than Mars. I can't even absolutely exclude it from Mercury if solar tides permitted it; it could make that world much more colonizable.
But around Earth, the Skyshade band should work much easier if the Sun need only be blocked to 24 north and south or so.
As with most modern things there is an ancient antecedent. Cartographer Andreas Cellarius
http://en.wikipedia.org/wiki/Andreas_Cellarius painted armillary spheres https://en.wikipedia.org/wiki/Armillary_sphere that remind us of this --these are attributed to his Harmonia Macrocosmica of 1660, a major star atlas, published by Johannes Janssonius in Amsterdam.
Just rotate the Zodiac band over the equator and widen it between the Tropics of Cancer and Capricorn. Make the reflective panels openable and closable as the Sun goes overhead and you're done.
As Adam Crowl wrote :
Clearly a Dyson Sphere wouldn't work. A Dyson Ring might prove useful? Imagine a Band, its mass-centre on the GEO orbital plane, with immense walls up and down. Such a Wall would have supra-Keplerian speeds everywhere not on the equator, flexing it outwards, but not as much as a Sphere would be flexing inwards from gravity. A Hyper-Bolic Wall...
Very low LEO Skyshades would save on material but even if possible would be a bad idea because of the reentry times (at a guess ~1 million years at 1000 km?) I have seen speculation on GEO lifetimes before reentry in millions or billions of years. If any reader has a table of satellite lifetimes at various heights, feel free to share in the comments below..
LAGEOS 1 for example, is 5800 km out, (3600 miles) 2 ft across and with a core of depleted uranium for maximum density and orbital stability, (least atmospheric perturbation relative to volume) it weighs half a ton and will not decay for 8.4 million years. http://www.satobs.org/seesat/Aug-2010/0445.html
If it were much larger, like say a few meters across, its’ orbit might decay much sooner even at that altitude. With a big enough surface area like a balloon, solar sailing pressures and acceleration rates apply and you are not in a stable orbit, you are playing tag with sunlight and gravity.
According to this reference GEO orbit is good against reentry for many millions of years, perhaps over a billion:
an amateur satellite spotter named Ted Molczan…pointed me towards a satellite catalog called the Royal Aerospace Establishment Table of Earth Satellites, an old British publication that listed all the (non-secret) spacecraft in Earth’s orbit, along with their orbital characteristics, one of which was the lifetime of the orbit. The catalog has been out of print for decades, but orbits are relatively standardized so if you want to know the orbital lifetime of a recent satellite, you can just find an older satellite in the RAE Table with similar orbital characteristics and the lifespan will be about the same.
The vast majority of satellites are in what are called “low earth orbits” at an altitude between 300–1000 kilometers. At these altitudes, satellites slowly accumulate drag from the last wisps of Earth’s atmosphere, and the accumulated drag pulls them back toward earth. For low earth orbiting satellites, it takes anywhere from a few days to about a hundred years for this to happen.
As I scanned the tables, I noticed something strange: some satellites, especially geostationary and geosynchronous satellites, had lifetimes listed as “one million years” or “indefinite.” I asked Molczan whether these numbers were correct, and when he told me they were, I realized that these spacecraft will be some of the longest-lasting things humans have ever made, and perhaps will ever make. Molczan agreed, saying he thinks of them as “artifacts.”
Given that level of GEO orbital stability, IF the thing can be built with real materials like aluminum foil, quartz fiber etc as opposed to say 30 nanometer thick, world-girdling-wide diamond sheet, the question is why bother?
First of even a small practice version would obviously solve any global warming problems. If you can shunt off 900% of sunlight you can shunt off .001% with impunity.
On the other hand haters of light pollution would probably want the Skyshade unbuildable except in case of solar or thermal emergency.Given that a small object the size say of a major skyscraper would be visible in GEO to the naked eye the light pollution alone would dominate the night sky like the Rings dominate the sky of Saturn.
On yet another hand, doom is not necessarily 600 million years away but may be much more conveniently accessible than that, if our models of solar stability are wrong.
About 1969-70 there was a paper about a possible superflare on the sun 30000 years ago, based I think on fused lunar samples.
Larry Niven was presumably inspired by this paper to write the SF story Inconstant Moon.
https://en.wikipedia.org/wiki/Inconstant_Moon The second possibility turns out to be correct: the Earth has "merely" been struck by an enormous solar flare – by far the worst disaster in human history, with most (if not all) people in the Eastern Hemisphere presumed dead, but humans in the Americas have a chance of surviving the cataclysm.
Half the world taken out but not the whole world because of less than 12-hour event duration.
There was a 1906 story about Olber's Paradox whose premise is not credible today but is still terrifying to read-- http://en.wikipedia.org/wiki/Finis_(short_story) In pure form, Olber's Paradox would kill us by having every inch of the night sky be the glowing surface of a hot star and we would fry. In this story the central object of the universe is so far away its' light hasn't had time to reach us and just now does and the Solar System is far too close the the center of the Universe to be in the life zone and we fry.
Unlikely? As presently understood, impossible.
However, any say week long superflare on the sun tripling output would have the same effect. Impossible as we understand it today? Sure. Does the geological record say it NEVER happened? Not that I am aware. The Permian boundary, Cretaceous–Paleogene (K–Pg) boundary (formerly known as the K–T boundary, etc) say a lot of things died quickly. It doesn’t say who or what was responsible.
I have written with Bolonkin and Turchin about the danger of massive solar flares caused by H-bombs by future crazed dictators. Or other existential dangers.
One can imagine such a dictator reading the Niven story and designing an attack with the same effect :( His half of the world there, the other half gone. But he miscalculates--- (story ends)
And of course even a 1 % coverage Global Shield(TM) could end global warming.
Adam Crowl thinks superflare odds are low. And he points out that strengthening the electric grid against Carrington events https://en.wikipedia.org/wiki/Solar_storm_of_1859 is kind of a higher priority than a massive shield literally bigger than the Earth against hypothetical events, and reasonable minds agree.
In any case this wouldn’t do much against hypothetical ionizing radiation events, just the Sun turning into a lethal source of light and heat far in excess of what we are used to. Or it doesn't have to be a solar event but a extrasolar event that our culture is not old enough to have seen.
Note that this Skyshade is only good against vast amounts of heat and light radiation; not ionizing radiation. Ironic it would be if we built it and then got destroyed by an extrasolar hypernova. Note though that as mentioned here https://en.wikipedia.org/wiki/Ordovician%E2%80%93Silurian_extinction_events#Gamma_ray_burst_hypothesis
the killing mechanism was NOT the radiation but the ultraviolet coming in after the ozone layer was gone. Theoretically a Skyshade could be tailored not to pass ultraviolet. The central problem is, you can build a bulletproof vest but if there are bazookas aimed it you it may not help. So a further question is:Is it worth it? Probably not on a cost accounting basis unless you KNEW something was going to happen. Barring faster than light communications warning of doom, that is most doubtful.
Any increase in X rays would penetrate the Skyshade and other radiation events could also cause swelling of the atmosphere. Lots of satellites reentering is one thing but you don't want a trillion tons of Skyshade falling down, (or even a few billion tons if done in nanotech) (another reason against LEO placement of the shield)
But GEO should be high enough to assuredly be above the atmospheric swelling.
At GEO the strength of materials might be problematic though. The idea would be an GEO band of mass say 10x the exstensions; anchoring diagonal extensions (modular) going up and down to cover up to the celestial Tropic of Capricorn and Cancer. A vast amount of material even if sub micron thickness (30 nm minimum for good reflection if I recall)
The idea is to see if we could survive if insolation went up the ~50 tiimes we saw in the Finis story
or if some other brief but lethal long-wave (ie not talking X-rays etc) emission would otherwise burn up the biosphere
For lethal X-ray brief episodes the population can go in shelters (and animals and electronics and seeds) and structures are intact afterwards.
The key thing is: Will the strength of materials permit this kind of differential rotation with the equator band under little force but the further to either pole bands wanting to differentiate their velocity and being tied to the (more massive) equator band by tethers?
Could it be done? Even if present day materials don't work, the future may have great motivation to make it work with new materials.
In the far future when the Sun approaches the red giant stage even long before it ecological pressures will strongly motivate survival oriented engineering.
However it is comforting to know that when the Sun heats up we can buy another billion years to develop the technology to move the Earth by building a Skyshade (presumably far cheaper). Eventually we will have to move the Earth outward if the Sun would tend to expand and engulf it-- or mine down the sun (What David Criswell calls star-lifting). Moving the Earth is easier but more delicate. Mining the Sun has a small chance to cause massive solar problems. Moving the human race is easier but then we lose the old home.
Building the Skyshade is an insurance policy and probably it won't be paid for until the inhabitants of the far-future Earth see a definite need to do so. But it does cover certain existential risk scenarios and give a huge margin against global extinction. If you believe in runaway global warming being a present unstoppable fact, too late to change-- and I do not but you may--the only option other than enduring it would be to cut the incoming sunlight. In that way too the Skyshade provides existential risk insurance.
However there is a joker in the deck which is that some writers, including Sam Dinkin believe that within 300 years Mankind's energy consumption will equal the amount of solar energy reaching Earth.
But even if population stops growing, our waste heat level will hit the level of solar flux in less than 2,000 years. Long before waste heat surpasses the Sun in our budget, it will be a bigger problem than carbon dioxide.
Whatever the time line, given an amount of energy output several thousand times today (presumably all beamed space power
or nuclear power or deep geothermal power) It would all add heat that wouldn't be here before. Barring forced emigration from Earth (which may yet happen) the ONLY option to keep the Earth habitable would be to block out a major fraction of the incoming sunlight.
So just to deal with the waste heat of mankind a Skyshade might be built within 300-2000 years or so even if not a gram of carbon is burned at that time!
For those readers with an interest in the vastness of the area to be covered-- how many square degrees of the sky, * 180 * 180 / pi degrees or almost 41253 square degrees is needed for Dyson Sphere coverage..
535 billion square arc seconds
Of this a fraction of around a third would have to be blocked at least some of the time.
Discussion of area calculations in the sky
of http://sci.tech-archive.net/Archive/sci.astro.amateur/2005-08/msg01796.html. (regretfully a dead link)
Number of square degrees in sky
From: William Hamblen <wrhamblen@xxxxxxxxxxx>
Date: Sat, 20 Aug 2005 17:21:10 -0500
On 20 Aug 2005 13:15:27 -0700, "callisto" <pjgrim@xxxxxxxxxxxxxxx>
>Can one of you physics or math guys tell me exactly how many square
>degrees are in the whole celestial sphere?
The area of a sphere is 4 * pi * r * r with pi being 3.14159265... and
r being the radius. If a sphere has a circumference of 360 degrees it
has a radius of 180 / pi degrees. Plugging that into the formula you
get 4 * 180 * 180 / pi degrees or almost 41253 square degrees.
1 square degree = 12 960 000 square arcseconds
534 billion 638 million 377792square arcseconds
148 510 660. million square minutes
>Also, how many degrees of
>sky can be seen at different latitudes (taking into account the 23.5
>degree tilt of the spin axis of the earth). For example I am at 40
>degrees north and I cannot see the Southern Cross at any time of the
>year but how many square degrees of sky can I see? I presume that under
>ideal conditions I could see something on the horizon with a
>declination of minus 50 degrees but how does this translate into square
The tilt of the Earth's axis doesn't affect how much of the sky you
can see, although it does affect which part of the sky you can see.
The thing that affects how much of the sky you can see is where you
are on the Earth. Because you can't see through the Earth it blocks
part of the sky. The fraction of the sky you can see at any one time
depends on your latitude. At the poles half of the sky is always
below the horizon. At the equator all of the sky is visible over the
course of a day. The formula is ( 1 + cosine( latitude ) ) / 2. At
40 degrees North or South you can see more than 88% of the sky. Which
part of the sky depends on which hemisphere you are in.
>On the other hand, people at the equator I think could see the entire
>celetial sphere if you ignore atmospheric effects at the horizon.
Refraction means you can in principle see more than half of the sky at
any one time.
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