May 02, 2012

Adam Crowl Design for Dyson Bubble of Statites at 0.1 AU

Adam Crowl describes a Dyson bubble at 0.1 AU.

Wrapping the Sun in “statites” – optically levitated structures – is perfectly reasonable and avoids the issues of the science-fictional Shell Habitat. Such structures, however, have a vulnerability, from in-falling meteoroids and comets.

For a perfect absorber the ratio between the outward force of sunlight to the inward pull of gravity is 1:1300. That means energy collecting statites need to be very thin. Interestingly, because the sunlight and gravity decline in intensity via the inverse square law, except in very close proximity to the Sun, a statite able to levitate near the Earth will do so at any radial distance from the Sun. The exception is when close to the Sun and instead of being a “point source”, the Sun is a great big wall of light. For materials purposes we’ll assume an operating temperature of 1000 K and 50% conversion efficiency, which puts our collector at about 0.1 AU. Here the sunlight is 100 times stronger than at Earth’s orbit.

To levitate the collector’s areal mass density is 0.77 grams/m², which is very thin. A possible design is large reflectors concentrating onto an energy converter, though the exact details we’ll leave for future engineers. What that figure lets us do is estimate the total mass required. At 0.1 AU the total area is 2.81 x 10^21 m², meaning the total mass of our 50% coverage Dyson Shell is 1.08 x 10^18 kg (NOTE- This is 0.5% of the mass of the asteroid Pallas - 2nd largest, you could also take apart something like the 100th largest asteroid for the mass or about 10% of the 35th largest asteroid). About a quadrillion tonnes. Being so thin each collector can solar-sail its way inwards to its operating position around the Sun.

To transfer the energy collected, solar pumped and energised lasers, presumably solid-state, will be used. With half coverage of the Sun and 50% conversion efficiency, the total energy supplied to the Solar System civilisation is a staggering ~10^26 W. Essentially a million tonnes of energy per second is available.

So what do we do with it all? One possibility, which would go a long way towards making a Dyson Swarm, is transferring the power to distant objects and terraforming them. Not just the planets we know, but the potentially thousands of planet-sized objects between the stars, the Nomads of the Galaxy which were recently in the science news. Again, the difficulties of managing so many planetary sized laser streams is an exercise for future engineers, but even with 100,000 Earth-sized worlds illuminated (the Sun’s output is equivalent to 2.2 billion times what Earth receives) the total amount of sky covered by each stream is minute so streams crossing planets will be rare and predictable, thus can be mitigated.

There has been some theoretical speculation about using molecular manufacturing techniques to create advanced, strong, hyper-light sail material, based on nanotube mesh weaves, where the weave "spaces" are less than half the wavelength of light impinging on the sail. While such materials have so far only been produced in laboratory conditions, and the means for manufacturing such material on an industrial scale are not yet available, such materials could mass less than 0.1 g/m², making them lighter than any current sail material by a factor of at least 30. For comparison, 5 micrometre thick Mylar sail material mass 7 g/m², aluminized Kapton films have a mass as much as 12 g/m², and Energy Science Laboratories' new carbon fiber material masses 3 g/m².

Nextbigfuture looked at Dyson Bubbles and Statites in 2010

Another type of Dyson Sphere is the "Dyson bubble". It would be similar to a Dyson swarm, composed of many independent constructs.
Previously, nextbigfuture had written about Dyson Swarms and dyson Spheres

Unlike the Dyson swarm, the constructs making it up are not in orbit around the star, but would be statites—satellites suspended by use of enormous light sails using radiation pressure to counteract the star's pull of gravity. Such constructs would not be in danger of collision or of eclipsing one another; they would be totally stationary with regard to the star, and independent of one another. As the ratio of radiation pressure and the force of gravity from a star are constant regardless of the distance (provided the statite has an unobstructed line-of-sight to the surface of its star), such statites could also vary their distance from their central star.

If you placed the statites closer to the sun at say 2.5 million miles from the surface of the sun, then the surface area would be about 28 trillion square miles or about 1000 times less than the 1 AU surface area. 2.17 × 10^17 kg (217 trillion tons) of material would be needed. The surface area would be about 12 times the surface area of the sun and about 150,000 times the 197 million square mile surface area of the Earth. About 100,000 tons of material (deployed as 2.5 million mile from the sun statite energy collectors) would be needed to capture the energy for a Kardashev level One civilization (equal to the solar energy hitting the earth). If you could get another one million miles closer then the amount of material would be halved. (2 million mile diameter sphere instead of 3 million mile). The systems would need to be able to handle the heat, variable magnetic fields and flares.

Let me repeat some key takeaway from this:
1. when we have nanotechnology that is able to produce carbon solar sails/solar power collectors/statites that are about four times lighter than we can make now and produce and launch 100,000 tons of it and get it in close to the sun and transmit and use the power then we are at Kardashev level one. It would be early molecular manufacturing capability or good high volume carbon nanotube and graphene capabilities. The amount of material would be about 20,000 times less than the surface area of the earth or about 10,000 square miles.

2. It would be even simpler and easier to make a weaponized version of this. You would not need to collect the energy but just focus it and guide it where you wanted. 100,000 tons of near molecular nanotech in space and nuclear bombs would be like firecrackers. Molecular nanotech also provides the technology for insanely powerful access to space.

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