Re: [GZG] Shifting planets

[Robert N Bryett <rbryett@xxxxxxxx>]

On 29/07/2006, at 04:14 , Richard Kirke wrote:

> Was chatting last night to my housemate. The conversation moved (I  
> honestly cannot explian how...) round to Dyson spheres. And I  
> suggested that possibly the easiest way to create more living space  
> in the correct orbit would be to just shift a planet into the  
> correct orbit. E.g., we just ease Venus a bit further out and  
> terraform it.

Easiest!?! Moving planets around implies a pretty colossal ability to  
manipulate matter and energy. A civilisation that achieved it would  
have other options that might well be "easier". Some of these options  
would be available at *much* lower levels of mastery, and might  
almost be within our reach now.

1. A spherical cloud of "O'Niell Cylinder"-style orbital habitats  
around the sun, in carefully chosen orbits not restricted to the  
plane of the ecliptic. Such a cloud could be built up in incremental  
steps, adding living space as required for relatively modest  
investment (compared with moving and terraforming planets!).

Even two habitable Earth-sized planets would still intercept only the  
most minute fraction of the sun's energy. A cloud of habitats could  
literally "englobe" the sun. Since the internal environment of the  
habitats would be essentially independent of their orbits (just add  
bigger solar mirrors further from the sun), the cloud could be deeply  
layered until no solar energy was wasted on interstellar space. It is  
this energy capture that Freeman Dyson discussed in his famous paper  
"Search for Artificial Stellar Sources of Infra-Red  
Radiation" (Science, 1960). Dyson did *not* propose the solid  
contiguous sphere round the sun to which his name is popularly  
misapplied. As Dyson himself put it: "The form of 'biosphere' which I  
envisaged consists of a loose collection or swarm of objects  
traveling on independent orbits around the star."

2. Depending on the civilisation's level of mastery, very large  
orbital habitats could become possible, without resorting to  
Ringworlds etc. Some of the orbitals described in Iain Bank's  
"Culture" novels are interesting. A few back-of-the-envelope  
calculations suggests:

Imagine a gigantic ring with a cross-section like a U-shaped valley  
(from the point of view of a hypothetical resident standing on the  
inside surface of the ring), placed in a suitable orbit round the sun  
(rather than encircling it), with the ring positioned edge-on to the  
sun but inclined so that light can shine on the opposite inside  
surface. Make the ring about 1,850,000km in radius, and the rotation  
required to produce a pseudo-gravity of 1g would be one revolution  
per Earth day, and the inclined, edge-on orientation would produce a  
fairly natural day-night cycle. Make the ring 100km wide to provide  
more than double the total surface area of the Earth...

Best regards, Robert Bryett
rbryett@xxxxxxxx


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