Venus is practically a twin of the Earth. Or it could be, once we've cooled it down to 290K from its present molten-lead heat; removed the excess CO2 (it has around 100 atmospheres at present — and practically all of it must go); provided breathable oxygen, reduced the day to something like 24 hours (because the Venusian day lasts about 120 Earthly days — and that's a bit too long to stay out of bed, and provided upwards of 100 metres of water over the whole parched planet.
We could proceed as follows.
First we cool the planet with a sunshade (Fig 5.6), quite similar to the Mars soletta. It's a little more complicated than a simple shade — sunlight is deflected sideways just enough to miss the planet — but this way we eliminate most of the light pressure, making it easier to hold the shade in place with light from the annular support mirror.
At a later stage, when we want to occupy the planet, we can orbit another soletta in a 24-hour polar orbit; the sun will then appear in the sky 90 degrees away from its true position Venus is now in shadow and starts to cool down Unfortunately, because the atmosphere is so very think, it contains an enormous amount of heat and thus takes a long time to cool down — something like 200 years. Not so long to a planetologist, but to an engineer it's ridiculous. So we look for ways of speeding things up. There are several possibilities.
One way is to construct gigantic heat pipes connecting the hot dense lower atmosphere and the cool thin atmosphere around the 1 bar level (Fig 5.7). This keeps the upper atmosphere radiating as high a temperature as possible. Such heat pipes, although tens of kilometres high, are entirely feasible with fused rock construction. The way they work is this: at the bottom of the pipe the working fluid (water, to begin with) boils, flashing into steam through an expansion nozzle; at the top, the steam jet spreads out, cools and condenses; water drains back clown to the bottom and closes the loop. As the temperature falls, water is progressively replaced by ammonia. With heat pipes the cooling period can be cut to about 90 years.
Ninety years is still rather a long time, so recently I came up with a better scheme: heatballs (Fig -5.8).
Heatballs are hollow spheres containing a small amount of water. Down at the Venusian surface, they get hot: the water inside them evaporates. Now fling them up into space from the north pole. Out in space, they cool; the water re condenses. Wandering along magnetic field lines, they find their way back to the south pole and plunge towards the surface.
Guided now through evacuated conduits deep in the atmosphere back to the north pole, they heat up once more before swinging back out into space.
The heat balls are electrically charged, and follow magnetic field lines at orbital speeds without loss of kinetic energy. The required magnetic field can be generated by a pair of solenoids, one at either pole; the field strengths are quite small, so the amount of energy stored in the magnetic field is not enormous.
Because the heatballs can spread over a considerably wider expanse than that of the planet's surface alone, they can radiate from a much greater total area, and consequently radiate a correspondingly greater amount of heat. If the heatballs swing out to, say, three planetary radii cooling rates can thus be increased by a factor ~10, bringing cooling times down to as little as a decade,
The total mass of the heatballs is surprisingly low (equivalent to only ~16 mm of water over Venus) because the water (which has a high latent heat of vaporisation) is effectively reused every orbit, say every 10,000 seconds.
As Venus cools, carbon dioxide rains out of the atmosphere, forming oceans in the low-lying regions. I don't know whether dry ice is denser or lighter than the liquid CO2, so I'm not sure whether those oceans freeze over; however, any water ice will naturally float on top of the CO2. Now because we don't really want oceans of liquid carbon dioxide we can cover them over with a floating platform of lightweight hollow blocks (Fig 5.9). The water ocean goes on top.
To get that water ocean we have to find some water. Where from? The icy moons of Saturn are the best bet — Enceladus, for example, could provide enough water to cover Venus to a depth of ~140m.
A steam-powered rocket drives the iceman out of its orbit, bouncing it off the gravity fields of other satellites, flinging it away from Saturn and into the inner Solar System. Eventually it approaches Venus, where we break it in half, one half swings round one side of Venus, the other half round the other (Fig 5.10). Now divide each half further into, say, 100 moonlets. These moonlets orbit the Sun with the same period as Venus; every half orbit then, that is, every 112 days, they return to the vicinity of Venus, where they collide, a pair at a time, just, short of the planet. Water vapour from the vaporised moonlets falls onto the planet and cools to become rain.
During icefall, it's a good idea to protect the surface from the heat and flash. We use a sky canopy, not unlike a para-terraforming roof, but a good deal thinner (we're not trying to hold in an atmosphere, just providing a sort of lightweight tent around the globe).
You can live on the surface during icefall; simply cover your colony with a transparent tent (Fig 5.1 1); the atmosphere inside is soon made breathable, but the pressure inside and outside is the same (this makes it much easier than para-terraforming on Mars). Enlarging the colony is easy; just make the tent bigger.
In the early stages of terraforming, the construction of aerial colonies (Fig 5.12), floating like enormous dirigible balloons high in Venus' atmosphere — at around the 1 bar level, where the temperature is not excessive — would enable us to move colonists in straight away providing useful economic returns early on.
After terraforming, we have a planet very like the Earth, with both land and seas, and a sun crossing the sky once every twenty-four hours. However because day and night is produced by an orbiting soletta, instead of by the planet's spin, the sun's path across the sky is peculiar Fig 5.13). This feature is likely to lead to climate patterns more even than on Earth; nowhere as persistently cold as the Arctic and Antarctic, nor as persistently hot as the equator.
. Its pretty obvious that conditions would be more extreme on earth I just had no idea how extreme. I'm inclined to think that life would not develop beyond single celled organisms or perhaps the oceans would still provide harbour for more complex life?
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