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Some things to note; Venus has already been terraformed in OA, and most of these technologies were used (active cooling, import of hydrogen/water and oxygen sequestration). Even Landis balloons were used in the earlier history of that planet.

But there are lots of other cytherian (venus-like) worlds in the Terragen Sphere; they may even outnumber lifeless gaians, although we've never run the numbers. So any technique that is at all plausible will probably have been used somewhere.

Finally, as I always do when we discuss terraforming Venus, I'd like to mention that Venus probably has an oxygen surplus; assuming it once had a lot of water, this was split by photolysis and the hydrogen was lost, but the oxygen (and some of the deuterium) remained behind. The most useful way to get rid of this oxygen would be to import hydrogen and create water on the planet. Trouble is, hydrogen is volatile and low density, so it is expensive to import hydrogen rather than drop water ice on the surface; if you import a lot of water then you would need to get rid of a larger quantity of oxygen before the planet becomes fully habitable.
(04-24-2015, 07:42 PM)stevebowers Wrote: [ -> ]Trouble is, hydrogen is volatile and low density, so it is expensive to import hydrogen

At the risk of becoming a parrot (given how often I squawk this) Expense is a strange term in OA. It might be quicker to let your assemblers spawn a comet-capture fleet and crash water ice over a hydrogen mining outpost along with transports. But either case requires little input (at least in the mid setting, in the early setting there's still a lot of work to be done designing the protocols and equipment) and is really a question of how long you want to wait.

To add something beyond this hydrogen as a gas and liquid are very low density but metallic hydrogen has been reported as possibly having a density of 0.6g/ml IIRC. Given OA tech it wouldn't seem that far fetched to believe that mt-hydrogen could be mass produced, stored and transported.
Expense is a consideration early in the scenario, and also in the early developmental stages of colonies on the Periphery, where colonies have to pass through a bottleneck in resources after arrival. If a new system includes a gas giant with an extensive ring system and a dry, hot venus-like planet, the ring system would be a better target for early colonisation efforts since there is a lot of volatiles there. Terraforming a Venus-like world takes longer, and would generally take the most economical route, although this may not be such a big consideration once civilisation is well-established in the system.
It's not so much an either/or situation. A colony ship could arrive and go into orbit around the gas giant. They launch their stock of "industry seeds" (a package of bots, an assembler and tools like power lines, solar panels etc) and general bots to appropriate sites with the order to grow. Then they wait a while (given that most of them will be in stasis it's not much of an issue) until there's now two assemblers with bot crews. At that point they can just order one of the crews to begin terraforming the Venus like planet, whilst the other works on building a hab. Both keep replicating with breaks to build more infrastructure, bots etcetera. The hab will be finished first but all the while the other crew will be building shipyards to send out tech around the system and start the terraforming.

Total cost: the time it takes that original assembler crew to replicate because rather than use the second in the hab building process it gets set on something else.
Time is a very valuable commodity in an advanced civilisation; other valuable commodities are energy, raw materials and processing power. These last three can each be converted into the other, with varying degrees of difficulty, but time is a little more difficult to convert.
Even a self-replicating system goes through a period of slow growth at first, when it seems for a long time nothing much is happening, then a lot happens at once. A very large process like terraforming an inhospitable planet like Venus would pass through a long phase when nothing much seems to be happening. During this time the colonists could concentrate on the smewhat lower-hanging fruit of the construction of modestly-sized habitats elsewhere.
Incidentally, I was thinking of budgeting 1000 years for this. The future residents already have a habitable planet on which to build their mud huts and are quite a ways short of spaceships, so the terraforming team can take its time. Shorter is better, it gives more flexibility with the timeline, but 1000 years is fine.
What about this thing?
By Paul Birch.
Yes; that paper includes the idea of a bouyant layer that shades the surface, gradually cooling and eventually settling on top of a layer of frozen carbon dioxide. This idea requires that we not only cool Venus, but make it so cool that it has CO2 permafrost; an interesting idea, and sure to find application in the OA universe somewhere, but it seems a little reckless. If civilisation suffers a Ringworld-like collapse, the CO2 would start to form geysers eventually, making the planet uninhabitable again. On the other hand, many OA megaprojects have the same shortcoming- they are not all futureproof.
(04-25-2015, 06:17 PM)Dalex Wrote: [ -> ]What about this thing?
By Paul Birch.

I favor the "artificial planetary surface" idea myself.
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