RuBisCO

Yeah but that would take trillions of years, longer then the lifespan of the sun, a solar sail with say a newtron of thrust (which out in oort cloud space would be a huge stail measuring hundred of kilometers wide) would take 17.4 trillion years to de-orbit a 10^18 kg comet. ---- Anyways another option is to mine hydrogen from comets. Hydrogen would reduce the amount of water needed on venus, plus soak up all of venus CO2 by converting it to water (and solid carbon). Hydrogen could be mined from the gas giants but that would require crawling to the bottom of the gas giants gravity well and stripping atmosphere off the top (will countering for drag) then crawling out of the gas giants gravity well. The energy required to convert 1 kilogram of hydrogen from water is roughly 200 MJ (assuming 70-80% efficency) that the same amont of energy needed to move 1 kg of material to 6.3 km/s, So if mining a comet direcly saves you more then 6.3 km/s in delta-v it might be worth it. Of course we also needed to add the mass of melting equipment, electrolysis equipment, fusionable extractors for making fuel for the fusion reactors, cryogenics plants to cool the hydrogen down to a liquid and massive fuel tanks to move the hydrogen. We can use the waste liquid oxgyen as propellant though, though it would provide worse ISP then water. Assuming we don't blow away venus's atmosphere we would need 4.2*10^19 kg of hydrogen to convert all of venus's atmosphere or about 400-500 10^18 kg comets would need to be completely coverted (assuming they are 10% hydrogen by mass, nearly completely water-methane-ammonia, 800-1000 if they are 5% hydrogen). Still 97% of the mass moved to venus would need to be water, not hydrogen (assuming there are negliable level of oxides on the surface of venus) and that would be at least 1.4*10^21 kg of water. The numbers I provided assume 10^22 kg of material smashed into venus which provides plenty of overhead, if we were to mine water directly and deliver it directly it could save some mass, but that depends on how much water a comet is made out of, if it 80% water is it worthwhile to melt and extract all the water? Probably not.

Anyways back to Terraforming Venus So I did some spread sheet caculations on moving large comets and plantiods. There are two realistic means of proplusion we can consider: somekind of fusion engine or high powered fission engines like the nuclear salt water rocket. The fusion engine we can assume can opperate off the comet completely for fuel, both as propellant and for fusionable hydrogen, deuterium, boron, etc, assuming we ever develop a means of sustaining such fusion. I give this a thrust to weight ratio of 0.001. The nuclear salt water rocket from zubrin paper has a thrust to weight of 40, the only problems is it will need to bring all its uranium or thorium with it (and breed the uranium from the thorium) while the rest of the propellent can come from the comet.. oh and technoloigically building a rocket that can contain a continuous nuclear explosion is... questionable. So lets get to the numbers: 4000 AU in the oort cloud a 1*10^18 kg comet (~120 km wide) has an orbital velocity of just 471 m/s. To cancel all that out would require 15,000 kg per second of fuel at an Isp 4000, 588 MN of thrust at 14.4 TW, for 305 years. 60 million tons of fusion propulsion plant and equipment would be needed, or just 1500 tons of fission propulsion equipment plus 1.5 million tons of Uranium (assuming 90% efficiency). 0.01% of the comets mass would need to be consumed as propellant. It would take 45,200 years to fall to venus. It would require the same amount of power and propulsion for a 1*10^16 comet (about ~25 km wide) in the kepler belt at 40 AU and 4710 m/s delta-v needed, except 1% of the comets mass would be consumed as propellant, it would take ~45 years to fall to venus. The maneuver is not instantaneous (obviously) so there will be no Oberth effect (except for the oort cloud body) and the cost in delta-v would thus increase, maybe even double but it may also be possible to fly past one of the gas giants for a gravity swing. At Pluto space/Keplar belt of 40 AU, a 1*10^18 kg comet has an orbital speed of 4710 m/s, It would require 1.5 million kg per second of propellant at an ISP of 4000 for 305 years, 58.8 GN of thrust at 1442 TW to cancel out that velocity in 305 years. 6 billion tons of fusion tug, or 150,000 tons of fission tug, plus 150 million tons of uranium/thorium. Clearly the Fission "tug" is the lighter option, it is just we need to extract millions of tons of uranium or thorium and ship it up there. Now it would take 1400 of the 10^18 kg comets to eqaul the mass of water on earth (assuming they are 100% water) I would say a full 10,000 of them to blast away venus's atmosphere, give it spin and add enough hydrogenated and carbon seqestering materials to completely soak up all the CO2. For the 10^16 kg comets we would need a million of those. Once a "tug" moves a comet in for collision, it can detach in the final days, fly by venus and back out to kepler space to get another comet, minimal delta-v need be spent, but we are talking roughly 500 years per cycle, so to get if we built 500 of these things it would take them 10,000 years to move all the comets. If we use the fission engine option it would require at least 1.5*10^15 kg of uranium/thorium, but that is 0.0066% the mass of the largest M-type asteriod (16 Psyche) so if just that one asteriod has a uranium/thorium concentration of 66 ppm (about 5-10 times earth's crust concentration) we are good to go, we would just need to process all 2.27*10^19 kg of Psyche to get it all. The fusion tug option would forgo this, but instead each one of those tugs alone is a gigantic asteriod size ship! Added together and assuming 20 reuses they weigh 2 times as much as the fission ships and all their uranium/thorium fuel. The only diffrence is the fusion ships would be made out of much more common stuff, aluminium, copper, steel, carbon composite, etc, use "all" the parts of an asteriods. I guess both options could be done at once, keep building fusion tugs while collecting enough uranium for the much lighter fission tugs. Imagine a 100,000 ton standardize fusion tug produce via produce and operated automatically, it would require 60,000 of these to move a 10^18 kg comet to venus and back out to another comet in under 500 years, we would need 300,000,000 of these ships to do it all in 10,000 years, add in all the supporting infrastucture to keep these ships tuned up and operating for 10,000 years of operation. Perhaps a better option will come about, cheap antimater, gravity and anti-gravity drives, wormholes, etc, but yes it could be done within less fantastic technological limits, it just would require a massive solar system wide economy in which the largest of asteriods and in which hundred of millions if not a billion ships can built and kept operating for at least 10,000 years.

Well frankly it not easy to make sense of what you say. All flippant assumptions. Again for an asteroid mission there are no need for a heat shield, no need to aerocapture to save delta-v, no need for exotic heat resistant materials, heat shields or inflatable shields or ships that can withstand high gees or aerodynamic friction. Those things all add weight. Yes, those are just drawings, no I did not say "Geoffrey Landis and its team are just a regular internet guys" there paper is a “paper study†that is what I said. It is not a proposal, there is no designed rover, no built rover, all he present is a handful of experimental parts which provide some proof of concept. All of this is a very long ways way from machines on Venus's surface mining tons of ore, processing that ore and extracting vital elements out, all the while working in 500 C at 92 atmosphere, with sulfates mind you. All of which will weigh a heck of a lot more then a scientific rover. Again with the appeal to authority. Sure he has designed rovers for NASA, but he has not built or designed a rover for Venus, all he presented there is that it is possible. I don't deny that it is possible, I'm just saying it is Impractical to scale that up to a fully automated mining industry on the surface of Venus! And that even if such an industry was built it would be heavy and expensive, more so then an Asteriod mining industry. So far all you have done is provide strawmen, red herring and other fallacies like the one above to avoid acknowledging this fact. No it is an issue, denying it without premise does not make it so. Many components that work here on earth do so under earth pressure of less. Take a capacitor for example, at 92 atmosphere the insulators between the plates will be crushed and the cap won't work like it does. At 92 atmosphere the arcing from a rotor to a stator in a motor could happen, any kind of conventional bearing or seal will be shot, etc, etc. These are not impossible to solve problems, they are just expensive to solve and add weight. Are you suggesting human should work on the surface of Venus? Actually at extreme pressure proteins fold differently, it requires some evolution to adapt to life at extreme pressures or be able to operate at those depths, in short: human's are not spermwhales. No I don't think or have said they are from dust, only that C-type asteroids are primordial, and have all the elements, including the most popular, hydrogen, oxygen, carbon, iron, aluminum, in large quantities. Some asteroids like the M-types were in fact part of the cores of failed planets, those ones a could provide a lot of rare earth minerals in concentrations not see on earth (because our core is not exposed), but for a singular colony a C-type asteroid would provide everything they need materially. A M-type asteroid is for a secondary mine for getting the really valuable stuff in bulk and for potential profit on earth. I've explained how to mine an asteroid, and no it not like mining on earth. I've explained how to do this already: a boring mining or 'mechanical worm' can eat out an asteroid from the inside. It remains fixed to the walls of the tunnels it bores. Such a machine would not need to be the size of terrestrial tunnel borers, as its tunnels are not designed for functional purpose (like trains), instead it can be small, like a meter across at most. The boring head would go through C-Type asteroid material at 1.3 g/ml like butter! Inside the mining tunnels the machine would push against the walls and climb back out, bring with it crushed rock to a station on the surface. The mode of locamotion would be the same as a worm (hence the name) like this: 1. Expand section A 2. Deflat section B 3. Extend piston connecting section A to section B 4. Expand Section B 5. Deflat Section A 6. Retract piston connecting section A to section B The 'inflated' sections of the 'worm' hold it firm against the walls of the tunnel. They don't need to be inflatable badder, they could just be hydraulic walls just like the boring machines here on earth. The material is mechanically compressed into a chambers that makes up segments of the mechanical worm. Once full it crawls back to the station on the surface. In the station it “excretes†what it has collected into the stations enclosed containers. If you don't believe such a system can work then stand on your head and drink, you will find that your throat is preforming what you would call a miracle. The boring head is pressed against the rock, as it spins, crushed rock is forced through holes in the crushing face, mechanical pressure pushed it back into the storage segments, Piston walls in the segments allow it to excrete its contents later. After that material can be compressed into bricks which can be grabbed and move about robotically. Again you have the walls to push against, like this: http://www.youtube.com/watch?v=IB19qOzX-qY except not as cute and with no gravity to fight against. No they have th compete against heavy lift helicopters and aircraft, sure those consume more fuel but they have entrenched industries and require a fraction of the storage costs. Pratical things like that. All plentiful in C-type asteroids in concentrations as high concentrations. Even argon and xenon can be found though they would most likely be imbedded into the surface layers of an asteriod via solar winds Again any rock contains ALL the natural elements, it just some of them will be concentrations of parts per trillion. The C-Type asteroids on the other hand being undifferentiated matter contain all the natural elements in higher concentrations then that. Actually this is what C-Type, S-Type and M-Type asteroids do as well, as they are formed differently and have different elemental compositions. The C-Types contain volatilities, common elements as well heavy metals, while the M-type are concentrated metals. Movement from one asteroid to another may not be much delta-v if they are both NEOs. And again one C-Type asteroid can provide all the necessary elements. So there is no need to move around. But I'm not saying asteriod minign solves all earth problems, I only saying it more pratical than Venus mining. A venus mine is not a heavy lift zeppelin for a rare and specific task, it has not use what so ever. ...WHY??? Ok let me get his straight you boil water for something, you then compress it back into water... why? What need is there for boiled water at the surface of venus? Why not just use the mechanical work of the windmill directly and avoid all the energy transformation cycles? Sure. You gave me a figure of 80%, so I told you the answer is a saving in weight moved is 20%. Now sure if you minning a body that is only 20% water that might be best, but how do you move that much water? Again the impacting body will not be delivering as much energy as what created the moon which weighed several or orders of magnitude greater (I theory suggest it was mars sized) Second was the early earth covered in the shadow of a sunshade devoid of solar flux? Your changing the meaning of the word: building floating cities is not “terraformingâ€Â. Hey if your going to give me generic and vague statements like “fusion with the ambient†I'll interpret it any way I want.

I think all this depends on exactly what is wanted. Lets say you want a chicken, do you just want one to magically appear in a second flat, yeah that not going to happen. Do you want a machine that can take raw organic material, maybe some bioroid cells, insert printed out DNA of chicken genome, have it grow a live chicken, then kill it and serve it for dinner, sure that might be doable. Heck we could have it make copies of you, now before you complain they wont be "you" lets just assume that for this copy to be made you had to die, your brain cryogenicallly frozen in a brick of wax, ablatively scaned by an array of high powered electron microscopes until there is nothing left. And the copy of you is a bioroid made of engineered cells with your genome inserted (like the chicken) and a brain formated to match the one that was scaned... if it works it would be good enough, because it is better then just being dead. What I'm saying is the "Santa Machine" is possible, if your willing to accept pratical constraints of time and process.

Lots of launch windows don't make a price go down, A heat shield can be 15% of the mass, as well has having a ship designed to withstand the heat and the Gs. Asteroid colonies don't need aerocapture, there is no gravity well to fall down, the ships can be flimsy solar sails. Skylon has yet to fly. Those are paper rovers, not actually built. A robot on the surface will need a pressure vessel (heavy) for pressure sensitive components like capacitors, optics, etc, cooling system (heavy) a powerplant for the cooling system (heavy). A robot that can operate at 500 C and 92 atm will require a lot of advance engineering, advance engineering aim at a rather esoteric task (operation on Venus) No a mining vessel on an asteroid does not need to be massive, first off the 1.4 g/ml rock is soft and does not require big and heavy crushers, the machines do not need to support their own weight for they have virtually none. There is no benefits of mining at 0.9gm there are many benefits to mining at 0g though, as I explained. And it is huge and requires massive expensive storage facilities and investment. Why would they need it in big amounts? Take ruthenium for example, all the worlds production is under 40 tons a year, it is not needed much. But lets go with that logic, why would they on Venus not also for some reasons need "bigger amounts" of a rare earth mineral: how would they mine it? Scorer the surface of Venus for a good ore source, build specialty extraction system for extracting it from the ore. The asteroid mine on the other hand can start TRADING resources mined for other resources and equipment from earth, unlike the Venus colony which is mainly a one way trip. The asteroid mine can on just one spot (the asteroid) get EVERYTHING, While the Venus colony is going to need mines all over Venus different ores. Google the energy cost of aluminum production. Near Earth Space is not far from the sun, it going to be between 500-2000 W/m^2 of solar flux. Remember these asteroids can even cross Venus's orbit. If you boil water on venus's surface, how are you going to cool it and close the cycle, you need to pump the steam up 50 km to cool it down. I don't know about that: you have to consider the delta-V needed to get out of Saturn's gravity well. Also again Keplar space is good enough. There are plenty of Enceladus size bodies there (you would need at least 10 of them). Orbits closer to the sun require more delta-v to drop down than orbits further from the sun, and since terraforming Venus is going to a many thousands of year process anyways just for all the heat rejection and complete repocessing of the planet titanic atmosphere, time is not a consideration. Again Keplar Belt is good enough. What I mean is that an object like Pluto needs less then 5 km/s to completely cancel out all its orbital velocity, it would then drop straight into the sun, a little less to fall as low as Venus space. The further the object is from the sun the less delta-v is needed to do this. An object orbiting Saturn would need to first get out of Saturn orbit (unknown delta-v), and then would need twice as much delta-v for pluto to fall to venus space. An object orbiting jupiter would need to first get out of Jupiter orbit (unk delta-v) and then would need three times as much delta-v. Again even if you want to just send the water (magically) your still talking about 10^21 kg of water. Extracting and using star trek teleporters to move the water from a body that is 80% water will have saved you only 20% is mass, for the added cost of a extracting system to extract all the water. You would not need to wait millions of years (assuming the whole crust is not molten). The surface of a planet can lose several dozen degrees in just a night! That temperature loss can go down through 2 meters of soil in just a few months. Imagine Venus with a sunshade shadowing the whole planet, it would cool down very rapidly, in just a few centuries at least. The only problem is the rate and size of the impacts, the really big ones could melt the whole crust of the planet, and if this allows convection of heat liquidity from below it would really slow cooling down. We aren't impacting the moon, at least not in just one impact. You "believe"??? This is religion and not science? a 100 km wide body traveling at 50 km/s will penetrate through Venus atmosphere! There are in fact impact craters on venus: http://www.solarviews.com/eng/vencrate.htm That nothing, we are talking about delivering 10^21 to 10^22 kg of water to venus, one hundred thousand to one million times greater amounts of water then is already there. Now you want to talk practical? Well I recommend going to or starting a thread about "colonizing Venus the way it is" and leave this thread about Terraforming Venus. I really don't think "fusion us with the ambient" is a good idea, I don't think living in a tribe out in nature, constantly warring with my neighboring tribes, murder each other and dragging the women back kicking and screaming is a good idea. No changing the world for our convince has overall been a benefit, then again it has allowed us to populate into the billions, I guess we could murder 99 out of 100 people so that 1% can go back to living in "harmony with nature", either that or we keep with progress and technological development and try to build better worlds.

AngelLestat, For cons you forgot 1. High delta-v to return, though atmosphere no less. 2. Requires heat shield to enter 3. Mass of surface equipment increased by having to deal with extreme pressure and temperatures, this is a perpetual difficulty. Another appeal to authority. Yes I'll bet they are wrong. Its been nearly 80 years now and air-travel is nearly completely dominated by airplanes and helicopters, airships are the vinyl records of the shy. And again the C-type asteroids have ALL the elements, in fact any rock has ALL the elements its just a matter of concentration. C-type asteroids being the undifferentiated material the started the solar system, have all the elements, at least in concentrations of a few dozen parts per billion for the most rarest (and most rarely used) elements, enough to be extracted and separated by the technique I describe of solar thermal vaporization in low pressure hydrogen reducing atmosphere followed, electrowinning in a fluoride or chloride molten salt, within the energy limits I describe (based on vaporizing iron and electrolysis). We are talking of a good overestimate of 50 kw/hour per kilogram (Aluminum electrolysis is 15 kw/hr per kilogram) at least half of that energy provided by solar concentrators afloat in zero gravity. That right no giant windmills high in venus atmosphere, no generators operating at 500 C at 92 atmospheres, just a thin Mylar like foil. You on the other hand need rather "innovative system" and heavy for having a mining, ore processing, refining, all over Venus mining at different ore deposit, utilizing at least megawatts if not gigawatt, nearly everything operating at least a 500 C and 92 atmospheres. My solution is simpler, cheaper, more practical. .... Back on topic: And what is wrong with the oort cloud? Add up the delta-v needed to pull water off of europa, out of jupiter's gravity well, out of Jupiter space and to Venus, verse flying out to a comet and nugging it into free-fall into the inner solar system. And we don't need to go that far there are plenty of comets or other concentrated volatile material objects only as far as Neptune space, with no gravity wells to climb out of. The only hindrance is size, now if hundreds of thousands of small impacts of just a few kilometer wide comets can do just as good of a job as a few world colliding impacts of smacking plutoids into Venus, so be it. The Delta-V required in pushing either would be small. Pluto for example has an orbital speed of 4.7 km/s, so to get it to crash into the sun would require 4.7 km/s, to get it to crash into Venus would require a little less. Further out the amount of Delta-V required is less (but time goes up). Of course moving a comet of a billion tons a few hundred m/s over the course of decades could be done with multi-terrawatt fusion engines or that nuclear salt water engine, you would just need 10 million of said comets, each roughly 100 km wide, but only a single planitoid/eer I mean "dwaft planet" of 10^19 tons, I don't know maybe the starship enterprises D with its "multiphase tractor beam" or some other BS. So lets take pluto (what good is it anyways?) and somehow smack nearly all 1.3*10^22 tons of it, which is made of roughly 10-50% water or 93%-464% all the water on earth, into Venus. What would we get? Well a few percents of that mass would be blown off in the impact, this would include much of Venus present atmosphere, if we impact at an angle to the equator we could also impart a fair amount of spin to venus, perhaps a spin of just a few earth days in length instead of its present spin of ~4 earth months should be possible (a pluto size body impacting venus at radius length from venus at 45 km/s would impart a spin of 3.7 days, that without taking into account angular momentum which means only the mass at the surface of venus at equator is at full spin, not all of venus's mass). Shallow enough of a impact we might be able to make a tiny moon around Venus as well if we wanted, definitely a ring for a few thousand years. Venus would become a molten mass until its crust cooled after a few thousands years, assuming we also built a solar shade. The oceans would rain down, new Venus would likely be remarkably flat, an ocean world until it crust got thick enough to support continents which would take millions of years. Assuming I'm wrong and some of Venus crust remains intact to form islands right way (around the poles?) Venus would be perfectly habitable thousands of years after impact, with a solar shade letting in controlled amounts of sunlight. Perhaps it would be best to smack smaller bodies into a venus, really bigger comets, to get the right ratio of spin imparted, atmosphere knocked off and water/hydrogen delivered, without destroying enough of the crust to require thousands of years of cooling and render the planet into an ocean world. Of course Venus equator would take most of the punishment so expect at least that area to be melted flat. Let see assuming a density of 1.3 tons/m^3 and 70% water that would require 50,000, 40 km wide impactors, or 3000 impactors of 100 km wide to equal all the water on earth. It would require only 120, 300 km wide impactors (at 50% water and 1.7 tons/m^3). There should be enough bodies of these sizes in the Kepler belts alone, forget the Oort cloud. In fact the more I think about this the more just smacking Venus with 500-500,000 comets totaling roughly 10^22 kg is a really great way to terraform Venus! 1. It will impart spin, how much, well that a good physic test question: 1000 impactors each weighing in at 1*10^19 kg impact Venus's surface at the equator a full radius from the center of Venus, each impactor is traveling at 50 km/s upon impact. Venus has a mass of 4.867*10^24, assume angular momentum of a sphere and 50% of the mass of the impactors imparting angular momentum, how much spin would Venus gain in m/s, and in revolutions per hour? My guess based on velocity imparted just from a direct strike is that a total spin will be less than 2 day. This is because a direct strike would impart 267 m/s change in Venus's velocity, calculate that velocity over Venus circumference equals a 40 hour long day. 2. That spin imparted will not be uniform, a magnetic field would arise! Even after a more accurate measure of its spin is calculated from angular momentum of a sphere, it still won't account for a difference in density of Venus at depth as well for fluid motion of Venus's mental, crust and core. It is likely a spin up of Venus's surface will not translate directly throughout, the surface will end up spinning slightly faster then the core, this difference in spin would generate a magnetic field (sort of like on earth) which would protect Venus from solar striping over the long run. 3. Blow off Venus atmosphere. These impacts at such an angle could also end up blow off a good percentage of Venus's atmosphere. When each impact strikes against the equator a wave of venus's atmosphere will be blown off into space. This of course would also start blowing off what was already added to venus's atmosphere from previous impacts, so we can strip all of Venus's atmosphere in this manner, only a percentage, I would just throw a number out there an say we could get ride of 50% of Venus's atmosphere this way tops. 4. Adding all the required water, plus more. All the water of earth, plus more, hopefully all the residual CO2 can be converted to solid carbon and carbonates. Venus may end up with even more nitrogen though. Venus would after all these impacts likely still have 2-4 atmosphere air pressure of almost all nitrogen gas. Problems: how to move that many gigantic comets, how not to have all of Venus's surface melt down flat.

Everyone get your paddles!

So has anyone had any luck making asteriods, tiny worlds only a few kilometers of less across with gravity lower the Gilly?

So how about the density of particles at that altitude? From the charts in the book Venus Revealed the clouds end at 48 km (replaced by “thin haze†or “Virgaâ€Â) so your cloud city is literally but inside clouds of sulfuric acid. What the point was is that the idea of going outside on Venus at that altitude with open skin is a bad idea, I think you agreed already. This is all counter to the idea of going outside in a vacuum, what I was getting at is: why do either? We can have machines working in either environment, and vacuum is more preferable to machines then working on the surface of Venus. Its a matter of logic, the C-type asteroids are the primordial material all the planets were made off, they have ALL the elements. And the methods I describe could theoretically separate any element for any other element within the energy usage limits I provided. http://www.philipmetzger.com/blog/type-of-asteroid-to-mine-part-3/ " C Type accounts for about 75% of all asteroids. They formed in the outer portions of the asteroid belt closer to the frost line where it was cooler so carbon compounds could condense. They also contain hydrated minerals so we can get lots of water out of them. Some estimates are that we can get over 20% of the mass of the asteroid out in the form of water. Since chondrites are undifferentiated they also contain primitive metals, sometimes as much as 40% by mass. These would be extremely good asteroids to mine, having water, metals, and carbon compounds, all three in one. Because they are dark, they are rather hard to find." http://www.uapress.arizona.edu/onlinebks/ResourcesNearEarthSpace/resources21.pdf No, machines are going to have problems with that, they are going to be very heavy machines, needing pressure chambers and heat pumps capable of maintaining nearly 500 K temperature differentials! There are extensive engineering challenges in making components capable of operating mechanically under those conditions. In Near Earth Space the engineering requirements are going to be significantly less. Yeah and zeppelin travel was eventually found to be uneconomical, same will be for making a floating city on Venus when other options are cheaper and more economical like asteroid colonies. Hey and we should have atomic vacuum cleaners and flying cars by now to... see there is a difference from what is practical and viable from what is just daydreams: asteroid colonies are more practical and more likely then a Venus cloud colony. Although frankly both may end up at just dreams. If we are going to limit this discussion to being practical enough to not terraform Venus and live in its clouds instead, we might as well ask why not be even more practical and not even live on Venus at all? Yes "mine" I guess we could call it "extract", We would need to suck in cloud particles, condense them, purify the sulfuric acid, undergo electrolysis, it would be rather energy intensive, at least more so then taking chunks of chrondrite asteroid, heating them in a solar ovens to 400 C and boiling out all the water at up to 20% per kg of raw material. No it is much higher, just to get out of Venus is going to take 10.3 km/s, you can get to some asteroids and back in less than that! Appeal to authority fallacy. One does not need to be a nuclear engineer to see the problems in a Nuclear Salt Water Rocket: first off the amounts of Plutonium, U235 or U233 it requires is prodigious, the nuclear salt water needs to be stored in geometry regulated, boron or neutron absorbing fuel tanks to prevent accidental criticality, hence 'unstable', and it will shoot out a beam of radioactive waste when operating. The practical, economical, political difficulties all of that entails means it not likely to happen. One does not need to be a nuclear scientist to point that out, just as one does not need to be a mathematician to do basic mathematics. I was suggesting bringing an asteroid to earth orbit in counter to your claims of bring them on to Venus (why Venus, why not earth?) Ideally we go out to one in near earth space and only hull back refined material. My point is not simply in getting there, it is also is getting back, getting back from Venus alone is more delta-v then getting to and from most asteroids, and that not include cutting through venus's atmosphere. Time is not simply money, fuel is too. And if your gong to talk about things like solar sails than your being contradictory counting the cost of time when many other forms of propulsion can get the job done much faster than solar sails. Also solar sails can't get one off venus, but they could easily be used around an asteroid. This thread is talking about things like terraforming planets, a task that would take tens of thousands of years for Venus, might as well talk about solar system engineering to add billions of years of habitability to a system. Oh so you do have a practicality limit. Well sure a Jupiter colony would not be for the faint of heart, but anything is possible. Well you fail to disprove my points or even acknowledge them. For example you devise complex schemes to extract energy when my solution is simply to have solar panels face the sun, no need to energy storage or multiple energy sources. No need to worry about much in the way of structure in building solar arrays kilometers wide in zero-gravity. The oort cloud is estimated to weigh in at 1.9 earth masses the amount of delta-v required to get out there would be less then the solar escape velocity from earth (42.1 km/s) of which much of that can be provided by a gravity assisted from Jupiter. Once out at an oort cloud comet, with only a few hundred meters per second of delta-v we could have it hurdling into the inner solar system. Sure all of this would take a few hundred years, but consider the time span for terraforming Venus would be in the tens of thousands of years it would be a viable option. Heck we could probably grab just one plutoid like Eris or pluto its self, weighing less than Europa and having a higher percentage of water per ton, and send it flying into the inner solar system. Don't ask me how we move it, but technically it would be easier than Europa. Anyways we would have it smack Venus. The impact alone would likely knock off much of venus's present atmosphere. Eris for example weighs in at 12.5 times as much as all the water on earth, assuming just 10% of water which is probably an under estimate it would still weigh more then all the water on earth. Of course you would not want to be on or anywhere near Venus during such a collision of worlds, any cloud cities would need to be abondoned or suffer a trully epic death. but the new world produced afterwards would have a lot of water (all of a sudden), now in just one (or a handful of truly GRAND impacts) all the materials are present for terrafroming. The surface though would have become completely molten but its not like Venus has not done that before and probably recently in geological history (last few hundred million years), going back to its present crust thickness of just a few hundred meters would probably take only a few thousand years. A combination of solarshade and bio-chemical engineering as previously describe could probably bring Venus up to habitable in a few thousands years. Highlighted because it is very relevent to the thread, for the people that think they can defeat rule 25 of the internet. Wormholes... and maybe wizards. Both the continent and the moon were named after one of Zeus's aaah “Ladiesâ€Â. See with google you can learn something new everyday. yeah I'm pretty sure climatology does not work like that! First of all the reason winds are slow on the surface has little to do with pressure, and everything to do with friction with the planet its self, its call Laminar flow. Honestly its anyones (other then a group of climatologist with a supercompueter) guess what kind of weather venus would have at 3 atmospheres of mostly nitrogen on a planet with a solar day of 4 months. I would hope it still super-rotates and I would put a good bet due to frictions with mountains and hills surface winds would be low, but that as far as I'm guessing.

Sulfur Hexfluride is safe to breath (as long as you also bring in your requirement of oxygen, no inert gas is safe to breath pure of course), it also hilarious gas to breath:

First: Raise mars temperature One could either use gigantic orbital mirrors out at Mars-Sun L2, or produce a supergreenhouse gas on mars, I would prefer sulfur hexfloride, its extremely stable, very dense and the most powerful greenhose gas known to man. besides that Zubrin covers the rest: http://www.users.globalnet.co.uk/~mfogg/zubrin.htm

I did not say it was the worse option "of every single body in the solar system". I covered that on my first post, and the thread is about TERRAFORMING Venus, not simply colonizing venus. I was simply replying to AngelLestat comments about not terraforming and "living in the clouds." Again I beleive I answered that, no one replied to it, in fact and I quote: and I told him that is inferior to asteriod colonies, so why do it? If this is off-topic I was mearly going along with where others were taking the thread. Flame war? Things here seem very civil to me, AngelLestat has not insulted me, no ad hominiems, etc, and has stayed high on the arguement pyramid, and so have I, I don't see any flame war at all. But if you do want to return to the topic, then please do so, perhaps you can critique my ideas on terraforming venus? They would also need to deal with the extra heat, not only from the sun but reflected off venus, as well as have to live with the extra delta-v of working in Venus's gravity well. If you want close to the sun there are NEO that cross even venus's orbit.

Can you cite the size of droplets at that altitude? I've handle surfuric acid, don't tell me how to play with it though. No "in my head": the added delta-v to get to Venus, be trapped there because of all the delta-v needed to get off, to do nothing of any profit, does not add up to being worth the ability to walk outside if I hold my breath and don a latex suit. Again safe living can be had in an orbital spacestation of the one I already describe, all the elements can be extracted from one 500 m C-type asteroid for decades to centuries, and it could all be done with solar power in Near Earth Space, no need to go to different asteroids. Zero gravity work, is not as hard as working at nearly 500 C at 92 atmospheres. www.nss.org/settlement/nasa/70sArt/AC75-1086-1f.jpeg http://www.nss.org/settlement/nasa/70sArt/AC76-0628f.jpeg You were saying? That not much water, that 20 ppm of water, Water would need to by mined by extracting it from the sulfuric acid clouds via electrolysis. How about the delta-V to get back out? I doubt such an engine will every be used: its fuel is very expensive, highly unstable, and it shots out a beam of radioactive waste. I'm sure the anti-nuclear nuts will go ape if it was used even within earth's magnetosphere. Its a matter of what is practical, what is easier, frankly humans colonizing space will likely never happen, and if they do the asteroids will be the first place they go to do it (either that or mars, people are just obsessed with mars). The asteroids are the easiest place in space to make money, easiest place to build a colony, easier than Venus, that's the hard serious truth. I don't care. http://www.permanent.com/space-transportation-lunar-gravity-assist.html They mention nothing of a breaking burn being needed. We would need to remove almost all of Venus's atmosphere, while simultaneously engineering it to deflect much of the light that hits it, while keeping just enough CO2 for plant life. That a hard undertaking, harder then building a solarshade. Sure, why not? I could design a city on Jupiter too, what's your point? Dreams and reality are different things, A Venus colony is highly unrealistic, an asteroid colony is more realistic, even then any human space colony is unlikely. I have no clue what you just said. The energy needed would be phenomenal, frankly if you want water, go to the oort cloud, grab comets Hey and maybe we can strip off the oxygen and just beam protons, either way you would need to figure out how to keep the beam coherent over millions and millions of kilometers. I don't think you need to worry about the heating much, Venus is already really hot. Also it is Europa not Europe, all this time your talking about taking all the water of Europe and de-orbiting Europe, the EU must hate you. I already covered that is my first post on this thread. I doubt the surface wind would be so bad, the present surface wind is pretty low even. 4 mouth days is liveable. The nitrogen partial pressure will be high, but humans should be able to adapt.

I don't play via steam, not for this game at least for I got it before steam and never ported it over to steam.

NRO, as in roughly 1 au from the sun. We can acheive 1300 W/M^2 of solar flux and passive temperature control there. Can you summurize it? Maybe a spreedsheet? I really doubt that, first the sulfuric acid particles in the haze at that altitude (another reason 60 km would be better then 50) would likely cause rashing and burns even for 1 minute of exposure, second just the pure CO2 alone would drop the pH in the water on your eyes in seconds, your eyes would start to tear up and burn even if no sulfuric acid cloud matterial entered your eyes. Anyways the problem is the same: human need to kept in a seperate enviorment, your saying all that need on venus is to seperate atmosphere, bouyant atmosphere there no less, sure that nice but the needing to keep it afoat, keep it powered, to bring it to venus, to maintain the robotic work force that must be designed to operate in a literal hell, to get things off venus, etc, etc, these problems are far more extensive, expensive and impratical then asteriod colonies. And we don't have materials for vaccum? I disagree, lack of water and high delta-v are the BIGGEST problems! Water is fundemental to starting a colony, the C-type asteriods have that in aboundence, some of them require less delta-v to reach and return from then venus or mars, and delta-v is such a big problem it why we have not gotten outside of LEO in over 50 years because of how costly it is! I would guess transhumanism will occur long before civilization collapses due to the idocracy effect. Darwinian evolution simply becomes overridden once we start forcibly redesigning our genomes, inserting cybernetic implants and even upload thoughts, memories and personality into a non-organic frame. Second of all I would imply thrid world people are stupid or of inferior genetic stock: sure they are un-educated and ignorant, but the intelligence needed to survive there is quite intensive, frankely they are "evolving" better then in developed countires were luxuary amd medicine allows the geneticaly weak to survive and prosper. The moons gravity! If you fly by the orbital tailing side of the moon, velocity will be lost from you as it sucked by the moons gravity, then instead of flying by the earth and out, you will enter a High Earth Orbit instead. No its not, especially as the sun gets older, Even the earth will need to be moved out in order to avoid frying. Well the earth ocean's are 3% the mass of Europa, so assuming europa was 10% water it would be like 3 earth ocean's worth in water. Since venus is already so dam hot and water vapor is a great greenhouse gas, all the water would simply add to venus's atmsphere and increase it mass by ~9 times, I would assume conditions would get much worse on venus, not better. You need to reduce venus's solar flux, drop it temperature, get rid of all the CO2, then dump water and even then bringing back venus to it normal solar flux would still put it perilously close to not being habitalble. If venus was a black body radiator (no atmsophere, made of some kind of perfect black material that absorbs all light and re-emits all energy as infrared) it would have a surface temperature of 55 C, compare to earth's theoritical black body surface termperature 6 C. Venus would thus need a global cooling effect, very little heat retention! Either it surface, or it atmsphere would need to reflect back more light, especially infared light, then it lets in. The best solution I can think of is a gigantic sunshade in Sun-Venus L1, it would need to be ~4 times wider then venus out at that distance so that its shadow completely covers venus. Then venus would cool down. Assuming you did dump all that water and you bring venus's temp down so then it can become liquid you would then need to let the water and the carbon dioxide react with sodium and other metals in venus's soil to form carbonate minerals, pulling out all the CO2. Does venus have enough of those metals exposed to pull out all that CO2, maybe.

I would say why earth took billions of years to have a breathable oxygen partial pressure had little to do with energy concerns. Let say you want to make a partial pressue of oxygen that is breathable, That would be ~1.1*10^18 kg of oxygen (based on earth's atmospheric mass). To convert CO2 to Oxygen is 393.509 kj/mol, CO2 is 40 g/mol, the radius of venus 6052 km and area facing the sun is 1.15*10^14 m^2 with a solar flux of 2622 W/m^2... sol lets assume 0.1% of all light hitting venus is used by hypothetical bioengineered cloud organisms at 1% effiency to make oxygen (reasonable effieceny of terrestiral plants is 1%) it would take only *spreedsheet drum role* 112 years to make enough oxygen. Earth's history was one filled with a constant war between organisms that consumed oxygen and those that produced it, geological processes that consumed oxygen, geological history that foiled life's progress, etc, etc, a bioengineered cloud algae we assume would not have those problems. The problem is again how to get ride of all that carbon, and how to get in incredible amounts of water. Slowly moving venus out to a more habitable orbit (as well as the earth, maybe mars as well) over the next billion years would not be that difficulty if you fingued out how to solve the first problems. Perhaps someday we could put venus and the earth in orbit about each other, knock out the moon, maybe put in orbit about mars, I don't know, what ever.

Well I don't know if you want your products evolving.

Yeah there is never going to be such a machine unless they discovery a way to break all of physics and make 2+2=fish. A more realistic option would be a machine that can take in energy and raw elements and push out any product made from said energy and elements, so just remove the whole making new atoms from scratch part. How much energy would it require, probably not that much. Do you know how much energy it takes to mine and melt down and make a steel hammer? About 10-12.5 MJ, or about as much energy as a single human being consumes in a day. So depending on how common the elements of your product is the amount of energy needed to make it could vary by several orders of magnitude. If it's a lump of food all you need is a little bit of carbon, hydrogen, oxygen, a dash of phosphorous and sulfur and your good to go at a few MJ per kg of chick nugget goodness, if you want a solid Ruthenium paperweight on the other hand we are talking thousands of giga-joules, at which point atomic synthesis might start to look like a good option. As for making perfect replicates: there is perfect and than there is 'good enough'. Has anyone ever watched the classic, "Citizen Kane", supposedly one of the greatest movies ever... no you haven't! For the original celluloid tape of Citizen Kane has long since fallen to pieces and oblivion. The original Citizen Kane does not exist, what you have watched is a copy, of a copy, of a copy, usually 'digitally enhance' and reformatted even, this is true of just about every movie you have seen... I don't hear anyone complaining.

... I'm not sure what you just said. Completely manageable energy usage as I've shown when you can build many kilometer wide solar arrays and solar concentrator arrays afloat in solar orbit. Indubitably Oh if we are considering that then your Venus plans are grossly unprofitable, well technically all manned space travel is at present and probably in the future if the machines get any smarter. Via capitalism there would be no point in sending people to Venus, or to mars, or the moon or asteroids, so I don't think you want to consider budget as a factor. Or, just hear me out, we can just face some solar panels at the sun in solar orbit. As a certified "scientist" I will tell you self-replicating machines are probably going to happen long before antimatter drives, considering antimatter is a colossal expense to make and you can see a self-replicating machine in the mirror. An AI that can manage an asteroid mine, build more mining equipment from the material it harvests and build cargoships is not a far cry technologically, creating antimatter without having to consume fantastic amounts of energy to do it and having enough of it for propulsion is on the other hand ridiculous, not to mention also very uneconomical. Then we will have them programed with "safe limits" or transhumanism will work out and we will become the machines, what ever. And a scorching hot CO2 atmosphere and sulfuric acid clouds, won't? As I pointed out before radiation, not a problem, temperature: if this is NEO space that not a problem either, as long as heat can transfer from hot to cold side the average will be comfortable. Big distance: in many cases less then a flight to Venus. Hey I'm just reading out of the book here... Oh I see the problem you want room temp, I'm figuring the cloud city is going to need to dump waste heat (as well as take on some thermal buoyancy) so I figure it needs to operate at 0 C. Didn't you say a 1 km wide balloon? Again we don't need to be in the asteroid belt, there are plenty of NEO instead, flying between mars, earth and even Venus. Using every part of the asteroid including the economically useless stuff not sent back to earth, is wise budgeting. Again if you want to talk about expensive the cheapest space enterprise would be the asteroids as they require the least delta-v to get to and from and have some of the best ore in the solar system. Does not make up for living in a gravity well, surround by a unbreathable atmosphere filled with corrosive acid. Exactly what are they going to do for business there, oh that right get diamonds from the hellish surface, and launch them out of venus atmosphere all the way to earth.... yeah that going to happen. Or they could spend a fraction of the energy mining rare-earths (and everything else) off of a NEO asteroids and bring them back to earth. I'm not going to wonder how you came up with that math, did you add in the cost of getting people to Venus and getting things back... probably not. Except for the part about the air killing you, or that if you lose height your start to cook. With 2 meters of aforementioned shielding both radiation and meteors are not going to be a problem. A meteor that could penetrate would need to be big enough to detect ahead of time, and could be shot out or deflected with an interceptor. And sending people to Venus is a better idea? Also I would not speak of the "population problem", as it appears to already be self solving: just look at the developed countries birth rates, mind you some of them even have negative birth rates, raise the standard of living high enough and people seem to stop breeding. But hypothetically if we did want to colonies space, the asteroids would the most economical place to star, that and the asteroids, venus and mars, no so, well mars maybe if it can be terraformed as easily as hoped, why we could easily bring it surface temp and pressure to habitable in under a century if there is enough CO2 frozen in its soil, sure it will take longer to make the air breathable but its a much safer and more roomy existence then living in a balloon on venus. No not at all, all you need to do if fly past the moon at the right trajectory, no extract delta-v needed, the moon's gravity can easily provide it, 1 km's should be more then enough for an asteroid capture. Again zero-g can make the fragile strong enough. If it all about cost then why are you going on about mining Venus, that is grossly uneconomical, the delta-v is too high, the engineering considerations to extensive! How do you get a mining machine too venus, how do you keep it working on Venus, how do you get products off Venus? Your considering mining Hell. And what for, theoretical diamonds? How about this I bet that by the time technology comes about to make mining Venus a good business plan, manufacturing diamonds like plate glass will already have been invented.

*sitting on Santa Claus's lap* I want a rotating core nuclear thermal rocket, 3800 C core temps and specific impulses over 1000 on LH2, thrust to weight ratio of 30. Plus a Helium/Xenon Closed Brayton cycle power conversion system. Oh and I also want a dense plasma focus fusion engine capable of fusing protons and boron aneutronically and a specific impulse in excess of 100,000. *Santa Claus looks confused*

Hydrazine is just such a pain to handle, imagine nerve gas as a rocket fuel, oh wait we don't need to image that its hydrazine! Hydrogen peroxide may have pathetic specific impulse, but we are talking about attitude control here not main propulsion, and hydrogen peroxide is much easier to handle and easier to produce in situ then hydrazine which needs a source of nitrogen, not just water.

Huum Dragon or Orion, both are bigger then 2.5 m, both hold like 7 herbals... well options are good right?

Well in real life after we blow up a cliff side we have truck and scopes clean that all up and crushers break down the bigger pieces, its a rather complex system of machines. At 1.38 kg/l they probably are very easy to cut through, that is desity far below rock (or metal) and just barely above ice. Most likely has the consistency of rubble with a little bit of snow mixed in. Well again the C-type asteroids have a bit of everything, including metals, and precious metals, as well as water and volatiles, and are very "soft" So we don't need to go to the M-type asteroids, I would assume though for an M-type asteroid that is one solid piece of metal, melting chucks out would be the best option, in the vacuum of space electron cutters would be an option, or we could just use concentrated sunlight and collect the vapors with an ion trap, refining and mining all in one. The asteroids generally have "extra concentrations", like the M-type have some rare-earth metal concentrations higher then any place on earth (or venues I assume). I mean unless you have evidence Venus has particular deposits of purified ultrarare metal like nothing on earth, which may be possible, I mean what is with the snow cap effect there? Something got to be coming out the atmosphere and plating at that altitude and it sure is not snow! But barring some kind of geochemistry where platinum concentrates in pure metallic form on Venus here and there, mining Venus is simply not going to be economical again asteroid mining. No we don't. There no limit to how large we could make the solar panels or mirror arrays in space. On venus though we would need something like that, to make up for floating around the nightside, difficulty at facing panels at the sun, holding them up against gravity, etc Well I was assuming you wanted a colony, not just a mining crew. Need at least 150 people, to maintain genetic viability after several generations. But with the way AI is developing I would think by the end the century we could do Astrid mining completely autonomously with Von Neumann machines. Vacuum is not a problem either, what your point? From the chart I was looking at in the book "Venus Revealed" temps between 0-32 F are beyond 60 km. Also still some cloud cover/haze there as well. Except a 1 km wide balloon, that can hold the mass of 2 empire state buildings without breaking, covered with solar panels or windows to let in light. Well considering the station is lined in several meters of glass fiber, carbon fiber and other overstock materials, it would need to be a big rock to penetrate. As well pressure barriers can be made inside it so a hole won't cause a leak for the whole station. The cloud city of yours would have the same problem, for any hole that forms for any reason would lead to a painful and hot death for all it occupants. Why would we want to put an asteroid down Venus's gravity well? We could just put one around the earth instead, use the moon for a gravity assisted capture, no need for risky aerocapture at all. Building an orbital city adds space for people. Yes, so? It would not be hard to make such a structure, again it weighs only 6 tons at 3 g/m^2, and that is the present limit with earth construction of fabric, in space we could make it even flimsier, a lithium sail just 20 nm thick would be only 0.011 g/m^2. Can you explain any show stopping technical problems in making as sail that is 1414 m x 1414 m verse 400 m x 400 m?

Oh no we do have electronics that might work at 500°C, they are called "vaccum tubes".

But you could do with shaft mining. A mechanical “wormâ€Â, could eat out an asteroid from the inside. Being able to grip the walls of the tunnel to move about, no need for gravity. Because of its extremely low gravity a good percentage of an asteroid should be able to be dug out in this way before the asteroid collapses. Likely even then the collapse would be very slow and would not damage the “worm†which under such low gravity could not be crushed and could just re-tunnel any collapsed tunnels. Same problem on the surface of venus. As is some types of asteroids have specific elements in concentrations not found on any mine on earth, so the difficulty in extracting and purify could not be much harder then those mines. Lets assume a C-type asteroids because it has a bit of everything, and not a M-type asteroids that practically just solid stainless steal. Material that is dug up by the aforementioned worm, can be place in a solar thermal oven, with quarts window to let in concentrated sunlight, magnetic or electrostatics or gas jets can be used to keep a ball of raw feedstock floating in the center of the chamber preventing thermal contact with the walls. First few hundred K would boil off all the water or any volatiles in it, even chemically bound water. Hydrogen gas would be added to chemically reduce the feedstock into metals and hydrides. Oxides would reduce to metals and water, the water would be electrolyzed back into hydrogen, with oxygen as the product. Carbon would convert into methane, excellent starting material for making any kind of organics. At different temperatures different elements would boil off and could be caught in cold trap collectors. If the floating molten glob of raw material can be heated to 4000 K every element would boil off eventually. Further refining could be done by “burning†semi-refined product from the cold traps in with chlorine or fluorine gas, the fluorides are then dissolved in molten salts and electrowinned back into Florine and specific metals. This process could separate any element from any other element. Sure it would require a lot of power, for example boil a metric ton of Iron would take roughly 100 kw continuous for a whole day (8.53 GJ) (also assuming very little heat lose) to convert a metric ton of water to hydrogen and oxygen would take 155 KW continuous for a day, (assuming 100% efficiency, quadruple that 600 Kw for a reasonable 25% efficiency from sunlight to electricity to electrolysis, or 50% efficient, 310 KW for a thermal cracking process). So a safe over estimate would be 2 MW per ton of material processed in a day. A 1000 tons per day processing capacity would require 2 GW continuous. but with sunlight available continuously and no structural restriction by gravity on solar array sizes, it would not be that hard to achieve that. Most of the energy would be needed as heat which could be provided by solar thermal, the waste heat could drive generators that would provide some of the power for electrolysis and electrowinning. Yes, that what the asteroid is for, providing all the materials to build that. A giant torus 500 m wide could produce earth “gravity†at it edge with less then 2 rpm, making Coriolis effect unnoticeable. If it internal space is is 30 meters wide and 30 meters tall (10 floors) it would have an internal volume of 1.4 million cubic meters and 450,000 m^2 of floor space, about the same volume as a very large cruise liner. If we assume equal weight to a cruise ship that would be 50-100 thousands tons, or 111-222 the mass of ISS. Occupancy would be enough for several thousand people to live in cruise ship style luxury. Some of that floor area would need to be given up for food production, assuming from the study below 50 m^2 per person of food space, and hydroponic stacks 5 racks high that would be 10 m^2 per person, lets give each person another 90 m^2 of living space and such a ship could hold 4500 people. Or 1000 m^2 per person for 450 people or 1/10 the density of a luxury cruise ship. And building cloud cities that need to stay afloat and house an internal breathable atmosphere from a mildly toxic, highly corrosive atmosphere of CO2 and sulfuric acid droplets is way easier? According to this study we should be able to feed and maintain a person on 50-100 kW continuous, easily. Lets assume 500 colonist, that would be 250 MW to 500 MW of power needed. Now unlike on venus power is continuously coming from the sun (no dark side, no night) and there is no gravity so there is very little in the way in structural constraints to building gigantic solar collectors, assuming only 25% efficiency, that would be a solar collector 1.2 km wide at the power levels you gave. Of course water and oxygen comes from the asteroid, as well as everything else. Likewise you need resources, water, plants, food, oxygen for a Venus colony, and you need to keep all this afloat 60 km above venus surface. All the left over asteroid material would do just fine. A 500 m wide C-type asteroid weighs 90 million metric tons (assuming 1.38 g/ml density) a M-Type asteroid of that size would weigh 348 million metric tons (assuming 5.32 g/ml density), most of that metal. It would take a long time to mine all that! For example that last one is one third to one half the earth's present annual metal production. An asteroid mine that can process 1000 tons a day would take 248 years to go through a single 500 m wide C-Type asteroid. What matters more is delta-v. Some asteroids require less energy to get to and back then getting to and back from the moon! An asteroid colony is not going to need to come back and yet are going to be able to build automated cargoships at the asteroid and have them bring cargo back to earth to help finance themselves, that not going to happen for a venus colony. Again the C-type have at least a few percentage points of water, either as ice under the surface or as hydrated minerals, both can be easily extracted. The C-type asteroids represent 75% of asteroids. Well plenty of propellant can be produced at an asteroid as well as the delta-v needed to get it back to earth can be very small, with no gravity well to climb out of. Lets say your at an asteroid that is 3 AU away from the sun when you leave it, with a solar sail you could at best get only 1 N of thrust per km^2 of sail at that distance (because sunlight is 1/9th its intensity at earth), lets assume 1 km^2 of sail are exposed to the sun moving a 10 ton automated cargo ship (assuming it at a 45° that would be a sail loading of 5 g/m^2, or a 2 km^2 sail that weighs 3 g/m^2 would weigh 6 tons and could move 4 tons of cargo), even at that distance it would achieve 8 m/s of delta-v per day, and could achieve 3 km/s in a year, more then enough even for a non-Oberth effect transfer orbit to Earth.