On Dec 17, 2012, at 6:46 AM, Abd ul-Rahman Lomax <a...@lomaxdesign.com> wrote:
> >> There is also radiation hazard in orbital habitats. > > Probably the biggest problem. Radiation shielding has been part of space > colony proposals. Actually radiation shielding is simpler than what is previously thought, because Near Earth Asteroids contains lots of rubble that serves well as radiation shield. > You want to build in a place it is easy to travel from. Easy to get to any > destination from earth orbit. Hard to get to earth orbit from Earth. Hard > from Venus. If we are to build colony for millions of people, I would guess that getting back from there is not important. People who move into Venus will stay there. In Venus there should be room for hundreds of billions of people in a long term. In Earth we are struggling with few billion (western) people, if there is not going to happen breakthrough in clean energy production. Solar electricity might get cheap enough also here on Earth to support civilization, but many people do not believe that the cost of PV cells will be halved every eight years ad infinitum. I believe that they do, but I will not give you any proofs. However, today energy production is utterly unsustainable, because energy production is based on fossil fuels and very unstable nuclear power. Therefore there is urge to migrate into Venus, where there is abundant energy resources. > Once in space, you can use solar sails to move even very large mass, all you > need is some patience. Modern ion engines are as good as solar sails. Such as well served Hall thrusters. There are also few promising concepts in drawing board. NEAs have plenty of hydrogen for ion propulsion purposes so it is not required to lift from Earth. > Hope was, eventually, to build a space elevator. Earth bound space elevator is not good idea, because reusable rockets are cheaper to operate than space elevator. Also the development costs of reusability are lower and there is no need for qualitative breakthroughs in basic material science. And we do not have any means to estimate the safety aspects of space elevator. However in Moon we have possibility to construct space elevator in 2018, because it is possible within existing technology and it will cost only few billion dollars, including development costs. That is less than Curiosity rover! I would predict that space elevator even in moon will get obsolete in 2030's due to reusable space crafts and orbital refueling. But my estimation is that there is at least 10+ year window while space elevator in moon is profitable. > For humans to live in space, the biggest expense is lifting *hydrogen*. > Oxygen is readily available on the moon, as oxides. Hydrogen is scarce in > space. Problem with moon is that there very little gravity. Orbital habitats are better, because artificial gravity could be more confortable. We do not even know how well human body will adapt into Mercury and Mars ⅓-gravity, but I would guess that well enough, as I am going to book one way ticket to Mars in 2013. However hydrogen is abundant. There is huge amounts of water-ice in Mercury and C-type Near Earth Asteroids and sufficient amounts of water ice in the moon. Basic specs for 1200 ton C-type NEAs: transportation cost to high lunar orbit (Δv 100-500 m/s) are 2 billion dollars (or less if Falcon Heavy will be as cheap as promised) and that will contain ca. 200 tons of water and 200 tons other volatiles such as nitrogen and carbon compounds. This is kind a silly, but there are billions of small (<1200 tons) bodies near Earth that can be harvested as a resource. People just did not realize this before because we cannot see them. Currently orbits are calculated only for few dozen NEAs, but none of them are observed accurately enough that we could estimate the mass or type of NEAs. Hydrogen was thought to be scarce resource in space, because it was not found until recently. Therefore it has not made into scifi visions. Why Venus is ignored in all scifi visions is just something that I cannot understand. Even floating city in Star Wars relied on antigravity technology although it would be easy to float e.g. in Saturn where temperature, gravity and pressure are in goldilocks zone. Using hot hydrogen balloons for floating in Saturn is not anyway futuristic technology! —Jouni
