Earth is rare

[nexium]

I understand the role of the strong tides (due to the moon) to help the very first spark of life to evolve, but the sun produces a modest tide even if there were no moon. Does our moon have a role in evolution after that first spark of life?<br /> Oppressive atmosphere? Would we not expect life to adapt even to a thousand bar of atmosphere = 14,700 PSI, if the temperature and chemical composition were reasonable? Neil

 

[thnkrx]

<blockquote><font class="small">In reply to:</font><hr /><p>claims something on the order of 12K 'habstars' within a 450 LY radius." <br /><br />That's using very questionable and highly arbitrary, not to mention unsubstantiated assumptions. <p><hr /></p></p></blockquote><br /><br />However, it is the guideline catalogue for SETI, specifically the new `Allen Telescope Array'. Turnbull & Tarters `HabCat' was prepared just for this radio telescope.<br /><br />That said, I do find some of their criteria to be a tad dubious: they included way too many very dim red dwarf stars (averageing around 1% of Sols luminosity), and placed a bit overmuch faith in the accuracy of stellar metallicity figures (a big item as to whether or not a star is likely to have planets). But, it does look like a good initial local comprehensive survey.<br /><br /><blockquote><font class="small">In reply to:</font><hr /><p>The quest for earthlike planets is a terribly misguided one. Space inhabitants will NOT be living on their planet of origin for long, if they want in the long run to survive. They'll go out into space and lose their gravity adaptations as unneeded. Then they will not be able to live on planets, again. <p><hr /></p></p></blockquote><br /><br />Maybe. Maybe not. I would point out that humanity has been confined to earth for the whole of its history.<br /><br />As to the hunt for terrestrial planets...that hasn't even really begun yet. Unless it got canceled, the first space based mission with a realistic chance of finding such is the KEPLER mission. An analysis I read of that stated that they expected to find something on the order of several hundred to a few thousand terrestrial planets over a three or four year period. <br /><br /><br />

 

[nexium]

Put a habitat anywhere? If we wish to minimise station keeping energy, we need to orbit a planet without a large moon or a star without a large planet. Alternately we can use L1 etc points with modest station keeping energy. If the fusion is very reliable, perhaps we don't need solar energy and can orbit the galaxy in a swarm of asteroids to use for raw materials. Is it probable that 1000 times as many asteroids orbit the galaxy as orbit planets? How about 1000 asteroids (over 30 meters) per cubic light year average for 100 trillion cubic light-years = volume of our galaxy.<br /> If we locate much closer to a star than the equivent of Venus distance from our Sun the disposing of waste heat becomes difficult. Neil

 

[nexium]

If we concede that many future humans will live in (or very close to) free fall = zero gravity; then we can perhaps blow giant bubbles in space, cut them in half and reassable them concentrically. Construction will start near the center on the surface of the smallest sphere.<br /> Where the radius difference is less than 6.5 feet = 2 meters, the extra sphere will be cut up for walls. The walls keep the concentric spheres evenly spaced and divide the habitat into a hundred or more separate rooms each with two, or more air locks to adjacent rooms. That way we can expect some survivers, even if more than half of the habitat is destroyed. The humans will live mostly near the center where radiation is reduced by passing through the less valuable supplies, and possibly reusable trash near the outside. Micrometeorites will rarely pass through more than 3 or 4 layers, so the inner portion of the habitat will be safe except from larger meterorites. The inner layers can also have the highest air pressure allowing the stress to be distributed, over many layers. The air may be so thin in the outermost layers, that some humans can not go there even briefly with an oxygen mask. The habitat can be enlarged by adding more concentric spheres to the outside. Neil

 

[nexium]

~A comment pasted from another forum:~<br />Interesting hypothesis, and fairly accurate; but your willingness to 'sacrifice' a sizeable portion to the 'project' (" That way we can expect some survivers, even if more than half of the habitat is destroyed.") is obviously unacceptable. <br />I would suggest working on a method of protecting the colony from space junk is a more urgent problem, than you suggest. <br /><br />[and in such a 'basic' construct, methods of 'storage' would become an important design challenge.] <br />BoGoWo/ www.able2 know.com <br /><br />~Most of the man made space junk is in low Earth orbit or GEO sychronous orbit, so the earliest habitats are vulnerable. My guess is habitats at L1 are not significantly vulerable to present human space junk. The hazard from natural projectiles will be significant nearly everywhere closer to the sun than Jupiter in the solar system. The cost of protecting habitats will be greater than protecting all of Earth, as habitats will be vulnerable to even millimeter size projectiles which burn up every few seconds in Earth's outer atmosphere. My guess is the only practical way to prevent violent death in space is not go to space. I'm not sure advanced technology can even halve the hazard, but of course we should try. Present electrostatic shields and man made magnetic shields are so ineffective, they have not even been tested significantly in space. <br />I agree, storage is an important consideration. If the habitat is to survive the extinction of all humans on Earth, a century of essential supplies are needed aboard. This will provide a large mass to reduce the radiation hazard and micrometeorite hazard. The larger rooms which regularly have humans need to be close to self sufficient as adjacent rooms could be at vacuum for weeks following worst case disasters. Rooms that frequently have people should have a space suit, even though it is likely death will occur before the space suit can be put on fully. Perhaps the more

 

[asafotidaman]

Oh Absoultely ... Kinda like the rare grey cells one thinks you have while the actual rest stay unrevealed ...

 

[nexium]

Wow, everyone made one to several good points. I suppose there are several million considerations. Two+ tests on Earth indicated that we can make some of the oxygen needed from algae and other green plants. We need to invent the material from which the giant bubbles will be blown. One pound of an oxygen/nitrogen mixture may be enough to blow hundreds of bubbles as the pressure outside the bubbles is essentially zero. A means to make the bubbles strong is needed to allow them to be cut and assembled. A further strengthening is needed after assembly. The material needs to let most of the light useful for photosynthesis in, without letting air escape. We have not done large scale photosynthesis experiments in space because the material is not available and may never be.<br /> Approximately zero gravity relative to the habitat is called free fall. There is some evidence free fall is unhealthy, but we have not exhausted the possibilities. We may end up acccepting that colonists are un-healthy and will be cripples if they return to Earth. Artificial gravity makes photosythesis more difficult and docking and communication and astronomy etc. If it is done by a tether between two habitats, failure of the tether is dangerous. Neil