keithl wrote:Energy? The sun wastes 380 trillion terawatts on empty space. If that was converted to terrestrial electric power with 5% efficiency,
If I recall correctly, what you're describing there is a Dyson shell?
Yeah, having one of those would be mega handy in anything we do... although, I think any biologists might cringe at the idea of blocking out our sun. Maybe if it was a Dyson hemisphere that only ever blocked the half of the sun that we never see? Although, having read Wikipedia last night, that's now sounding like a different megastructure, a Stellar Engine... and might have the unintended effect of dragging the sun away...
(Hehe, 6 posts into this topic and I'm already sounding like an expert in my own head ^^ )I have another idea
about the space elevator, though. Maybe in the future I would do more calculations to check the 'feasibility' of this, but for now I'll just tell you in description.
So, the whole reason space elevators are kind of impossible is because they need to have their centre of mass (henceforth referenced as COM) at 36 megameters above the Earth, right? And the reason for the height is because they have to be in Geosynchronous orbit.
But do they? Why can't they just be in a normal orbit?
So my idea is to build a Ring Rail inside the stratosphere, i.e. where the atmosphere is sparse enough not to cause too many 'air resistance' issues, but not too high for it to be completely impossible to build. Also, if you build outside the stratosphere apparently you have a chance of being hit by meteor debris...
This Ring Rail would sit at about... 30km above the Equator, and follow it around the entire Earth. There would be parallel magnetic tracks. Upon these tracks would sit the carts that would also form the foundations of the elevator. The COM of the elevator would be at about as high as the ISS - 380km (This data collected from http://freemars.org/jeff/speed/index.htm
this site, which has a really
helpful pictogram and corresponding table!) so the speed of the COM would have to be about 7.68 km/s.
The COM would orbit in the same direction as the Earth's rotation. Also, since the foundations are closer to the centre of the Earth, they would be moving much slower compared to the Earth. I'll do this calculation:
1) The velocity of the Ring Rail: v = 2(pi)r/T v = 2(pi)Radius of Earth + 30km /24 hours = 2(pi)(6378+30)*10^3/86.4*10^3 = 6.3*6408/86.4 = 466 m/s - which checks out, given Wiki's data of 465.1 m/s on the surface.
According to the website, the period of the ISS is approx. 92 mins. Whilst the COM has a tangential speed of 7.68 km/s, the foundations would not share this speed, as mentioned earlier, since they are closer to the centre. So:
2) The velocity of the foundations: v = 2(pi)(6378+30)*10^3 / 92 mins
= 6.3*6408 / 5.520 = 7294 m/s
Difference in velocity between Ring Rail and foundations: 7294 - 466 = 6828 m/s or 6.8 km/s
So... still way, way faster than any other terrestrial object, but only about half of escape velocity, and almost 1km/s slower than the tangential speed of the COM. According to Wiki, the effect of sonic booms actually decreases as you push further past the sound barrier? And there is far less air to cause resistance 30km up, anyway.
The construction of the Ring Rail itself seems pretty implausible - it would have to be about 40 megameters long (Circumference of Earth) and probably need huge supports at regular intervals - although possibly the ring structure would hold itself up, and it would only need 'spokes' to tether it in place? Also, since the elevator is flying round the tracks at 6.8km/s, there'd need to be huge slip-roads like on motorways, to get the cargo up to speed before docking with the base of the elevator. The planning permission would also probably be pretty hard to get!
However, once in place, if this idea was feasible, we could put almost infinite elevators onto the Ring Rail - the base of each would be less than 1km, so thousands could be installed on 1 Ring Rail, and with more elevators pushing the air around the Earth, the individual air resistance for each elevator would decrease...
---I was half way though writing this long post when,
I hate to say, I thought up another idea. (aside - I'm new to these forums. I write a lot when I get going. Please inform me if I'm verging on spamming. I'm really enthusiastic but if it's filling up the topic too much I'll tone it down a little bit!)
Anyway, really briefly, here's my other idea: Magnet on the moon?
Just place a big magnet on the moon, and use it to pull objects out of the Earth. Simple.
Further, why don't we use magnets for the space elevator? The tensile strength of a string of electromagnets depends on the strength of each electromagnet... so why not intersperse steel cables with magnets? The 'gaps' between the magnets would be inefficient at achieving tensile strength, because the effect of the magnet would decrease sharply (inverse square law) as the gap becomes longer, but the space in each 'gap' would weigh nothing...