Thread: Space Elevator Feasibility

Presented as mechanical engineering challenge for dotcomrades in this specialty and other interested parties with thanks in advance for participation from Prince. Related topic, "space fountain" consisting of pellets in evacuated tubes propelled by linear induction motors out into space where path is reversed and potential energy recovered in closed loop.

http://www.spaceward.org/elevator-feasibility

Plus "orbital siphon" variant:

http://www.idlex.freeserve.co.uk/siphon/siphon.html

Pure Bollocks.

Thank you ever so much for your insightful and lengthy analysis of the proposals, dotcomrade. Certainly your other posts will be similarly illuminating.

Originally Posted by Home200

Pure Bollocks.

Prince has discovered an existing thread devoted to this topic, already infested with skeptical and rude goons, so your further services will not be required, dotcomrade.

I think space-elevator will work, but more importantly it has both pros & cons (which meant they are realistic). Firstly: space-elevator allow easy access to space without the use of expendable rocket (the payload tug on the space-station), but secondly: it still require the same amount of fuel to lift the payload to space (conservation of energy). Each time the payload tug on the tether: the space-station must do an orbital correction to maintain its orbit, and the amount of fuel for orbital adjustment will be the same with the amount of energy to get such weight to space with a rocket but without the expendable payload/instruments.

The thing is: a space-station with tether is not like a typical space-station we have in orbit; the tether is an additional weight in addition to the weight of the space-station itself, and thus the space-station has an additional centripetal force needed to balance the force of gravity for both. The space-station must be in an orbit where the NET centripetal force is greater than the weight of the space-station & the weight of the tether: so the station is exerting some tension on the tether and there's a slight 'artificial gravity' on board. The weight of the tether on earth's end is greater than the weight of the tether on the space-station's end because of difference in gravitational strenght along its lenght, and the centripetal force must be greater than the weight of the space-station (it is equal to the weight of the space-station + tether): so there's a slight 'artificial gravity' on board where object tend to 'fall' to the top of the space-station due to positive NET centripetal forces on board.

When a payload is tugging on the tether: the weight of the tether outbalanced the centripetal force: so the space-station descent and orbital correction must be done. The amount of fuel for the orbital correction should be similar with ground-to-space rockets but perhaps is less than usual because rocket engine perform better in vaccuum and there's no expendable part to jettison. So the advantage is: you could bring more payload with the same amount of fuel, and a greater fuel efficiency due to the nature of rocket engine.
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I think the construction of space-elevator is something of a mega-construction; either it be a "mega big space ferris-wheel/tower" or a "super-thin/super-lightweight/super-strong wire + super-strong climbing motor", it is something we couldn't afford right now. There's even a problem like "how to get this tether to space?" which nobody even mentioned yet: meaning that nobody is prepared to do it "right now" yet. Maybe it is like a moon project in comparison... maybe...

Thank you for commentary! Perhaps we can discuss at greater length soon, be well until such time.

In case you don't know, the main problem is designing a strong enough tether. The tether has to support its own weight, and if it's a very long tether then it's going to weigh quite a lot. Indeed, the weight of the vehicle climbing it as well as any excess pull from the space station at the top of it (if the space station is off course or something, instead of perfectly sync'ed up) is negligible compared to the weight of such a long cord. We're talking thousands of miles here. Geosynchronous orbit is somewhere in the vicinity of 22,000 miles up, about 3/4 as far up as the world is around. The space station has to be slightly higher than that, in order to hold up the big long cord. Actually it might need to be a lot higher.

Originally Posted by msafwan

I think space-elevator will work, but more importantly it has both pros & cons (which meant they are realistic). Firstly: space-elevator allow easy access to space without the use of expendable rocket (the payload tug on the space-station), but secondly: it still require the same amount of fuel to lift the payload to space (conservation of energy). Each time the payload tug on the tether: the space-station must do an orbital correction to maintain its orbit, and the amount of fuel for orbital adjustment will be the same with the amount of energy to get such weight to space with a rocket but without the expendable payload/instruments.

Normally, the problem with lifting into space is that you have to both generate enough thrust to counter gravity, and enough thrust to accelerate toward escape velocity. So, if you accelerate slowly, you'll end up wasting a lot of fuel just countering gravity over the time it takes you. That's one of the reasons why launching unmanned rockets is so much cheaper than launching manned ones. It's not just the air and life support. The human body can only handle ~4 g's of sustained acceleration. An unmanned rocket is free to exceed that.

The thing is: a space-station with tether is not like a typical space-station we have in orbit; the tether is an additional weight in addition to the weight of the space-station itself, and thus the space-station has an additional centripetal force needed to balance the force of gravity for both. The space-station must be in an orbit where the NET centripetal force is greater than the weight of the space-station & the weight of the tether: so the station is exerting some tension on the tether and there's a slight 'artificial gravity' on board. The weight of the tether on earth's end is greater than the weight of the tether on the space-station's end because of difference in gravitational strenght along its lenght, and the centripetal force must be greater than the weight of the space-station (it is equal to the weight of the space-station + tether): so there's a slight 'artificial gravity' on board where object tend to 'fall' to the top of the space-station due to positive NET centripetal forces on board.

The weight of the space station is irrelevant once it's orbiting at a sustainable orbital velocity. If it weighs 10 tons or a billion tons, it doesn't matter. Keeping it at its orbit while a person is pulled toward it will consume the exact same amount of fuel either way. The heavier the better, really. That way it's less prone to go off course.

When a payload is tugging on the tether: the weight of the tether outbalanced the centripetal force: so the space-station descent and orbital correction must be done. The amount of fuel for the orbital correction should be similar with ground-to-space rockets but perhaps is less than usual because rocket engine perform better in vaccuum and there's no expendable part to jettison. So the advantage is: you could bring more payload with the same amount of fuel, and a greater fuel efficiency due to the nature of rocket engine.
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This also isn't much of a problem so long as the space station is massive enough. If it's not sufficiently massive, then there might be trouble trying to calculate well enough to keep everything in position. If it's super massive, then course changes are very slight and slow, and you can adjust as you go.

Kojax, your comments are always thought provoking, thank you for participating. In future it might pay for Prince to search for existing threads addressing such topics more consistently to avoid duplication. Best regards to all and must go now, unfortunately.

We don't have the necessary materials to build a space elevator or as it is sometimes called a "sky hook' and if we did we might find better ways to employ them. The danger inherent in such a project is very great and would endanger a large population. Picture the falling elevator wrapping itself around the earth's equator. the political problems involved are staggering.