A Conversation for Man-made Satellites

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Post 1

Amigo

I came here looking for a space elevator....or can I call it a lift?
This is anchored somewhere on the equator and runs up to a satellite
in geostationary orbit at 40,000km above the earth,where it takes
exactly a day to complete one orbit (fortunately staying above the
anchor point on the ground..8^D )


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Post 2

Serendipity

You sound crazy enough to be interested in a forum I'm promoting. I'm trying to develop a theory to compete with the Big Bang theory of the universe. Come visit at http://www.h2g2.com/forumframe.cgi?forum=31029&thread=35442
You'd be very welcome.


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Post 3

The Cow

Of course, a space lift would have to be on the equator, or the coriolis effect (bathwater-down-plughole-rotating effect) will snap it. The energy to go up would be quite a lot - but 90% of that could be recouped on the way down. Perhaps this would be sufficient to recover ancient satellites. Of course, I am quoting Clarke (poorly, from memory). You -do- realise the big advantages of these (as told in 3001) - attach comms to it without space costs, hoist spaceship without vast launch costs, low-gravity for jumping around slowly in large padded rooms smiley - smiley


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Post 4

kwigibo

This may be a stupid question but could the vacuum of space be used to propel the space elevator?


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Post 5

The Cow

Hmmm... the high air pressure could push the lift up [assuming vacuum at the top] but you would need a tube rather than just a pole and motors. Then you'd have to fight against the vacuum to get back down... but gravity would help. I don't know... I think it needs to be worked out mathematically.


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Post 6

stragbasher

There is a vacuum outside the earth's atmosphere all the way around, not just where the space elevator would stick out.

Pumping air in/out would be a less efficient method of propulsion than, say, an induction engine that could provide an upwards push using electricity reclaimed from braking the downwards cargo.

I expect.


spacelifts

Post 7

Amigo

I think its a good idea to use vacuum as a partial source of power,
but on the whole a linear electric motor seems to be the ideal,as
you would have access to solar power at the top,and as Stragbasher
says,you could use gravity to generate power from the bottom 8^D.


spacelifts

Post 8

A Man In Black

Powering a "beanstalk" elevator ("beanstalk" being the name normally given to a cable between the ground and geosynch orbit, and it would probably wind up as a whole bundle of cables at least as thick through the middle as a house!) would be even simpler than you think. Remember that Earth has a significant magnetic field and run a conductor or two or so along the side of the beanstalk. Because that 35,000 kilometer conductor is rotating through a magnetic field, you will generate some EXTREMELY serious electrical power: so much so that it could run the elevator, power the "high" spaceport at 35,000 km and contribute substantially to the total electrical energy available to the country at the bottom end of the beanstalk, probably enough for them to both satisfy their own needs and become a net exporter of power to their neighbors! The best way to create a beanstalk out of buckytubes would be to forget a factory in space, just get nanotech off the ground and into geosynch orbit and have spaceborne nano-machines build it: all you gotta do is put enough carbon (coal, graphite, or even nearly cost free charcoal dust) up in geosynch as raw material for them to build the tubes...

Another thought: look at the countries lying along the Equator. They are all "Third World" backwaters, as I recall. There they sit on the most prime real estate for future space transport terminals. If the developed nations had any brains, they'd work out a deal with the potential "downport" countries to get this whole thing off the ground (swap tech for real estate leases, etc.)...'cause if they don't the "big winners" in the space age will be these present Third Worlders, because as the first beanstalk is built, all the lower satellite orbits will have to be cleared for the obvious safety reasons of preventing collisions and once it's completed, it or other beanstalks will be the only way to get to any altitude below 35,000 kilometers, again, simply for safety reasons! The beanstalks will define the "high" spaceports and the "downports" and anyone wanting to travel between the two will have to pay a toll at the downport end...and guess who'll be collecting the tariffs?!

Pleasant dreams...smiley - winkeye


spacelifts

Post 9

Amigo

Of course you don't need those satellites in the lower orbits,cos you
can just nail all that stuff to the beanstalk at any altitude you want.
You can put any other stuff in polar orbits to target specific areas.
8^D


spacelifts

Post 10

The Cow

And you don't need them in geosynch as that's automatic: you could have them higher (better coverage) or lower (better reception)

How does polar orbit work? Do you mean just normal satellites, or some tower, because you can't have space lifts off equator.

Apparently Sri Lanka is the best place, there's a huge mountain just a short distance of the equator... see Arthur C. Clarkes 'the mountains of paradise' or something.


spacelifts

Post 11

stragbasher

Sir Arthur moved Sri Lanka south for his book (The Fountains of Paradise), although there is apparently a 'gravity well' (whatever that might be) south of the island on the equator that makes it still the favourite place. There's an interesting story about that in the notes at the end of 3001.

The problem is that big winds have a lot more density at lower altitudes and are going to play hell with the base of any structure. Anyone who's ever been to the top of the Eiffel Tower will know what I mean - imagine that effect rippling up the whole beanstalk? Ever seen the film of the Tocoma Narrows Bridge in the '40s?

The Maldives are the nearest dry land apparently, although they barely peek above the ocean's surface. Mt Kilimanjaro gets an honourable mention, as it's almost on the equator, and I was looking at my map a few days ago and found an island called Sao Tome just off the west African coast that would do good too. Presumably there's a suitable mountain in the Ecuador Andes, too?

I personally like the idea of a beanstalk that continues all the way to the seabed - after all we'll be exploring down there in large numbers by the time we're able to build the space elevator.

Presumably any remaining satellites would have to be able to maneuver (how do you spell it?) to avoid hitting the tower(s). I suppose it's possible that dependence on constellations of LEO satellites for communications and navigation would make it politically rather hard to get the tower built. Goodbye GPS, goodbye Iridium, goodbye to all the other similar projects that will be spawned between now and then..

Can I take this opportunity to invite everyone here to the H2G2 interplanetary society at http://www.h2g2.com/a180190


spacelifts

Post 12

MMmmmmmm....

Interesting conversation, people. But that link doesn't go to the Interplanetary Society. It goes to a user page. Oh well, guess we all make mistakes sometimes Stragbasher. Give us the correct one and I'll check it out.


spacelifts

Post 13

stragbasher

Er?

How about

http://www.h2g2.com/a190180

If I'm still being useless then there's a link to it from my homepage that does work.


spacelifts

Post 14

The Cow

Doesn't GPS work by geosynch, therefore could be put on the tower anyway?

Polar orbits could be awkward... they're at a low altitude, and orbit every two hours. Could we put a spacelift at the pole? It'd just spin every day. Except for the fact the 'day' is 6 months long, not the 24hrs I mean.


spacelifts

Post 15

stragbasher

I believe the GPS satellites are in a variety of 'relatively' low orbits. Some go west-east, some north-south, and I'm sure I heard somewhere that a few of them go east-west - ie against the earth's spin. The idea is that wherever you are there should always be a few of them visible in some or other direction. 24 satellites in all, anyone?

I suppose you could increase the altitude of any satellites that needed to be in a polar orbit to clear the tops of the towers - but the time-lag due to the immense distance would probably make that impractical.

A tower at the north pole would just collapse under it's own weight as there's no spin to throw the top end outwards, but there is an alternative.......

But you'll have to go the Interplanetary Society to find it!


spacelifts

Post 16

Amigo

By polar orbit I just mean a low earth orbit that goes north-south
over the poles instead of west-east over the equator.
You just need to ensure that it doesn't intersect your lift.....
LEO's will still be needed for mapping,prospecting,spying etc.
You would also need to offset any shuttle orbit (if you still used
reaction vehicles).


spacelifts

Post 17

stragbasher

Sure,

but while the satellite goes north-south the world keeps turning, which means that the satellite passes over every point on the earth's surface - and eventually bumps into anything that sticks up high enough.

Presumably by the time we're able to build the space elevator we'll be able to build polar orbiting satellites that can shift their paths enough to avoid the occasional obstruction though.

I guess the big problem would occur while the tower was under construction - it would be in everyone's way but you wouldn't be able to do anything useful with it like replacing all the orbital stuff.It would probably take a couple of decades to build a full scale tower so the disruption would be pretty immense.


spacelifts

Post 18

The Cow

You could build an elevator with a hole in it for the satellites to go through smiley - smileysmiley - fish


spacelifts

Post 19

stragbasher

That's brilliant!

You should get a job at NASA.

If the tower was 'springy' enough the satelites would bounce off anyway, or you could fit them with airbags.

Or fire ping-pong balls at incoming objects until they are deflected enough. You could probably charge people to operate the guns, too. I sense a whole vista of new possibilities opening up here.


spacelifts

Post 20

The Cow

Ah yes, but I keep getting confused between miles and kilometers smiley - smiley
If you fired the pingpong balls to the side of the satellite, gravity would pull it out of orbit and to safety!
I wonder... what is the probability of a collision? Probably very low.


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