Question about space elevators:

Originally posted by twhitehead
Why?

Because it's got a space elevator attached to it...

Because it's not an antenna mast, it has to carry people and equipment
up to high altitude, it has to withstand the jet stream and strong winds
from multiple directions at different levels, ect ect...

Again this thing would likely have a structure similar to the Eiffel Tower,
but 20~25 miles tall. Which puts it several miles wide at the base.

Originally posted by googlefudge
Because it's got a space elevator attached to it...

Because it's not an antenna mast, it has to carry people and equipment
up to high altitude, it has to withstand the jet stream and strong winds
from multiple directions at different levels, ect ect...

Again this thing would likely have a structure similar to the Eiffel Tower,
but 20~25 miles tall. Which puts it several miles wide at the base.

All in all an unworkable project, the cost would be probably in the trillions. It would make more sense to develop space elevator technology in the first place. Besides, even at 25 Km the air resistance would be very bad. Remember, space craft incoming starts getting very hot at 200,000 feet altitude.

I would imagine an Earth bound rail would have to be a lot higher at the top than 25 Km, probably more like 50 km. That will never happen because simpler technologies will win out.

Originally posted by sonhouse
All in all an unworkable project, the cost would be probably in the trillions. It would make more sense to develop space elevator technology in the first place. Besides, even at 25 Km the air resistance would be very bad. Remember, space craft incoming starts getting very hot at 200,000 feet altitude.

I would imagine an Earth bound rail would have to be ...[text shortened]... Km, probably more like 50 km. That will never happen because simpler technologies will win out.

I think you have misunderstood.

I am talking about a space elevator base tower.

There is no 'air resistance' problem at 25miles because it's stationary.

Originally posted by googlefudge
I think you have misunderstood.

I am talking about a space elevator base tower.

There is no 'air resistance' problem at 25miles because it's stationary.

Why would you want a tower that high? You do know you have to build the base on the equator or close to it? So you just build the base on a mountain top like in South America where there are a lot of mountains. You get up 20,000 feet like those in Chile, there is not a lot of atmosphere left there.

Originally posted by googlefudge
I think you have misunderstood.

I am talking about a space elevator base tower.

There is no 'air resistance' problem at 25miles because it's stationary.

Modulo wind speed. To be honest, while it's quite fun to think about space elevators, I'm with sonhouse on this. On the moon a rail gun looks to be a practical set up, with conventional rockets as back up. On earth it makes sense to use the atmosphere, rather than fight it, so space plane technology appears the most sensible, or possibly some system with dirigibles to get above the soupiest layers of atmosphere. The space-plane just has to get to low earth orbit, then have a space station where the vehicle is unloaded and a different specialised vehicle to get to high earth orbit and beyond. The plane has to cope with re-entry, the other vehicles are designed for orbital manoeuvres. I can see that being achievable with current technologies and a sane budget. Twenty five click high towers on the other hand look too expensive and requiring not yet known technology.

Originally posted by DeepThought
Modulo wind speed. To be honest, while it's quite fun to think about space elevators, I'm with sonhouse on this. On the moon a rail gun looks to be a practical set up, with conventional rockets as back up. On earth it makes sense to use the atmosphere, rather than fight it, so space plane technology appears the most sensible, or possibly some system w ...[text shortened]... e click high towers on the other hand look too expensive and requiring not yet known technology.

It's certainly expensive, but the only bit that requires 'unknown technology' is the cable.


The trouble with space planes is that you just committed to lifting wings and a heat shield
into space with every launch.

And you cannot do really large lifts [in terms of numbers or unit size] because the only energy
source dense enough is nuclear, and nuclear atmospheric spacecraft are not a good idea.

If you want to life large numbers of people, or stuff, off the Earth then rockets are a really
lousy way of doing it. Certainly if you don't want to destroy the biosphere doing it.

Space elevators are one of the very few options [not requiring 'magic' scifi technology] that
allow efficient and sustainable mass lifting into orbit.

They are no doubt expensive to build, but the running costs are so much lower once built.
[in terms of resource usage]


The only thing that makes them not possible [in terms of currently known technology] is
the cable.

The space-plane just has to get to low earth orbit...

Just?? get to LEO?

That's the hard part, everything after that is easy by comparison.

Originally posted by googlefudge
Because it's got a space elevator attached to it...

Because it's not an antenna mast, it has to carry people and equipment
up to high altitude, it has to withstand the jet stream and strong winds
from multiple directions at different levels, ect ect...

Again this thing would likely have a structure similar to the Eiffel Tower,
but 20~25 miles tall. Which puts it several miles wide at the base.

The Warsaw radio tower, was about 650m tall. It had an elevator.
A space elevator once contstructed should not have significantly variable forces, and if anything will support the tower rather than knock it over.

The wind forces would be higher than for the Warsaw radio tower, but surely not significantly higher. I would expect the guy ropes to spread to several miles at the base, but there is no need for the tower itself to be so. An Eiffel Tower type structure is simply not necessary.

Originally posted by twhitehead
The Warsaw radio tower, was about 650m tall. It had an elevator.
A space elevator once contstructed should not have significantly variable forces, and if anything will support the tower rather than knock it over.

The wind forces would be higher than for the Warsaw radio tower, but surely not significantly higher. I would expect the guy ropes to spread ...[text shortened]... s no need for the tower itself to be so. An Eiffel Tower type structure is simply not necessary.

Your talking about something 40 odd times taller. The downwards force has to be spread at the base. I think what googlefudge is getting at is that the point of an Eiffel Tower type arrangement is that most of it is empty. The idea is to keep the mass down but maintain a strong structure.

The problem with using the elevator part to offset the weight of the tower is that you have to build the tower first. It has to have structural integrity before the elevator is attached. Aside from which it needs to be overengineered as a 25 km high structure toppling over could do some pretty impressive damage. It would need to be able to withstand terrorists flying airliners into it for one thing.

Originally posted by googlefudge
It's certainly expensive, but the only bit that requires 'unknown technology' is the cable.


The trouble with space planes is that you just committed to lifting wings and a heat shield
into space with every launch.

And you cannot do really large lifts [in terms of numbers or unit size] because the only energy
source dense enough is nuclear, an ...[text shortened]... ote]

Just?? get to LEO?

That's the hard part, everything after that is easy by comparison.

The tower's a little pointless without the cable.

It depends on how much stuff you want to get up there. I was assuming enough to be able to get a largish station at earth moon L1 and small industrial or scientific outposts on the moon. If you are thinking in terms of mass colonization then sure, you need to be able to get much more material up. But given the difficulties of living in the kinds of hostile environments in the rest of the solar system I'm skeptical about plans of mass colonization.

For the foreseeable future I think space plane type technology is the most viable way of getting into space. The trick with re-entry is to avoid fast re-entries. I don't know how feasible it is, but getting the re-entry speed down to Mach 5 or so makes the whole thing much more manageable.

If the moon can be mined for resources then most of the heavy equipment can be fabricated there and there aren't really any environmental considerations.

Originally posted by DeepThought
The tower's a little pointless without the cable.

It depends on how much stuff you want to get up there. I was assuming enough to be able to get a largish station at earth moon L1 and small industrial or scientific outposts on the moon. If you are thinking in terms of mass colonization then sure, you need to be able to get much more material up. Bu ...[text shortened]... eavy equipment can be fabricated there and there aren't really any environmental considerations.

I'm thinking in terms of mass colonisation, so I need something other than space-planes
to do it.

In the near future... I'm not convinced space planes are the best way to go.

By which I mean I have yet to be convinced either way, not that I am
convinced that they are not the way to go.


The reason being that, as I said before, space planes have to carry all these aerodynamic
surfaces up into space, and the heat shielding to protect them.

And ~80% of your velocity increase happens after they become essentially useless.

It may well be that the route SpaceX is taking is the best solution in the near term.

The other thing is that if you launch something that is supposed to stay in space
with a space plane, then you have wasted a huge bunch of your fuel lifting up the
plane that is only going to come back down again.
The SpaceX approach means you don't waste any energy lifting stuff only to bring it back
down again.

But given the difficulties of living in the kinds of hostile environments in the rest of
the solar system I'm skeptical about plans of mass colonization.

The difficulties are those of scale, you need a large enough volume and usable area to
grow enough food for a decent sized resilient self sustaining population to thrive.
There is nothing intrinsically undo-able about that IF you can shift enough stuff and
people into space in the first place.

There is more than enough matter out their to build with, and turn into habitats for
people to live in.

For power you have solar and nuclear, which gets you everything you need.

It's just hard to do small scale, and small groups face catastrophe if one person dies,
or if there is any wrinkle or bump in the road.

Large groups fare much better, but you need to be looking at million+ settlements.

The tower's a little pointless without the cable.

Not necessarily, launching from 20~25 miles up solves an awful lot of the "have to
waste fuel dealing with air resistance" problems with launching space craft.
As you are already past 80+% of the atmosphere.

Plus you don't have to worry about the weather effecting the launch.

So a tower alone does have potential uses.

For the foreseeable future I think space plane type technology is the most viable way of getting into space. The trick with re-entry is to avoid fast re-entries. I don't know how feasible it is, but getting the re-entry speed down to Mach 5 or so makes the whole thing much more manageable.

Sure... But the only way you have space craft with enough deltaV to slow to Mach 5 for re-entry
are nuclear rockets. Otherwise you basically have to put something the size of an entire current rocket
at launch into space so you have enough fuel to slow down again.

And rockets already have something like a 20:1 fuel:dry mass ratio as it is.

No, the most viable way of getting back down is to use atmospheric friction to slow you down for the
price of a heat shield.

If the moon can be mined for resources then most of the heavy equipment can be fabricated there and there aren't really any environmental considerations

Sure... But you still have to lift millions of people into space [plus starter biomass and their life support]
to be able to do serious space colonisation.

Originally posted by googlefudge
I'm thinking in terms of mass colonisation, so I need something other than space-planes
to do it.

In the near future... I'm not convinced space planes are the best way to go.

By which I mean I have yet to be convinced either way, not that I am
convinced that they are not the way to go.


The reason being that, as I said before, space planes ...[text shortened]... ace [plus starter biomass and their life support]
to be able to do serious space colonisation.

Arthur C Clarke wrote a book called Fountains of Paradise where they succeeded in building space elevators but took it several steps further, having 10 or more going up from the equator but then started expanding the geo sync
stations sideways till they all met, a 25 K plus circular station going all the way round Earth making for a huge housing structure and securing the cables in such a way as any one crashing would not bring the structure down. He certainly had a huge imagination.

It would not work. It would be very difficult to build something that strong without it being destroyed by lightning.

Originally posted by Metal Brain
It would not work. It would be very difficult to build something that strong without it being destroyed by lightning.

How would you know lighting striking it would destroy it?
Lighting often strikes lightening conductors and aircraft but usually without destroying them so it wouldn't be highly unreasonable to think the same could be true for these space elevators unless you have a specific reason to think the contrary.

Originally posted by DeepThought
Your talking about something 40 odd times taller. The downwards force has to be spread at the base.

The Warsaw Tower was 40 odd times taller than a 30m radio mast. It still didn't need the downwards force to be spread at the base. What changes?

I think what googlefudge is getting at is that the point of an Eiffel Tower type arrangement is that most of it is empty. The idea is to keep the mass down but maintain a strong structure.
And a guy rope stayed structure has even more 'empty', and still maintains a strong structure.

It would need to be able to withstand terrorists flying airliners into it for one thing.
I doubt it is possible to build a structure that tall capable of withstanding that. It is probably more economical to shoot down any aircraft that get too close.

Originally posted by humy
How would you know lighting striking it would destroy it?
Lighting often strikes lightening conductors and aircraft but usually without destroying them so it wouldn't be highly unreasonable to think the same could be true for these space elevators unless you have a specific reason to think the contrary.

How are you going to put the lightning conductor into place without getting fried by electricity? Are you volunteering? Better you than me.