Is a space elevator a real possibility?

[Tex]

I'm not one who excels in physics and science, so I thought I would bring my question to the community here.

Just as the title says, is a space elevator a real possibility? I'm having some trouble understanding how exactly it could work. As I see it there is a big problem. First, say you ride this thing up to space. If you ride this thing straight up then you wouldn't have enough forward velocity to maintain your altitude... or would you? Once the elevator reaches the top, I would think the planet's natural rotation would be the only velocity you would maintain at that point. If that is the case, how would it be possible to ride a space elevator up to space and step off into a spacecraft without Earth's gravity pulling you back down?

Then there is the question about anchoring this thing up in space. Anchoring it on the Earth seems straight forward, but how would you keep it in place up in space? Also, how strong do you think the cable would have to be since it would have to withstand weather in the lower atmosphere and the constant tugging of the Earth's rotation?

 

[T.Neo]

It is possible, if you have both some sort of superstrong cable and cars that can efficiently climb/descend along it.

However, due to the fact that Earth orbit is littered with space elevator compromising debris, the limited orbit that an elevator can deliver to and the fact that all satellites and/or spacecraft in the zone of the tether must have some sort of control to avoid it, it is a shaky idea at best.

It's like trying to replace all transatlantic traffic via a very, very large bridge.

Rather develop a cost effective means of surface-to-orbit transportation (reusable spaceplanes for manned use and specialist goods, and disposable heavy launch vehicles for bulk goods) and ship them throughout cislunar space or beyond using ion tugs or something similar. Such an approach to space access would be far less ambitious and not as prone to failiure as an "elevator".

 

[TSPenguin]

The key to understanding a space elevator is, that it goes up to a geostationary orbit.
You are being accelerated while riding it up and at that point the angular velocity of the earths rotation matches that needed for staying in a circular orbit.

Hope this helped.

 

[Artlav]

The structure itself is rather stable - a tether from the ground to a station in GEO, a tether from GEO up to counterweight or just tether keeping going long enough to be it's own counterweight. The Earth rotation is what keeps it strained.

You need a powered climber, much more energetic than a rocket but without a mass limit - it can be powered from the ground, or be rather huge to carry at least a sizeable reactor to power itself. The climber can pull on the tether to climb up, or be pushed from below by a laser beam, or something like that.

The problems with the design are manyfold - space debris and satellites, which will tear the line on impact regardless of how strong it is, lack of practical material to build it from, being essentially a short circuit of the Earth's atmosphere, being a big and notorious target for terrorists and disasters, lack of profitability within modern short-sighted business's attention span, etc.

How strong a material is required - hard to say, stronger than anything we can make in the scales needed. It also should be able to withstand various loads - thermal from cryogenic to several hundred C, electric currents from short-circuited atmosphere, dynamic loads and shear from various tether vibrations, etc.

In essence, possible, but not yet practical.

 

[Linguofreak]

I'm not one who excels in physics and science, so I thought I would bring my question to the community here.

Just as the title says, is a space elevator a real possibility? I'm having some trouble understanding how exactly it could work. As I see it there is a big problem. First, say you ride this thing up to space. If you ride this thing straight up then you wouldn't have enough forward velocity to maintain your altitude... or would you? Once the elevator reaches the top, I would think the planet's natural rotation would be the only velocity you would maintain at that point.

The answer is that the top is above geosynchronous orbit. So the Earth is dragging the base around once every 24 hours, and the base is dragging the top around once every 24 hours, but the period of a circular orbit at the top is greater than 24 hours. The elevator is long enough that centrifugal forces at the top balance gravitational forces at the bottom.

If you step off below geosynchronous altitude, you will be at the apogee of your orbit and will lose altitude (if you step off low enough, you will be on a suborbital trajectory). If you step off at geosynchronous altitude, you will be in geosynchronous orbit. If you step off above geosynchronous altitude (say at the top), you will be at the perigee of your orbit, which, if the elevator is long enough, may be an escape trajectory.

If that is the case, how would it be possible to ride a space elevator up to space and step off into a spacecraft without Earth's gravity pulling you back down?

See above.

Then there is the question about anchoring this thing up in space. Anchoring it on the Earth seems straight forward, but how would you keep it in place up in space?

Centrifugal force, as above.

Also, how strong do you think the cable would have to be since it would have to withstand weather in the lower atmosphere and the constant tugging of the Earth's rotation?

At least 100,000 kN·m/kg, according to Wikipedia.

Carbon nanotubes *may* be able to do this (they certainly can at microscopic scales, but it remains to be seen if they retain such strength at macroscopic lengths.

The question you didn't ask was "How do we avoid satellites with perigees lower than the top of the elevator colliding with the tether?"

My answer is "It's a really cool concept. Please don't ruin it with details..."

 

[T.Neo]

My answer is "It's a really cool concept. Please don't ruin it with details..."

If you ask me, colliding with satellites is pretty large "detail"...

 

[Ark]

Someone once said the technology, funding, and legal clearance to build a space elevator would take 20 years after everyone stops laughing.

They haven't stopped laughing. Talk to any random person on the street and they will laugh in your face at the concept. Why would anyone invest in something they find completely rediculous?

 

[TSPenguin]

If you ask me, colliding with satellites is pretty large "detail"...

Not really. It is a singular event anyway

 

[vonneuman]

There are several major problems with a space elevator. First: if the cable brakes at the top of the elevator you would have a cable long enough to wrap around the world several times crashing down at orbital speeds. Not good. If it brakes at the bottom you have a massive cable swinging around for several hundred miles in every direction. Second: something few people think about is that you will have to take it down some day; and a space elevator is nearly impossible to disassemble. Third: most of the materials we need to make one don't exist yet. Carbon nano tubes may hold part of the solution but no one has ever made one longer than a few centimeters.

A more practical solution is this variant of the space elevator http://en.wikipedia.org/wiki/Space_fountain

 

[streb2001]

Tex,

read "The Fountains of Paradise" by the late, great Arthur C Clarke. Space elevators are explained very well along with a cracking sci-fi story.

s2k1

 

[Tex]

Thank you all for the comments, keep em coming! Another question about this...

If you have this long cable with a counter weight keeping tension on the whole thing with the earth rotating it all around, what are the chances over time that it could effect the Earth's orbit around the sun from this mass constantly tugging on it?

I guess it would be so little in comparison to the Earth's mass that it wouldn't really be a factor, or would it?

 

[T.Neo]

Talk to any random person on the street and they will laugh in your face at the concept. Why would anyone invest in something they find completely rediculous?

Indeed, but unfortunately this is the reality about any kind of space exploration.

 

[Artlav]

If you have this long cable with a counter weight keeping tension on the whole thing with the earth rotating it all around, what are the chances over time that it could effect the Earth's orbit around the sun from this mass constantly tugging on it?

I guess it would be so little in comparison to the Earth's mass that it wouldn't really be a factor, or would it?

Each launch will slow down the rotation of the Earth around itself by a unmeasurably small amount.
The presence of the system will shift the COG of the Earth by even less measureable amount, causing it to alter orbit by a way more unmeasurable amount.
It's a BIG^BIG^BIG planet.

 

[Ark]

Each launch will slow down the rotation of the Earth around itself by a unmeasurably small amount.
The presence of the system will shift the COG of the Earth by even less measureable amount, causing it to alter orbit by a way more unmeasurable amount.
It's a BIG^BIG^BIG planet.

It's like when you explain how gravitational slingshots rob the planet of a small amount of momentum around the sun, and people go "OMG, the year's gonna be longer!!!!" :beathead:

 

[Linguofreak]

Thank you all for the comments, keep em coming! Another question about this...

If you have this long cable with a counter weight keeping tension on the whole thing with the earth rotating it all around, what are the chances over time that it could effect the Earth's orbit around the sun from this mass constantly tugging on it?

I guess it would be so little in comparison to the Earth's mass that it wouldn't really be a factor, or would it?

It would be much too small to be a factor. In fact, if you ignore nonspherical gravity effects, and if all the material comes from Earth, it will have no effect at all, except to make the day a teeny bit longer (conservation of momentum, energy, etc.).

 

[Orbinaut Pete]

This is an analogy that I find is very explanative of how & why a space elevator would not fall down.

Imagine you have football, and you tape a piece of string to it. The string would fall down.
But if you then pick up the football and hold it at arms length in front of your face, and start to rotate your body, the string would "stand" straight up due to centrifugal force.
It is exactly the same principle for a space elevator, with the rotating Earth and elevator in place of the football & string.

NOTE: Of course, I refer to a British football...

...and not the American version.

 

[DagoO]

I don't think so, in my opignon it is not possible because of the Earth's rotation, it could be an enemy for a so big and high buildin.

But why not try it and determine ..!

 

[cjp]

I think it is possible IN THEORY, but there are too many unsolved practical problems. Collision with space debris is an important one.

Besides that:
I've seen a video of a laser-propelled cable-climbing device, which was supposed to be an early prototype for a space elevator. Now that I think of it: if that works up to geostationary orbit, then why would you still need the cable? Just use RCS thrusters and a good control computer to keep the thing on top of the laser beam!

A space elevator makes no sense if it doesn't have convincing advantages over traditional launch methods. I think the most important advantage would be that you wouldn't have to spend energy on accelerating huge amounts of fuel, or have to deal with low-efficiency rocket engines. So, a power source that makes sense for a space elevator has to be something like an electricity line, or maybe some mechanical device pulling the cable up/down.

I think a space elevator can be deconstructed the reverse way as it can be constructed: construction starts at geostationary orbit, destruction works towards geostationary orbit, and ends there.

 

[Linguofreak]

I think it is possible IN THEORY, but there are too many unsolved practical problems. Collision with space debris is an important one.

Besides that:
I've seen a video of a laser-propelled cable-climbing device, which was supposed to be an early prototype for a space elevator. Now that I think of it: if that works up to geostationary orbit, then why would you still need the cable? Just use RCS thrusters and a good control computer to keep the thing on top of the laser beam!

Well, said climbing device was using the laser as a power source. The reaction mass would be the cable, just as when you walk you are using the Earth as reaction mass. (It would have to be a very powerful laser indeed for the laser to be the reaction mass).

Of course, any laser sufficient to power a climber up to geosynchronous altitude has significant military applications.

 

[Ark]

Another problem is where to build it. A project of this magnitude and expense would of course be run by the US or EU, but it needs to be built at the equator. What countries occupy the equator? Kenya, Congo, Indonesia, Brasil, Columbia, Ecuador...

We'd have to pay those people for the land, the right to build, and whatever tax they decide to levy against goods going to and from orbit. It's a political nightmare.