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"given enough time every satellite will hit the tether"

Let's do a back of the envelope calculation: https://www.google.com/search?q=(pi%20*%20(radius%20of%20the...

If a satellite in low-earth orbit has a cross-section of 10 meters, then the timescale for hitting the space elevator is about 300 years.

Given that there are about 3600 satellites in orbit (http://en.wikipedia.org/wiki/Satellite), a satellite would crash into the space elevator about once a month.

1. How fast can a satellite travel up the tether? Let's say 50km/h, and it's going to an altitude of 35,000km. That's a month just in travel time. Using the tether for that period of time would be extremely costly. Currently, around 125 satellites launch a year, so they would need to be going up the tether at 500km/h, one after the other, day and night. And if we need to wait for a platform to descend, they need to be moving at 1,000km/h. Otherwise, we need multiple space elevators, or multiple shipments climbing at once and passing one another to meet current demand.

2. What's the cost of building and maintaining a space elevator?

3. What's the cost of having a satellite climb the tether to an altitude of 35,000km? That's a lot of energy.

Taking this into consideration, is it tantalizingly cheap compared to strapping on a rocket? SpaceX has run tests with a reusable Falcon 9 rocket. Cost of fuel for a launch is $200,000. I'm skeptical the space elevator would be much cheaper.

The magic of SpaceX...

http://www.youtube.com/watch?v=9ZDkItO-0a4

Downside of a rocket, it's heavy, and most of the energy is wasted lifting the rocket, and not the payload. Advantage, you don't have to pay to maintain cables that are long enough to wrap around the entire Earth.

Couldn't you launch multiple satellites at a time?

Seems legit to me - a bunch of robots on the elevator that are each responsible for perhaps ten kilometres of travel, and they pass the parcel to the next one in line then move back down. You could launch way more things in pseudo-parallel that way.

Or just an up line and a down line like most cable cars.

Many activities are affordable only as long as the true costs are not paid in full. The world had to allow massive burning of fuels, even if it's costly for the environment, only because the alternatives were not feasible yet. When better technologies allowed even a mild reduction of the pollution's effects (like combustion engine improvements, and later development of hybrid/electric solutions), things started to change and the reckless burn of fuel is now discouraged. Don't stop at the level of 125 launches per year, expect it to grow orders of magnitude, and the effects to grow proportionally. The market cost for fuel may be only $200,000 and it might get even lower, but the true costs... well, I think you got the idea.

We already monitor very small debris (anything 1cm or larger), and move things out of the way if needed. The ISS moves about 6 times a year, mostly to maintain a very large margin.

Orbits are quite predictable, and moving the tether around isn't all that bad--after all, it makes getting fuel to LEO altitudes cheap. Also, I would expect active sats to avoid the tether, and the presence of a tether will make removal of dead sats both desirable and much easier.

One would also expect the tether to be multi stranded (which is not so hard once you already have one). You would want at least two, up and down. If erosion or collision in LEO looks problematic, you could run even more stands in that area. It's only a few hundred miles.

My main concern is the lack of a good market to justify investing in a tether. It's only a good deal if there are enough trips to amortize the cost. Hopefully we'll see rockets become cheap enough to help develop larger uses in space that will justify something like a tether.

Also I guess any space elevator system will deploy a 'tether maintenance' activity every some interval with intermediate stations. There will be likely bots moving up and down the tether to keep it free from debris and other approaching objects.

Would a satellite/tether collision damage the tether, or just destroy the satellite?

If it just destroys the satellite, I'm kind of tempted to say "who cares", because by then we will have other solutions, or satellites out past the counterweight, or we can easily launch more now that we have the fancy elevator, or whatever... but then we'd have the problem of an unimaginable amount of space junk orbiting the earth.

Everything in low earth orbit has 30MJ/kg worth of kinetic energy. TNT has 4.6MJ/kg worth of chemical energy. A rule of thumb: when the kinetic energy of things goes above the chemical energy of high explosives, you can assume that nothing survives.

I was going to bring this concern as well. I expect that in theory we could build a space elevator but I doubt we could keep it in space. Between space junk, meteorites, and regular gear flying around like GPS nodes, items in a non-orbit (which they would be in this configuration) will be hit with more than enough energy to destroy even the strongest materials we have out there.

I would also want to know the impact of a counter weight attached to the earth and it's effect on our ability to orbit naturally while it's drag is attached to even water. Could an impact on this force it into a spin around Earth creating Centrifugal force or something not studied before?

If I understand you correctly: the Earth is way way way way way way way way to big for something like an orbital tether too have any real effect on its movement. Besides the fact that due to the counterweight there's minimal tension on the ground.

I almost wrote "nothing man made", which is true for anything we can do now. But if you think scifi enough there's little that can't be done. Turning the Earth inside out is quite possible for certain levels of civilization.

I'm not quite sure I am parsing your question correctly, but:

The Moon is yanking the Earth around, but even something that stupendously massive doesn't do much damage (the tidal forces are nothing to sneeze at.. but the 'wobble' caused by the difference between the Earths center of mass and the Earth-Moon barycenter (the point that the Earth and Moon both orbit) is negligible in nearly every consideration).

This would absolutely not be a concern.

Actually if you look at the orbital mechanics, it would offset the center of mass for the earth in relative proportion to its mass. That said, the Earth has a lot of mass and so that effect would certainly be imperceptible and probably unmeasurable (although things I used to think we'd never measure directly we seem to do so now). It would do any "damage" in the sense you are using the concept.

> The main problem with the elevator, in my opinion, for many years already is not in the strength of the material. After all, nanotubes are known for many years, and their properties are sufficient for the tether, so in principle it can be done.

You say that now, but I remember that years ago, when nanotubes were hailed as the material that would make the space elevator possible, people quickly pointed out that nanotubes were still not strong enough to carry their own weight over such a tremendous distance.

What changed? Why are nanotubes now strong enough?

I think you are essentially talking about a 'traffic signal' equivalent of space.

If launching satellite becomes cheap with space elevators. You are going to have absolute mad rush to launch satellites, any way. In any such situation, you will have a lot of satellite traffic up there and merely managing that traffic among satellites itself is going to be difficult.

But even if you discount space elevators, if cost of launching satellites gets cheaper by the day. At some point you have to worry about this satellite traffic problem.

In theory, could elevators replace satellites? If so perhaps an initial batch of elevators could also be used to clean up the space junk (including the now obsolete satellites).

The counterweight platforms would be a great place for services now performed by geosync satellites. Probably you would also have major GEO platforms in areas not (yet) served by a tether. Take a tug there from the nearest tether. Would really cut down on discrete sats.

Services that need to be done away from the equator (monitoring of the surface, communications at high latitudes) would still need orbits like todays LEO sats. The same model of discrete satellites may prevail, but you might also see larger platforms housing multiple services.

We might see a tether vastly increase the amount of orbital activity, but decrease the number of discrete objects.

It's not as big a problem as it seems. Space is big, even tethers are small, the amount of time between a collision occurring would normally be quite long. Satellites can have their orbits adjusted just enough every once in a while to avoid the tether.

The value of the tether would be so high that it would be worth the cost of keeping every satellite diverted around it.

That would assume you could adjust all the satellites' orbits. Whilst some satellites have proper propulsion, I think many just have minor systems to only adjust their rotation, and a lot have none. And don't forget all the dead ones that are orbiting space junk.

So you decommission and deorbit anything that can't be controlled. Once you have a functional beanstalk the entire cost/benefit of doing everything in space changes. It becomes a lot easier to put things in orbit and it becomes a lot more important to keep the beanstalk up.

Couldn't the tether just have a friendly robot in charge of what I'll politely refer to as "catch and release"?

Fast moving objects are quite hard to catch even micro meteorites could do considerable damage a fast moving satellite would be a disaster.

The best option energy wise would be to have the satellite adjust its obit however that would deplete its energy reserves a lot quicker then not having an elevator to avoid colliding with.

Then again satellites should never have energy problems ever again since the can just be refueled cheaply via the elevator.

"The best option energy wise would be to have the satellite adjust its obit"

The best option is to do the math first and plot an orbit that will avoid all the existing known objects for the given satellite's entire active period. And maybe a built-in decommissioning mechanism that will throw it back to the ground afterwards.

Another problem never answered: Do we have the resources (funds and material) to create the amount of material needed?

Lets say the cable is 1m2 thick: 1m2 * 100000m (Kármán line) = 100000m3. Maybe this doesn't sound like a lot until you check the prices of nanotube-like materials.

It will likely be much thinner than that. But that is a problem. Most plans assume "once manufacture becomes possible and cheap enough". Of course, ordering that much (once a process is proven) will quickly drive down the price. Talk about scale!

Your length is off by three orders of magnitude. Fortunately, the surface area is off by four. In the most serious proposals, the space elevator "cable" is a flat tape with a cross-sectional area of a few square centimeters. Thus, we get:

2 cm^2 * 10^8 m = 20000 m^3. Yes, it's a lot of nanotubes, but the price of nanotubes per unit mass has dropped exponentially for a long while now, and the economies of scale involved in building a space elevator will lower the prices even more.

How about making the elevator start in the North pole (or South pole) and go vertically from there. That way, we can be sure that it will never meet the trajectory of a satellite?

Of course, it would prove harder to build it in those cold regions.

Impossible. It must be on the equator. Attaching a line from the ground to a large object in geosynchronous orbit is the essential plan, and GEO only happens above the equator.

You could attach the tether at a higher or lower latitude, but standing on the ground next to it, it would appear to rise into the sky at a rather alarming angle (more or less parallel with the equatorial plane). More of the cable would be going through the atmosphere. Centrifugal force would hold it taunt and a great deal of tension at the base would be required to keep the entire system in that configuration. At no point along the cable would the cable be following a valid orbit (the center of mass of the cable would not be in geosynchronous orbit). You would need a much stronger cable, and the result would be far less useful.

Edit: http://gassend.net/publications/NonEquatorialUniformStressSp...

The benefit with space elevators is that you can use mechanical energy to move payloads up the gravity well, as opposed to the chemical energy we use now. What do you think of rail guns, which use electrical energy?

You would never make it through the atmosphere. At the speeds required to achieve orbit from a surface launch, the projectile leaving the apparatus and hitting the atmosphere would be like smashing it into an ocean of water. Even on a very tall mountain the air density is still enough to stop any projectile-based solution in its tracks.

http://en.wikipedia.org/wiki/Project_Babylon

Iraq (with a Canadian scientist) almost made an artillery piece capable of putting material into orbit. Obviously, international sanctions gummed up the project a tad and it was basically over when the scientist was assassinated. Still, it was within the realm of possibility. Only recently have rail-guns started to usurp chemically propelled artillery in some roles, so it's not out of the question that rail-guns could put material into orbit. Even if the associated forces are too extreme for most equipment to survive, it could provide a way of getting raw materials into orbit at the very least.

Into space, or into orbit? The two are vastly different in terms of energy required.

https://en.wikipedia.org/wiki/Quicklaunch was trying. Looks defunct now.

If launching from vacuum directly into atmosphere, sure.

I think that it poses an interesting engineering problem, not unlike the space elevator. If given enough velocity, a projectile with retractable wings could be launched into an atmospheric gradient and generate lift after leaving the accelerator.

Whether or not we have materials used on the craft could survive the acceleration to escape velocity is the big question. It would take some serious testing.

They're still less efficient. With a gun, you have to put all your energy in as kinetic energy at the start of the trip, which means the payload leaves the earth at a considerable speed. Objects passing through the atmosphere with that sort of speed lose a lot of energy as drag.

There's a continuum between guns and rockets: you can fire a projectile with a motor on board. That lets you launch with a lower speed, but you have to lift fuel along with your payload. It's a tradeoff.

Space elevators step outside the tradeoff because they add energy to the payload during the trip, to avoiding the drag cost, but don't have to lift the energy as fuel, so avoiding the weight cost.

Couldn't the elevation of the satellite be at a specific elevation that no other satellite is allowed to orbit at? I.e. using the z-axis to your advantage?

No. The elevator's tether is a continuous object of length at least 36 000 km, from atmosphere to geostationary orbit. Practically all satellites are flying within that range of heights.

If by 'elevation' you mean 'latitude', then no. The elevator has to be on the equator. Or rather, the geosynchronous anchor has to be over the equator. I think the elevator cable could run to any point on earth, but it's going to hang as a curve where most of it is vertical over the equator, and so is in the way of satellites in equatorial orbits.