Space Elevators Are Possible
techblog.co
techblog.co
Just a reminder - every satellite crosses the equatorial plane twice for every rotation around the Earth. Majority of satellites are below the geostationary orbit. So, given enough time every satellite will hit the tether - and even if tether is near-zero width, the satellite isn't.
One of ideas was to dynamically move the tether - from the Earth, making propagating wave along the tether, which would avoid the satellites. This means we need the good means of watching the space and predicting satellites movements - even small satellites can bring trouble. But that's not enough, we might get a situation when we need to perform conflicting movements, considering the current state of the wave.
This problem is well known for decades. Attempts to launch satellites from the elevator - and the elevator makes it tantalizingly cheap, so we'll want to launch many - will exacerbate the problem. The whole world astronautics will have to adjust to accomodate the elevator - and nobody knows how it is going to look like.
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.
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.
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.
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.
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.
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.
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.
Or just an up line and a down line like most cable cars.
Of course, it would prove harder to build it in those cold regions.
Edit: http://gassend.net/publications/NonEquatorialUniformStressSp...
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.
The value of the tether would be so high that it would be worth the cost of keeping every satellite diverted around it.
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.
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.
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.
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.
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.
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 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.
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?
Here's a great book that came out of a NASA funded study that breaks the issues down well, including costs, necessary tech, and methods for dealing with potential issues like cable breakage: http://www.amazon.com/Space-Elevator-Earth-Space-Transportat...
Their conclusion was that it would be much more cost effective than most people think, and that it would enable an incredible reduction in cost to orbit due to not needing to use a pyramid of fuel to carry other fuel for later, or enormous one-time-use precision machinery, and instead using simple containers with electric motors and transmitted electricity.
But shielding seems to be doable with pretty thin layers of metal.
It's like saying "Warp drive is possible" then saying all you need to do is build a ship that can manipulate the fabric of spacetime. Well of course that's all you need to do.
Sure, producing carbon nanotubes is easy. I've seen them make the it in a lab. It's making the tubes to spec and making thousands of miles of the stuff that is the hurdle. It's the equivalent of asking computer engineers in the 60s to mass produce 22nm CPUs with billions of transistors. Can it be done? Sure. In about 50 years.
Why would they be similar? The space station is only in LEO. That's not remotely comparable to geostationary orbit, or the Van Allen belts.
Fortunately, shielding is a lot cheaper than on anything a rocket carries.
The first few years will enable 20ton payloads without humans [radiation
tolerance an issue for the two week trip]...
Radiation is not a problem for tether climbers, as the designers will
incorporate this threat into the design requirements and ensure operational
success through any radiation environment. Historic precedence supports this
conclusion as the space community runs spacecraft in all regions where the
space elevator will be operating. However, when people are included in the
tether climb [after some years of robotic success], the radiation problem
becomes an order of magnitude more difficult. There are many ways to reduce
the radiation and shorten the trip, which will have to be incorporated when
the human element is added.
There is a fairly long section on debris. The authors note that significant debris only exists in low earth orbit. They think the chance of collision is small, but large enough that the situation needs to be monitored. They think debris can be tracked and that if a collision were forecast, the cable could be moved. Also, they think space faring nations should be tasked with removing some of their junk from orbit.
Is it the other way around? Where is the original post?
[1] http://motherboard.vice.com/blog/space-elevators-are-totally...
1. What exactly holds the counter weight in position?
2. Such a long rope, which the article says is around 62000 miles, won't it function more like rubber band than function like a rope? Due to mere stretching/elastic effect?
3. I'm sure traveling 62000 miles is nothing like fuel efficient especially when you travel in the direction of highest friction(Up). So how do you store the fuel and of what weight that would be? Will such a vehicle be even practical?
2. One of the reasons you need a very strong material. The tether will be in tension, but probably will have quite a bit of movement to it. The tether dynamics are not a solved problem.
3. Most plans suggest that power will be beamed from the ground to the climber, either as microwaves or visible light. Some plans might use a paired tether to carry electricity. In either case, no onboard fuel is needed, which us pretty nice, as that's a lot of weight you don't have to pull against gravity. There have been several competitions in this area already.
But with all the remaining two points look in the domain of SciFi to me. I'm sure tether dynamics are going to a materials engineering problem like never seen in history of mankind.
Plus the energy problem is still by and large a very problem. Sending electricity down the tether looks very inefficient give the article says it will 62K miles long.
In short we are still may be what, say 50 years away from this?
The tether materials are obviously the long pile in this tent. We have theoretical materials that will work, which is great, but we really need practical materials. The day you can go buy nano tube thread you can formulate an actual timeline for a space elevator. Until then, its only a dream.
On the tether there is a "zero" point. Below that point things fall toward the Earth, above that point things "fall" away from the Earth.
So it depends on where it broke and how much weight there is above vs below that point. (To keep the tether in the air they put lots of weight above the point, which falls away from the Earth and pulls the tether taught.)
If I were making one of these I'd make several tethers, spaced such that a single object can not break more than one at once. Then tie the tethers together periodically.
This object is about max: https://en.wikipedia.org/wiki/Tunguska_event so I'd make the multiple tethers at least 200m apart. That's pretty far apart, so I'd invest in better detection technology to reduce the size maximum undetected object. (Although that raises the question of what to do if you do find a big one and it's headed right toward you.)
What I'd worry about is security, honestly.
What if some nation decides that the space elevator existing isn't in the best interest of their national security, or some paramilitary group wants to make a point?
Bombing the base station would hurt the elevator. But of course, we should expect that to be secured. That still leaves the entire length of cable running up and down the elevator -- that's a huge volume of space to secure against anything explosive or fragmentary.
Let's just hope he didn't mean that literally. But early attempts may include some disasters, as often is the case.