This CNN story is interesting.
Traveling thousands of miles into the cosmos up a length of super-strong material, it is believed that the space elevator could revolutionize space exploration by providing an affordable means of transporting satellites, space station supplies, and one day even tourists into space.
The concept of the space elevator was first mooted by Russian engineer Yuri Artsutanov in the 1960s, and until recently has remained more familiar to fans of science fiction, such as Arthur C. Clarke’s1979 novel, “The Fountains of Paradise.”
Previous ideas, such as lassoing one end of the elevator cable to an asteroid in geo-stationary orbit, haven’t helped the concept to be accepted as a serious project.
However there is a growing recognition that what once seemed a starry idea is not merely feasible but probable.
Regular readers of this blog know that I am a strong supporter of the space elevator. I do believe it is inevitable that we will eventually have several space elevators, and that will in fact turn space travel from an exotic, expensive endeavor into a boring process of hauling cargo in both directions.
I’m glad to see it getting some mainstream attention.
14 users commented in " Space Elevator in the news "
Follow-up comment rss or Leave a TrackbackBut it’s _still_ in the Science and Technical sections, darn and blast it. When it’s on the front page in the general news catagory we’ll have made some progress.
I’m somewhat concerned about the tensile strength/density of the materials. Everyone keeps hoping that carbon nanotubes will have the desired tensile strength. While they might, as individual molecules, you’ve still got to assemble them into a macroscopic material somehow.
The strength of a macroscopic material never approaches the strength of the individual grains, and nanotubes tend to slip against one another. I’m afraid that the actual tensile strength of the cable material is going to end up being bounded by fiber pullout, and the strength of the bonding with the matrix, rather than the strength of the individual nanotubes.
I wonder if there might be other ways to do this whole space elevator thing that doesn’t involve such a long cable in tension.
If you could somehow create two very very tall towers, and run a track between them, you may be able to put a catapult track above the enough of the atmosphere to throw something into LEO (if not towers, then supported by dirigibles? No idea, I’m just thinking out loud).
I once wrote a sci-fi book with a concept of orbiting skyhooks that would descend down into the atmosphere and hook up with high-altitude “airplanes” and lift them into orbit. The hooks were anchored to a small asteroid in earth orbit, each asteroid had six hooks that were hundreds of miles long, so the tensile strength was much less than the full space elevator.
The concept is basically an orbiting, rotating system of six hooks attached to a central hub that “walks” around the equator. The rotation of the asteroid is synchronized with the orbit, and is also synchronized with the earth’s own rotation, so that the hooks appear from earth to drop straight down from the sky. The payloads would be on ballistic arcs and would meet the sky hook at the peak of their trajectory where they would hook on to the skyhook and be pulled into space. The rotation of the asteroid provides a significant boost of kinetic energy to the outgoing spaceplane which boosts it into a much higher orbit when it disengages from the skyhook.
Incoming payloads return the energy to the rotating system so that over time launching and retrieving payloads balance each other out.
I still think this is a workable system. The editor who read the book thought the idea was great. But the story (which was about terrorists who planted a bomb on one of the skyhooks) sucked. So it never got published.
I wrote the story around 1980. I lost both the paper and electronic files long ago. Sigh.
While they might, as individual molecules, you’ve still got to assemble them into a macroscopic material somehow.
This is being done – but not in the strenght required. The most recent test I’m aware of – and I am not at all current nor terribly knowledgable – is at UTD where Boughman’s group was churning out meters of the stuff at a time, in thin sheets.
The strength of a macroscopic material never approaches the strength of the individual grains, and nanotubes tend to slip against one another. I’m afraid that the actual tensile strength of the cable material is going to end up being bounded by fiber pullout, and the strength of the bonding with the matrix, rather than the strength of the individual nanotubes.
I’ll defer to your knowledge – I run computers for a living. All I know is that the guys who do this for a lving seem confidant they can make it happen.
If you could somehow create two very very tall towers, and run a track between them, you may be able to put a catapult track above the enough of the atmosphere to throw something into LEO (if not towers, then supported by dirigibles? No idea, I’m just thinking out loud).
It’s not the atmosphere that’s the problem it’s getting your vehicle to accelerate to 17500 mph that is the problem. Sure the atmosphere gets i the way but the rocket is very quickly above the thick part of the atmosphere at any rate.
The real problem with towers 20 or 30 miles in height is that a structure that tall under compression is going to be a seriously big structure and require ridicously strong and light materials to construct. You’d need CNT for the job …
I still think this is a workable system.
Google rotating tether, I think. I read up on the idea a few years back – asteroids are a new wrinkle, I admit. Can I nit?
If you can go _get_ an asteroid and it’s not a huge State-run program run without worrying about cost you’ve probably already solved the problem of cheap access to space. If you have, you don’t need a space elevator – or this system. If it IS a state-run program that doesn’t worry about ROI then who cares about making access cheaper?
It doesn’t scale; your throughput is fixed and can’t get no bigger. Over time it becomes an impediment to growth. Eventually someone will work out something better and cheaper and poof you’re obsolete.
Okay those aren’t story nits but real-world ones.
lost both the paper and electronic files long ago. Sigh.
I’m sorry to hear that.
Brian:
I certainly concede that you have far more experience and expertise in this area. But I still want to respond to what you call your “nits.”
The system will scale. You just put more of them in orbit. What’s the limit to how many you can have in orbit at any one time? dozens? hundreds? I’d have to do the math. If this doesn’t scale, how does a space elevator itself scale?
Solving the problem of getting some major construction effort done in space once doesn’t solve it forever. This is like saying “There’s no point to building a bridge over the Golden Gate. If you can get that much material to hang over the bay, then you’ve solved the problem of putting material there already.” The skyhooks are bridges. And even a single one would be able to move tons of material into space and back down to earth again every day. That scale of operation is vastly superior to what we have today, so I’m OK if that is the limit for a while, until we can build something that scales better. Becoming obsolete means we’ve done something better. That’s good. Cars will be obsolete one day and so will oil tankers. Does that mean we shouldn’t have built them?
I have a new blog entry on the subject of orbital launch catipults. It might be possible to launch mass from earth using a massive launch catapult, as well as from places like the moon. While the track would have to be very long, and have miles of clearance, and the spacecraft would have to built with a submarine-like expendable shell around the outside, they might make it through the atmosphere into orbit.
What do you think?
Qwerty:
Well, I didn’t mention it in the earlier comment, but the story I referred to also utilzed linear accelerators to launch the vehicle to the height needed to get picked up by the skyhooks.
In my story the linear accelerators (basically electro-magnetic catapults) were built into strategiclaly located mountains along or close to the equator. This allowed them to both utilze natural geography to gain the optimum trajectory and allowed them to launch into the much thinner air at high altitude, thus reducing drag.
Because the payloads were only being launched a few miles up and being picked up by the skyhooks at the peak of their ballistic trajectory, they did not need full escape velocity for the trip, which meant they needed no specialized materials or heat shields.
Your idea is one that has been put forth many times in the past. I think it is a completely workable one, and all of your points seem valid, with two minor quibbles.
1. The system does not scale easily, building the 4th such system is no easier than building the first.
2. The power needed to accomplish this is substantial. You may be able to run it from the power grid (I am too lazy to do the math) but even if you could, the political reality is probably that you’d have to build your own power plant, and that means either having your own hydroelectric plant, or a nuclar one. Both are problematical to get permission.
Still, I do think your proposal is no more “whimsical” than if someone for the first time proposed launching payloads into space on barely controlled chemical bombs.
The system will scale. You just put more of them in orbit. What’s the limit to how many you can have in orbit at any one time? dozens? hundreds? I’d have to do the math. If this doesn’t scale, how does a space elevator itself scale?
Where a rotating skyhook fails to scale is throughput (you can never put more than X through the system). Also you are – if I’m understanding the concept and I may not be – limited by available sites ground-side. Hundreds in orbit – and how pretty that would be if you stungs lights on them – but they can only accept cargo when they’re withing X miles of the base.
A space elevator – in theory – can expand it’s throughput by making the ribbon bigger. Pesky theory – we’ll know more when (if) we put a few online. What worries me is that past a certain point a space elevator will be too big and massive. We need to plan for failure – a really huge ribbon failing would be a catastrophe for folks on the ground. Perhps not a natural limit but a self-imposed one.
And to a space elevator (in theory) can be used to luanch the components for a new one, slashing the costs to build more.
Cars will be obsolete one day and so will oil tankers. Does that mean we shouldn’t have built them?
Course not – from our point of view. The guys who build cars may not be so happy to see their product made obsolete.
“We need to plan for failure – a really huge ribbon failing would be a catastrophe for folks on the ground.”
Wouldn’t a space elevator, broken near the ground, tend to fall upwards? If it were broken near the counterweight, then I guess it would fall downwards.
That is what is or is supposed to happen, yes.
I once tried to calculate the failure energy released from a broken space elevator. The math kept telling me that the kinetic energy released would be comparable to a small nuclear explosion. I finally gave up on it, but came away thinking that a broken space elevator would be truly catastrophic to anything on the ground.
A broken space elevator would pose no hazard to the ground. Qwerty is correct – the part above the break would float away. The part below the break would either flutter to the ground or burn up in the atmosphere. Remember, the proposed nanotube ribbon is about the thickness of a sheet of paper. Now the lifter ON the ribbon, on the other hand, that could pose a problem. There would need to be some sort of “graceful descent” mechanism built into it. But that’s doable.
Ted:
I’m not sure I agree with you. The tension on the ribbon would have to be tremendous. Breaking it would cause some sort of shock wave to travel through the ribbon and/or the air. The kinetic energy of the break has to go somewhere, it is not likely that things will just flutter delicately to the ground. Or at least that’s what I recall from studying the problem years ago. But my brain has ossified since then, I doubt I could recreate the analysis even if I wanted to.
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