How do we build a space elevator?

[Kyle]

[Mike]

That's not that difficult in theory. You've got a 20 ton cable. You attach one end to the earth and the other to a rocket which takes off. I don't know how you keep your rocket blast from destroying the cable trailing behind it, but presumably their engineers are smarter than I am. Once you reach geostationary orbit (22,000 miles up), you're done, and now you have a counterweight up there in orbit that keeps the cable barely taut. With the cable in place, you send a climber up the cable dragging an identical cable behind it. Now you have 2 cables. Repeat, until your 20 ton cable now weighs 7,000 tons. This is how it's going to get done.

Where I'm seeing the holdup is in the carbon nanotube cable we have to make. They casually say that the cable needs a tensile strength of 150 GPa. I just looked that up, and that's 150 GigaPascals, which is 150,000,000,000 newtons of force per square meter. The theoretical limit for carbon nanostructures is 300 GPa. The strongest carbon nano-material we've made so far is 63 GPa. So Obayashi estimates we'll have it up past 150 in about 20 years. I hope so.

If Obayashi is right, we'll have an operational space elevator by 2060. I'll be 90 then. Fingers crossed.

[Kyle]

All I want is for construction to start before I die. I get that I won't see it finished. But just have a serious effort where construction starts. I'm satisfied dying and knowing that my grandkids are going to say to there kids, "When I was your age, we didn't even have a space elevator!"

[Mike]

By the way, though, a 20 ton cable, stretched over 22,000 miles, means that each mile of cable only weighs 1.8 pounds. That blows my mind.

Imagine that you've got yourself a spool of this magic space-elevator cable, and the cable in your hand weighs as much as a U.S. quarter... that's 36 feet of cable. It's like sewing thread that holds space platforms in place over immense distances.

I'm thinking my math is bad, but I know geostationary orbit is 22,000 miles up, and the article says clearly 20 ton cable. Maybe I'm missing something in how the terms are being used, because this really looks like wizardry to me.

[Kyle]

Hmmm. How thick is this cable? I mean, I'm envisioning something that's the diameter of my arm (seriously- 22 inch pythons). But maybe it only has to be as thick as twine.

[Mike]

Yeah, twine is about right. From what I can determine, using the density of current nanofibers, that mile of fiber at 1.8 pounds is roughly 1 cubic foot of material. Stretch that out, and you have a cable that is about 1/6th of an inch thick. But still superlight and stronger than your pythons by a few factors.