One of the Red Mars, Blue Mars, Green Mars trilogy by Kim Stanly Robinson had a failed space elevator cable falling to the surface; created quite an equatorial scar all around the planet.
One thing’s for sure. Any space elevator failure on any planet would be one of the largest uncontrolled releases of man-arranged energy in human history.
Kinda like the 9/11 tower collapses. Nobody stops to think that every crane-load going up the budding building is accumulating potential energy into a really big stack. 2 years’-worth of carefully controlled accumulation of PE can be turned loose to run wild in just 8+ seconds. Whoomp!!
Well yeah, you’re not talking about a 1" cable a couple of miles long. You’re talking something likely to be quite large in diameter* and going to Geostationary Orbit, a bit over 22,000 miles.
*remember, it has to accommodate numerous heavy lift ‘cars’ at any given time. Since, you know, it is going to take a while at any speed to go up and down 22,000 miles.
In the Arthur C. Clarke story, two guys were discussing the feasibility of using this new material when one asked the other why he was missing part of a finger. The other explained that this polymer chain was a few molecules thick but incredibly strong: it sliced off the end of his finger faster than the sharpest knife possibly could in a careless moment. This was basically the same kind of stuff as Niven’s shadow square wire that cut off one of Nessus’ heads.
So, yeah, it could be very large in diameter, or it could be hundreds of individual strands of Clarke’s magical wire. In the latter case, not only would there be lots and lots of redundancy (one or two wires breaking would not cause total tower failure), individual breaks would not result in damage and might not even fall to the ground, being so diaphanous.
Really, I have a hard time taking this notion seriously outside of Spec-Fictiosy. Sorry about that.
If the cable breaks, whatever portion falls to Earth isn’t going to leave a scar on the surface, because it’s never going to reach the surface. Carbon burns.
And you’d want the base to be mobile, anyway (and hence probably on a floating platform at sea) to maneuver the cable around space debris.
Meanwhile, if you want the ring for rapid transit, why bother with the ring? For any given point you want to reach, there’s a height along the cable where you can just let go and orbit to that point.
Just put the ring a bit lower than LEO so that the satellites would miss.
Actually, I’m thinking that you should build it much lower. Let’s make an “orbital” ring 3 miles above sea level (just high enough to miss the highest point on the equator.) The gravity balancing effects would be roughly the same, the unobtanium cables would be much shorter, and it would look damned cool hanging overhead like the world’s largest Macy’s Thanksgiving Parade balloon. (Don’t worry about wind–the unobtanium can handle it.)
Darren, you seem to be missing the fact that you can’t build the ring in low earth orbit and still have it stationary with respect to the Earth’s surface. If it was that close to Earth, gravity would just collapse it like an under-engineered bridge, or like it would pull down the ISS were it not whizzing along at extravagant speeds.
The speed necessary for an object to remain in orbit is proportional to the square root of the inverse of the objects distance from the centre of the Earth, which means the closer you are to the Earth, the faster you need to be going for the centripetal forces generated to keep gravity at bay.
Of course, the Earth is spinning at about 25k miles/hr too, so it is possible to plug in numbers into the equations to calculate the necessary orbital radius for an object whose speed in orbit would exactly correspond to the speed at which the Earth’s surface is rotating, a so-called geostationary orbit. But as others have observed, that’s way out at about 23k miles.
At low Earth levels, the ring would have to be spinning so fast there is no practical way to even connect it to the towers.
And you are making the same mistake others of us were making earlier in the thread. A solid, rigid ring surrounding a star or planet (or any other object with sufficient gravity to matter) is experiencing the same gravitational attraction from all downward directions, which for all practical purposes is the same as having no gravitational attraction at all. (As long as you keep it centered–nudge it off center, and the attraction will be a smidge higher on one side and a smidge lower on the other, causing the ring to start a slowly accelerating fall to the ground.) The ring isn’t “in orbit”, it is dangling there–you can then spin it at a thousand revolutions per hour or a revolution every thousand hours. Spinning it at one revolution per 24 hours means that you can anchor it to the ground on all sides, keeping it from drifting off center.
But you couldn’t build it in place. You’d have to build it away from the earth, and move it into place very carefully. And make sure nothing ever disturbs it. It just would not do to have a 24000 mile long “bridge” crash into the earth. The impact would be…impressive!
Well, you couldn’t do this with my proposed 3 mile high one, but for an orbital one, you could build individual segments that are moving at orbital velocity, connect them all together, then slow it down and drop the cables to the ground.
Wait, what? You’re talking about building parts of a ring in some orbit presumably a fair bit lower than geosynchronous, then connecting them up, then slowing the ring down to the same rotation period as the Earth?
So it’s like a big, (bigger than world-sized) arch supporting itself by compression. Do materials exist that would be strong enough for that?
Isaac Arthur thinks an orbital ring is more doable than a space elevator, and starts talking about it around the 4 minute mark of this video. His idea doesn’t require elevators to provide support or keep it up. It sounds more like tethers dangling down from it, so I don’t think where they’re positioned is important.
His idea doesn’t require unobtanium the way an elevator would, for what it’s worth.
If you’re building it out of unobtanium you will only need to build one unobtanium tower to hold it. It’ll be strong enough to hold it in place against minor perturbations.
Or, you could build the actual tower/cables up to geosynchronous satellites but include sleeves at the much lower level through which the ring could freely pass. Best of both worlds, since you could climb up and stop at the ring or go all the way to the top, where launching a space vehicle would require somewhat less power.
I disagree about strength under tension. Whatever punched through and made Fist of God mountain did quite a number. Stretched the scrith to the thin breaking point.
Now why THAT impact, or the impact of a GP#2 hull at orbital speed, didn’t knock Ringworld into the sun, but a comparatively tiny solar flare disturbed it enough to doom it, well, Niven never bothered to explain.
Did you not read Engineers? There are attitude thrusters all around the rim, controlled by the thing in the place (where the most excellent scene took place).