The next stage beyond an orbital tower is an orbital ring. You’d have it connected to the surface by several orbital towers. But the thing is, those towers are on moving surfaces, and, just like when you swing a pole, a lateral movement of only a few cm at the base is going to translate to a considerable movement at the height of the ring. How do you solve that problem? And how many towers would you need?
What is an orbital tower? Google coughs up something about a “drunken party of a building” – that can’t be right. And “orbital ring” conjures for me an image of Saturn – I doubt that’s what you have in mind.
An orbital tower is also known as a space elevator. An orbital ring is a giant tube that goes around the Earth’s equator linking the towers.
Hmm… I don’t really see a great advantage to an orbital ring myself. Is it for travelling along? That would be quite slow even compared to fairly low-energy rockets, I think…
If you really want an orbital ring you make the attachment points dynamic and you build a new tower every few thousand years if the drift moves one too far from the equator.
The drift at the bottom is only going to “swing the pole” if you insist that the angle between the ground and the elevator cable remain absolutely fixed to infinite precision.
If, OTOH, the designers do something sensible like make the base connection even microscopically flexible the problem goes away. The fastest moving tectonic plate moves ~160mm year = ~6". If we assume the elevator is 40,000 (4E5) miles tall to the top of the counterweight, the base connection only needs to lean arcsin(6/(4E55E31E1)) = arcsin(6/2E10) = arcsin(3E-10) = 2E-8 degrees. Also known as 2 hundred-millionth’s of a degree For damn sure anything ever built by or ever *to *be built by Man flexes more than that naturally.
If it lasts 1000 years with no updates or modifications now we’re looking at arcsin(3E-7) = 2E-5 degrees of deformation. Still negligible. And that the absolute worst case. In much of the world tectonic motions are 1/10th as fast.
Not to mention that the whole and entire point of space elevators is that the vertical component is a flexible cable, not an infinitely rigid rod. Yes, it’s under tension. But even insane values of tension don’t produce infinite rigidity.
I remember seeing a documentary about the Sears Towers (as it was known) in Chicago. A resident on an upper floor mentioned that the water in the toilets really splashed around on windy days. The tops of such a building easily moves several cms all the time.
And that’s for structures ridiculously shorter than geosynchronous orbit.
Would the pulling the ring out of true cause problems?
That is a very ridiculous amount of tension. You could have a really big mobile anchor mass at the bottom – just about would have to – but I am imagining some very strong lateral deflection forces due to cars having the wrong orbital moment in transit. Then there is the braking force at the top. If your cars average 3000 mph (not that unreasonable), you have sixteen transit masses (ascending and descending), the lateral forces on the cable would be pretty large.
Has anyone done real math on this idea?
Let’s not forget-- GEO is a hellstorm of radiation due to the Van Allen belts. Funny looking kids, anyone?
Not on the scale we’re talking about. Said another way, any engineered structure tens of thousands of miles long is not a rigid object; it stretches and flexes.
Having said all that, a Dyson ring is inherently unstable. Building elevators looks to be simple enough once we can make a material with needed strength/weight to be the cable. Connecting the various elevator stalks with large structures is the problem.
These other instabilities are thousands of times larger than mere tectonic drift of centimeters per year.
Yes real space experts have. The issues you raise are rounding errors once we can solve the basics of building the cable and counterweight.
One idea for a space elevator is to base it at sea. This can be close to land but the advantage of the sea is that it provides hydraulic cushioning for flex in the elevator. Any design is going to have to allow for storms, uneven loads, and simply things going wrong. An elevator based on land would be ripped out of the ground.
A space elevator will need to be at the equator to minimise coriolis effects.
I can’t see the need for a ring habitat when it will be much easier to build habitats in space. Probably close to the outer elevator terminal.
A little… As people observed with Larry Niven’s Ringworld, rings of this sort are not stable. A little perturbation begins to accumulate.
But, as LSLGuy notes, the amounts are small, and, anyway, you could just mount attitude-correcting rockets (just like Ringworld) to fix the problem.
(Serious question: do modern satellites, such as GPS and weather sats, have small correcting jets to maintain them on station? Or once they get into position, is that sufficiently stable for their lifetimes?)
Small corrections are necessary. Most are reaction motors that vent gas one way to push the spacecraft the other way. Other techniques are starting to be used.
See Orbital station-keeping - Wikipedia and Reaction control system - Wikipedia for a bit more
Not if it used some sort of maglev tech to accelerate cars to thousands of miles an hour (no friction).
I suppose it would be used as a massive space habitat or for housing various manufacturing facilitates.
Continental drift is at a speed and scale as to be irrelevant to a space elevator or similar structure. Local weather at the cable, tidal forces, the suns rays and pretty much anything else would have a much grater impact.
Unless you built the base of the cable on a fault line.
Is it a valid comparison? Niven’s Ringworld was a free-floating ring; this ring would have spokes. Or, how many orbital towers / spokes would be necessary for this to not be an issue?
The real issue is that building either a space elevator or an orbital ring would require obtaining unobtanium.
(Some math in this link.)
Even if Clark did extend his tower to a ring at the end of Fountains of Paradise, that’s really about as ridiculous as a Dyson sphere. It’s just TOO big.
At the geosynchronous orbit height, the distance between spokes is yuge. Assuming 6 spokes spaced evenly around the earth, it is 23000 miles between the spokes on the arc segment of the ring. That’s nearly the circumference of the Earth. The amount of material required is unbelievable.
And what’s the point of a ring? There’s no way it would be efficient to go from any two distant points by going up one elevator, traversing the ring, and going down another. The only point would be an ego thing. A giant beacon to spacefaring cultures - Look on my works, ye Mighty, and despair!’
Of course, it also would look like a crosshair, with the earth at the center.:eek:
I was thinking of ISS altitude or similar.
Then you can’t have spokes connected to a ring.