Can’t you place a space elevator below or above the equator? The tether would leave the ground at an angle but it would be parallel to the centrifugal force from the planet’s spin.
In: Physics
I scrolled way down through a lot of answers to not see anyone say… it doesn’t need to be tethered at the equator. It will end up curved if it’s tethered elsewhere. Google “non-equatorial space elevator”.
It’s down to what’s at the other end of the space elevator, and where it is.
The tether would need to be attached to a satellite at geostationary orbit. In this orbit, the satellite would remain directly over the same point on earth all the time. And this orbit can only exist directly over the equator.
The tether, therefore, would also need to be attached at the equator, for two reasons:
– it’s the shortest distance to the satellite
– if it’s not on the equator and is, say, 100km North then the tether would be exerting a small sideways force on the satellite, trying to pull it out of the orbit a small bit. If the satellite were to be pulled out of the geostationary orbit then it would enter a geosynchronous orbit — it’s still over the same line of longitude, but from a viewpoint on earth would move slightly north and south in the sky. The tether isn’t going to let it move south and remain at the same altitude, so it would then start to get out of sync with it’s own orbit. This wouldn’t be good.
In short, if the tether was not on (or very close to) the equator then the satellite’s orbit could become somewhat chaotic.
Having some boosters on the satellite would help, but only for so long. Satellites in geostationary orbit still need to use boosters on occasion in order to fix their orbit if they start to wander. But having to over fix it because of the tether would use up more fuel.
Notwithstanding, the “satellite” here would be something massive anyway, like an asteroid — nothing man made. Also, in order to keep it in balance there would need to be something on the other side stretching out into space, with the same mass as the tether. But these are just nitty-gritty details…
Any orbit around the Earth will be in a full circle around the center of the Earth. The only full circle around the center of the Earth that matches the Earth’s rotation is the equator.
If you tried to do it somewhere else, the object in space holding the other end of the elevator would be moving in different directions in different speeds and it would rip itself apart.
Everything orbits around the planet’s center of mass, that means all orbits *must* cross the equator
If you build a space elevator you need to put a big counterweight in orbit to pull it tight. If you built your space elevator in Miama (25,-80) then the orbit of the counter weight is going to take it over to (-25,-80) at some point which puts it off the coast of Chile and requires you have a stretchy space elevator because its going to get a bit longer
Building the elevator on the equator means that the center of mass can be placed in geostationary orbit so it always hangs out over the exact same place without you needing to have constantly running motors to keep it there
If something orbits the earth it has to keep the center of the earth in the middle of the orbit. If it’s at the equator it can stay over the same latitude. If it is at the right distance it can stay over the same point.
If it’s going to be anywhere other than over the equator at any time it is going to have to be at a sloped angle compared to the Earth’s rotation. It will then go north and South like the Sun does in the sky but much faster.
If you are suggesting having the cable at an angle that could add a 1000 miles to it’s length and not only is that much harder but the orbit would be harder maintain.
You’ve gotten a lot of imperfect replies here, let’s see if I can do better or just add one more.
Think of the simplest and most commonly envisioned type of space elevator, from the perspective of the ground. I’m not talking about material, size, anything like that, but the direction. It goes straight up, and it always goes straight up. That means that the station/anchor of the elevator is always directly above the ground location. The only way that that can occur is on the equator.
The reason for this is that objects orbit the center of mass of an object. Take a ground location at around a latitude of 30 degrees (southern US). A point far above that location (space elevator anchors need to be very far away, a lot closer than the moon but way farther out than lower earth orbit) would be even more “north” than 30 degrees. Honestly it would probably be way higher than the Earth, but lets say that it was around 80 degrees. If this anchor was fixed there so that it was always straight above the ground at 30 degrees it would be making a big circle around the North Pole, nowhere near the center of mass of the Earth, that’s not an actual orbit.
For an actual orbit whatever the highest latitude the object passes over, it also needs to pass over the same exact value south of the equator, so a satellite that went as far North as 30 degrees would also have to go 30 degrees South.
That said perhaps the elevator doesn’t need to be going straight up. If the Anchor was still orbiting at the Equator (or very slightly below it technically, because our forces are about to be weird) then maybe it could attach to that point in the Southern US, but instead of the elevator going straight up it would only being going 60 degrees up, with a slope of 30 degrees to the South. The most extreme example of this would be an elevator at the poles, which would actually go out almost perfectly horizontally.
This has a couple ramifications though. First off your are spending a lot more time and distance in the Earth’s atmosphere, which isn’t great, that’s where the wind and weather that most of the hazard to a operating space elevator is. (I’m ignoring how the heck you’d build it, and assuming that at this point space has been mostly cleaned so that cutting the tether is a minimal risk, I feel like those need to be solved problems in order to even get to an operating space elevator).
Once again I’m not going to do the math (especially considering that this math is actually way more difficult) but I suspect that many examples of a system like this would be much less stable than a typical space elevator. For example if a normal space elevator would be expected to wiggle half a degree in any direction over the course of multiple orbits, the ground location of something like this may be expected to move a handful of degrees north and south, and a different handful of degrees east and west.
Another downside is that no point on the cable would be in a real orbit. With a typical space elevator you have an anchor way out past geostationary orbit, but the location at geosynchronous distance is at a real geostationary orbit point. This means it’s basically weightless, that means that the station can grow very, very large with minimal strain added to the cable there. That means that vehicles or cargo coming and going has very little effect on the cable. That also makes attaching to the station very easy, or at least a similar level of difficulty to docking with any other non-accelerating object in space.
None of that is true with an angled elevator, the non-symmetrical force from the tension of the ground point always pulling the system north means (I’m almost positive) that every single location on the cable on the way to the anchor is going to be under some sort of active acceleration, meaning that mass would indeed have weight. I’m sure at some point that acceleration would be very low, maybe even less than a percent of Earth gravity, but I’m pretty sure that (at least for something as far from the equator as 30 degrees) it would be orders of magnitude more than the microgravity you’d see on a “vertical” space elevator, and enough to be an issue in many ways.
It may be important to note that the challenges to building a Space Elevator on Earth are significantly larger than on many other bodies, because our gravitational well is so strong and our atmosphere is so dense. That means that scenarios like this that may have enormous challenges on top of the the already incredibly difficult task of making a vertical Earth space elevator, may have far less difficult ramifications on a body where space elevators are easier to handle. I suspect that humanity will create Space Elevators on the Moon, and then on Mars, many dozens of years before it’s ever done on Earth. Kevlar is plenty strong enough for a Lunar space elevator. Hell if someone wanted to spend dozens and dozens of billions of dollars I bet humanity could have a lunar space elevator within 20 years (I am not anticipating that happening, but my point is that nothing about a lunar space elevator seems to require any technology or materials that humans don’t have, and indeed have had for decades. It would “only” be one of the most difficult engineering challenges that humans have ever accomplished. (Maybe the hardest one, not really sure how you would rate the comparative engineering difficulty of that compared to, say, the Saturn V or the Large Hadron Collider, for example).
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Follow up: what if we placed a giant ring around the entire planet at the equator, and had multiple elevator points. Would something like that work, if cost and resources weren’t part of the equation?
follow up. why does it have to be tethered to earth? couldn’t the cables just hang into the atmosphere around 35000 feet at we just have airplanes move loads up to the cables?
lets take it to the extreme and go to the north pole. there, the forces acting on the elevator are:
– Gravity
And when we’re at the equator, we’ve got
– Gravity
+ Centrifugal force from earths spin
So for that reason, the closer to the equator we are, the more balanced the two forces are and the less tension is on the majority of the structure.
Edit: stop telling me centrifugal force is not real. I don’t care. It’s a tool and it works.
Edit 2: people have given up on replying to this comment and are DM’ing me about it
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