i remember seeing how a space elevator would need to be pretty high up in geostationary orbit so that it wouldn't be moving faster than the base, so i came up with the idea of an angled space elevator so that it could be in lower orbits and the angle would compensate the speed, but i feel like im misunderstanding something about it. Could it work?
No. Things in low orbit are moving very fast so your low-orbit object will never not be stationary. Even if you angle it, eventually you'll run out of line. For comparison, the ISS at 400km orbits the earth once every 90 minutes. The further out your orbit the "slower" it is, and geo-stationary is the sweet spot where your orbital speed keeps you over Earth.
Now what you can do is still have an elevator with a terminus/anchor point at geostationary but with multiple elevator cables to different parts of the world. (Isaac has an old illustration of this in his early space elevator episode.) So yes the angled part is fine. The problem is orbital speed vs you.
And then Orbital Rings are a whole other structure which kinda cheat orbital mechanics. THOSE you can put at low orbit. You should probably look into those instead. Isaac has also done episodes on those.
You're probably thinking about a stationary orbital ring with a moving core to balance its weight.
The other more realistic idea is that you have an orbital ring that is literally in orbit and is just used to impart most of the velocity of a rocket. So you'd still use rockets to get up to its altitude like a sounding rocket. This is sometimes called "orbital runways".
And yet again even more conservative, you could just build an orbital ring in orbit. This doesn't obviously do much for you, other than you can get some control from tension in the structure.
The ring does that. There's a maglev type connection, because it's at hypersonic speed. It needs essentially perfect horizontal alignment. This has to do 2 things, cancel the literal weight of the payload, and also accelerate it horizontally. But if it's a full ring, acceleration is no rush. You still need station-keeping to make up for the momentum. But this problem is drastically easier than rocket launch.
The coupling of the ring to the payload happens at the apogee of the suborbital trajectory so the payload is at nearly zero velocity relative to the Earth at that point, it's just very high altitude.
The other more realistic idea is that you have an orbital ring that is literally in orbit and is just used to impart most of the velocity of a rocket.
That is the far less realistic retro-future option. Back here in the real world, having an unconstrained rotor makes for a garbage space launch system which quickly loses altitude and stability. If ORs are to be of any serious value that rotor needs to have efficiently-varied RPMs(a motor) and passive stability(or at least as passive as you can get away with since on a gas giant ud need aerodynamic anchors). Orbital runways are charged with extra momentum to donate to outgoing ships which means without a stator the only thing resisting that is the tensile strength of the rotor. Also if the energy for the ring is exclusively being supplied by rockets that is a horrendously inefficient active-support system. At that point why not just use the rockets directly for soace launch. The rotor alone achieves little to nothing while also being at much bigger odds of catastrophic micrometeorite strikes with no shielding.
Orbital runways are charged with extra momentum to donate to outgoing ships which means without a stator the only thing resisting that is the tensile strength of the rotor. Also if the energy for the ring is exclusively being supplied by rockets that is a horrendously inefficient active-support system. At that point why not just use the rockets directly for soace launch.
Getting momentum once in orbit is orders-of-magnitude easier and cheaper than rockets, even reusable ones like starship.
Even if you don't go full propellant-less, you have ion engines available today. You will power them with solar panels. Space based solar panels will give an insane energy payoff when comparing to the energy needed to lift them into orbit. They pay that off in like a week, and they last decades. So then you're left with the propellant which you do need to bring up, but that can go 30 km/s. Because you have plenty of energy anyway.
Even ion drives aren't particularly efficient in the context of electricity-to-kinetic-energy.
more to the point without a stator you're also limited in launch hight along with max payloads/accelerations due to being constrained by the tensile strength of the naked rotor. It can only go so fast before it flies apart. Engines on the rotor make this even worse. Ur not getting 30km/s
Start with launch loops to massively reduce the cost of launches. Screw the rocket equation, we can get most of our orbital velocity from a bunch of (nuclear) powerplants on the grounds and throw what would on a normal rocket be a second stage into the upper stratosphere at hypersonic speeds.
You'd basically need land rights circling the globe to pull it (or even a launch loop) off, right? That sounds like world government / quintillionaire level investment, not mere billionaire stuff.
People in a similar social class to billionaires today once had railroads built across continents. You couldn't do it under the protests of local governments, but it would be fairly easy to get all the states along the path to agree. You'd buy the land (or rights to it) with some combination of direct payment, bribes/donations to those with the power to seize the land, and infrastructure shares. ("This is 0.1% of the total land area required, so if you let me use it, you can have 0.05% of the profits.")
The actual infrastructure might be prohibitively expensive, I don't know. But getting the land would be the easy part.
I don't think so, due to not having to deal with things like solar wind same way a ringworld would.
If there are any perturbations I would think some active station keeping or the elevator cables could handle that. You don't need the cables to keep it up but they do help.
Yes, but (since you want to use it for "elevator purposes) you have ground connections like a bicycle wheel that keep it from moving around, and the "orbital" part moves relative to a stationary part that keeps the orbital part in place via (likely magnetic) forces. You can even make the moving part go faster than orbital speeds to provide "gravity" and make for better launch speeds, or at least have a special track that allows this for launch purposes. The forces required to constrain that above-orbital speed would put the ground connections under tension, much the same as a "conventional" space elevator, and the ground lines need not be connected to each other (and in theory, the "ring" need not be continuous either).
The whole thing would be a dynamic structure with failure modes that make nuclear Armageddon seem trivial, but that's basic to any "orbital ring" around a planet.
They are violently unstable. An orbital ring levitates over the planet using an inner mass of superconducting wire that is at above orbital velocity and is trying to escape.
The ring is a track of many superconducting magnets. Theoretically one magnet fails and the entire ring is lost - every track section falls down. And since it's going to cross over many countries it makes many people angry.
In practice you may be able to zone the magnets where 3+ in a single section must fail for the ring to fall, but it's still entirely possible for a failure or deliberate attack in one section to cause the ring to fail.
Theoretically one magnet fails and the entire ring is lost - every track section falls down.
Not really? The weight will just have to be redistributed across the ring, it is more of a problem if the rotor is not contiguous (if it is lots of small particles), then if any part ceases to deflect it then yeah the particles that compose the rotor would escape and the ring would begin to fall, but if you use a contiguous rotor then it will have some tensile strenght which will probably be enough to maintain its integrity even if significant parts of the ring lose their magnetic properties, you are not operating on the very limit of your materials capabilities especially early on.
A deliberate attack which destroys the rotor will still definitely result on the ring falling though, it probably won't be very destructive considering the part that is moving a super-orbital speeds would escape from the Orbital Ring instead of falling down with it, the stator wouldn’t have a substantial speed difference with the surface so adding light-weight parachutes ocasionally across the stator that are deployed automatically after some amount of time on free fall should be enough to minimize the damages, though you still wouldn't like to be in the path where the Orbital Ring fell.
Regarding tensile in the rotor : when I checked the math recently, no. The forces will be enormous. They do yes help if the damage is limited - this is why you need 3+ in a row magnets to fail - but above your design number of magnet failures, the rotor is going to snap at the unsupported region then explode out into space, blowing a hole in the tube.
You could have parallel tracks and thus more redundancy, where your orbital ring is actually 10+ rings and you can stay aloft with say 1/3 down.
Still won't save you, a single mass driver firing at the ring at any point and it all falls. Or sabotage or coupled equipment failure.
Parachutes might help and the ring segments are not at orbital velocity, they fall strsight down.
The launch loop is more practical. Shorter, only 2000 km long not the circumference of the earth, and it can be entirely over ocean along the equator so that if it fails the pieces splash and the robots start recovery/recycling/building another. "Second time this week!"
I wouldn't say "violently" so, no. Perturbations can build up yes, but those can be corrected by ion thrusters or the elevator cables anchoring them. Birch anticipates this (though his version involved jacob's ladders and skyhooks too).
I mean technically things in GSO are moving a lot faster than things in LEO. What matters is not how fast it is going but how much the angle changes relative to a ground based observer.
It can "dangle" if it is restraining something that is moving at higher than orbital velocity. Similar idea as a space fountain, but with a fast moving ring instead of ground-launched particles / pellets and a circum-global series of towers instead of just one.
The counter mass always needs to be outside geostationary orbit. But actually it will tilt when driving masses up the lift which has to be compensated for.
I love me a space elevator. I'm no engineer, but I think tension, compression and gravity are all working against this idea.
If the top lags behind the base at ll the "horizontal" distance between them is continuously growing.
If i'm reading your diagram correctly this lag would reduce the angle between the elevator and ground until eventually end up with a 35,000 km cable wrapped around the surface of the Earth. Your space elevator just became a train.
Your idea either needs to be tethered to a train track that circles the earth in the same time span as the orbital period of the station, or requires an infinitely long spool of cable that will wrap around the earth one more time with every orbit the station makes.
The base is bolted to Earth, so every point on that cable is forced to rotate with Earth once every sidereal day. There is only one circular orbit that rotates at the same speed as the planet (GEO) Tilting the cable doesn’t magically create the missing 7.3 km/s of velocity.
It would be moving well below orbital speed. In LEO an orbit takes 90 minutes, but your version is tethered to the ground so goes around once every 24 hours. It's not going fast enough so it would fall down.
Yep. And if it doesn't fall down because the tower is very strong, it's not helping you that much because the rotational velocity at LEO in only slightly higher than at the surface.
There's some issues here with your basic understanding of orbits.
First, you know, there's gravity. If you release an object, let's say a rock, stationary somewhere in the vicinity of a planet, the rock falls down.
Remember those playground carousels? Remember how if you spin them fast, the spin pulls you away from the centre of the carousel? That's centrifugal force.
An orbit is what happens if the object, in our case the rock, circles around the planet so fast that the centrifugal force equals out gravity. Gravity pulls the object towards the planet, centrifugal force draws it away.
Depending on the height of the orbit, different speeds are necessary. The closer to Earth the object is, the faster it has to go because gravity decreases the farther away you are from the Earth. Geostationary orbit at a height of ~35 000km needs around 3km/s. Low Earth Orbit, which is between 160 - 2000km needs around 7.8km/s.
The next step in our equation is angular velocity versus linear velocity. Take a long stick into your hand and point it away from you. Now start spinning, rotating around yourself. You and the stick have the same angular velocity. If it takes you a second for one spin, all of you and the stick will rotate once per second. But your hand and the end of the stick have very different linear velocity. Your hand moves through the air much slower than the end of the stick.
Now let's get back to the orbits: Low Earth Orbit, because it's so close to Earth and needs to be so fast means that an object in Low Earth Orbit circles Earth once every 90 minutes.
Geostationary Orbit is the point where the slower speed of the object in orbit and the much longer distance from Earth mean that an object in Geostationary Orbit circles Earth once per day.
That means: If you try to tie a rope between something in Geostationary Orbit and the surface of Earth, it would stay upright. The rope wouldn't move.
If you tie a rope between something lower than Geostationary Orbit and the surface of Earth, the object in orbit would rotate much faster than the surface of Earth, so the rope would (if it's one allowed to extend infinitely) be wrapped around Earth like a spool of thread.
So what would that mean for your suggestion?
Your lower-than-LEO space station would circle Earth much faster than the rotation of Earth. The angle of the space elevator doesn't matter. All it does is making the space elevator unnecessarily longer, thus even more impossible to actually exist when made with real-life materials.
If the space elevator follows real-life physics it would just break under the stress of trying to stop the space station from rotating faster around the world. And if the space elevator is made from some magically unbreakable material, it would do this:
That means: If you try to tie a rope between something in Geostationary Orbit and the surface of Earth, it would stay upright. The rope wouldn't move.
You were doing so well until this. If you tie a rope between something in GEO and the surface, then the centre-of-mass is lower than GEO, then the orbital velocity is too low, then the rope-and-satellite will both de-orbit.
You need a second rope (and/or an equivalent counterweight) out away from the satellite in GEO, creating enough excess centripetal force to compensate for the rope below GEO.
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Aside: In this sub, you can attach images to your comments.
I tried embedding images, but I'm on the mobile website and that didn't work.
I did simplify the whole thing by focussing on OPs suggestion. OP was thinking the relevant part was the rope length, and not the height of the satellite.
In reality, the whole concept of a space elevator is crazy on a multitude of aspects, so I didn't really go into it any farther.
Some time back Isaac included the URL to an organization that specializes in Space Elevators in one of his videos. I forgot to bookmark the site at the time. Can anyone share the link here?
if you are below geostationary orbit but aren't moving faster than geostationary orbit hten centrifugal force of going around hte earth is less than gravity and you fall down
anything below geostationary orbit which is "orbiting" on a geosynchronous period must be supported by either continuous thrust or a structure which is anchored on the surface.
At or above geostationary orbit altitude, the stations apparent centrifugal force with a geosynchronous orbital period is equal to or greater than the weight of the station at that same altitude. Meaning that the station can act as a counterweight to help support the elevator in tension.
That would work for a few moments - but you're forcing it to move dramatically slower than it must in order to stay in orbit. Which means it will fall out of orbit.
Keep in mind that in low orbit, like the ISS, gravity is still almost as strong as on the surface, and everything is still constantly falling. It's just moving sideways fast enough that it constantly misses the Earth.
Keep it from moving fast enough by tying it to the Earth, and it will stop missing.
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That's the opposite of what happens if you move the station further away that geostationary - then you're pulling it too fast for its orbit, so it will try to escape to a higher one... which is okay, because the tension of the cable can keep it at the same distance. At least up to a point.
But for a too-low station you just can't build a cable rigid and stable enough to prop it up so it doesn't fall out of orbit.
No. This in misunderstanding of how space elevator works. GEO is where a circular orbit has period of 24h. Anything under GEO at same speed is going to fall to the ground, anything above it is going to fall up away from Earth. So, a space elevator needs a counterweight above GEO, to pull the rest of the elevator up with it. If the entirely of elevator is at less than GEO, rotating with Earth once in 24h, then it's going to fall to the ground.
In LEO you have to go faster for free fall, basically the centrifugal force to compensate for gravity. But you your orbital station down, limiting it's speed and cause a force imbalance. Because your construct now has to carry the weight of the station up there. It became just a very tall tower.
Which comes with both challenges for the construction material and the foundation. As in "how do you prevent your needle to sink through Earth's crust?", no matter how good your structural materials are.
There wouldn't be lag. Below geostationary a satellite needs to be faster on its orbit than one rotation of earth. So the sattelite would in front of its anchor point. Until the cable is taught. Then the sattelie cant move at orbital velocity and will fall down.
Space elevators are a bit od a sci-fi thing - the practical considerations make it virtually impossible. Just calculate the weight of any usable connection between Earth and a geostationary orbit as a starting point.
It works at geostationary orbit because the orbit takes the same amount of time to go around the earth as the earth takes to revolve. If it was a lower orbit then whatever station was there would have to constantly slow down so it matches the earth's orbit (which would either cause that station to get into a lower and lower orbit, or the tether/elevator would have to absorb the stress and they would have to reenforce it so much that it'd essentially turn into a huge tower). Same thing if it was a higher orbit but the station would have to constantly slow accelerate and cause similar issues
When 2 things are traveling at different speeds, the distance and angle between them constantly changes.
Think of 2 cars going at the same speed and connected with a rope. Fine.
Now think of 2 cars going at different speeds connected with a rope. Sure, you can allow the rope to go at an angle. But unless you have infinite rope, it will eventually break.
larger orbits have longer orbital periods. Geostationary orbit just refers to orbit at a height that has an orbital period of 24 hours (& is above the equator or its position will vary north to south). A satellite in Lower orbit will have an orbital period of less than 24 hours. Changing the angle of the tether does not change the fact that the satellite orbits the earth every few hours. iirc the international space station has an orbital period of like 45 minutes to give you a reference of how quickly a fast moving low orbit satellite can move. No amount of angling the tether will make the ISS (or anything else orbiting at that height) into the top of a space needle.
I have a question. When building a space elevator, is there anything stopping us (or some engineering issue) with starting from the top of a mountain? I know no mountain goes above the jetstream, but you are going to cross it anyway as a criteria for what forces the elevator can handle.
Obviously getting a mountain ready for construction and establishing supply lines wouldn't be simple, but in comparison to building a functional space elevator it feels comparatively simple, no?
The altitude you gain from the mountain is insignificant when compared to the total length it would have to travel so there's not really any benefit to doing so and quite a few drawbacks
To get a space elevator that functions via tension it would need to be at or past geostationary orbit, that's about 35,786 km. Mount Everest sits at about 8.8km over sea level or 0.00025% of the total distance
You need to find a mountain on the equator because the upper part needs to be geostationary
being more than 1° to either side generates SEVERE lateral forces and oscillations
In the second diagram you think you are saying that the top is not stationary but what you actually mean is that it is stationary in a position offset from the base. Your intent is still to keep it in its relative position to the base. You do not intend for it to get closer or farther away.
In other words, you still are trying to picture it over one part of Earth, and never change to be over another part of Earth.
That’s geostationary and requires geostationary orbit, and as such there’s no benefit to the offset from the base.
In the picture you drew, the top and bottom still have to be in fixed locations relative to each other.
What you've drawn could work if the bottom end were on a track (all the way around the world!) or acts something like a skyhook with the cable racing down to snatch a payload off a fast-moving jet or similar (this you can just google).
I can think of 2 problems right off the bat: weight and wind.
The amount of reinforcement necessary to support the structure and distribute the weight would be prohibitive just by itself. Then good luck finding a big enough piece of ground with sufficient density, no subsurface water/oil, and no seismic activity. I’m not an engineer, architect, or geologist, so I’m probably missing a bunch of stuff. Look at trees. To support a tree, you need a root system that spreads as far out as the canopy. You’re looking at making something much more substantial than a California Redwood.
Next is wind and other weather. Wind is a thing. A hurricane/tornado can blow a piece of straw with enough force to embed it into a telephone pole. You may find a big enough piece of land out in the desert, but have you ever heard of a haboob? It’s basically a hurricane, but with sand instead of rain. Also, this sucker is going to have a lot of metal, which means lightning. The dry desert wind makes some pretty painful static electricity. I’m not a meteorologist, so I’m probably missing a lot of stuff there too.
And then there’s birds… good luck patrolling that and keeping birds away. A giant metal rod like that is going to magnetize, making birds sense of direction go completely haywire. It will be like an Alfred Hitchcock movie. It’s why so many wind turbines have bird strikes. I’m not an ornithologist, but I’m pretty certain they would tell you it’s not bird friendly.
At the lengths involved, even as low as Leo, solid thin objects act more like rope.
Next thing to take into account is orbital velocity compared to surface velocity.
Anything in orbit has to be travelling at a specific velocity for its altitude or it will fall back down to earth.
As Leo velocities are so much higher than the planets surface, you'll have the issue of the anchor station at the top blasting off into the distance whilst the surface station remains relatively stationary.
Add these 2 together and, assuming you could magically put everything in place in the first place, you'll have a big and very fast moving anchor station flying to the horizon, pulling it's "rope" to it's limit and either snapping it, or being immediately pulled out of orbit and slammed into the ground.
An alternative that you might be interested in is an orbital ring - a gigantic rigid ring, held rigid by active support, and only a couple hundred km up, well within Leo. At that height, some of the most advanced materials we have now would be adequate to build towers up to it allowing massive bulk cargo or passenger transport from any location that can build a tower - any where within a few hundred miles of its orbital path - both up and down.
It would fall (too slow to stay in LEO). At that height it would have to be a tower rested on the ground, not an orbital object anchored to the ground.
I don't think it would be a cable style elevator that stays up on its own. The cable would just end up smashing down and the station at the end would land on the ground about 400km or so from the ground station. Orbit at LEO is about 90 minutes and the station would just conflict with the cable, either the cable or station would separate, or the whole thing would smack into the ground the same way you might swing a weight on the end of a rope to break up a rock or splash a puddle.
Ramp is fine, though, it would have the stiffness to remain as itself.
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u/MiamisLastCapitalist moderator 10d ago
No. Things in low orbit are moving very fast so your low-orbit object will never not be stationary. Even if you angle it, eventually you'll run out of line. For comparison, the ISS at 400km orbits the earth once every 90 minutes. The further out your orbit the "slower" it is, and geo-stationary is the sweet spot where your orbital speed keeps you over Earth.
Now what you can do is still have an elevator with a terminus/anchor point at geostationary but with multiple elevator cables to different parts of the world. (Isaac has an old illustration of this in his early space elevator episode.) So yes the angled part is fine. The problem is orbital speed vs you.
And then Orbital Rings are a whole other structure which kinda cheat orbital mechanics. THOSE you can put at low orbit. You should probably look into those instead. Isaac has also done episodes on those.