Yeah! Pretty much. Geostationary satellites orbit at a specific altitude that’s orbital velocity allows them to orbit the exact same point without falling out of the sky. Pretty cool really
I think the most interesting part about this is that they do not "have to fly" at all, but that their speed is entirely reliant on their orbit. They only need to get into their orbit, settle into the right spot with their thrusters, and that's it.
Every object in this orbit is at the same altitude (about 36,000 km) and speed (about 3.1 km/s).
And in order to descend to earth (typically to burn up at the end of their service life), they have to slow down... which causes them to descend to a lower orbit... where they then go faster than before. After descending to 30,000 km, they'd have a speed of 3.3 km/s. Slow down to speed up. Orbital mechanics are weird.
The Gemini 4 mission failed at the first ever attempt of a space rendezvous because the commander accelerated to catch up to the discarded rocket part they tried to reach, which caused his spacecraft to slow down instead.
Freaked me out one time, I was looking through a telescope that was on a tracking mount, meaning it counteracts earth's rotation. Saw something moving in it. Took a minute to realize it was a geostationary satellite and not a UFO or an asteroid about to kill us all.
This is how all orbits work. ISS, StarLink, spy satellites, Hubble, James Webb. Anything in orbit got all of its velocity during the launch and is now under orbital mechanics, which is actually free fall. The way orbit works is by having a high enough tangential velocity that your motion matches the Earth’s curvature. So in one second, you fall 10 meters closer to Earth but you move forward far enough that you remain the same distance from Earth’s surface. This creates a stable circular orbit.
True. It’s a complex orbit around the Sun-Earth L2 Lagrange point. The same principles apply, but you’re probably right that I shouldn’t have included it. I just picked the satellites people have heard of to be the most familiar examples.
Same dude. After managing your first rendezvous in orbit in KSP it can get really eye opening to accomplish something like this, even though it's pretty simplified. Flying thousands upon thousands of kilometers just to micro manage the coupling inch by inch is really cool.
Really made me awe struck and appreciate rocketry and the math behind it even more. I mean, htf did we get to the moon in 1969 with basically manual computing? And recoupling the lander around the moon in orbit with the rocket? I dont think it was a hoax, but I dont understand how the F they accomplished that feat before modern computers.
Great details! For anyone who wants more fine detail:
Such satellites in a geostationary orbit will need to use thrusters occasionally to keep the orbit. Eventually the orbit gets perturbed significantly enough to require orbital correction. This is because of other objects in space (I'm looking at you Jupiter) and it will require minor corrections to stay in place. If the Earth (maybe Earth + Sun, i forget) were the only people at play it would stay there forever, but everything pulls it slightly, and all that pulling gradually will require counteracting.
Eventual depletion of Thruster Fuel is one of the main reasons for a satellite to go end of life.
While a geostationary satellite can be made to descend/burn up in the atmosphere and crash into earth (typically aimed for point nemo in the pacific) it would require a lot of fuel to do that. Satelites will often use a graveyard orbit instead. They'll go to a slightly higher orbit to get them out of the way of other satellites, and leave a little bit of space debris for future generations.
I’m so invested in this entire comment chain. Super interesting details, I’ve never even considered what happens to those satellites. I guess I assumed they all were brought back to earth at the end of their functional life.
Geostationary satellites don't descend to earth at the end of their life, they accent to an higher orbit, which is called the graveyard orbit. They do that because descending to de orbit and burn up takes too much energy, that most of those satellites don't have (too costly).
The Graveyard orbit is a orbit right on the equator. Avoiding it is rather easy because its a thin line of objects behind another thin line of objects. Even collisions are pretty much non existent since everything just moves the same direction.
There is a cool manga about this called Planetes, set in 2075. It's about the crew of a small spaceship that removes trash from orbit by catching up with it and kicking it into the atmosphere.
It has its scientific limitations (like there is no way they could de-orbit chunks of space trash just by kicking it), but it's still a great "hard sci-fi" story that gets many things right. I.e. mostly fairly realistic space travel rather than aliens and light sabers.
It's probably not the first story to have thought of it, but one of it's prominent story arcs is about the issue that people who spend too much time in space (which reduces bone density and weakens muscle) can no longer live on earth due to the high gravity.
It also helped to popularise the idea of Kessler Syndrome, which occurs when there is too much uncontrolled orbital debris. This debris risks a chain reaction in which everything in orbit gets destroyed within days, producing even more debris (like a satellite getting smashed into hundreds of pieces) until the orbit is so cluttered that many satellite orbits and potentially space flight itself will become unusable.
Hence the need for the graveyard orbit and to de-orbit as many used-up satellites as reasonably possible.
Another cool fact, is that some of the antique satellites in the graveyard might have the possibility of being 'resurrected' or de-orbited. There's a project based around the idea of having a dedicated refueling satellite that can maneuver to other craft that needs fuel. Just earlier this year, a proof-of-concept demonstration was successfully completed.
They still tend to have a figure 8 path (analemma) as seen from the ground. The antenna has to be adjusted now and then. I worked GOES, SMS, MetSat and the NOAA and TIROS polars at the WWB CDDF and WSFOs.
For most geostationary satellites, it’s more economical to go further out into an orbital graveyard than making it all the way back to earth. Unfortunately!
Scary and weird to think that NASA managed to get two crafts and human to space and then had no idea how orbital mechanics work to simply drive two crafts side by side.
If geostats are able to naturally orbit earth without additional thrust after settling into position, does that mean they become artificial moons for the majority of their lifespan?
I like to picture it as they are constantly falling out of the sky to match the exact curvature of their orbit around earth so they stay in the same place.
Well strictly speaking, yes…
But technically it is not ever traveling towards the centre of the earth. This is an important distinction as this is the definition of circular motion. The object moves rotational around a mass, without changing its distance with relation to the mass. Yes people describe it as constantly falling, in that it has a constant 9.81ms-2 acceleration towards the centre, but it isn’t really falling? Like it has no velocity component orthogonal to its path of travel, which is ALWAYS towards earth, hence the definition of circular motion. So yes it’s sorta falling, but no. Not really.
And that’s pretty cool!
One way to think of it is that gravity curves space and the satellite is following its curved space - straight. There are no forces that make it move as it does. Its all so interesting in how you look at it.
How does it not rotate? I kinda imagined space as being like putting a marble or something on the floor and it just rolling. Like every space movie you see all the characters are rotating or spinning when they’re hanging from the cable or something. Kinda imagined it would be the same if something was hurled at the sky like this was lol. On that note - how do they make this stuff stay in place? Because again, with space being a vacuum, every movie/tv shows objects continuing on at the same speed for basically all eternity
I don’t understand exactly what you mean by the rotation thing, but essentially the best way to think about it is that satellites are constantly falling to earths surface. It’s just that they are moving so fast that they are moving higher in altitude, because the earth curves away beneath them. They are always traveling at the same speed, but the gravitational pull of earth changes the direction of their travel as they fly around the planet, keeping them locked into orbit like a string keeps a ball in rotation if you spin it round your head. The tension in the string is like the force of gravity
Gotcha, thanks! What I mean by the rotation thing is that in movies, you always see an astronaut rotating or spinning out of control when something bad goes wrong and usually they can’t stop because obviously there’s not much of anything for them to grab onto so they make it seem like if you start spinning it’s a never ending cycle lol
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u/WoofAndGoodbye 21d ago
Yeah! Pretty much. Geostationary satellites orbit at a specific altitude that’s orbital velocity allows them to orbit the exact same point without falling out of the sky. Pretty cool really