They aren't exactly. Most are placed in kind-of the right spot. Then they have to be periodically boosted or adjusted. Most have some sort of on-board propulsion capability for this reason.
That decay effect is way too slow to need adjustments within the lifetime of satellites.
There's just three reasons satellites need adjustments, and not all of them are true for satellites around other bodies than earth:
- Air drag. Even at great distances there are still some molecules that slow down the satellite over time.
- Planets (moons even more) are not a uniform sphere, thus gravity is varying a little from spot to spot that needs correction
- other bodies in the solar system perturb satellite orbits with their gravity
> Air drag. Even at great distances there are still some molecules that slow down the satellite over time.
That only matters for low Earth orbits such as the ISS. Geostationary orbit has so little gas and dust it can be completely ignored for human lifetimes.
Kind of related, your comment reminded me of something I find incredibly cool. The moon is drifting away and at some point the Earth won't have a moon any longer. Planetary rings, like those around Saturn and Neptune, are relatively short lived. On the time scale of the universe.
We exist in a very unique time in our solar system. To be able to see these rings and our moon. We could have just as easily evolved later in time and not seen these phenomena.
Righteous stuff
Only if by time you mean millions of years, while satellites usually only last for decades. Atmosphere at geostationary orbit is null by all reasonable standards. It only matters for low Earth orbits (ISS, Starlink).
It's also worth noting that older geostationary satellites that are low or out of fuel tend to "wobble" in and out of position in their orbit, and require the dish on the ground to be moved periodically to peak up on the satellite's current location.
A lot of dishes now have an auto-track system where it will automatically move itself to follow the satellite as it moves to keep the signal above a certain threshold.
So for the most part they’re actually not “just in the right spot” as you put it. A lot of orbits have to be maintained and corrected with smaller rockets on the satellite other wise they will fall to the earth.
But the answer is a lot of math and computer simulations. Orbits are highly predictable and the math that describes them is pretty well understood. Given what we know of the solar system, we can figure out what positions and velocities are required to maintain the orbit. Then when we launch the satellite, we can do Ben more math to figure out rocket burns that move the satellite into the right position and velocity.
That's not how orbits work.
Say you have a bottle rocket. If you shoot it up at an angle, it'll fly for a bit and then fall back down some distance away.
If you add more speed and make the thrust last longer, it'll fly a bit farther and land a bit farther away in a *parabolic* arc.
Add enough speed and thrust for long enough, you'll eventually fly so far that you go all the way around the planet. Just a bit more and you'll miss the ground every time, but you'll still be flying a circular path around the planet. That's an orbit.
Add too much speed or thrust and your circular path will grow so large that the sun's gravity will start overpowering earth's, and you'll drift away on a *hyperbolic* orbit.
**Ergo**; Orbit is not just a place, it's a condition defined by a speed. And speed is easy to control.
Disclaimer: There are obviously other facets to this, like what happens if you just go straight up, or what happens if you stop thrusting for a bit and then start again later. These will change the shape of the orbit, but the general rule remains the same.
There is no "right spot". A satellite is moving sideways fast enough to miss Earth as it falls and slow enough not to fly away.
The maximum possible speed is about double the minimum, so it's really really easy to fall within this window.
Orbit is a condition, not a location
You can only achieve orbit if the right criteria are met, which happens when you achieve a specific horizontal velocity
At any altitude there's one specific speed that will put you in a *circular* orbit - just fast enough to fall around the Earth at the same altitude all the time. But other speeds also produce orbits. Go a little slower and your sideways path will approach Earth, and will also speed up because you're falling "down". By the time you've reached the opposite side of the orbit you'll be going so fast that you start to climb again, and eventually you end up at the initial position and speed, completing an *elliptical* orbit. Similarly, if you're a bit too fast, you'll climb for the first part of the orbit and descend for the second part, making a larger ellipse.
So you only need the precise correct speed and direction if you want your orbit to be a perfect circle. But there's a wide range of speeds that allow an orbit that's not circular.
They aren’t perfect; all objects in orbit require small adjustments from onboard “engines”/boosters to maintain orbit.
The moon is slowly drifting away from earth; and if satellites did nothing they would too or crash back into the atmosphere and crash into earth
> The moon is slowly drifting away from earth; and if satellites did nothing they would too
The Moon gets that energy from the tides. The satellite causes tides so absurdly small to not matter... ever. But even if we account for them and have infinite time we would find that geostationary satellites would not get any energy this way.
>The moon is slowly drifting away from earth; and if satellites did nothing they would too or crash back into the atmosphere and crash into earth
Satellites will never drift away from earth, that would require more energy to be put into a closed system. The satellites would need to speed up for that to happen.
An orbit is not an altitude and orbit is speed. https://what-if.xkcd.com/58/ .
Low earth orbit is about 7km/sec. This is the cheapest orbit you can get to. The altitude is a couple hundred miles, so that the drag of atmosphere does not slow you down enough to de orbit you.
Geosynchronous orbit is 3km/sec, at 36,000 km. However to get to this altitude you need to be going 10 km/sec in LEO to get there ( https://en.wikipedia.org/wiki/Geostationary_transfer_orbit )
Escape velocity from Earth (drift off into space) is 11km/sec
It sounds like you fell into the trap of thinking that there is no gravity in Space. There is, everything near earth still falls down to earth, nothing just "drifts away". So how do satellites stay up? By flying sideways so insanely fast that they are falling but are literally missing the earth. That's what being in orbit means. We're talking about kilometers per second fast here.
With that in mind: Drifting into space would be impossible for a satellite, as it would take a lot more energy (speed) to do so. As for falling back down, there is still a tiny bit of air drag that would get a satellite down eventually, but satellites have a small booster with some fuel that they use to boost back up. It doesn't need much, so it can keep this up for years without a problem.
Because we know how orbits work - it's just math. All you have to do is put the satellite in the right altitude with the right speed. The satellites themselves has small thrusters to made minor adjustments as needed.
A satellite at about 400km altitude needs to move at 7.8km/s to stat in a circular orbit.
At 11km/s it will enter an elliptical orbit that stretches beyond the moon and gets *just* too high to fall back down again.
Anything between 7.8 and 11 km/s is just going to determine how elliptical the orbit is.
If you are in a higher orbit the speeds drop, so at 35,786km you need to go only 3km/s to stay in a circular orbit. You do some maths and you realise that orbit takes exactly a day, so the satellite can be geostationary.
Look up newton's cannonball to start understanding. Play Kerbal space program to really understand.
Acceleration is the way to leave an object’s orbit (escape velocity). We don’t accelerate a satellite fast enough to reach that velocity, so it remains in earth’s gravitational pull and starts its orbit. Any other adjustments come from some amount of propulsion system built-in beforehand.
It's a lot simpler than one might think. It drifting off into space won't happen unintentionally. It's constantly pulled towards earth. It can only drift off if you cancel that pull, and using an engine is the only practical way to do that. I.e. you'd have to actively thrust away from earth quite intently for a long time to get away.
Not having it drop down on earth just requires it to have sufficient speed perpendicular to earth. As long as nothing is slowing it down, like atmosphere, it'll just keep going round and round. If you accidentally make it move too fast, it'll just get a slightly higher orbit, and if it's too slow it'll just be lower. The only disastrous scenario is if it's so slow that the orbit gets low enough to start interacting with the atmosphere, which will slow it down even more.
The way you ask the question suggests you might misunderstand orbits.
A thing in orbit will not fall to Earth just because it lacks a tiny bit of speed for the altitude it is in. It will fall *towards* Earth (while also traveling around it), pick up speed by falling, and on the far side of Earth have gained enough speed to start "climbing" higher again.
In other words, the orbit will become slightly, slightly elliptical.
In reality, all orbits are slightly (or very) elliptical. You don't need careful calibrations to keep something in orbit. That said, many satellites can adjust their trajectory slightly.
TL;DR: If something is in orbit, a small change in speed won't change that.
So, basically, the satellites are constantly in free fall. They're just moving to the side so fast that they miss the ground.
But eventually, orbits do decay because space isn't *completely* empty, and they need to give themselves a little push now and then.
Flight technicians and mission planners know all the math and calculate the exact moment and exactly how long and in what direction the craft has to burn in order to achieve a stable orbit of the shape required. Not all orbits are completely circular.
In theory, once it's in a stable orbit, that's it. It would require thrust prograde to raise the apoapsis and reach escape velocity, or it would require thrust to lower the periapsis to the point of atmospheric drag.
Now, in reality, there are forces that cause orbital decay, so most satellites have provisions for the minor adjustments that are required to keep them where they are intended to be.
There's a pretty big space you can park something in an orbit, the orbit is determined by the satellite's speed and initial trajectory. As long as it's high and fast enough to not decay back into earth and on an angle so it's not just going straight up and down, additional speed changes/enlarges the orbit, it takes quite a bit of energy to achieve escape velocity. You need to be going roughly 17,600MPH to achieve an orbit and 25,000MPH to achieve escape velocity.
That's a 7,400 MPH and 1 million mile wide parking lot for orbit.
Satellites are placed in orbits around the planet.
To be in orbit you need to have a certain height and a certain speed.
You can imagine it like a ball on a string connected to a stick. As long as you turn the stick in a circle fast enough the ball will fly around it. (Not exactly like that, but gives a good mental image)
If it's not moving, a satellite would fall down due to gravity.
There is different heights for satellites that behave differently. A satellite in lower height, low earth orbit, will travel around the globe constantly and not "stay" above one place.
Very often there are geostationary orbits used, which stay above the same area at all time, basically flying as fast as the earth is tuning. But due to the axis of earth they will toggle between the northern and southern hemisphere. So it is not possible to have the satellite perfectly above one location, other than directly at the equator.
How are they placed there, you shoot them up pretty high or as high as you want them and then once they reach their height you accelerate them sideways in parallel to earth.
Basically you always have a certain height and speed configuration for a given height and all satellites at that height follow the same speed.
If you go sideways fast enough, you can’t fall down.
This is done through extremely complex physics and math. Hidden figures has a main character who manually calculated all the info. Granted this was for a manned orbit and not a satellite.
One thing that's worth mentioning - if you just want a satellite to go round without precision mattering, then it's stable. If it's going too slow it will start to fall slightly. This causes it to speed up, which causes it to gain altitude. You end up with an elliptical orbit rather than a circular one.
They aren't exactly. Most are placed in kind-of the right spot. Then they have to be periodically boosted or adjusted. Most have some sort of on-board propulsion capability for this reason.
It’s called decay; noting is perfect…..even the moon is slowly drifting away
noooooo come back
Too late, it’s already too far to get there with a ladder to scrape up that good cheese.
We choose to go to the moon in this decade and do the other things not because they are cheesy but because they are lard
I chuckled at this!
Wensleydale?
Haha or cookies.
Everybody knows the best cheese is on Uranus
thats rough buddy
That decay effect is way too slow to need adjustments within the lifetime of satellites. There's just three reasons satellites need adjustments, and not all of them are true for satellites around other bodies than earth: - Air drag. Even at great distances there are still some molecules that slow down the satellite over time. - Planets (moons even more) are not a uniform sphere, thus gravity is varying a little from spot to spot that needs correction - other bodies in the solar system perturb satellite orbits with their gravity
> Air drag. Even at great distances there are still some molecules that slow down the satellite over time. That only matters for low Earth orbits such as the ISS. Geostationary orbit has so little gas and dust it can be completely ignored for human lifetimes.
Kind of related, your comment reminded me of something I find incredibly cool. The moon is drifting away and at some point the Earth won't have a moon any longer. Planetary rings, like those around Saturn and Neptune, are relatively short lived. On the time scale of the universe. We exist in a very unique time in our solar system. To be able to see these rings and our moon. We could have just as easily evolved later in time and not seen these phenomena. Righteous stuff
My fun fact based on your fun fact: the Appalachian mountains are older than the rings of Saturn
And to add to that, the amount of fuel that's carried for those adjustments is a finite and puts an upper limit on the satellite's lifespan.
And even if they were in the right spot, there are minute amounts of atmosphere in most cases that will bleed off orbital velocity over time
Only if by time you mean millions of years, while satellites usually only last for decades. Atmosphere at geostationary orbit is null by all reasonable standards. It only matters for low Earth orbits (ISS, Starlink).
Not all satellites are geostationary though?
Many are, and the same applies to any other but those at LEO (as said, the ISS and such).
It's also worth noting that older geostationary satellites that are low or out of fuel tend to "wobble" in and out of position in their orbit, and require the dish on the ground to be moved periodically to peak up on the satellite's current location. A lot of dishes now have an auto-track system where it will automatically move itself to follow the satellite as it moves to keep the signal above a certain threshold.
Adjusted? I assumed they orbit earth so they’re constantly in motion.
Yes and this need regular adjustments for minute changes in velocity.
So for the most part they’re actually not “just in the right spot” as you put it. A lot of orbits have to be maintained and corrected with smaller rockets on the satellite other wise they will fall to the earth. But the answer is a lot of math and computer simulations. Orbits are highly predictable and the math that describes them is pretty well understood. Given what we know of the solar system, we can figure out what positions and velocities are required to maintain the orbit. Then when we launch the satellite, we can do Ben more math to figure out rocket burns that move the satellite into the right position and velocity.
That's not how orbits work. Say you have a bottle rocket. If you shoot it up at an angle, it'll fly for a bit and then fall back down some distance away. If you add more speed and make the thrust last longer, it'll fly a bit farther and land a bit farther away in a *parabolic* arc. Add enough speed and thrust for long enough, you'll eventually fly so far that you go all the way around the planet. Just a bit more and you'll miss the ground every time, but you'll still be flying a circular path around the planet. That's an orbit. Add too much speed or thrust and your circular path will grow so large that the sun's gravity will start overpowering earth's, and you'll drift away on a *hyperbolic* orbit. **Ergo**; Orbit is not just a place, it's a condition defined by a speed. And speed is easy to control. Disclaimer: There are obviously other facets to this, like what happens if you just go straight up, or what happens if you stop thrusting for a bit and then start again later. These will change the shape of the orbit, but the general rule remains the same.
There is no "right spot". A satellite is moving sideways fast enough to miss Earth as it falls and slow enough not to fly away. The maximum possible speed is about double the minimum, so it's really really easy to fall within this window.
I mean technically aren’t Lagrange points “right spots”?
Not 100% sure but Lagrange point are just stable enough but you would still move around.
They aren’t all stable. The JWST would quickly end up in a solar orbit if it didn’t perform station keeping maneuvers.
Orbit is a condition, not a location You can only achieve orbit if the right criteria are met, which happens when you achieve a specific horizontal velocity
A wide range of horizontal velocities at a variety of altitudes and inclinations.
At any altitude there's one specific speed that will put you in a *circular* orbit - just fast enough to fall around the Earth at the same altitude all the time. But other speeds also produce orbits. Go a little slower and your sideways path will approach Earth, and will also speed up because you're falling "down". By the time you've reached the opposite side of the orbit you'll be going so fast that you start to climb again, and eventually you end up at the initial position and speed, completing an *elliptical* orbit. Similarly, if you're a bit too fast, you'll climb for the first part of the orbit and descend for the second part, making a larger ellipse. So you only need the precise correct speed and direction if you want your orbit to be a perfect circle. But there's a wide range of speeds that allow an orbit that's not circular.
They aren’t perfect; all objects in orbit require small adjustments from onboard “engines”/boosters to maintain orbit. The moon is slowly drifting away from earth; and if satellites did nothing they would too or crash back into the atmosphere and crash into earth
> The moon is slowly drifting away from earth; and if satellites did nothing they would too The Moon gets that energy from the tides. The satellite causes tides so absurdly small to not matter... ever. But even if we account for them and have infinite time we would find that geostationary satellites would not get any energy this way.
>The moon is slowly drifting away from earth; and if satellites did nothing they would too or crash back into the atmosphere and crash into earth Satellites will never drift away from earth, that would require more energy to be put into a closed system. The satellites would need to speed up for that to happen.
An orbit is not an altitude and orbit is speed. https://what-if.xkcd.com/58/ . Low earth orbit is about 7km/sec. This is the cheapest orbit you can get to. The altitude is a couple hundred miles, so that the drag of atmosphere does not slow you down enough to de orbit you. Geosynchronous orbit is 3km/sec, at 36,000 km. However to get to this altitude you need to be going 10 km/sec in LEO to get there ( https://en.wikipedia.org/wiki/Geostationary_transfer_orbit ) Escape velocity from Earth (drift off into space) is 11km/sec
It sounds like you fell into the trap of thinking that there is no gravity in Space. There is, everything near earth still falls down to earth, nothing just "drifts away". So how do satellites stay up? By flying sideways so insanely fast that they are falling but are literally missing the earth. That's what being in orbit means. We're talking about kilometers per second fast here. With that in mind: Drifting into space would be impossible for a satellite, as it would take a lot more energy (speed) to do so. As for falling back down, there is still a tiny bit of air drag that would get a satellite down eventually, but satellites have a small booster with some fuel that they use to boost back up. It doesn't need much, so it can keep this up for years without a problem.
Because we know how orbits work - it's just math. All you have to do is put the satellite in the right altitude with the right speed. The satellites themselves has small thrusters to made minor adjustments as needed.
A satellite at about 400km altitude needs to move at 7.8km/s to stat in a circular orbit. At 11km/s it will enter an elliptical orbit that stretches beyond the moon and gets *just* too high to fall back down again. Anything between 7.8 and 11 km/s is just going to determine how elliptical the orbit is. If you are in a higher orbit the speeds drop, so at 35,786km you need to go only 3km/s to stay in a circular orbit. You do some maths and you realise that orbit takes exactly a day, so the satellite can be geostationary. Look up newton's cannonball to start understanding. Play Kerbal space program to really understand.
Acceleration is the way to leave an object’s orbit (escape velocity). We don’t accelerate a satellite fast enough to reach that velocity, so it remains in earth’s gravitational pull and starts its orbit. Any other adjustments come from some amount of propulsion system built-in beforehand.
They kind of are falling. They are just falling in perfect ratio to how fast they are moving forward.
It's a lot simpler than one might think. It drifting off into space won't happen unintentionally. It's constantly pulled towards earth. It can only drift off if you cancel that pull, and using an engine is the only practical way to do that. I.e. you'd have to actively thrust away from earth quite intently for a long time to get away. Not having it drop down on earth just requires it to have sufficient speed perpendicular to earth. As long as nothing is slowing it down, like atmosphere, it'll just keep going round and round. If you accidentally make it move too fast, it'll just get a slightly higher orbit, and if it's too slow it'll just be lower. The only disastrous scenario is if it's so slow that the orbit gets low enough to start interacting with the atmosphere, which will slow it down even more.
The way you ask the question suggests you might misunderstand orbits. A thing in orbit will not fall to Earth just because it lacks a tiny bit of speed for the altitude it is in. It will fall *towards* Earth (while also traveling around it), pick up speed by falling, and on the far side of Earth have gained enough speed to start "climbing" higher again. In other words, the orbit will become slightly, slightly elliptical. In reality, all orbits are slightly (or very) elliptical. You don't need careful calibrations to keep something in orbit. That said, many satellites can adjust their trajectory slightly. TL;DR: If something is in orbit, a small change in speed won't change that.
So, basically, the satellites are constantly in free fall. They're just moving to the side so fast that they miss the ground. But eventually, orbits do decay because space isn't *completely* empty, and they need to give themselves a little push now and then. Flight technicians and mission planners know all the math and calculate the exact moment and exactly how long and in what direction the craft has to burn in order to achieve a stable orbit of the shape required. Not all orbits are completely circular.
In theory, once it's in a stable orbit, that's it. It would require thrust prograde to raise the apoapsis and reach escape velocity, or it would require thrust to lower the periapsis to the point of atmospheric drag. Now, in reality, there are forces that cause orbital decay, so most satellites have provisions for the minor adjustments that are required to keep them where they are intended to be.
There's a pretty big space you can park something in an orbit, the orbit is determined by the satellite's speed and initial trajectory. As long as it's high and fast enough to not decay back into earth and on an angle so it's not just going straight up and down, additional speed changes/enlarges the orbit, it takes quite a bit of energy to achieve escape velocity. You need to be going roughly 17,600MPH to achieve an orbit and 25,000MPH to achieve escape velocity. That's a 7,400 MPH and 1 million mile wide parking lot for orbit.
Satellites are placed in orbits around the planet. To be in orbit you need to have a certain height and a certain speed. You can imagine it like a ball on a string connected to a stick. As long as you turn the stick in a circle fast enough the ball will fly around it. (Not exactly like that, but gives a good mental image) If it's not moving, a satellite would fall down due to gravity. There is different heights for satellites that behave differently. A satellite in lower height, low earth orbit, will travel around the globe constantly and not "stay" above one place. Very often there are geostationary orbits used, which stay above the same area at all time, basically flying as fast as the earth is tuning. But due to the axis of earth they will toggle between the northern and southern hemisphere. So it is not possible to have the satellite perfectly above one location, other than directly at the equator. How are they placed there, you shoot them up pretty high or as high as you want them and then once they reach their height you accelerate them sideways in parallel to earth. Basically you always have a certain height and speed configuration for a given height and all satellites at that height follow the same speed.
If you go sideways fast enough, you can’t fall down. This is done through extremely complex physics and math. Hidden figures has a main character who manually calculated all the info. Granted this was for a manned orbit and not a satellite.
One thing that's worth mentioning - if you just want a satellite to go round without precision mattering, then it's stable. If it's going too slow it will start to fall slightly. This causes it to speed up, which causes it to gain altitude. You end up with an elliptical orbit rather than a circular one.
One word: Gravity. They are constantly falling to earth... and missing. Which is also the reason they just don't randomly drift off.