How do satellites not fall back to Earth due to gravity if they are not traveling at escape velocity?
In: Physics
So a sattelite is constantly falling to earth. It’s not falling straight down though, it is falling along a curved path since we pushed it sideways too.
Remember the earth is round so let’s imagine a ball. If we look straight down on a ball this would be like a sattelite’s perspective of the earth.
Now notice that if you move sideways from there in any direction the surface of the ball (or the ground) is lower from you than the point directly under your eyes.
So that is to say you have further to ‘fall’ if you move slightly in any direction and that distance gets bigger the further you move to the side. If we move fast enough sideways we will essentially have infinite room to fall, that’s what an orbit is, something that is falling but also moving sideways such that it will never actually get to the ground.
Fun little side note – this is why when we want to get something out of orbit and back to earth, we don’t point the rocket towards the earth we actually do a “retrograde burn”. Which means we point in the exact opposite direction we’re going sideways and just slow down so that we’ll fall back to earth with gravity (it’s way more fuel efficient).
Escape velocity is not the speed required to orbit the Earth, it is the speed required to *escape* from orbit and leave the Earth behind forever. There’s a range of speeds in between the minimum speed for Low Earth Orbit (about 7,800 km/hr) and Earth escape velocity (about 11,000 km/hr, from LEO).
[EDIT] I’m stupid, don’t listen to me, someone below said smarter things.
You said it yourself ‘escale velocity’- it’s velocity needed to escape Earth’s gravitational pull. When you’re far enough there is little pull from Earth’s gravity so it doesn’t float away but it isn’t affected as much to fall on earth.
Satellites *are* falling back toward Earth due to gravity. But because of their sideways velocity, they keep missing it.
Escape velocity is the velocity and object needs to travel away from a gravitational source such that it can continue forever away from that source without needing additional boosts to its velocity. Literally, the velocity needed to escape the effect of its gravitational pull.
Satellites aren’t meant to escape Earth’s gravity, but rather to come into equilibrium with it.
There’s three sets of velocity that matter: suborbital velocity, orbital velocity, and escape velocity.
Anything going at suborbital velocity is going to come back to earth. Anything going higher than suborbital, but less than escape, is going to keep circling the earth almost forever. (Or at least until something slows it back down to suborbital velocity.) Anything going higher than orbital velocity is going at escape velocity, and isn’t sticking around.
If you want a more intuitive understanding of this, download the game ‘Kerbal Space Program’ and play around.
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