So I’ve just heard they’ve set a year of 2032 to decommission the International Space Station. Since if they just left it, its orbit would eventually decay and it would crash. Rather than have a million tons of metal crash somewhere random, they’ll control the reentry and crash it into the spacecraft graveyard in the pacific.
But why not push it out of orbit into space? Given that they’ll not be able to retrieve the station in the pacific for research, why not send it out into space where you don’t need to do calculations to get it to the right place.
In: Planetary Science
That’s the weird thing about space. No matter how much you “kick” something into space, it will *always* return, unless you manage to hit something else with it.
So it’s a lot easier to give it a slight bump and hit Earth than give it a massive WELL AIMED push to try and hit something else.
Also, the ISS isn’t really made to be pushed around with a lot of force. So chances are high that something would break off. Those pieces might then collide with important satellites or crash into a house on Earth. With a bump towards Earth it will definitely break apart but everything will still go pretty much to the same spot (which you can choose)
so orbit is basically moving so fast horizontally that even though you’re falling you miss the ground (buzz lightyear was right!)
basically things in orbit “want” to hit whatever they’re orbiting (and if left alone the ISS’s orbit would EVENTUALLY decay naturally and it would crash into the earth) to get something to break orbit requires a TREMENDOUS amount of energy (think about how big a saturn V rocket is, it’s mostly rocket fuel, it took all of that to get something about the size of a van out of earth’s orbit).
so it’s way easier and cheaper to just make sure it comes down somewhere in the pacific. and it’s not going to be that hard to hit the pacific ocean, it’s sort of hard to get a sense of how big the pacific is but it’s 60 MILLION square miles (and if you miss there’s a decent chance you’ll hit the indian ocean which is 20 million square miles) basically if you closed your eyes and just hoped for the best there most likely outcome is you’d hit the pacific
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There’s this misconception that something in orbit is not bound to gravity anymore. Even though astronauts in the ISS experience weightlessness, this because de ISS is falling (continuously) around the earth.
An object in orbit around earth is still under the influence of earth gravity. Let’s forget about the ISS and let’s think about a hanging lamp you want to decommission. What is more expensive, cut the hanging cord to let it fall to the floor or attempt to throw in the sky so hard that it escapes earth gravity?
It is the same logic for the ISS, it’s way cheaper to just let it fall back to earth, letting gravity do its thing than spending a lot of very costly fuel to throw it into space.
Everyone is explaining how leaving orbit requires a lot of energy but nobody seems to really touch upon exactly WHY, because orbital mechanics and motion without air resistance is highly counterintuitive.
The first mental model people often have about space and orbit is that “there’s no gravity up there”, so the spacecraft is just “floating”. There may be some awareness that it’s not staying still, that it’s rotating around the earth (every 90 minutes it turns out) but it’s hard to connect that to something intuitive of what that REALLY means. After all, maybe the rotation around the earth is just an artifact of the fact that we had to get up there in the first place, and didn’t want to slow down? Or maybe we want to see many parts of the earth? All of these would be plausible.
But the reality is just a bit more weird. Let’s start with the facts essentially nothing in the universe moves unless there is a force applied to it. And once applied, once motion is occurring, you need another force to slow it down or stop it, otherwise it keeps going indefinitely. This is [Newton’s first law of motion](https://en.wikipedia.org/wiki/Newton’s_laws_of_motion) Right away this is already not intuitive to our experience on earth because nothing behaves like that here, but that’s simply because of friction. Objects in land/water/air slow down by themselves because of friction or air resistance. In space they don’t do that.
So when you have a spacecraft in space near a planet there are two forces to think of (we can ignore the rest of the universe).
* There is the engine of the spacecraft – and keep in mind the speed here is not just relevant when the engine is firing, but also whatever the engine fired at the start to get it moving to a certain speed (like a rocket taking off into space)
* And there is the force of gravity of the earth pulling the spacecraft towards it.
So if these are the only facts that you had – the first law of motion, the engine of a spacecraft pushing it away from the earth, and the gravity of the earth pulling it back – you might think there’s only 2 options – get away from the earth, or crash back onto it. This is where the frankly magic (aka insanely complicated science) of orbital mechanics come in.
Being in orbit is like balancing a coin on it’s edge. It turns out there is just the right distance, just the right speed, and just the right direction to put the two in balance. You set a rocket on it’s path, and it’s trying to get away from the earth. But at just the right time the earth pulls it back. Only there’s still enough speed in the rocket that it can’t bring it back to it, so instead it just rotates around.
But what makes orbital mechanics hard is that this isn’t just a middle ground where if you overshoot too much in one direction, and you’ll head directly for the earth, and if you overshoot too much in the other, you escape it. There is a pretty wide stable range where you just well, stay in orbit. You can visualize this by taking a ball and spinning it in a large bowl, and noting how it keeps going around, and eventually circling towards the middle, but it stays pretty reliably spinning. This is a decent model for gravity “curving” spacetime, but that’s a discussion for another day.
That’s basically it other than a few other factors (there is SOME friction in orbit, it’s not a perfect vacuum, which is why the orbit naturally decays over time). This is also why rockets on spaceships need such powerful engines. It’s not that it takes that much energy to “lift” something above the ground to overcome gravity. We can lift a ton of mass way up high just with a hot air balloon or a drone. The powerful rockets aren’t there to overcome gravity, they’re there to **speed up** the payload fast enough to be able to spin around the earth without falling back down.
Think of the ISS like a car that’s just a little way up a hill. The car is almost out of gas, janky, beat up, barely drivable. You could haul enough gas up to take it to the top of the hill (maybe, it’s a real POS), or you could use the tiny bit of gas left to position it, put it in neutral, and let it roll perfectly into a pit in a junkyard at the bottom of the hill. Which one would you do?
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