I used to love watching shuttle launches, and they would sometimes delay missions a day or two due to weather, even if the rain/snow would be over in a few hours. Why couldn’t they just wait instead of delaying?
In: Planetary Science
We will try analogy.
Imagine you’re on a field throwing a ball (payload, astronauts or satellite) to a friend (iss or particular orbit). If your friend is standing still, it’s easy. But your friends moving. Back and forth in front of you, always getting nearer or farther. To throw the heaviest ball using the least amount of strength (rocket fuel), you time your throw so that it reaches your friend when they are closest.
So far so good, humans can do that with a bit of practice. However we now add a scary wasp buzzing around you that could sting you if you throw near it (bad weather, a stuck valve or something that could make a gazillion dollar rocket and payload blow up). So you intentionally use a lighter ball so you have more strength to throw a bit earlier or later than the ideal time. That is the window.
Here’s a good interview that gets into the orbital mechanics reason a bit: https://youtu.be/I5Ey92K7L2k?si=cs-cOqJgFvqoTg08
Sometimes the launch window can be a short as a second, if you’re trying to get multiple satellites (I’m thinking of the Iridium satellites from quite a few years back) into specific orbits. In some cases, the more things you have happening at once, the tighter your window is for getting everything launched at the right time.
It wasn’t an issue with the space shuttle, but you can have public launch windows and actual launch windows. If you’re launching a classified satellite, you don’t want to announce to the world your exact launch window, as other nations could figure out what you were aiming for. Instead, you’ll have a public launch window of “we’ll be sending something up in this six-hour window on this date.”
Think of it like a bus you want to catch as it orbits around the earth. However once you leave you can’t stop walking although you can change your pace slightly.
The bus goes along its route but it’s only near your stop for a short period of time. If you aren’t there at the time you can’t get on. You can’t get there early as you would have to keep walking so would need to leave the bus stop.
The distances and speeds involved are so big that you can’t go significantly late or early without being a long way away. The earth makes a rotation in 24 hours so if you are 2 hours late you are nearly 10% of the earth away from where you want to be.
As well as having to make sure all the other things around the launch are clear such as the airspace, emergency services and potentially where the rocket might land if things go wrong
You know when you’re play mario bros and you get to the level where you gotta jump onto the moving grass strips in the sky, and you have to do it at the right time or you fall to your death…that timing is the launch window
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