Aircraft are drifty, they don’t magically fly in the direction they’re pointing. The better your wings the better you can fly in the direction you’re pointing instead of flying sideways.
This isn’t such a big deal for rockets since they don’t make sharp turns, so the body of the rocket is far more than adequate for this purpose, they just need to keep themselves pointing straight up.
A missile without fins would just point straight at it’s target but wouldn’t be able to curve it’s flight path in time. Thanks to it’s wings it can pull 30G turns, compared to the 8-9G turns a fighter jet can.
The fins are also articulated, so they don’t just help it fly in the direction it’s pointing but also change the direction in which it is pointing.
Rockets/Missiles are use (mainly!) solid fuel and it’s easier/cheaper to stick a few fins on the side to steer the rocket. The rocket is light enough for the fins to change the direction of travel quickly and easily.
Larger Solid Rocket Motors (that are strapped to Space Rockets) use a nozzle that can be moved, There is usually too much mass in a rocket for steering fins to be useful. Also another method is changing the concentration of fuel at certain points inside the rocket so it burns hotter or cooler at certain points BUT can only be used on a predetermined trajectory (i.e. from the ground into a specific orbit.
Modern Space Rockets use Liquid Fuels and it’s easier to have some or all of the rocket motors on a gimble to steer the ship as it flies.
A missile with fins flies a bit like a bird with tiny wings being pushed VERY hard. It can use its tiny wings to turn because it’s moving VERY fast so it’s little wings do more, like when you stick your hand out the car window when you’re going fast.
That’s not a good use of energy though, because if instead you can turn the thing pushing the missile very hard it will turn faster and more accurately. Then the best use of a fin is to keep it from turning *too* fast. Like when you balance a stick on your hand if you move your hand too fast it falls over, the fins keep the rocket motor pushing the missile from “pushing it over” where it would just spin in circles until it goes out, like those fireworks.
BIG missiles, like the rockets that go to space, are VERY heavy. The motors pushing them are very strong but they don’t get moving very fast right away. They also don’t really need to make sharp turns. Mostly they need to go almost straight up for a bit, and then make a gentle slow turn to line up going in a circle around the earth. Even though they get started slow they just keep going faster, but the amount of time they spend in the air is actually very short, and the time they spend in the air at a speed where a fin would be useful is even shorter. Since they’re so big and so heavy once they get going it’s pretty hard for them to turn anyway, and they only turn a little bit. They just don’t need fins.
Lots of reasons. Here are a couple.
First, fins don’t work in space, so you’d need a different system, like steerable engines, in space. Since you need that anyway, adding fins would just be some extra weight, and it’s very expensive to add weight to a rocket that’s aiming for orbit. Missiles generally spend their whole flight time in the air, so fins work fine for them.
Second, missiles need to be able to turn fairly quickly, in order to hit their target. Fins work better for fast turns. Rockets really don’t need to turn that quickly, because they’re going to be flying much longer, and there’s time to make small corrections to get where they want.
SpaceX boosters use a kind of fins when they land, because they’d need legs to hold them upright anyway, so having those legs work as fins on the way down just makes sense. They don’t add much drag, because they’re folded during launch, and when they’re coming down, drag is a good thing, because it slows them down a bit.
JFC… how can so many people be wrong?!
Rockets still have control surfaces. They’re called grid fins and they’re right near the top of the rocket. These perform the same function as fins on a missile but in a different way. The reason a rockets doesn’t have fins at the base is because the base is the booster and it it jettisoned almost immediately.
Missiles have fins because they help keep the rocket stable.
Old rockets (the first stage) had fins for the same reason.
Modern rockets do not have fins, because the technology has evolved where instead of needing air pressure to stabilize the rocket, the engines can point and tilt (called gimbal) to put added thrust and tilt (and correct an intentional tilt) in the desired direction.
To put it into perspective, imagine you have a fan, and you are on a chair. If you wanted to turn, with fins, you’d need to angle the fins and ensure that you have a good amount of air flowing on those fins to turn your fan-chair. But if you have the ability to gimbal your engine, you can turn the fan and achieve even better rotation
Missiles typically operate in the atmosphere where the movable control surfaces can provide directional control. However, a control surface creates drag even when in a neutral position. Fins are only effective below about 100,000 feet.
A space rocket is only effective if it can transport cargo to orbit so anything that creates drag, without providing a substantial benefit, is eliminated. It takes a rocket only a few minutes to get to 100,000’ after which they would be pointless anyway.
As rockets get bigger and heavier it would take much larger control surfaces to provide directional control. Engine gimbals are much more effective and add little to no additional weight.
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