Why do rockets go in a curved path right from the beginning?
In: Physics
Because Douglas Adams was right. Orbit means throwing yourself at the ground and missing. Earth is kinda big, so to miss it you have to be going very fast horizontally.
If Earth was perfectly flat and had no atmosphere, rockets would lie flat on the surface at take off and go East immediately to achieve orbit. However rockets have to get out of the atmosphere to be able to reach, and maintain the speed needed for orbit, so they go up a bit first and start going sideways. They usually stop going up around 200km up and are going completely sideways.
So really, a rocket going upwards is the strange thing, not sideways. It only starts going up initially to get out of the atmosphere.
If you watch [this video](https://www.youtube.com/watch?time_continue=30&v=HyWVGa6I7Gk) of Apollo 17 leaving the Moon, you can see within a few seconds its going almost completely sideways (away from the camera in this case) as the Moon doesn’t have any atmosphere so there’s no need to go up for an extended period of time.
The earth is moving through space at about 67,000 mph, and rotating around its axis at about 1,000 mph. As your rocket leaves the earth heading for wherever it’s going, it needs to get out of the way of this large mass it just left. It could go “straight up,” which means “sideways” at 1,000 mph, and it would eventually (it starts at 67,000 mph while attached to the earth) have to go faster than 67,000 mph as it loses the initial speed it was carrying thanks to being on the planet.
Since it “only” needs a speed of about 18,000 mph to get to an escape velocity, heading sideways solves lots of LOOK-OUT-FOR-THAT-PLANET problems.
In addition to the other replies, here’s a really cool mobile game that illustrates rocket mechanics: [Simple Rockets ](https://apps.apple.com/us/app/simplerockets/id663068211)
Lack of rifling + gravity?
It is not hard to go to space. It is hard to go to space and stay there.
So stay in low earth orbit you need to travel at 7.8 km/s parallel to the ground. The rocket you launch would accelerate to around 9.4 km/s if there was no gravity or air resistance. So an acceleration if around 1.6km/s is needed to get to space, that is close to 20%
So in a simplified way, you can say 1/5 if the rocket is used to get to space and 4/5 to stay there.
The result is that you go relative straight up initially to get out of the dense part of the atmosphere and then you fly accelerate close to parallel to the surface.
Straight up and the midway is not the most efficient way to do that because you can use the gravity so slowly turn the rocket in a gravity turn so you do not need to use thrust for the turn.
There is another reason to start to turn immediately and that is if something goes wrong you do not like to have burning rocket parts falling down on the launch facility damage it so some initial sideways motion to get away if something happens is a good idea.
Making a sharp turn at high velocity within the atmosphere would be incredibly destructive. The aerodynamic forces would rip apart any material known to man. Keep in mind that rockets go a lot faster than even hypersonic jets.
Making a sharp turn after vertically escaping the atmosphere would make it entirely impossible to put satellites in orbit with current technology. As it is, escaping Earth’s atmosphere and gravity is only just barely possible using the most advanced technology we have.
In order to stay in orbit, when falling down, you need to miss the Earth.
To do that, you need to be going really really fast to the side.
So rockets eventually start pointing all the way to the side and start firing in order to build up enough sideways speed to miss the Earth.
However, if you tip the rocket slightly, you make if slightly off balance, meaning gravity is going to pull it in the direction it’s tipped. Sorta like a pole falling over.
Since you want the rocket to turn that way anyway, you can save some turning equipment and let gravity do the work.
But if it’s tilted the wrong way, your rocket turns the wrong way, and that’s really bad.
So you tip it early yourself.
You still want to get out of the thick air as soon as possible, so that’s why it’s mainly still going up.
You also still don’t want to turn too fast, so you keep some control to stop it from flipping, but otherwise you let gravity do the work.
Another consideration is that the buildings to launch rockets are expensive.
If something goes wrong and your rocket can’t go to space today, you want the exploding flaming wreckage to fall somewhere there’s nothing important.
So best start pointing it away from the expensive rocket buildings.
Because going up into space is the easy part. Going sideways fast enough that you continually “miss the earth” while falling down (being in an orbit) is the hard part.
You want to start with going sideways early, so that your trajectory starts to point in the right direction. Of course, you can’t go *just* sideways immediately, you first have to get fast enough so that you can go “up” in the first place. The math works out so that the most efficient path is starting mostly upwards, and then going continually more sideways the higher you get.
To go into orbit you dont need to be moving away from the earth, you just need to be moving a certain speed over its surface. So rockets go into orbit by flying across the sky at great speed and at a great height.
Further, for fuel efficiency reasons, the best way to get out of orbit and into space is to first get into orbit.
Latest Answers