In light of the recent launches I was wondering why rockets launch straight up instead of taking of like a plane.
It seems to take so much fuel to go straight up, and in my mind I can’t see to get my head around why they don’t take off like a plane and go up gradually like that.
Edit – Spelling and grammar
Edit 2 – Thank you to everyone who responded. You have answered a life long question.
In: Physics
The shortest distance between two points is a straight line. Air resistance and gravity will be constantly applying forces that require fuel to overcome. Why would you want to take the long way?
There have been experiments with so called spaceplanes. The problem with them is that in order to reach orbit and leave the atmosphere they need to get really high and fast. Using aerodynamics to fly really high is contrary to get really fast, because the higher you get, the thinner the air becomes, yet you’re not nearly as fast as you need to be for orbit. So you need to accelerate more and more, but still are too low to neglect air resistance. The result is that you burn much more fuel in order to get fast enough than if you just puncture straight out of the atmosphere and start turning at sufficient height.
Airplanes have air breathing engines (edit: and wings). This is great, since it means they don’t need to carry their own oxygen, but it’s not as effective at producing thousands of tons of thrust with a smallish device and they can’t run in space.
Rockets don’t use air breathing engines (edit: or wings) because they’re too heavy, not powerful enough, and don’t work in space. As a result, they don’t benefit in any way from being in the atmosphere, and since the atmosphere has air resistance they’d like to get out of it as quickly as possible – especially the lowest, thickest, parts of it.
The higher up you go, the less air there is, a plane can only go so high before there is too little air resistance plus lift and can therefore never really get into space. Also you need a certain vertical speed to escape the earths gravity which you just aren’t going to achieve whilst flying like an airplane or horizontally in general.
Fuel is mainly burnt to accelerate to the speed you want to be at and to counter air resistance. If you were to fly more diagonal instead of straight up, you encounter more air due to flying a diagonal, therefore you have more resistances against you and therefore you burn even more fuel.
If you were able to launch a rocket from 10 kilometres up it would help, but launching from an aircraft is quite hard. There is testing in that field though, I believe by Virgin Atlantics space detachment, but I could be wrong about that.
To get out of the atmosphere as fast as possible.
In theory you are right, a rocket on a planet with no atmosphere should ideally go sideways, after all 90% of the energy of getting something into orbit is horizontal speed, not vertical.
The issue is achieving that horizontal speed is difficult inside an atmosphere, so we launch up then slowly curve horizontally to eventually push our craft sideways.
There is a case for launching sideways though. Air breathing engines are generally more efficient than rocket engines, mainly because they give something to push back on. To propel something forward it must also push back on something else, a normal rocket brings its own fuel which it pushes back but a plane takes air from its surroundings and pushes it behind to accelerate.
There have been a few concepts of such a launch. For instance one solution has been strapping a rocket to the bottom of a plane and launching it from the plane at high altitude at decent speed and low atmospheric pressure to get in the way, this has been done successfully a few times but isn’t without its problems.
The difference is that planes use air to rest on, and rockets don’t. Why? Iamgine that instead of escaping the atmosphere you try to exit a sea. Think of a plane as a submarine. With little propulsion you don’t rest on the seabed and instead fly through the sea. Think of a rocket as, well, a rocket. A rocket that tries to jump out of the sea. Now using the lift of the water doesnt help much, as the angle required to do so is near horizontal, while you want to go straight out. That’s kind of how it works for airplanes and rockets aswell, but now instead of water in a sea, they deal with the air in the atmosphere.
You’re right in the sense that in order to get into orbit, a rocket has to go sideways very, *very* fast. The International Space Station is whizzing along at over 17,000mph!
However, spacecraft in orbit can only get to (and stay at) such ludicrous speeds because there’s no air resistance to slow them down. The ISS is a fairly low 250 miles from the ground, most satellites are much further up.
In order to use their fuel in the most efficient way possible, rockets go straight up to get to thinner atmosphere as fast as possible. Then they begin to turn sideways, and increase their lateral speed.
Planes have wings which generate lift, the wings do the lifting up part and the engine pushes, so push and lift.
Rockets have no wings and will simply push, to get them into orbit you need to point them upward. They then PUSHHHHH into orbit.
There are some good answers already on why rocket launches don’t go more horizontal than they do, but I think the thing that’s really missing is to point out that actually they don’t go straight up. Most rockets go at a slight tilt very quickly if not immediately and then gradually tilt over more and more as they get higher.
It looks like it’s going straight up in certain shots, especially if you’re zoomed in on the rocket, but this is largely because you don’t have a great frame of reference for what is actually up in that view. If you got a side-on view of the rocket as it took off that kept the launch pad in view the whole time you’d notice it was going sideways as well.
This graph isn’t very ELI5 friendly, so ignore it if you wish, but if you want an example, you can look at the [top left graph here](https://i.stack.imgur.com/hTuuH.jpg), which is showing the launch profile of a Falcon 9. In this graph it shows how far the rocket has travelled downrange (how far horizontally from the launch pad) vs how far it has travelled upwards (the different graphs are different launches).
As you can hopefully see it doesn’t really go straight up at all. If it did, we’d expect all of the lines to go upwards along the left edge of the graph for a while before moving over towards the right.
Another reason which I don’t think has been mentioned yet is that most rockets aren’t strong enough to support themselves horizontally. Just think about how hard it is to crush a drink can (the same shape as a rocket fuel tank) vertically verses how easy it is to crush one from the side.
Rockets can be moved around horizontally while empty but would collapse under their own weight if they were on their side and full of fuel. Making a rocket strong enough to launch horizontally would add weight and make them less efficient.
Space X was originally going to create an [air launch version of the Falcon 9](https://external-preview.redd.it/b6T7XT4Qi0KKqH5RV18G-S018R-yPQ-kUtfVynUI1w4.jpg?width=960&crop=smart&auto=webp&s=753ac5ca1a8c906aa50dd1843aacf56a40e40ac0) for the Stratolaunch company but dropped out of the project, partially because it would have been too expensive to change the Falcon design to be able to hang horizontally like that.
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