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
In order to get into the air you need to generate enough lift to overcome your weight, planes use air passing over the wing in order to generate lift and maintain it over the long flight times. Lift increases with increasing speed so planes use a long ground run to generate the speed and therefore lift to fly. The engines then continue to provide enough forward thrust to overcome the air resistance created whilst flying.
Rockets however are trying to get into orbit around the planet. This actually involves going sideways really fast however, air resistance at that speed would destroy any vehicle used. The rocket only flies straight upwards to clear the launch tower and get clear of the ground, it then pitches over at angle to gain altitude quickly, getting out of the thickest parts of the atmosphere where air resistance is highest whilst beginning to gain horizontal speed. As they get higher up and the atmosphere begins to disappear they pitch over almost flat to allow them to build up the speed required to stay in orbit.
I can eli5 how orbiting works if anyone is interested
There are hybrid jet rocket engines being developed which allows for take off like you describe. https://en.m.wikipedia.org/wiki/Skylon_(spacecraft)
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.
Planes go up mostly because of their wings. Wings work by turning forward speed into a push that pushes the plane up. So, if a plane wants to go up fast, it also really wants to go forward fast. For that reason, the best way for a plane to go up a lot quickly is to go diagonally. (The exact diagonal direction depends on each plane.)
Rockets don’t have wings. The only way for them to go up is to push upward really hard with their rocket engines. If they pointed diagonally like a plane, they wouldn’t get as much upward push as if they just point directly up, and go.
But there’s more! That’s just for rockets that want to go up as high as possible. Rockets that want to go into orbit have to go up high, but they also have to be going sideways fast. It takes both things to make it into orbit. So rockets actually kind of want to go diagonally too, but for different reasons than planes. For rockets, when you’re close to the Earth you really want to concentrate on just pushing up with your engines. The further you get from the Earth, though, the less you have to concentrate on just going up, so the more you start to push sideways.
That’s why you will see rockets launch directly up, but gradually start to tilt diagonally. Eventually, the rocket engines are pushing pretty much all sideways, and not up at all! Watch a rocket launch and see if you can spot the slow change in which way the rocket is pointed.
If you want to know how they figure out how fast to change direction, you will need to learn something called “calculus,” but you can wait another 10 years or so and post your questions to “ELI15”.
Technically they do eventually end up horizontal sort of like a plane. The entire point is to get high enough and go fast enough so you basically fall endlessly while the Earth curves away. This is how we make things orbit our planet.
Down at sea level the air is quite thick and gravity its most effective. Space rockets go sort of straight up (they tend to start turning over in an arc early on to start their horizontal acceleration) to get up to the thinner air as quickly as possible as they have limited fuel.
Rockets need to carry everything that makes them fly with them including oxygen to make the engines work. The issue there is it increases weight, which means the rocket needs to be bigger to hold more fuel to lift it, which increases weight, and so on. We get past the problem now by staging, where we throw away spent engines to reduce weight while in flight.
In theory starting higher is more efficient. There are projects being tested that would launch rockets from large, high flying aircraft. The problem is that these planes need to get up to altitude as well which restricts the size of the payload they can bring. You will not be launching a Mars mission from a Virgin Galactic in its current state.
Still, the dream is to make it as cheap and efficient as possible so more and more people can have access to the space industry.
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.
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 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.
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.
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.
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