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
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 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.
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.
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.
There are a lot of answers about air breathing engines and orbital speeds and air resistance on here, all of which are correct. I just wanted to say that space planes do exist and some rockets do launch from high-altitude jets. Space plans just definitely can’t get into orbit as they are much much much too heavy and slow. Also, Launching a rocket from a high altitude plane also does seem like a great solution, but then a plane is basically just doing the job of a first stage booster but can’t get it going very fast or high compared to boosters. Dropping a rocket from a plane is also very technically challenging, as is all of aerospace engineering, but we have a pretty great handle on how to do staged rockets
TLDR; rockets can and do launch from high altitude planes and space planes are a thing. Just a lot less do-able for pretty much any orbit.
Here’s one big reason. Rockets are strong in compression as they are meant to carry themselves and the payload straight up. To add the strength to support the lateral g loading of other-than-vertical flight would require the rocket to be heavier. Thus reducing the payload the rocket can carry.
Rockets basically are not ‘straight up’. It’s only the take off part. After that it turns in the same direction of earth spin and make use of it to reach 1st, 2nd, etc. cosmic velocity.
Airplane can use its wings to lift itself from ground but it cannot go fast, while a rocket needs to not only lift but to be fast enough to offset gravity. And with wings, it causes too much air drag and thus less efficient to accelerate.
Eventually you need to understand rocket uses its speed to generate centrifugal force to offset gravity while airplane uses its wings to lift it up.
Dont think top answer is right. Planes have wings to get lift. Wings only work where there is enough air, that is, within 50,000ft of the surface. A rocket gets to that altitude in minutes (or less). After that, the wings would be excess mass that require more fuel to get into orbit.
FYI, something else to note, besides all of the great answers and info below, rockets assume a fairly horizontal trajectory, relatively soon after liftoff. Just think of it, the end goal is an orbit, which is horizontal.
Plane is like paper. Rocket is like a ball.
Throw them both sideways and upwards with same energy and you’ll understand why.
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