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
Plane is like paper. Rocket is like a ball.
Throw them both sideways and upwards with same energy and you’ll understand why.
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.
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
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”.
There are hybrid jet rocket engines being developed which allows for take off like you describe. https://en.m.wikipedia.org/wiki/Skylon_(spacecraft)
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.
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