Why do space rockets not take off like planes (i.e. straight up vs sideways and up)?
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They need massive amounts of fuel to get into space. Most of that fuel is just used to get the rest of the fuel into space. Launching vertically limits the amount of time the rocket needs to be fired. It’s just immediately going up instead of building up speed along the ground and then transitioning to going up.
Planes use “lift” created from the air they move through to fly and therefore need the horizontal motion to create this lift. This is why they have wings
The “lift” is a force created by the pressure difference across the wing due entirely to their horizontal motion through the air.
Rockets are designed to fly in space / low atmosphere and so they cannot rely on lift from air pressure / horizontal motion. Therefore they do not have wings and can go straight up.
Being in air is actually pretty undesirable for rockets as they move so fast that the air friction generates a lot of heat and resistance to motion, so getting to upper atmosphere/ no air quickly is desireable.
Also, most rockets have liquid oxygen source so there is truly no benefit of flying longer in dense air. Only drawbacks.
Going sideways is because planes have wings in order to fly. Wings need air moving over them to produce the lifting force for flight, and a runway is just a straight paved road for the plane to accelerate up to the minimum speed (plus safety margin) needed for the wings to produce enough lift.
But there’s no air in space, so the wings would be useless weight once you’re out of the atmosphere. In general, the higher up you go, the less effective wings become since the air becomes thinner. Regular planes compensate by going faster – 500+ miles an hour is downright normal at 35,000 feet. But a spaceship is aiming for more like 500,000+ feet.
And of course, there’s drag. Wings do produce drag in the air. More than you might think, but totally worth it for ordinary flying. But that’s going to be a problem because…
Orbit requires you be going *fast*… like, a full orbit of the earth takes under 2 hours. That’s how fast you have to be going. That’s how much acceleration you’re going to need to do to get into orbit. Otherwise gravity will just pull you back down again. And that much fuel needs to be brought to perform that acceleration. That’s many many times the speed of sound, so you definitely don’t want to be going that kind of speed in the air. (higher orbits require slower speeds to maintain, but that climb is just more rocket vs gravity)
All things considered, rockets prefer their current method: straight-ish up to get out of of the atmosphere about as fast as possible, then accelerate into orbit once there’s no air to drag you down. A horizontal launch isn’t going to help make up for anything, and the massive wings required for all the weight of fuel coming with you…
They launch straight up because that’s the quickest way to get out of the thickest part of the atmosphere, and thus to minimize drag due to air resistance. The whole goal here is to go as fast as possible as quickly as possible to achieve escape velocity while using the least amount of fuel, so getting out the atmosphere directly makes the most sense. They do however then follow curved trajectories to orbit. In theory, you could launch space vehicles like planes down a runway, the problem is achieving escape velocity while going through more of the atmosphere. If the atmosphere were thinner, like on the moon or mars, or we had radically more efficient propulsion systems, maybe that would be viable.
Because space rockets don’t have wings, so going fast down a runway wouldn’t create any form of lift for it to fly.
To fly sideways, you need wings. Those wings need air to create lift. At some altitude, but before you have reached “space” the air becomes too thin to create any more lift. So you’d never get there. There’s lots of other reasons too as others have commented.
Currently, around 90% of the total weight is dedicated to fuel alone, taking off horizontally, would be less efficient and would require even more fuel for the same performance
Rockets take off vertically because they can quickly get to the upper atmosphere where the air is much less dense and provides much less resistance
Since the air provides less resistance, they can be more efficient and require less fuel
Good answers already, here are a couple additional comments.
Planes travel at about 500 mph. Rockets travel at 17,000 mph. That’s quite a difference. The atmosphere provides drag, and it gets worse (i.e. way more drag) the faster you go.
The atmosphere gets thinner (less dense) as your rise in height. You see this if you go up on a mountain, you can actually feel dizzy due to the less dense atmosphere (and lower oxygen density). If you go up one mile, it’s noticeable. Go up 10 miles, and you will die.
So, from the rocket’s point of view, you want to get vertical as fast as you can, to get out of the atmosphere, so that is what they do. straight up initially.
Fun fact, the rocket (for low earth orbit) is only going up about 300 miles. The ISS is only 250 miles above earth’s surface. But, they have to travel around 17,000 mph horizontally. So rockets go straight up initially (to get out of the thick part of the atmosphere) and then roll and start going horizontally very quickly (like, one minute into the launch or so).
Ok am I tripping? Iv always understood that rocket go up and sideways to get out of the atmosphere to save on fuel compared to going straight up.
With enough thrust and no atmosphere a rocket would actually be more efficient at taking off horizontally. It would be a typical hohmann maneuver with the starting point at very low altitude. This would work on a perfectly spherical body with zero atmospheric drag. Rockets only go up first to get out of the thick atmosphere and to have enough time to reach orbital velocity.
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