Why do space rockets not take off like planes (i.e. straight up vs sideways and up)?
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Rockets go up first because they need to get out of the atmosphere as fast as possible to reduce air drag. You’d need air breathing engines and wings to make taking off worthwhile, which basically means your first stage is a plane. There are a few rockets designed to be launched from planes, but it doesn’t save you much delta v, and it dramatically reduces your maximum payload to orbit unless you designed and built the biggest plane in the world for this. That’s an awful lot of work compared to just making the rocket a little bigger.
When you want to reach orbit, you actually need to go horizontal more than vertical. BUT for this to be fuel efficient the first thing you do is going nearly straight up to reach thinner parts of the atmosphere. You do this because the air resistance close to the ground is so high that you would burn up before reaching the requires speed to leave the atmosphere. So you start straight up and then change Direction to a parable. Before reaching the highest point you accelereate more to make a circle out of this parable. Congrats, you have achieved orbit.
The simple answer is we don’t have a powerful enough fuel source and/or any reactor light enough to be carried into space with a craft similar to a plane.
Someone Smarter please elaborate and stop explaining how we deal with this inefficiency by barely escaping our atmosphere on controlled explosions.
Planes rely on the atmosphere to fly. They’re not trying to get away from the atmosphere, they need the lift to fly.
With a rocket, the atmosphere is getting in the way, it’s slowing it down. It doesn’t need any atmosphere to accelerate either.
Ultimately, a rocket wants to go sideways very fast. But the best way to do that is to first go up fast to get to where the atmosphere is thinner so you can go sideways as fast as possible.
So while we usually only see the first part of the launch, the actual path of a rocket is a curve. It starts straight up then curves until it’s eventually going horizontal.
The real ‘why’ is because the goal of a rocket is very different from the goal of a plane.
A plane wants to travel a distance and do it efficiently. To do this it uses jets which breathe air and it uses the atmosphere for lift. That means it doesn’t have to carry oxidizer and it can rely on wings rather than pure thrust to stay in the air, but because its in the air it has a big limitation on top speed.
The goal of a rocket is basically just top speed; get fast enough to orbit the planet. To achieve this they try to get out of the atmosphere quickly and that means they can’t rely on it for lift or oxidizer.
That being said there have been attempts at ‘space planes’ that use lift and breathe oxygen while in the atmosphere, then get into space. Usually its not worth it though. You need to carry these different kinds of engines and wings around and the benefit you get from achieving normal plane speeds and heights before having to switch over to ‘rocket mode’ just isn’t worth it. Its easier to just make the first stage a big rocket and brute force through it.
Well, where is it trying to go? Space / orbit. The most direct way to high altitude is straight up. It will actually turn sideways at some point, but it takes off and climbs rapidly to reach thinner air, which provides less resistance.
Notice that a rocket might have boosters to help it lift off, which it ejects, and at some point it ejects the first stage and switches to the 2nd. The second stage needs much less power to fly in space than the rocket did to leave the ground. So the idea is to get there with as little fuel as possible because a rocket will be mostly fuel and that cuts into the profit margin. Going sideways from the ground would waste fuel going farther through lower altitude and higher pressure air with more drag.
The biggest problem with getting an object into orbit isn’t getting high enough, it’s going fast enough to stay there. A polar orbit requires a speed of about 17,000mph relative to earth’s surface.
Speeds above about 600mph become problematic while in earth’s atmosphere. Even the SR-71, flying at 90,000 feet at 2400mph, experienced such extreme air resistance that most of the plane was made of titanium – aluminium would have melted, and steel was too heavy. Flying up to orbit requires going 6-7x that speed, and the power requirements, and use of fuel, become absolutely vast.
A vertical launch profile allows the vehicle to punch through earth’s atmosphere as early and as quickly as possible. This means as little fuel as possible is wasted fighting air resistance and as much as possible can go towards gaining altitude and speed.
Airplanes work by “manipulating” air pressure and temperature, and they are designed to fly in air.
Rockets work by pushing themselves (think like a garden hose moving because the water coming out is pushing it), rockets also ‘fly’ in space, where there is less stuff and less air pressure/temperature.
It takes a certain amount of energy to go from Earth’s surface to orbit. Rockets are launched straight upwards because that is the most efficient route out of Earth’s gravitational field.
Could a rocket fly sideways, climb, and *then* shoot out of the atmosphere from a higher vantage point? Sure, but that would require a lot more fuel, and thus would be less efficient. Using wings to generate lift doesn’t use less energy per unit of altitude gained than a rocket does, it just applies that energy differently.
Typical rocket have two stages, and you are correct that pretty much all the first stages take off vertically.
It *is* possible to build a rocket-propelled plane as the first stage of a two stage rocket – there’s a company named Dawn Aerospace in New Zealand trying to do exactly that.
Wings help a little because you gain a little from their lift right when you take off and you can glide down and land easily when you return to the earth. On the other hand, wings and landing gear are heavy.
So it’s not clear which is better.
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