Why are space rockets shot straight up? Wouldn’t it be easier to make a spacecraft that ascends like regular aircraft until it’s out of the atmosphere?
In: Technology
Everyone posting earlier hit on various elements regarding escape velocity, regardless of actual trajectory, rockets provide the most efficient means to reach the escape velocity (25000 MPH). There have been a few engineering attempts with Virgin Galactic, but no one, as yet, has been able to engineer the amount of energy needed into a flyable form.
It takes a *ton* of energy to build up momentum to exit the atmosphere, be it entering orbit or flying outward towards distant stars and planets. That energy comes from burning fuel up. And you have a limited amount of fuel. So you want to maximize the energy spent for the *vertical* (up-down) climb. Any energy you spend to move laterally (side-to-side) is energy that you could have spent … for that upward climb. So it’s really inefficient.
Eventually rockets do start to shift towards lateral movement as they burn up fuel, become lighter, and need to start entering an orbit trajectory to deliver their cargo/satellites. But if they started doing that directly on the ground they’d never get up there to begin with.
They aren’t shot straight up.
They start pointing straight up, but very gradually turn so that by the time they have exited the atmosphere, they’re more or less parallel with the ground.
The reason is aerodynamics. The wind slows down the craft, so we have to make the rocket very pointy to cut through that. If we tried to slowly go up like a plane, it would need too much fuel, and fuel is heavy. The more weight you carry, the more fuel you need, so it goes in a big loop getting worse and worse.
So the most efficient way we know of is to go straight up, then slowly level out. Even this is tricky with the amount of fuel needed, so there’s lots of math and weight considerations.
They aren’t shot straight up. They’re shot in an arc. And to escape Earth’s gravity you have to reach a certain speed. It’s very difficult to reach that speed with an aircraft. Rockets provide much more thrust than aircraft engines. An aircraft engines push on air. The higher you go, the less air there is, and at some point aircraft engines won’t work any more, and wings can’t provide lift. Rockets carry their own propellant rather than pushing on the air.
A simple answer is that an aircraft use the air to create lift and as you get higher and higher in altitude you have less and less air to create that lift, until eventually you get none as you get into space. You could design a rocket to be like an aircraft, using air as lift to get up in the atmosphere, but pass a certain point the wings are becoming less and less useful, until they are just dead weight.
There was several test done and so far the wings are simply not worth it, it’s more costly to make a rocket that start like an aircraft, than a straith up rocket using an arc as their trajectory.
Now you could point to the american shuttle which had wings. But those were used to slow down the craft in re entry and then provide enough lift when closer to the ground where air is more dense, to land the craft. They were not designed to carry the weight of the craft at launch, which is a LOT more massive at launch, than in re-entry.
We are also touching the subject of reusable craft. Most of those aircraft type of rocket are reusable, which is for cost saving. But the issue we realized in the last couple of decades is that the stress of launching into space is just too big. The amount of testing and maintenance required to make the craft ready for the next launch just eat up any saving from reusing the craft several times. Some companies still try to achieve a design that is reusable, cost efficient and long term save, but so far it’s simply cheaper and safer to make single use craft for launching into space. Something that make the whole aircraft type of rocket even less economically viable.
You kind of answer your own question, don’t you? If it were easier, then that’s the way we’d be doing it, wouldn’t we?
It depends on your definition of “easy”, I suppose… In one sense, you’re absolutely right – air to orbit launches mean the rocket can be smaller, carry less fuel because it doesn’t have work as hard or go as far to achieve the same orbit as a conventional launch, and can be optimized for launching in high atmosphere rather than having to account for all the lower atmosphere it would otherwise have to cut through.
Virgin Galactic had heavily invested in this research. They built the plane, but never managed to get a suitable rocket. The plane, one of the largest ever built, was recently sold off to a company that’s going to use it for launching hypersonic research vehicles.
But now you have two problems. You have TWO vehicles instead of one, which VG had spent millions and millions on and only got one half of that equation done. That’s not simple, not in the slightest.
Weight is a big budget item in a rocket. The more weight you have to lift, the more fuel you need. The more fuel you need, the more weight you have to lift – because you can’t get your fuel along the way! They call this “The Tyranny of the Rocket Equation”. You need enough fuel that is energetic enough and a rocket efficient enough to hoist itself out of the atmosphere, or space travel isn’t possible. On larger Earth-like planets, with more gravity than here, conventional space travel as we know it isn’t possible, because there’s no fuel power enough that you can carry with you to escape those planets.
So if you consider mixed-mode engines, something suitable for a leisurely climb into the atmosphere, *wings*, the fuel it needs, and then the consideration you need in space, where you can’t use air breathing engines – there is no air, wings become dead weight which just eats your fuel budget, what you have is a large and overly complicated rocket with capabilities it doesn’t even need and can’t even use during the most critical part of its mission. The space shuttle, even for being a marvel of its era, was not without its undeniable criticisms.
To get something into orbit in space, you need to get it up high, past the atmosphere, and then get it going sideways really fast. We use rockets to go up, and then once they are high and the atmosphere is really thin, they turn sideways and then rocket gets up to a really fast speed. Theoretically, we could do as you describe, and get the spacecraft as high as we can flying like an airplane, then go the rest of the way like a rocket, then go fast with the rocket. Or similarly, we could have a plane carry the rocket as high as the plane can go, then release the rocket to do it’s thing. However, the big issue is that even if the rocket gets to skip that first step of getting somewhat high up, the rocket still needs to be big and carry a lot of fuel so it can get the rest of the way up and then do the go-fast step. If you want a rocket big enough to carry people, then the rocket would be too big for even the largest plane ever built to carry it. Additionally, when a plane is carrying a big rocket, it can’t fly as high due to all the extra weight, so really, the height gained wouldn’t be that big.
So, while there is research and tests being done on ideas like yours, they aren’t feasible yet.
There’s a similar concept called “[air-launch-to-orbit](https://en.wikipedia.org/wiki/Air-launch-to-orbit)”. Basically, you carry your rocket in an airplane, and launch it high in the air.
So, why not use the same aircraft to exit the atmosphere? Well, as you go higher and higher, the atmosphere is less dense. This presents two problems: first, jet engines need to breath air to ignite fuel. And second, you would need bigger wings in order to provide the same lift, or you could go faster, but we’re talking *faster* faster.
Now, the space isn’t that far, we’re talking about 100 km or 62 miles. A rocket going straight up can enter low-orbit in a couple of minutes. For comparison, a Starlink launch can be over 100 km in three minutes, while the last Virgin ALTO spent 50 minutes between takeoff and rocket ignition.
The main problems with rockets is that you want them to go fast not necessarily up.
The international space station for examples where a lot of rockets and spacecraft travel to is only 400 km (250 miles) above the ground.
400 km is a distance you could travel in a car in about 3 hours depending on local speed limits and traffic. It is really not far away at all. A supersonic rocket can travel that far in a couple of minutes.
The problem is not really getting to the place where the ISS is, but matching its speed.
The ISS is orbiting at a speed of 7,66 km/s or more than 22 times what would be the speed of sound down here.
The main purpose of a rocket is not to get that high up, but to speed up enough to match that speed.
The obvious issue is that if you tried to go that fast anywhere near the ground, you would have to content with extreme amounts of air resistance that would try to slow you down and heat up your craft in the process.
So rockets first go up until they reach an altitude where there is less air to get in their way and then they start doing their real work of speeding up sideways.
In order to save fuel you want to get to a place where there is less air in the way as soon as possible and that means going in a generally upward direction at first before curving to go into a more horizontal direction.
If you tried to make a spacecraft that started out like a plane you would end up wasting all sorts of fuel to gain latitude.
This does not mean that it is not a thing that has never been done.
In fact Richard’s Benson’s Virgin Orbit launched a rocket from a Boeing 747 this year.
They used the Boeing to fly up with a rocket suspended under its wing and then when they reach sufficient released the rocket to fly its own way. In practice this is using the large jet plane as a reusable first stage for the rocket.
This works to a degree, but there are obviously limits to how big a rocket you can put under a 747’s wing. It is a big plane, but not big enough to carry a rocket big enough to carry humans into orbit.
Many other ideas have been suggested in the past as theoretically possible like building a jet engine that you can turn into a rocket engine once the air gets thin enough. It is one of those things that sounds doable in theory but less so in practice.
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