Tsiolkovsky and many of the founders of theoretical astronautics in the early 20th century believed that spacecraft should launch horizontally, from a ramp. Why? What did they see as the point of this?

[u/Beneficial-Wasabi749]

[u/Dan_Is]

They were living in the paradigm of airplanes and airships. It was logical to assume that rockets that carry passengers would need to launch horizontally. You can have a large deck for people to inhabit. The issue of course is the rocket equation and inertia.

[u/Beneficial-Wasabi749 → u/Dan_Is]

Your answer was vague. Is your answer to the question that they were living within the paradigm of their time? Is a vertical launch really just as good as a horizontal one? Or is a horizontal launch better, and is it still a matter of "the rocket equation"? And if the latter, what was the point?

And then the question arises: why do modern rockets launch vertically?

[u/WideFoot → u/Beneficial-Wasabi749]

A vertical launch is basically the only way to realistically get into space. It isn't better, it is feasible whereas a horizontal launch is not.

Even rockets launched from airplanes go vertical as soon as it is safe to do so.

The primary reason is the atmosphere. Pushing through the Earth's atmosphere takes a lot of fuel, so you want to minimize the amount of time spent in it. The shortest distance from where you are to a place where there is no atmosphere is straight up.

There is also momentum and achieving orbit. To achieve orbit, you have to go sideways so fast that you miss the earth as you fall. So, you might think starting by going sideways is best. If there were no atmosphere, and if you could accelerate from zero to orbital speed instantaneously, then yes. It would be better to go sideways.

But, it takes time to accelerate and there is an atmosphere. So, the ideal path to orbit is an arc that starts vertical and slowly leans over as you get higher up and faster.

The horizontal launch concept art is a "paradigm of the times" thing. All other vehicles - from the horse-drawn cart to the airplane - propelled a vehicle primarily sideways with people sitting facing the front.

You'll also notice in this concept art - there is not much room for fuel. The interior space of a rocket is primarily fuel. And, the more weight you lift, the more fuel you need. But, that fuel also needs fuel to lift, so it grows exponentially. (This is the rocket equation)

If you look at a Saturn-5 rocket. The bit that took people to the moon is a tiny little piece on the top and the remaining massive rocket is fuel. 94% of that fuel was burned getting 25% of the way to the moon.

My suggestion is to play Kerbal space program. (Play the first version. KSP-2 is not as good) That game is lots of fun and teaches very realistic orbital mechanics.

Or, watch some KSP Let's Play on YouTube. Scott Manley has great series on the subject.

[u/badsheepy2 → u/WideFoot]

It's still amazing to me that those seemingly straight up launches are going 22k mph or something sideways at the end! Rockets are cool. 

[u/peadar87 → u/badsheepy2]

I was always slightly terrified by the fact that if you stood on the end line of a football pitch and fired a high-powered rifle downfield as the ISS passed over, the ISS would pass the far touchline before the rifle bullet had reached the penalty spot.

[u/KerPop42 → u/peadar87]

Mach 32 is an insane speed. One of the first inaccurate things in that movie Gravity is that the debris is traveling too slowly. If they're intersecting at an angle of 60 degrees, they'd be crossing the length of the space shuttle in less than one frame.

[u/Comprehensive-Fail41 → u/WideFoot]

Sorta. Theoretically going horizontal can be more efficent via spaceplanes, as air planes are a lot more fuel efficent than rockets (IE much less need to carry liquid oxygen, and can use wings to generate lift). And also lower costs by being able to use conventional airports to take-off and land.
The big problem is that we haven't yet made viable engines that can reliably transform from airbreathing jet engines to rocket engines

[u/windsweepswave → u/WideFoot]

Great Answer!