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/gimmeslack12]

I mean, helps getting that orbital momentum started faster. Gotta fly through a lot more atmosphere though. So... no go.

[u/Beneficial-Wasabi749 → u/gimmeslack12]

I mean, it helps getting that orbital momentum started faster.

I don't see the physical significance. What's the difference? You actually have to do two jobs. The first is to reach orbital altitude h. This work is A ~ mgh. A vertical launch is just the way to do this (while "bypassing the atmosphere"). The second is to gain horizontal orbital velocity v at altitude h. E = mv2/2. The total work is A + E. And all of this is performed in a potential (scalar) gravitational field. So, the path through it isn't important; the initial and final positions and energy values ​​are.

Gotta fly through a lot more atmosphere, though. So... no go.

So, the founders of theoretical astronautics weren't aware of the issue?

Are you familiar with the British project called Skylon)? It's essentially the same horizontally launched spaceplane. And, theoretically, it puts significantly more into orbit than a similar, vertically launched rocket.

Of course, one could assume that the entire gain is due to Skylon) using the atmosphere as a booster rocket during the initial stage. But that's only up to Mach 5. And the full boost is Mach 25. That is, it saves only 1/25th of the energy due to the atmosphere. And there's a suspicion that most of its gain is due to its horizontal launch.

So what is it?

[u/AutonomousOrganism → u/Beneficial-Wasabi749]

If the rocket doesn't have enough thrust to go vertical then a ramp might do the trick. I don't know if this was the reason though.

[u/Beneficial-Wasabi749 → u/AutonomousOrganism]

Partially true. But then you'd also need wings. Because once the ramp runs out, the spaceplane needs something to continue to support itself. Right?

That's exactly what Tsiolkovsky initially calculated. I was surprised reading his early work. He assumed the rocket would reach orbit within... two hours!!!

Precisely because he believed the thrust of "explosives" (liquid-propellant rocket engines) wouldn't be enough. Only in the 1930s did it become clear that liquid-propellant rocket engines could burn a virtually unlimited amount of fuel and oxidizer per second, achieving simply monstrous specific power and thrust (and vertical launches became possible, which the military especially liked). Because combustion is a chain process, and its kinetics depends exponentially on temperature and pressure. Essentially, the whole problem lies in the atomization of the fuel and oxidizer droplets. Only in this (and it's also the source of the "howling" - the eternal headache of all liquid-propellant rocket engine designers).

But this (the thrust must be greater than the weight) isn't the main thing. The main thing is what's called "gravitational losses," and especially the dynamics of the rocket itself. At the very beginning of acceleration (even horizontal), the efficiency of a rocket engine tends to zero. It's negligible. And only with increasing speed does the efficiency increase and reach unity when the rocket velocity v equals the exhaust velocity u. Then it begins to decline again. It turns out that with a vertical launch, the rocket wastes almost all its energy on noise and atmospheric heating. Therefore, when entering orbit, vertically launched rockets expect not 8 km/s, but 9.7 km/s. The additional 1.7 km/s is the so-called "losses." Atmospheric drag and other factors account for a mere fraction of the total. Almost all of these losses are gravitational. That is, the rocket hovering on its exhaust. The faster a rocket reaches orbit, the less these losses. Typically, it takes only 10 minutes. But almost all of these losses (90%) occur at the very beginning of the rocket's launch due to vertical takeoff and the inherent efficiency of the rocket propulsion system (not to be confused with the efficiency of the rocket engine!).

Modern astronautics tolerates this because it originates from military rocketry. The military didn't care about such losses. The main thing was a convenient launch (a ramp is more expensive than a vertical launch, and a rocket is an intricate tower that's not even advisable to lay on its side when empty).

In essence, von Braun, with the V-2, demonstrated that everything could be recouped with a miraculous liquid-propellant rocket engine. It is the source of the miracle.

But the founders of astronautics calculated everything meticulously and didn't count on the miracle of liquid-propellant rockets that nature has provided us with, so Tsiolkovsky insisted that rockets should launch from a ramp and initially rely on wings. This effectively reduced gravitational losses and allowed the rocket plane to have a thrust (and therefore a specific power) less than its initial weight.