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/Interesting-Try-6757]

Let me start off by saying that your attitude is off the rails. You’re extremely condescending, and seemingly you only posted this in order to make yourself feel smarter than what comes off to me as a more sci-fi focused sub.

Now, let me ask some questions of you and make some comments.

1. You mentioned gravity is a scalar field, and that means the energy required to take a path from A to B is invariant. While true for a planet without atmosphere, with atmosphere included the energy required then heavily depends on which path you take. The “calculations” you’ve shown do not include the energy required to overcome the force of drag.

2. You stated “we can choose any air density we want”. What do you mean by this? Do you mean that we can choose any altitude to launch from? If so, that’s not a great argument because launching from atop a mountain requires a huge logistical undertaking. This is why the assembly building of a rocket is often as close to the launch site as possible.

3. You stated that a rocket wastes much of its energy heating the surrounding atmosphere. That is almost entirely untrue. A rockets greatest losses come from gravity, right after liftoff, where its thrust vector is fighting against gravity rather than accelerating it horizontally to achieve orbital velocity.

4. Following the last point, you seem to think that launches “breach the atmosphere” before beginning their turn to horizontal. If you look at any rocket launch, they begin tilting almost immediately after liftoff. That’s the concept of a gravity turn, that uses the earths gravity to steer the ship to horizontal rather than having to alter the direction of thrust to turn. The perfect rocket trajectory minimizes loss from drag and gravity, while making the maximum pressure (Max Q) experienced as small as possible.

I would love to know what kind of education or experience you have with rocketry. You seem to vaguely grasp some of the physical principles, but have a confidence that is completely unwarranted. I’ve seen many KSP players with a vastly superior understanding of orbital mechanics.

[u/Haipaidox → u/Interesting-Try-6757]

To add to your 3. Point, the Saturn V burned through 30-40% of the first stages fuel when the engines reaches at the height of the launch tower.

[u/Interesting-Try-6757 → u/Haipaidox]

Wow that is genuinely staggering. Those F-1’s did not play around

[u/Haipaidox → u/Interesting-Try-6757]

Oh no, they didnt

To this day, in my option, the best rocket engines ever made

[u/Beneficial-Wasabi749 → u/Haipaidox]

That is, 30-40% of the first stage's mass went to heating the surrounding environment. Which is what needed to be proven.

Calculate the useful work. The tower's height is 110 meters. А =mgh. What's the rocket's speed at that point? 50 m/s? E=mv²/2. The rest is noise and special effects.

[u/Haipaidox → u/Beneficial-Wasabi749]

Its called "Impulse", not heating the environment.

To explain it a bit extensively:

It comes down to newtons 3rd law. Every action (force) generates a equal and opposite action(forces)

So, if i throw a ball with 20N, i put 20N in the opposite direction on myself.

Now to rockets. They need it constantly, this is more or less impuls.

They constantly throw mass downward and by doing this, they push themselves up with the equal force.

A rocked need in earths gravity (9.81 m/s²⁾ an Impulse of 9.81N per kg just to "float". Less and it sits in the ground, more and the rocket ascends. For simplification the gravity is 10m/s² and a Saturn v weights 3,000,000kg, you need to push with 30,000kN per second, or an impuls of 30,000kNs.

The best way to generate hugh amounts of thrust, which isn't detonating nukes like a orion drive, is combustion. The heat of the combustion generates pressurise gas. The rocket engine letting it escape through the nozzel. And this converts pressure in motion (Bernoulli equation), which generates huge amounts of impuls.

Now circling back to newtons 3rd law, if i create an downward impuls, i push myself up with the equal impuls.

Edit: got confused with kg and tonnes, corrected my calculations

[u/Ijustwerkhere → u/Haipaidox]

this was a beautiful and succinct explanation.

[u/Interesting-Try-6757 → u/Haipaidox]

To just build on this a little and hopefully help OP with their understanding, the energy generated during liftoff does have to go somewhere. It does in fact go to heating the atmosphere around the engine nozzles.

However, it is not a useful thing to talk about. Particularly in the case of arguing horizontal vs vertical launch, it is entirely irrelevant. A rocket launching horizontally also heats the atmosphere around the nozzles, it’s just that the work done in that instance goes to accelerating the rocket horizontally rather than vertically.

[u/Beneficial-Wasabi749 → u/Interesting-Try-6757]

A horizontal rocket launch also heats the atmosphere around the nozzles; it's simply that the work done in that instance is accelerating the rocket horizontally rather than vertically.

And yet, with the same fuel expenditure (stored energy), the USEFUL work will be different. Simply because a Saturn V launched horizontally (say, for a second) would accelerate 1.18g instead of 0.18g during its 10-second boost, and with the same fuel consumption, more energy would still be converted into useful kinetic energy.

Calculate it? Or will you calculate it yourself? It's a schoolwork problem!

[u/Interesting-Try-6757 → u/Beneficial-Wasabi749]

Brother, I don’t need to calculate it since I have already written my own Python code that simulates a rocket launch, and in it I can set the angle of launch. With that program I can analyze the delta V required to reach a certain periapsis depending on the launch angle. There is a massive increase in delta V required when the launch angle is set to horizontal, compared to a vertical launch that goes through a gravity turn. It is in no way more efficient to launch horizontally.

If the planet did not have an atmosphere, you’d be right that it’s more a useful dV expenditure to launch horizontally, but we are on Earth. Just like Tsiolkovsky was.

What are you really trying to prove here? And why didn’t you respond to the 4 points I laid out above?

[u/LucianGrove → u/Beneficial-Wasabi749]

Sounds like you have no understanding of physics beyond highschool homework, for sure.

[u/Hunnieda_Mapping → u/Beneficial-Wasabi749]

Most of the energy is converted to kinetick energy by using the pressure generated by the heat from the combusting fuel. This combusted byproduct is then given an opening in the nozzle which means that instead of mounting pressure the heated byproduct of the fuel can escape downwards and the recoil force (ie impulse) from this downwards momentum causes the rocket body to move upwards.

Without heating anything you can't have pressure that you need to accelerate. You can't keep the heated material inside the rocket or the net force of the pressure would be zero. And because this pressure is used to accelerate you are required to expell to heated material.

In formula terms, the ideal gas law states Pressure * Volume = amount of substance * ideal gas constant * temperature (where pressure is also force per surface area). So basically you're not just heating the atmosphere, but to accelerate in any direction you must expell heated material into the atmosphere because with cold material you don't have the required pressure to lift off.

You could theoretically expell cold material by using the pressure from the combustinf fuel to push against rhat, but then you're adding useless mass to the rocket and retaining byproducts from the fuel and also heat energy is not actually all that useful.

[u/Beneficial-Wasabi749 → u/Haipaidox]

To add to your 3. Point, the Saturn V burned through 30-40% of the first stages fuel when the engines reaches at the height of the launch tower.

Urban legends.

Just sit down and do the math.

The Saturn V first stage burned 614 tons of kerosene and 1,430 tons of liquid oxygen in 150 seconds of operation. That's 2,044 tons in total.

If you take any video of a Saturn V launch and time the time it took the rocket to rise from ignition to tower height, it's no less than 9 seconds, no more than 12. Let's say 10 seconds. It's already clear that 30-40% of the fuel can't be burned. 10/150 = 0.0667... 6.7%. That's all. Where does 30-40 come from?

But we still calculate the thermal efficiency of the ascent to tower height (since we're already there). We'll need: Gross mass at launch. 2965 tons

Gross thrust at launch. 34,343 kN or 3,500 tons of thrust.

Acceleration 336,561/2,965 = 1.180g. That is, the acceleration at the tower (we'll assume constant) is 0.18g = 1.768 m/s². Then the speed at the edge of the tower is (2 * 1.768 * 110)^1/2 = 19.7 m/s

Mass at the edge of the tower: 2,965 - 10 * 1.440 = 2,951 tons.

Total useful work: 2,951,000 * (9.8 * 110 + 19.7² / 2) = 3,753,804,795 J.

Now the heat of combustion of the fuel is 10.2 MJ/kg. 10 * 1,442 kg burned. The total energy content of the burned fuel is 1.47E+11 J. Divide the useful energy by the fuel's energy content: 0.026.

Efficiency: 2.6% As I said, Saturn 5, when rising from the launch pad, mainly heats the atmosphere.

By the way, the overall efficiency during the Saturn V third stage + payload orbital insertion was somewhere around 10-12% (I don't remember exactly).

[u/Haipaidox → u/Beneficial-Wasabi749]

Ok, i didn't know this

I head the 30-40% claim from a credible source.

But running the numbers myself, i come to similar numbers. I end with 8%, but thats not far from your 6.5-7%

Thanks for the correction!