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Question relates to this topic Horizontal space launch

Question is rewritten, so some details are probably lost.
Here I make a sketch of the launch principle and I want to know, if it could improve the whole launch process regarding its safety in first place. In other words, I suppose that this method should reduce the probability of a fault by a launch.
This is a possible carrier, which should be reusable in ideal case. The rocket is placed on the top and splits off at certain height: enter image description here
A ramp is ca 30 degrees on its end. This looks realistic, since more inclination means more construction complexity and thus safety. After liftoff it should smoothly correct it's trajectory to more vertical position, but that is not a must, it depends on how much fuel I can save due to total air resistance difference:
enter image description here Whole trajectory could be like that:
enter image description here
Rocket detachement happens when it is time to make the trajectory more horizontal again, lets say at 10 km altitude.
enter image description here


Mass of the vehicle I suppose should be also optimised, it should not be too big. The carrier should land after split off, how exactly, I don't know, it is subject to a separate question.

So main questions:

  1. This seems a much more intuitive and natural way to launch a heavy thing to the orbit. So I wonder, is vertical start believed to be safer or just some economical aspects?

  2. What can be a strong argument against my scheme, besides fuel consumption?

  3. What could go wrong by rocket detachement on high speed? Like for example a strong trajectory declination due to turbulence?

Please note, this all is to a known grade just a speculation, since I am not expert and do not know specific parameters. Also it is not focused on fuel consumption aspects in first place.
Main benefit as I see it, we don't need a huge engine on first stage, which I believe is unnecessarily powerful.
Also the vehicle by vertical start does not seem to be much controllable, if at all. Small crack on the nozzle edge - and it will loose stability. Mechanical vibrations in engine area, overheating, it all adds scepticism. Looks so freaking dangerous even compared to jet fighter take off from an aircraft carrier.

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marked as duplicate by kim holder, Nathan Tuggy, duzzy, TildalWave Aug 16 '15 at 21:14

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    $\begingroup$ I'm not clear why mechanical stress would be lower for a horizontal launch. $\endgroup$ – Nathan Tuggy Aug 15 '15 at 4:21
  • $\begingroup$ Are you suggesting an unguided rocket? Please note there is no vertical launch. $\endgroup$ – Deer Hunter Aug 15 '15 at 4:24
  • $\begingroup$ @NathanTuggy because it could be constantly accelereted and inertia helps here a lot. Here we don't need to lift the whole mass in first seconds on start. $\endgroup$ – Mikhail V Aug 15 '15 at 4:27
  • $\begingroup$ @DeerHunter do you mean, lift off is not the same as launch? $\endgroup$ – Mikhail V Aug 15 '15 at 4:37
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    $\begingroup$ It's also a possible duplicate of Why don't we use catapults to get to space? or What would make a rocket sled launch feasible? or Is non-evacuated tube maglev launch possible?, and so on. It's definitely a recurring theme here and it would help if you asked a more specific question than why can't we use it? $\endgroup$ – TildalWave Aug 16 '15 at 5:22
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Your premise,

More safety, since we don't have such mechanical stress on start, which is essential for the rocket itself and its cargo.

is incorrect.

In a vertical launch, mechanical stress due to acceleration is lowest at liftoff, and increases gradually as you go up: as fuel is used up, the rocket gets lighter while thrust stays the same. The point where acceleration stress is highest is somewhere near the end of the first-stage burn.
Also, mechanical stress is all in one direction: vertical. This means you can build a rocket that's strong in the vertical direction, but weak in the horizontal directions (because the forces in those directions are much smaller). Some rockets take this to such extremes that you can't transport them horizontally unless their tanks are pressurized.

A second source of stress is aerodynamic drag. The point where this is highest is called max-Q. This is a function of altitude (higher altitude=thinner air and less drag) versus speed (more speed = more drag). In a vertical launch, max-Q is at high altitude and often near the end of the first stage burn.

Now let's look at a horizontal launch. The acceleration force now has two components: you've added a lateral force throughout the bend in your ramp. You need to make the rocket stronger (=heavier) to compensate for this. If you want to decrease acceleration, you need to make the ramp longer. Pretty soon you're building a structure that's capable of supporting several hundred tons and has to be 10 km long and 1 km high. This is not cheap by any means.

Because you do some of the acceleration while horizontal, the rocket will be going faster at low altitudes. This means more drag, and a higher max-Q. Again, you need to make the rocket stronger (=heavier) to compensate for this.

As for safety: in a vertical launch, you can ignite the engines and make sure they're working well before the rocket leaves the ground. In a ramp launch, you have to start the engines while the rocket is almost at the end of the ramp. Any delays or engine problems, and your rocket will fall off the end of the ramp and be destroyed (or alternatively, you'll have to make the ramp twice as long to provide a safe runout area).

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  • $\begingroup$ "Some rockets take this to such extremes that you can't transport them horizontally unless their tanks are pressurized" - that's interesting, i didn't know that. I believe i'll ask a question about that. $\endgroup$ – kim holder Aug 16 '15 at 20:36
  • $\begingroup$ I'm sorry, but most of your statements strangely seem incorrect for me. I will try to expand my question with more details, also note I am not avionics engineer. Consider the third Newton's law and the colossial kinetical energy I must give on first seconds, I must have thrust power order of magnitude more than in my proposal. You treat mechanics too globally, thermal destruction and local mechanical shocks play role here. Indeed in any case the vehicle must have strength similar to a jet fighter. The more I think of it, the more it seems just a bad idea to perform a vertical start. $\endgroup$ – Mikhail V Aug 16 '15 at 20:45
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Any space launch system should be capable of taking the payload (satellite) to a certain altitude. The amount of work done in this lifting is the same whatever may be the method/trajectory used to do this lifting (because gravitational potential energy depends only on height).

So, the best launch design has to reduce the amount of time spent in the atmosphere to reduce drag and heating. Even if a horizontal launch system is used, the escape velocity is the same and the drag would be the same. However, the amount of time spent in the atmosphere and the required fuel goes up significantly.

As for the forces acting on the rocket, the aerodynamic forces will be the same and the only force that can be reduced thrust so that the acceleration is very small.

However, this increases the time spent in atmosphere and associated drag. It is important to note that all horizontal launch systems which have been developed use air breathing engines and are aimed at reducing the requirement of oxidizer to be carried.

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    $\begingroup$ Gravity drag should be mentioned too. The longer it takes to get up to orbital speed, the more propellant is used just to overcome gravity. $\endgroup$ – kim holder Aug 15 '15 at 15:22
  • $\begingroup$ Sorry, I don't understand how the time spent in atmosphere will be bigger in my scheme? (by the way, air resistance is significant only below ca 50 km). In about 10 second the vehicle can be put in almost vertical position. And the speed by leaving the ramp is say ca 500 km/h (vs 0 km/h by a vertical lift off). Probably I am blind, but still I see much more benefits in my scheme, even without doing any calculations. Now imagine how enorm must be be the engine force by vertical lift off and how easily it can all just blow up. This should also be taken in account. $\endgroup$ – Mikhail V Aug 16 '15 at 2:17
  • $\begingroup$ @MikhailV How will the craft interface with the ramp- wheels? What kind of undercarriage will you build that can support a space booster horizontally at speeds up to Mach 3 or so? $\endgroup$ – Organic Marble Aug 16 '15 at 3:13
  • $\begingroup$ @OrganicMarble See update $\endgroup$ – Mikhail V Aug 16 '15 at 4:55
  • $\begingroup$ @aeroalias From what I remember reading a long time ago on SSTOs and hypersonic concepts, it's not just oxidizer to be reduced with air-breathing engines. The total mass of thrust-generating exhaust is composed of fuel and everything in the ingested air (mostly nitrogen). It may represent some loss of efficiency to have so much inert mass going through the engine, but you end up with the majority of the exiting mass coming from the inlet air, none of which you had to carry. For lower velocities at least, that ought to net to an efficiency gain. $\endgroup$ – Anthony X Aug 17 '15 at 3:24

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