Question relates to this topic http://space.stackexchange.com/questions/1184/horizontal-space-launch

So the question is, why we cannot use the following method instead of vertical launch:  

[![enter image description here][1]][1]


Main problems, as discussed in linked topic:  

1. The rocket will stay in atmosphere a bit longer (air resitance)  
2. How to maintain the trajectory after lifting off.

Main benefits:  

1. More safety, since we don't have such mechanical stress on start, which is essential for the rocket itself and its cargo.  
2. More possibilities to make reusable components.

Argument about improving heat resistance and minimising fuel consumtion do sound a bit weak for me, since if we could find out a way to maintain the trajectory after start, it could be put in vertical position after lift off. And fuel consumption - is it really more important than safety? I doubt it.


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(Update)

**Sketch of the principle:**  


  
[![enter image description here][2]][2]


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After split:  
[![enter image description here][3]][3]


  [1]: https://i.sstatic.net/7KXWq.png
  [2]: https://i.sstatic.net/ZoMGy.png
  [3]: https://i.sstatic.net/5GTfA.png