Interest thoughts, but forgot one very practical calculation, unfortunately not easy to calculate. I say about shock-wave, which is known from practice on Earth

Interest thoughts, but forgot one very practical calculation, unfortunately not easy to calculate. I say about shock-wave, which is known from practice on Earth, and for Earth limit rocket starting mass about 10k metric tonnes at sea level. What it mean, shockwave from supersonic engine exhaust creates literally powerful pressure on construction, so on mentioned scale, nothing will withstand it long enough. If it is possible to create much stronger materials, as I know at the moment, is unknown and we cannot forecast. Sea level is important, because, at the moment I only remember TWO space rockets, which started from much different position, and high altitude (air) launch have very different atmosphere properties, which could be solution to shockwave problem (but have other limitations). https://en.wikipedia.org/wiki/Northrop_Grumman_Pegasus https://en.wikipedia.org/wiki/Northrop_Grumman_Pegasus https://en.wikipedia.org/wiki/LauncherOne https://en.wikipedia.org/wiki/LauncherOne