Getting To Low Earth Orbit and Back

There are two pictures and a lot of notations in the figure.  Near center is a plot of altitude versus velocity,  similar in format to a standard flight envelope presentation,  except that the values extend to low circular Earth orbit.  Top right is a diagram of Earth with low circular orbit at 300 km shown,  plus a transfer ellipse that grazes the surface at its perigee,  and grazes low circular at its apogee. 

Typical non-lifting vertical launch pretty much reaches the vicinity of the transfer orbit at ~90 km altitudes at low drag loss,  and accelerates onto it exo-atmospherically at no drag, by about 200 km altitude,  give or take.  From there,  the vehicle loses a little speed coasting to apogee at circular orbit altitude,  where a small burn speeds it back up to circularize.  

Typical entries start with a small deorbit burn onto the transfer orbit,  where significant entry forces begin at the “entry interface” altitude of 140 km.  From there,  peak heating precedes the peak deceleration,  which finally ends at the end-of-hypersonics point near Mach 3 speed and 35-40 km altitude,  as indicated on the altitude-speed plot.  This was figured for an Apollo capsule.  Be aware that the “circularize” and “deorbit” points need not be co-located around the circular orbit. 

Also shown is a winged lifting spaceplane ascent trajectory to orbit.  This trajectory is limited above by too little lift with a practical wing area size,  and by heating too intense to endure below.  It is essentially entry flown in reverse!  The point reached on this trajectory by the fastest of the X-15 rocket plane flights is also shown on the altitude-speed plot.   If your vehicle takes off horizontally,  it will inherently have to use this entry-in-reverse ascent trajectory,  incurring devastatingly-huge drag losses.

Vertically-launched non-lifting vehicles endure only very modest ascent heating,  with windblast forces being just as important for payload protection.  They must only endure high heating during entry,  where orbital-class speeds still exist at much lower altitudes.  In contrast,  the winged lifting ascent vehicle must endure entry-class heating (and drag) on that ascent,  and on the descent.   Its heat shielding must endure two,  not just one,  entry-level heating episode per flight,  which means it will “wear out” twice as fast!

This is why I strongly recommend that winged spaceplane designs be vertically launched on non-lifting trajectories!