An old way of looking at something new in space travel?

Question

I just watched the new Superman movie and it made me think. We often launch rockets and other aircraft from the belly of airplanes, why not spacecrafts? In the 1960's we originally developed the SR-71 Blackbird to be a spacecraft not an airplane. Then when the race to the moon developed we scrapped the idea of space travel and entered the space race. Now we have returned to the idea of traveling in space and returned to the concept of the SR-71 with the sapce shuttle. I understand why we can not launch it from a horizontal position on the ground, but why can't we launch it from an aircraft at altitude with much less payload to lift-off the ground and to worry about. The only exception would be the great loss if something malfunctions and it falls to the ground? Anyone able to offer the solution?

Please all, keep in mind the solid fuel booster rockets and giant fuel cell would not be necessary if launched from altitude.

Answer 1

It is done sometimes, using an aircraft-launched booster called Pegasus. The advantage is that the launch is fairly cheap. The disadvantage is that there is pretty severe restrictions on payload weight.

Answer 2

The SR-71 was always designed to be a spy plane and not a space craft. There's no airplane capable of lifting something the weight of the shuttle with its appropriate booster off the ground. The shuttle itself is not capable of reaching orbit from anywhere inside the earth's atmosphere on its own without carrying a huge tank of propellent.