When orbiters were transported atop one of the 747s, they were attached by the same three attachment points used to mount them to the external tank.
Here is an orbiter mated to the external tank. The green metal carries the attachment point (hidden):
The yellow connections carry electronics and the crygenic hydrogen and oxygen for the main engines at the rear of the orbiter.
Here is an orbiter about to be mated to the transport, the aft attachment points of which are visible:
On both pictures, note the pair of doors folded flat against the orbiter’s belly. These are aerodynamic and heat shield doors, and closed automatically after ET jettison so the orbiter could reenter the atmosphere safely.
The only difference between mounting for transport and mounting for launch was that no pryotechnics were installed when mating to the aircraft. The orbiter was transported unmanned and could not be jettisoned and landed independently of the carrier aircraft.
Here is the Enterprise (test vehicle) showing at three attachment points and the mate/demate device (overhead). Note: Enterprise is not a real spacecraft and has no thermal control tiles and no doors.
Mating the two huge craft was obviously a rather painstaking process. Someone stenciled this helpful note on one of the carrier aircraft attachment point pylons:
Author – C Stuart Hardwick
