Sorry Moowalker, one more question:
the roll maneouvre is done with the engines or with the ailerons?
It is done with the engines. After passing the launch tower, the speed of the Shuttle is still too slow and so the aerodyamic pressure on the aero surfaces as well.
By the way, there are three reasons why the Shuttle launches heads down:
1. For better communication between the Shuttle and the LCC - Launch Control Center (later into the ascent it turns heads up for better communication between the Shuttle and the TDRSS - Tracking Data Relay Satellite System)
2. The center of gravity of the entire stack is better controllable if the engines are located beneath the External Tank rather than on top (the thrust vector of the main engines is aimed at the center of gravity of the entire stack).
3. Heads down enables a slight angle of attack which puts the Shuttle in the supersonic shadow of the (big) External Tank. The structure of the Shuttle is quite sensitive. It's only .5 g more (3g all in all) than the load factor limit of a heavy passenger jet with gears and flaps retracted (2.5g). That's also why people and journalists are always wrong whenever they say and write that Challenger "exploded". Challenger broke apart as a result of aerodynamic stress due to the changed angle of attack after the External Tank broke apart (the propellant deflagrated quite fast; it was not an explosion). The accident happened 73 seconds after launch at a very high, supersonic speed. Any rapid change of the attitude can cause fatal stress on the vehicle, which we've seen on Challenger. Even fighter jets already broke apart during some maneuvers while flying supersonic. Those speeds have to be handled quite carefully.
