No. As the stack consumes LO2, LH2 and solid fuel everything is getting lighter at different rates. On top of that, the SSMEs only throttle down as we pass max Q (maximum dynamic pressure, to aleviate loading primarily on the Orbiter wings and ET protuberances, NOT Tracy protuberances). True, they throttle down again late in flight, just pre-MECO, to maintain 3 Gs longitudinal acceleration on the vehicle (cause by that time we've burned so much propellant that we are getting so light that the SSMEs can push the vehicle over 3 Gs). For the rest of the time they are at 104% rated thrust (unless an engine-out abort were to occur, then under certain circumstances they are cleared to 109%).

Not only that, but your description ignores a plethora of other forces acting on the entire stack such as aero loads, vibro-acoustics (they are tremendous), local shock impingement, etc., etc., etc.

Metal shield? Forget it! Weight alone would make it a non-starter. And then there are the other 50 reasons I can think of why it won't work. remember: at this point we have no choice but to live within the system's limitations that were designed into the vehicle system in the '70s.

Believe me, nothing about the National Space Transportation System is anywhere near simple in any way! Just part of the price to accelerate little pink & brown bodies safely to 17,500 mph.