Adding a Second Average Acceleration

Because of the assumptions you made with constant acceleration, 1 billion psf is most likely nowhere near the Max Q that a rocket experiences; the actual Max Q is likely far lower. On Earth, assuming you are not doing anything crazy like drag racing or flying a fighter jet, you are always experiencing 1 g of acceleration as the Earth rotates. 1 g = 32.2 $\frac{ft}{s^2}$ ...