Chapter 3 - Section 3.5 - Projectile Motion - Example - Page 45: 3.6

It can be launched at $90^{\circ}-.66^{\circ}=89.33^{\circ}$.

We call $\theta$ the amount below 90 degrees that the rocket can fire. Thus, we find: $x = \frac{v_0^2}{g}sin(2\theta)$ $50,000 = \frac{4600^2}{9.81}sin(2\theta)$ $.0231 = sin(2\theta)$ $2\theta = sin^{-1}(.0231)$ $\theta =.66^{\circ}$