A satellite attitude control system, as shown below, has a plant with transfer function: $ G(s) = \frac{1}{s^2}, $ cascaded with a compensator: $ C(s) = \frac{K(s + \alpha)}{s + 4}, $ where $ K $ and $ \alpha $ are positive real constants. In order for the closed-loop system to have poles at $ -1 \pm j\sqrt{3} $, the value of $ \alpha $ must be $\_\_\_\_\_$.