Figure 2.4-13. Periodic Motion Figure 2.4-14 illustrates the necessary initial conditions to eliminate the secular term for several values of the inertia ratio. Figure 2.4-15 illustrates the resulting motion of the vehicle. Note that in the worst case, the maximum deviation of the vehicle from its desired orientation is 18.8°. What the analysis has shown is that a form of ''neutral" stability has been achieved even in the presence of very large gravity gradient torques. Neutral stability in this case means that small disturbances to the vehicle will cause it to rotate, in the average sense, as though it has no restoring forces.