Intermediate-axis separatrix
= Intermediate-axis separatrix
On the invariant level $L^2=2EI_2$, the torque-free rigid-body orbit is a separatrix joining the two intermediate-axis rotations. With
$$
\mu=\sqrt{\frac{2E}{I_2}},
\qquad
\lambda=\mu\sqrt{\frac{(I_3-I_2)(I_2-I_1)}{I_1I_3}},
$$
one orientation has $\omega_2(t)=\mu\tanh(\lambda(t-t_0))$; the other components are constant multiples of $\operatorname{sech}(\lambda(t-t_0))$.