In this paper, we analytically and numerically investigate chaos in attitude dynamics of a flexible satellite composed of a rigid body and two identical rigid panels attached to the main body with springs. Flexibility, viewed as a perturbation, can cause chaos in the satellite. To show this, first, we use a novel approach to define this perturbation. Then, we employ canonical transformation to transform the Hamiltonian of the system from five to three degrees of freedom. Next, we approximate the system by a second-order differential equation with a time quasiperiodic perturbation. Finally, we apply Melnikov–Wiggins’ method near the heteroclinic orbits to prove the existence of chaos. Using the maximum value of Melnikov–Wiggins function and the small perturbation parameter, we find a tool to predict the size of the chaotic layers. Results show that this approach is useful even if the panels are not small. In addition, it is observed that though the satellite attitude dynamics is chaotic, in many cases the width of chaotic layers is very small and therefore negligible. © 2018, Springer Science+Business Media B.V., part of Springer Nature.