This version of the OrbFit package contains a modified orbit9 integrator. The integrator has been modified to integrate the spin axis dynamics of small asteroids, due to the YORP effect. At the same time, the Yarkovsky effect is modified according to the dynamics of the spin axis.

This is a modified version of the N-body code mercury, by J. E. Chambers, that includes the Yarkovsky and YORP effects for the dynamics of small solar system objects.