  We present an efficient transcription method for highly oscillatory optimal
control problems. For these problems, the optimal state trajectory consists of
fast oscillations that change slowly over the time horizon. Out of a large
number of oscillations, we only simulate a subset to approximate the slow
change by constructing a semi-explicit differential-algebraic equation that can
be integrated with integration steps much larger than one period. For the
solution of optimal control problems with direct methods, we provide a way to
parametrize and regularize the controls. Finally, we utilize the method to find
a fuel-optimal orbit transfer of a low-thrust satellite. Using the novel
method, we reduce the size of the resulting nonlinear program by more than one
order of magnitude.
