  For tracking and motion capture (MoCap) of animals in their natural habitat,
a formation of safe and silent aerial platforms, such as airships with on-board
cameras, is well suited. In our prior work we derived formation properties for
optimal MoCap, which include maintaining constant angular separation between
observers w.r.t. the subject, threshold distance to it and keeping it centered
in the camera view. Unlike multi-rotors, airships have non-holonomic constrains
and are affected by ambient wind. Their orientation and flight direction are
also tightly coupled. Therefore a control scheme for multicopters that assumes
independence of motion direction and orientation is not applicable. In this
paper, we address this problem by first exploiting a periodic relationship
between the airspeed of an airship and its distance to the subject. We use it
to derive analytical and numeric solutions that satisfy the formation
properties for optimal MoCap. Based on this, we develop an MPC-based formation
controller. We perform theoretical analysis of our solution, boundary
conditions of its applicability, extensive simulation experiments and a real
world demonstration of our control method with an unmanned airship. Open source
code https://tinyurl.com/AsMPCCode and a video of our method is provided at
https://tinyurl.com/AsMPCVid .
