  Relative attitude formation control systems are developed for multiple
spacecraft, based on the line-of-sight measurements between spacecraft in
formation. The proposed control systems are unique in the sense that they do
not require constructing the full attitudes of spacecraft and comparing them to
obtain the relative attitudes indirectly. Instead, the control inputs are
directly expressed in terms of line-of-sight measurements to control relative
attitude formation precisely and efficiently. It is shown that the relative
attitudes almost globally asymptotically track their desired relative
attitudes. The desirable properties are illustrated by a numerical example.
