Summary: The Gaia attitude may be described by four continuous functions of time q₁(t), q₂(t), q₃(t), q₄(t), which form a quaternion of approximately unit length. The quaternion formalism is elegant and computationally efficient, reducing the use of trigonometric functions to a minimum. As examples of the use of quaternions, I discuss the nominal scannig law, the inertial rotation of the instrument, and the determination of the instantaneous attitude from direction measurements.

Bibtex entry for this abstract:

@UNPUBLISHED{LL:SAG-LL-030,
editor = {L.~Lindegren},
title={{A}ttitude parameterization for {G}aia},
institution={},
year={2000},
month={July},
url={http://www.rssd.esa.int/doc_fetch.php?id=358607},
note={SAG-LL-030},
type={Technical note}
}