This paper presents an extension to the classical cones intersection technique, which was, and is, exhaustively used to estimate the spin axis direction of spin stabilized spacecraft. The resulting optimal cones intersection technique is derived from a demonstrated co-planarity condition and does not present ambiguities or singularities. The proposed method allows an optimal estimation of any on-board direction in a closed-form by fully complying with Wahba's optimality criterion of spacecraft attitude. Numerical tests show that the optimal cones intersection technique is faster than ESOQ-2, the presently fastest optimal attitude estimator, for two vector observation case. 2006 Elsevier Ltd. All rights reserved.