1. P. Kustaanheimo andE. Stiefel,Perturbation Theory of Kepler Motion Based on Spinor Regularisation. J. reine und angew. Math.218, 204 (1965).
2. H. Sperling,Computation of Keplerian Conic Sections, ARS J., May 1961, p. 660–661.
3. E. Stiefel,Many-body Problem and Interplanetary Flight, Published in: Dynamics of Rockets and Satellites, G. V. Groves, editor, North-Holland Publ. Co.