References ^eirovitch, L., Computational Methods in Structural Dynamics, Sijthoff & Noordhoff, the Netherlands, 1980. Hughes, P.C. and Skelton, R.E., Controllability and Observability of Linear Matrix-Second-Order Systems, ASME Journal of Applied Mechanics, Vol. 47, June 1980, pp. 415-420. Laub, A.J. and Arnold, W.F., ''Controllability and Observability Criteria for Multivariable Linear Second-Order Models, IEEE Transactions on Automatic Control, Vol. AC-29, Feb. 1984, pp. 163-165. / Iriman, D.J., Dynamics of Asymmetric Nohconservative Systems, ASME Journal of Applied Mechanics, Vol. 50, March 1983, pp. 199-203. . Inman, D.J. and Andry, A.M. Jr., Some Results on the Nature of Eigenvalues of.Discrete Damped Linear Systems, ASME Journal of Applied Mechanics, Vol. 47, Dec. 1980, pp. 927-930. Shrivastava, S.K. and Pradeep, S., Stability of Multidimensional Linear Time-Varying Systems, Journal of Guidance, Control and Dynamics, Vol. 8, Sept.-Oct. 1985, pp. 579-583. Andersoh, B.DiO.-and Moore, J.B., Optimal Filtering, PferiticeHall, Ehglewood Cliffs, NJ, 1979. Sage, A.P. and White, C.C. Ill, Optimum Systems Control, 2nd ed., Prentice-Hall, Englewood Cliffs, NJ, 1S>77. 9 Arnold, W.F, and Laub, A.J., Generalized Eigenproblem Algorithms and Software for Algebraic Riccati Equations, Proceedings of the IEEE, Vol. 72, Dec. 1984, pp. 1746-1754. are given too. First, the procedure evolves by assuming unbiased measurements, i.e., the clocks are assumed to be perfectly synchronized. Later, the bias is included with just a few modifications. , Procedure Envelopment Let n >3 be the number of tracking stations (or GPS satellites). Within a known inertial reference frame, the position and velocity vectors of the GPS stations and a target satellite are given, respectively, by Rif Vif i =I,...,«; r and v. Each station measures range yif and range-rate z/ is given by