The discussion about the manned spacecraft program was initiated at NASA in 1959. Only one year later, Dr. Kalman and Dr. Schmidt linked the linear Kalman filter and the perturbation theory in order to obtain the Kalman-Schmidt filter, currently known as the extended Kalman filter. This approach would be implemented in 1961 using an IBM 704 computer (running at approximately 4000 operations per second) for simulation purposes, and subsequently, in July 1969, for making the descent of the Apollo 11 lunar module to the Moon possible
