Prof. M. R. Ananthasayanam has contributed extensively to the field of Aerospace Engineering, in a career spanning more than 50 years. His research activities and contributions include about 200 publications spread over reports, conferences, and journals and have guided many M.Sc. and Ph.D. theses. He was involved in consultancy and design reviews for ISRO, CSIR, and DRDO. He has taken part in the committees for selecting faculty positions, thesis evaluations of various IITs. He has been a reviewer for Current Science, Acta Astronautica, Journal of Spacecraft and Rockets and many more. After his B. E. in Electrical Engineering from Madras University in 1961, he joined the Department of Aerospace Engineering at IISc, Bangalore where he obtained his M.E. and Ph.D. He has been with the IISc until 2004 when he retired as Professor. His Ph.D. thesis was on flight safety with Prof. Narasimha as an advisor is a spin-off from their work for Prof. Dhawan’s AVRO Evaluation Committee. Subsequently, they proposed the Indian Standard Tropical Atmosphere and the International Tropical Reference Atmosphere from sea level up to 2000 km. He has been a Member of the Task Team to revise the COSPAR 1972 document. He has further contributed to the modeling of space debris, and the ionosphere. Apart from research, his teaching, development, and consultancy activities also led invariably to research publications. He contributed extensively to the application of Kalman filtering for state and parameter estimation, in diverse areas such as aerospace flight test data analysis, tracking of aircraft and missiles, space debris, ionosphere, GPS/INS integration, attitude estimation and docking of spacecraft, and tomography. He continued his research pursuits after retirement. His vast research experience culminated in the recent publications [SADHANA, 2016] with his associates, provided the Reference Recursive Recipe for the notorious problem of tuning the Kalman filter statistics existing ever since 1960 Kalman proposed the filter. With the above, it is envisioned that a proper application of the filter will never be the same again.