Defence Secretary Sanjay Mitra on Monday got an additional charge for the post of the Defence Research and Development Organisation (DRDO) Chairman after eminent scientist S Christopher retired on the same day. “The competent authority has approved assignment of additional charge of the post of Secretary, Department of Defence Research and Development (DoDRD) and Chairman, DRDO to Mitra for a period of three months with effect from tomorrow, the Personnel Ministry said in an order issued. Last year in May, Mr Christopher was given a one-year extension which ended on Monday. In May, 2015, he was appointed as Director General of the DRDO for a two-year term. Christopher was then working as Distinguished Scientist and Programme Director (airborne early warning and control system) and Director, Centre for Air-Borne Systems in the DRDO.