Dr Mitra is one of the acknowledged authorities on ionosphere and on some aspects of space research. His pioneering work on the use of cosmic radio noise for upper atmosphere studies resulted in a whole series of scientific discoveries in ionosphere, solar physics and cosmic rays. He has carried out comprehensive studies on the ionospheric effects of solar flares and has established one of the most extensive radio flare systems at the National Physical Laboratory. He developed an atmospheric model from observations of satellite drag and initiated new D region rocket experiments. Dr Mitra’s work on ion and neutral chemistry in the upper atmosphere, especially on the minor constituent nitric oxide, provided the basis for much of our present knowledge about the lower ionosphere. He has contributed substantially to the establishment and operation of the International Spacewarn System and the International Ursi-gramme and World Day Service.