Radio astronomical measurements from earth satellites
It may be thought that radio astronomical measurements made on the earth are not subject to the influence of the atmosphere and ionosphere to any great extent and that consequently there is no demand for measurements from earth satellites or other space stations. Unfortunately this is not the case and certain measurements from outside the earth’s atmosphere are very much desired. The radio spectrum so far explored extends from a low frequency limit in the 10 to 20 Mc/s band, to an upper limit in the millimetre waveband. In the millimetre band the limitation to the extension of the spectrum arises from absorption bands in the atmosphere, whereas at low frequencies the extension is limited by absorption and disturbances in the ionosphere. In this paper some examples will be given of the need to overcome these obstacles.