The Possibility of Observing Features of Galactic Radio Emission from a Satellite-borne Radio Telescope

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Abstract
It has already been proposed to extend measurements of the spectrum of radio emission from the galaxy to frequencies of about 1 Mc/s by means of a satellite-borne receiver. If the satellite is in the upper ionosphere, where the refractive index is increasing with height, a focusing effect will occur which may allow individual features of emission to be observed. It is shown that a beamwidth of the order of 20° may be achieved under favourable circumstances; the most important limitation is the frequency bandwidth necessary in a sufficiently sensitive receiver, which inevitably means that dispersion in the refractive index effectively blurs out any narrower beam or any interference effects inside the beam. The experimental conditions needed for the realization of this degree of focusing in a satellite or a rocket flight are discussed. It appears that the frequency of a satellite-borne receiver should sweep over a range of about 3 to 5 Mc/s, with a bandwidth of 10 kc/s. The satellite orbit should be nearly circular, at a height of about 400–500 km.

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