Radar observations of the second Russian earth satellite (Sputnik II 1957 β )

Abstract

A description is given of the radar observations of the second Russian earth satellite (Sputnik II, 1957 β ) using the 80 m steerable radio telescope at Jodrell Bank on frequencies of 36 and 100 Mc/s. An investigation of the fading characteristics of the echoes suggests that the observed fading arises from (i) Faraday rotation, (ii) ionospheric scintillation, (iii) rotation of the satellite. Evidence is produced which suggests that (i) was not the principal cause of the fading under the conditions of these experiments, and that (ii) the scintillation effects arise in a diffracting region at a height not greater than 220 km, which is contrary to the results obtained in the study of the scintillation of radio stars. The effect (iii) seems to have been responsible for most of the observed fading and it would appear that the satellite was rotating about an axis which was nearly perpendicular to its major axis. The effective scattering area of the satellite at 100 Mc/s was of the order of 15 m 2 but at 36 Mc/s it varied between 10 and 500 m 2 . From this it is concluded that the satellite was a long object having a re-radiation polar diagram with one major and many minor lobes. No evidence was ob­tained to indicate that the satellite produced any ionization detectable at these frequencies, although it was observed as late as the third orbit before final bum up. Successful contacts were made on only about one-quarter of the transits observed. It has been possible to establish in retrospect whether the satellite passed through the main beam of the aerial. Such an analysis shows that on many occasions where no echoes were obtained the telescope was correctly positioned, and the failure to obtain echoes on these occasions is attributed to deep fading introduced by the rotation of the satellite and by Faraday rotation of the plane of the radio waves.