A Determination of the Atmospheric Oblateness from the Motion of Two Low Satellites.

Abstract

view Abstract Citations References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A Determination of the Atmospheric Oblateness from the Motion of Two Low Satellites. Nigam, R. C. Abstract An appropriate theory has been developed to derive the effect of the atmospheric oblateness on the acceleration n, defined as the rate of change of mean motion n. By mean motion is meant the number of revolutions made by the satellite in one day from one perigee to another. This effect is a periodic one, as one would expect, with half the period of the argument of perigee. For small values of eccentricity (e <0.2), it is expressed by [n2a2(1;;{{;) sin2i1 3 15H 67H 1 2e -e2- - O(e3) cos2 , 2 8ae 8a where k (r) = 2' (CDA /m) p (r), = ac/H, H is the scale height, f the atmospheric oblateness, q the geocentric perigee distance, etc. In order to get reliable values for the atmospheric oblateness, one needs a few low satellites in polar orbit having a lifetime in which the perigee has made several revolutions of the earth. Further, if the satellites are not spherical, reliable information about the mode of tumbling should also be available from some independent source. As none of the above-mentioned characteristics could be met in the satellites available for this investigation, we chose satellites 1958 and 1958 , both of which had their perigee altitude less than 200 km, for a preliminary check of the derived theoretical expression for the effect of atmospheric oblateness on the accelerations, and to derive the value for the atmospheric oblateness. The atmospheric oblateness at the altitudes of 176 and 186 km, which are the mean altitudes of the perigee points of the satellites 1958 and 1958 , respectively, are obtained as 1/284 and 1/238, respectively. The value of the atmospheric oblateness computed theoretically assuming the solid-body rotation of the atmosphere for an altitude of 176 km is 1/291. The quantitative results on the atmospheric oblateness are, therefore, far from being exact. These, on taking into consideration the uncertainty inherent in the two determinations, are, however, in conformity with the theoretical atmospheric models near 200 km, as given by T. E. Sterne (Astron. J. 63, 81,1958) and F. S. Johnson (J. Geophys. Research 65, 2227,1960). The results therefore appear to suggest that the atmospheric oblateness increases with altitude. An exact determination of the atmospheric oblateness must however await more extensive data. Publication: The Astronomical Journal Pub Date: September 1961 DOI: 10.1086/108423 Bibcode: 1961AJ.....66..292N full text sources ADS |