Densities obtained from drag on the Explorer 17 satellite

Abstract

Orbit elements for the active experiment lifetime of the satellite Explorer 17 have been obtained and utilized in the determination of atmospheric density in the region of the perigee of the satellite. The differential corrections, using minitrack interferometer data, covering data arcs of approximately seven days, were carried out by personnel of the Data Systems Division of the Goddard Space Flight Center. Table 1 contains the orbital data. Figure 1 shows density versus a converted local solar time. The angle between vectors from the center of the earth to perigee and to the sun (zenith angle) has been converted to an equivalent local solar time for comparison with the Harris and Priester [1962] model atmosphere. The density determinations were made by utilizing the formulas of King-HeIe [1960]. These formulas give the density one-half scale height above the perigee height and require an assumed scale height for calculation. The scale height assumed was 30 km, and hence the densities given are to be associated with an altitude of 270 km. An over-all confidence bound of ±10 per cent could be applied to each data point. The data are plotted as obtained and also with an adjustment for the 27-day variation of density with solar 10.7-cm flux. The adjustment is made because the Harris-Priester model does not include this short-period effect. The data are adjusted to a flux number of 84, the mean value over the three-month period. A first power law was used and the resultant data can be compared to the Harris-Preister model with an S number of 100. The solid line on the figure is the Harris-Preister model curve for S = 100.