Upper-atmosphere features revealed by the orbit of 1980-43A

The satellite NOAA-B (1980-43A) was launched in May 1980 into an orbit with perigee height near 260 km and apogee height 1440 km, at an inclination of 92.2 deg. The lifetime was 11 months. The orbit has been determined at 40 epochs between October 1980 and May 1981 from about 3000 radar and optical observations. The average orbital accuracy, radial and cross-track, was about 100 m, with rather better accuracy in the final 14 days. The variation of orbital inclination has been analyzed to determine two good values of atmospheric rotation rate, namely 1.10 + or - 0.10 rev/day at 300 km (average local time) and 1.15 + or - 0.06 rev/day at 225 km (evening). The effect of atmospheric rotation on the precession of the orbital plane of an actual satellite has never previously been detected; it is clearly apparent for 1980-43A in its last days, and conforms to the expected theoretical change. The variation of perigee height has been analyzed to determine ten values of atmospheric density scale height, for heights of 280-370 km. These values, accurate to about 3%, exceed by 15% the values indicated by the COSPAR International Reference Atmosphere. Solar activity was higher in the years 1980-81 than at any time since early 1958, and it appears that the CIRA model underestimates the density and density scale height at high levels of solar activity.