DETECTING THE DYNAMICAL STATE OF THE ATMOSPHERE FROM THE ORBITAL DECAY OF THE ODERACS SPHERES

The orbital decay curve of a satellite having constant cross-sectional area and in circular orbit can furnish valuable information regarding the dynamical state of the atmosphere. It is shown that a rectilinear decay curve having constant downward slope (zero curvature) should in dicate that the atmosphere was undergoing compression during that peri od. A decay curve having concavity upwards (positive curvature) will s trongly indicate that the atmosphere was in a contracting phase. A dec ay curve with downward concavity (negative curvature) may indicate an expanding, a stable or a contracting atmosphere. This theory, when app lied to the orbital decay of the Orbital Debris Radar Calibration Sphe res (ODERACS) satellites, indicates that, during the period from Day 9 0 through Day 240 in the year 1994, the atmosphere was very definitely in a compression mode. During this period, ODERACS Sphere 1 faced nea rly constant densities while Sphere 6 actually encountered progressive ly smaller air densities as they descended. The atmospheric scale heig ht as calculated from the orbital data of Spheres 1 and 6 diminished s teadily during the same period. It is shown that Spheres 1 and 6 desce nded faster and slower, respectively, than the level of constant air d ensity equal to 5 x 10(-12) kg/m(3). During a brief period from Day 24 0 through Day 290, the atmosphere reversed to a strongly expanding mod e. Thereafter, the atmosphere reverted back to a compression mode from Day 290 through Day 390, 1994-1995. The measured F-10.7 solar flux at Penticton, British Columbia, generally supports the findings of this study. Copyright (C) 1996 Elsevier Science Ltd.