Atmospheric drag effects on modelled LEO satellites during the July 2000 Bastille Day event in contrast to an interval of geomagnetically quiet conditions

Abstract. In this work we simulated the effects of atmospheric drag on two model SmallSats in Low Earth Orbit (LEO) with different ballistic coefficients during 1-month intervals of solar-geomagnetic quiet and perturbed conditions. The goal of this effort was to quantify how solar-geomagnetic activity influences atmospheric drag and perturbs satellite orbits. Atmospheric drag compromises satellite operations due to increased ephemeris errors, attitude positional uncertainties and premature satellite re-entry. During a 1-month interval of generally quiescent solar-geomagnetic activity (July 2006) the decay in altitude (h) was a modest 0.53 km (0.66 km) for the satellite with the smaller (larger) ballistic coefficient of 2.2 × 10⁻³ m²/kg (3.03 × 10⁻³ m²/kg). The associated Orbital Decay Rates (ODRs) during this quiet interval ranged from 13 m/day to 23 m/day (from 16 m/day to 29 m/day). For the disturbed interval of July 2000 the significantly increased altitude loss and range of ODRs were 2.77 km (3.09 km) and 65 m/day to 120 m/day (78 m/day to 142 m/day), respectively. Within the two periods more detailed analyses over 12-day intervals of extremely quiet and disturbed conditions revealed respective orbital decays of 0.16 km (0.20 km) and 1.14 km (1.27 km) for the satellite with the smaller (larger) ballistic coefficient. In essence, the model results show that there was a 6–7 fold increase in the deleterious impacts of satellite drag between the quiet and disturbed periods. We also estimated the enhanced atmospheric drag effect on the satellites' parameters caused by the July 2000 Bastille Day event (in contrast to the interval of geomagnetically quiet conditions). The additional percentage increase due to the Bastille Day event to the monthly mean values of h and ODR are 34.69 % and 50.13 % for Sat-A, and 36.45 % and 68.95 % for Sat-B. These simulations confirmed; (i) the dependence of atmospheric drag force on a satellite's ballistic coefficient, and (ii) that increased solar-geomagnetic activity substantially raises the degrading effect of satellite drag. In addition, the results indicate that the impact of short-duration geomagnetic transients can have a further deleterious effect on normal satellite operations. While none of these findings were particularly surprising or profound we suggest that a model of satellite drag when combined with a high-fidelity atmospheric specification, as was done here, can lead to improved satellite ephemeris estimates.