Abstract
Abstract. In this work, we simulated the atmospheric drag effect on two model SmallSats (small satellites) 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, with particular emphasis on the Bastille Day event. 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−1 (3.03×10-3 m2 kg−1). The associated orbital decay rates (ODRs) during this quiet interval ranged from 13 to 23 m per day (from 16 to 29 m per 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 to 120 m per day (78 to 142 m per day), respectively. Within the two periods, more detailed analyses over 12 d 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- to 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 (such as the Bastille Day storm) can have a further deleterious effect on normal satellite operations. Thus, this work increases the visibility and contributes to the scientific knowledge surrounding the Bastille Day event and also motivates the introduction of new indices used to describe and estimate the atmospheric drag effect when comparing regimes of varying solar–geomagnetic activity. 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.
Highlights
B, under different solar–geomagnetic conditions (Nwankwo et al, 2020a).Atmospheric drag describes the force exerted on an object moving through the atmospheric medium
The environmentally quiet interval of July 2006 is presented as the baseline for atmospheric drag, whereas the disturbed interval of July 2000 illustrates the deleterious impact that solar–geomagnetic activity can have on satellite orbits
While no significant geomagnetic storms occurred during the entire month, we note that the minor increases in the daily Ap for 5, 28 and, possibly, 31 July corresponded to slight increases in the atmospheric parameters and the peak orbit decay rates (ODRs) of 23 m per day (29 m per day) for Sat-A (Sat-B)
Summary
B, under different solar–geomagnetic conditions (Nwankwo et al, 2020a). Atmospheric drag describes the force exerted on an object moving through the atmospheric medium. Extreme space weather can cause satellite orbits to unexpectedly degrade, making it more difficult to manoeuvre spacecraft and to identify and track satellites and other space debris (Nwankwo et al, 2015 and references therein). Another detrimental impact of enhanced satellite drag is the unplanned loss of otherwise healthy spacecraft due to premature atmospheric re-entry. Under this scenario, a satellite would gradually decay from orbit (losing altitude) and would re-enter the Earth’s lower atmosphere, unless appropriate orbit-raising manoeuvres were implemented. We model changes in the orbital decay rate (ODR; in units of metres per day) and the monthly mean orbital decay (in units of kilometres) experienced by two satellites having different ballistic coefficients,
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