Upper-atmosphere mass density variations from CASSIOPE precise orbits

Abstract

Low Earth Orbit (LEO) satellites are significantly affected by variable air drag forces, which are mainly altered by atmospheric expansion/contraction driven by solar and geomagnetic activity. Air drag reduces the orbital velocity of a satellite, its nominal altitude, and shortens its lifespan. The effect of air drag pressure on the position of a satellite orbiting at an altitude of around 450 km may drag around 3 m per revolution in the along-track axis, limiting the satellite's lifespan to approximately 5-10 years. In applications, such as remote sensing or satellite altimetry and gravity, the orbital trajectory and velocity (ephemeris) of satellites must be known to an accuracy of a few millimeters. Moreover, the exponential increase in presence of space debris (consider the recent destructive events of Fengyun-1C, Iridium, and Mission Shakti) has highlighted the importance of orbital tracking and prediction of potential collisions. The dynamic Precise Orbit Determination (POD) method tracks and predicts the orbital ephemeris by calculating an orbital trajectory through a double integration and linearization of Newton-Euler's equation of motion (Montenbruck & Gill, 2013). In the POD method, by combining force models with empirical observations, used for example in laser-ranging, Doppler, accelerometer, or Global Navigation Satellite System (GNSS) measurements, the position, and velocity of a satellite can be stochastically estimated with significant accuracy (Jin & Su, 2020;Tapley et al., 2004).Due to variable air drag force being so important, in the last decade, thermospheric mass density (TMD) variations driven by solar and geomagnetic activity have been investigated using satellite technology to a great extent (e.g.

Thermospheric Mass Density Disturbances Due to Magnetospheric Forcing From 2014–2020 CASSIOPE Precise Orbits

“…In this study, the analysis of differences with the HASDM database have shown that scaling the CASSIOPE's drag coefficient of Calabia and Jin (2021a) by approximately 0.8 would provide a better match. Using this, the estimated altitude dependence on this scaling factor is given in Table 1.…”

“…These differences are mostly caused by inaccuracies in the models during geomagnetic storms. A deeper analysis for this particular storm can be found in Calabia and Jin (2021a).…”

“…However, the Dst index lacks time delay for early warnings of hazardous variability of the thermospheric mass density. Another suitable parameter that closely correlates with mass density variations during geomagnetic storms, and that has a larger time delay, is the merging electric field E m (Calabia & Jin, 2019, 2021a; Liu et al., 2010), in units of mV/m. The E m index assumes that there is an equal magnitude of the electric field in the solar wind, the magnetosheath, and on the magnetospheric sides of the magnetopause (Kan & Lee, 1979).…”

“…In the last 20 years, the only missions carrying accelerometers were Challenging Minisatellite Payload (CHAMP), Gravity Recovery and Climate Experiment (GRACE), Gravity field and steady‐state ocean circulation explorer (GOCE), and Swarm (Figure 1). Currently, continuous high accuracy GNSS observation on‐board LEO satellites has proven the capability to measure high‐cadence, non‐gravitational accelerations, and then estimate densities at a high resolution (Calabia & Jin, 2017, 2021a; Calabia et al., 2015; Li & Lei, 2020; van den IJssel et al., 2020; Yuan et al., 2019).…”

“…In Calabia and Jin (2021a), the GNSS ephemeris of the CAScade SmallSat and IOnospheric Polar Explorer (CASSIOPE) satellite were used to investigate at high resolution the thermosphere's response to the geomagnetic storm of February 2014. The CASSIOPE satellite was launched on September 29, 2013.…”