Effect of ionospheric drag on atmospheric density estimation and orbit prediction

Abstract

Accurate prediction of aerodynamic forces in Low Earth Orbit (LEO) remains a key challenge for space situational awareness (SSA) and space traffic management (STM) activities. A neglected aspect of the LEO aerodynamics problem is the force resulting from the charged aerodynamic interaction of LEO objects with the ionosphere, i.e. ionospheric aerodynamics. This work studies the effect accounting for ionospheric drag may have on the motion of LEO objects. This work aims to assess the influence of ionospheric aerodynamics on atmospheric density estimation and orbit prediction capabilities essential to SSA and STM services. The approach taken in this work was to apply Particle-in-Cell (PIC) simulations to develop a surrogate model that describes the variation of a charged drag coefficient (CD,C) as a function of plasma scaling parameters. This surrogate model was then incorporated into an orbit propagator, and the influence of ionospheric drag on body motion is studied for a range of conditions. Results indicate that, when inferring atmospheric neutral density from orbit data, neglecting the contribution of ions without accounting for electrodynamic phenomena, may cause an over-prediction of neutral density ranging between 1% and 45% for the space weather condition considered (F10.7=150,ap=5). Including electrodynamic phenomena was seen to increase this over-prediction for all cases. Objects with thick plasma sheaths were shown to be particularly sensitive to ionospheric drag forces; thick plasma sheaths caused by either a reduction in object scale (rB) or increase in surface potential (ϕ). This result has important implications for modelling space debris populations as thick plasma sheaths may arise at natural floating potentials (-0.75V) when debris fragmentation occurs. For example, accounting ionospheric drag on a spherical debris object with a radius of 0.005 m, area-to-mass ratio of 0.0157 m2/kg and floating potential of -0.75 V in a circular equatorial orbit at 350 km altitude was predicted to cause a change in along-track position of 299 m (and a reduction in semi-major axis of 4 m) over a 24-h period. Results also have important implications for modern satellites, where the trend is toward nano/micro-satellite platforms (e.g. CubeSats) with high-voltage powers systems that may inadvertently cause large artificial surface potentials and therefore enhanced ionospheric aerodynamic forces.