Simulation of the orbital decay of a spacecraft in low Earth orbit due to aerodynamic drag

Orbiting objects in space are exposed to the risk of collision with space debris over their lifetime. Space debris orbiting in space experiences orbital decay due to various orbital perturbations. This work considers only orbital perturbations due to aerodynamic forces, which spacecraft experience due to the presence of a rarefied atmosphere, causing tumbling motion and orbital decay. Analysis of the orbital decay of a spacecraft is carried out by considering the variation of the drag coefficient as a function of its shape, motion and angle-of-attack. An in-house Direct Simulation Monte Carlo (DSMC) solver is modified for aerodynamic analysis of a spacecraft orbiting in the free molecular regime in low Earth orbit. In addition, an orbital dynamics model is developed to simulate the tumbling motion of a spacecraft and its orbital decay. The orbital decay trajectory is predicted for two sample spacecrafts using the aerodynamic coefficients obtained from the in-house DSMC solver as inputs to the orbital decay model. This study analyses and explores in detail the effects of the aerodynamic coefficients and shape of a spacecraft on its orbital decay.

Extended analytical formulae for the perturbed Keplerian motion under low-thrust acceleration and orbital perturbations

This paper presents a collection of analytical formulae that can be used in the long-term propagation of the motion of a spacecraft subject to low-thrust acceleration and orbital perturbations. The paper considers accelerations due to: a low-thrust profile following an inverse square law, gravity perturbations due to the central body gravity field and the third-body gravitational perturbation. The analytical formulae are expressed in terms of non-singular equinoctial elements. The formulae for the third-body gravitational perturbation have been obtained starting from equations for the third-body potential already available in the literature. However, the final analytical formulae for the variation of the equinoctial orbital elements are a novel derivation. The results are validated, for different orbital regimes, using high-precision numerical orbit propagators.

Asynchronous and chaotic rotation for compact planetary systems

<p>We study the spin evolution of close-in planets in compact multi-planetary systems. The rotation period of these planets is often assumed to be synchronous with the orbital period due to tidal dissipation. Here we show that planet-planet perturbations can drive the spin of these planets into non-synchronous or even chaotic states. These asynchronous configurations are possible even for nearly circular orbits and will impact the habitability of these planets. We also present a very simple method to probe the spin dynamics from the orbital perturbations.</p>