The growing number of space objects in low-Earth orbit necessitates accurate orbit predictions to decrease the likelihood of operational disruptions. The challenges in accurately capturing how gas particles interact with the objects’ surfaces result in uncertainties in their aerodynamic coefficients, directly affecting the accuracy of orbital perturbation models. Currently, gas–solid boundary interactions are accounted for by empirical models like those proposed by Sentman and Cercignani-Lampis-Lord. These models have one or two adjustable parameters, typically tuned based on orbital tracking and acceleration data. However, these models are inadequate in accurately representing crucial processes at the gas–solid interface such as multiple reflections, shadowing, and backscattering resulting from the roughness of real surfaces. We propose a new, physics-based gas-surface interaction model that leverages electromagnetic wave theory to incorporate macroscopic effects on the gas particle scattering distribution resulting from surface roughness. Besides better describing the physics of gas-surface interaction, this model’s parameters can be determined by combining ground measurements to characterise the surface roughness and molecular dynamics simulations to specify the atomic-scale interaction. The model is verified for the entire parameter range using a test-particle Monte Carlo approach on a simulated rough surface. In addition, we successfully replicate several experimental results available in literature on the scattering of Argon and Helium on smooth and rough Kapton and Aluminium surfaces. We conclude by demonstrating the model’s effect on the aerodynamic coefficients for simple shapes and comparing these results with those produced with the Sentman and Cercignani-Lampis-Lord models, thereby demonstrating that previously observed inconsistencies between these models and tracking data of spherical satellites can be explained by surface roughness.

Parachute/flow interaction is dominant in evaluating a decelerator’s performance. Such interaction is characterized by nonlinear deformations and complex flow phenomena. While testing methods are available to investigate parachute performance, these are often costly and nonrepresentative of the desired flight conditions. To address the need for an accessible technique capable of modeling parachutes at the early design stages, this paper proposes a robust fluid/structure interaction methodology for three-dimensional subsonic simulations. This is attained by replacing the linear springs in Provot’s equation with polynomial expressions whose coefficients are fitted to tensile test data. The nonlinear cloth algorithm is coupled with the rhoPorousSimpleFoam solver in the open-source OpenFOAM toolbox, thereby establishing an iterative process that reaches steady-state convergence in at most six iterations. The transient response is obtained from the average distributed load of the steady-state pressure field and an inertial damping contribution. The simulations are performed for two disk-gap-band parachutes and a ringsail parachute over a velocity range of ring sail 5–30 m/s. The results are compared to the experimental data measured in the Open Jet Facility of Delft University of Technology, yielding errors below 5% for the steady-state cases and overestimations in peak loads of 4.4–12.4% for the transient simulations.