A Review of Gas-Surface Interaction Models for Orbital Aerodynamics Applications

Renewed interest in Very Low Earth Orbits (VLEO) - i.e. altitudes below 450
km - has led to an increased demand for accurate environment characterisation
and aerodynamic force prediction. While the former requires knowledge
of the mechanisms that drive density variations in the thermosphere, the
latter also depends on the interactions between the gas-particles in the residual
atmosphere and the surfaces exposed to the flow. The determination of
the aerodynamic coefficients is hindered by the numerous uncertainties that
characterise the physical processes occurring at the exposed surfaces. Several
models have been produced over the last 60 years with the intent of combining
accuracy with relatively simple implementations. In this paper the most
popular models have been selected and reviewed using as discriminating factors relevance with regards to orbital aerodynamics applications and theoretical
agreement with gas-beam experimental data. More sophisticated models
were neglected, since their increased accuracy is generally accompanied by a
substantial increase in computation times which is likely to be unsuitable for
most space engineering applications. For the sake of clarity, a distinction was
introduced between physical and scattering kernel theory based gas-surface
interaction models. The physical model category comprises the Hard Cube
model, the Soft Cube model and the Washboard model, while the scattering
kernel family consists of the Maxwell model, the Nocilla-Hurlbut-Sherman
model and the Cercignani-Lampis-Lord model. Limits and assets of each
model have been discussed with regards to the context of this paper. Wherever
possible, comments have been provided to help the reader to identify
possible future challenges for gas-surface interaction science with regards to
orbital aerodynamic applications.