4 research outputs found
Intake Design for an Atmosphere-Breathing Electric Propulsion System (ABEP)
Challenging space missions include those at very low altitudes, where the
atmosphere is source of aerodynamic drag on the spacecraft. To extend the
lifetime of such missions, an efficient propulsion system is required. One
solution is Atmosphere-Breathing Electric Propulsion (ABEP) that collects
atmospheric particles to be used as propellant for an electric thruster. The
system would minimize the requirement of limited propellant availability and
can also be applied to any planetary body with atmosphere, enabling new
missions at low altitude ranges for longer times. IRS is developing, within the
H2020 DISCOVERER project, an intake and a thruster for an ABEP system. The
article describes the design and simulation of the intake, optimized to feed
the radio frequency (RF) Helicon-based plasma thruster developed at IRS. The
article deals in particular with the design of intakes based on diffuse and
specular reflecting materials, which are analysed by the PICLas DSMC-PIC tool.
Orbital altitudes km and the respective species based on the
NRLMSISE-00 model (O, , , He, Ar, H, N) are investigated for several
concepts based on fully diffuse and specular scattering, including hybrid
designs. The major focus has been on the intake efficiency defined as
, with the incoming particle
flux, and the one collected by the intake. Finally, two
concepts are selected and presented providing the best expected performance for
the operation with the selected thruster. The first one is based on fully
diffuse accommodation yielding to and the second one based un
fully specular accommodation yielding to . Finally, also the
influence of misalignment with the flow is analysed, highlighting a strong
dependence of in the diffuse-based intake while, ...Comment: Accepted Versio
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
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