  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 $h=150-250$ km and the respective species based on the
NRLMSISE-00 model (O, $N_2$, $O_2$, 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
$\eta_c=\dot{N}_{out}/\dot{N}_{in}$, with $\dot{N}_{in}$ the incoming particle
flux, and $\dot{N}_{out}$ 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 $\eta_c<0.46$ and the second one based un
fully specular accommodation yielding to $\eta_c<0.94$. Finally, also the
influence of misalignment with the flow is analysed, highlighting a strong
dependence of $\eta_c$ in the diffuse-based intake while, ...
