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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 η c = N ̇ o u t ∕ N ̇ i n , with N ̇ i n the incoming particle flux, and N ̇ o u t 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 η c < 0. 46 and the second one based on fully specular accommodation yielding to η c < 0. 94. Finally, also the influence of misalignment with the flow is analysed, highlighting a strong dependence of η c in the diffuse-based intake while, for the specular-based intake, this is much lower finally leading to a more resilient design while also relaxing requirements of pointing accuracy for the spacecraft. • Intake: passive device, collection of residual atmosphere in very low Earth orbit (VLEO). • Use of diffuse and specular reflecting materials. • Design based on free molecular flow and gas surface interaction properties. • Collect residual atmosphere of celestial bodies to be used as propellant for an electric thruster. • Used in an ABEP system to compensates drag of satellites at very low altitude orbits (VLO) to extend mission's life time and enable new mission scenarios. [ABSTRACT FROM AUTHOR]

Challenging space missions include those at very low altitudes, where the atmosphere is source of aerodynamic drag on the spacecraft. To extend such missions lifetime, an efficient propulsion system is required. One solution is Atmosphere-Breathing Electric Propulsion (ABEP). It 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 planet with atmosphere, enabling new mission at low altitude ranges for longer times. Challenging is also the presence of reactive chemical species, such as atomic oxygen in Earth orbit. Such species cause erosion of (not only) propulsion system components, i.e. acceleration grids, electrodes, and discharge channels of conventional EP systems. IRS is developing within the DISCOVERER project, an intake and a thruster for an ABEP system. The paper describes the design and implementation of the RF helicon-based inductive plasma thruster (IPT). This paper deals in particular with the design and implementation of a novel antenna called the birdcage antenna, a device well known in magnetic resonance imaging (MRI), and also lately employed for helicon-wave based plasma sources in fusion research. This is aided by the numerical tool XFdtd®. The IPT is based on RF electrodeless operation aided by an externally applied static magnetic field. The IPT is composed by an antenna, a discharge channel, a movable injector, and a solenoid. By changing the operational parameters along with the novel antenna design, the aim is to minimize losses in the RF circuit, and accelerate a quasi-neutral plasma plume. This is also to be aided by the formation of helicon waves within the plasma that are to improve the overall efficiency and achieve higher exhaust velocities. Finally, the designed IPT with a particular focus on the birdcage antenna design procedure is presented. • Inductive plasma thruster: contactless device, avoids electrode erosion, adapts to any propellant. • Birdcage antenna design at resonance for an RF-fed thruster. • Partial acceleration of quasi-neutral plasma plume, does not need a neutralizer. • Collects and uses planet's atmosphere as propellant. • Compensates drag of satellites at very low altitudes (e.g. VLEO) to extend mission's life time and enable new mission scenarios. [ABSTRACT FROM AUTHOR]