ETD

• ABEP
• air breathing electric propulsion
• electric propulsion
• plasma
• plasma physics
• Very Low Earth Orbit
• VLEO
• wind tunnel

The recent advancements in Air-Breathing Electric Propulsion (ABEP) concepts have generated growing interest in spacecraft operations within the Very Low Earth Orbit (VLEO) region, where the residual atmosphere can be directly exploited as a propellant. These systems promise to enable long-duration missions at altitudes below 300 km without the need for onboard propellant storage, offering significant benefits in terms of mission lifetime, mass efficiency, and sustained low-orbit operations. However, the characterization and testing of such propulsion systems are hindered by the lack of ground-based facilities capable of reproducing the environment in VLEO.

In this context, this master's thesis work presents the preliminary design of a VLEO Wind Tunnel, a facility intended to replicate on the ground the flow conditions encountered by spacecraft orbiting in the 250-300 km altitude range.

The target conditions include a flow velocity equivalent to orbital speeds, a neutralization degree close to unity, and a gas composition representative of the residual atmosphere, primarily composed of atomic oxygen and molecular nitrogen. These specifications guided the conceptual design of the facility subsystems.

The resulting configuration includes two independent gridded RF plasma sources, one operating with oxygen and the other with nitrogen. Each plasma source may be equipped with a dedicated electromagnetic filter to eliminate the undesired ions (atomic nitrogen, molecular oxygen) from the flow. Downstream of the filtering stage, a surface neutralizer ensures the proper degree of ion-electron recombination. Finally, an additional filtering stage removes the particles that have been slowed down in the previous stages. \\
To support the design, a zero-dimensional global model of the entire facility was developed. This model enables an overall evaluation of the operating conditions of the plasma sources and provides a preliminary estimate of the vacuum and pumping system requirements needed to maintain the required pressure levels within the facility. Additionally, two 0D models were developed for the nitrogen and oxygen plasma sources to gain deeper insight into the behavior of the plasma under different operating conditions. In particular, the models investigate how variations in input power, frequency, chamber pressure, and geometric parameters affect key plasma properties such as electron temperature, absorbed power, and electromagnetic properties. Finally, a preliminary design of the surface neutralizer was carried out. \\
The results of this study establish a foundation for the future realization of the VLEO Wind Tunnel, providing an essential tool for the development of Air-Breathing Electric Propulsion systems operating in VLEO, as well as for experimental investigations into plasma–surface interactions and material degradation.