The technical work carried out during the project has reached the following results:
1) Characterization of specific application cases for the RAM-EP technology and definition of system requirements
Based on the preliminary assessment of relevant market opportunities and on potential Earth orbit payloads, the project team has identified and characterized the potential mission scenarios of interest for S/C operating with an air-breathing electric propulsion system (EPS). The characteristics of the solar system atmospheres, i.e. of inner and of outer planets and natural satellites atmospheres, have been investigated and taken into account.
A set of specific tools have been developed for the evaluation of key design drivers and EPS requirements derived in turn. Parallel activities have been carried out in order to derive the requirements at different levels (mission, platform, and subsystems).
2) On-ground experimental simulation of the environmental conditions relevant to the identified mission cases.
A particle flow generator (PFG) has been designed to reproduce on-ground representative conditions of the target application environment. Extensive analyses have been performed to analyze the expected properties of the plume flow and its evolution and to identify the necessary modifications of an existing Hall thruster to allow generating a representative flow. Finally, the prototype of the PFG has been manufactured and successfully tested in representative vacuum conditions.
3) Development of the critical technologies for the collection, ionization and acceleration of rarefied atmospheric flows.
The durability of materials that must operate in a harsh oxidative and corrosive environment is the most relevant life limiting factor for the air-breathing technology. For this reason, significant effort has been put on the development of material science knowledge beyond the current state-of-the-art. Specific modelling and experimental investigations have been performed to define suitable materials for extended contact with ionized corrosive atmospheric gases.
A thruster performance model has been set up to provide the sizing of the thruster and the main operational parameters (thrust, power, etc.) and allow EPS design. The specific subsystems have been designed, based on the specific requirements derived from the EPS. Most subsystems have been manufactured and successfully tested in standalone configuration, showing a behavior in line with expectations.
4) Assessment the performance of the RAM-EP system.
In order to characterize the engine operations in terms of integral parameters (thrust, drag, power) as well as local properties of the accelerated particle beam (composition, electron temperature, velocity), invasive and non-invasive diagnostic systems have been designed and assembled, on purpose for the specific test needs.
Intensive co-engineering activities have been performed to define the optimal end-to-end test sequence and test set-up for the RAM-EP system verification, as well as to timely highlight and prevent potential criticalities of such a complex test campaign. Dedicated tests have been performed at sub-system level with atmospheric propellant, i.e. PFG; acceleration stage; RF neutraliser; intake (reduced scale); hollow cathode. Such tests have prepared the ground for a future end-to-end test campaign, that was not possible to perform within the Project perimeter for programmatic reasons.
Even if the Project has not succeeded in completing the end-to-end test campaign and demonstrating the target TRL 5, significant advancement has been achieved by the Consoirtum in the development of the air-breathing technology: this overall achievement can effectively pave the way for further development to in-orbit demontration of the technology.
