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Air-breathing Electric THrustER

Periodic Reporting for period 1 - AETHER (Air-breathing Electric THrustER)

Reporting period: 2019-12-01 to 2021-05-31

Nowadays, Low Earth Orbits (LEO) are the most crowded orbits in space due to easy accessibility, very short lag in communication and frequent revisit times. Very Low Earth Orbits (VLEO) offer the opportunity to disrupt this paradigm and open new mission scenarios for space applications. Located between 160 and 250 km, VLEO could further strengthen the benefits of LEO thanks to its closer proximity to Earth’s surface.
One of the most demanding constraints of VLEO is the need to continuously counteract the drag generated by the interaction of the spacecraft with the surrounding atmosphere. The mission lifetime will then be determined by the amount of propellant stored on-board to produce thrust.
The RAM-EP concept combines the advantages of electric propulsion with the possibility to harvest the particles available in the upper atmosphere and use them as propellant. Once demonstrated that the thrust produced can counteract the atmospheric drag that typically causes rapid orbital decay, the use of VLEO and a significant extension of the mission lifetime would be enabled.
In recent years, the full ram-EP concept has become more realistic and somewhat appealing, as several theoretical and experimental investigations are being undertaken in Europe, Japan, US and Russia to develop a feasible prototype. The most advanced result in air-breathing electric propulsion was achieved in 2017, when SITAEL obtained the first operation of a full air-breathing system in representative conditions. The ram-EP thruster was successfully ignited with the atmospheric propellant, even though further development is needed to achieve full compensation.
Starting from the heritage of Sitael, the AETHER project (Air-breathing Electric THrustER), aims at developing the first propulsion system able to maintain a spacecraft at very-low altitudes for an extended period. The main objective of the project is to demonstrate, in a representative on-ground environment, the critical functions of an air-breathing electric propulsion system, and its effectiveness in compensating atmospheric drag.
The technical work carried out during the first reporting period can be described with reference to the Project specific objectives.
1) Characterize specific application cases for the RAM-EP technology and define system requirements.
Based on the preliminary assessment of relevant market opportunities, the project team has identified the potential mission scenarios that are considered 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.
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). A review of Earth orbit payloads used in past missions in LEO, including mass/power/data budgets and performance scalability in VLEO, was performed as well.
2) Reproduce on-ground the environmental conditions relevant to the identified mission cases.
A particle flow generator (PFG), based on the Hall-effect technology, 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.
A number of design considerations concerning the PFG thruster material compatibility with atmospheric propellant, especially oxygen, have been discussed, as well as advantages and implications of alternative solutions.
In parallel with the design and manufacturing of an Hall-effect PFG, an assessment of a possible ion engine PFG was performed. The critical design parameters were identified accordingly and the required design modifications to current devices, necessary to realize a PFG with the needed characteristics, identified.
3) Develop 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 efforts are put in the AETHER project on the development of material science knowledge beyond the current state-of-the-art.
A collection of material requiremens has been prepared for possible candidate materials of interest. A proposal for material selection has been derived preliminarily. Specific modelling and experimental investigations are planned for the second Project period, to define suitable materials for extended contact with ionized corrosive atmospheric gases.
A thruster performance model was set up to provide the sizing of the thruster and the main operational parameters (thrust, power, etc.) and allow EPS design. The specific subsystems, namely intake, ionization stage, acceleration stages and neutraliser, have been designed, based on the specific requirements derived from the EPS, including functional, performance and interface requirements.
4) Assess the performance of the RAM-EP system.
This project objective is the characterization of the system operation in terms of integral parameters (thrust, drag, power) as well as local properties of the accelerated particle beam (composition, electron temperature, velocity). To this aims, both invasive and non-invasive diagnostic systems have been designed and assembled, based on the specific test needs. Interface and integration issues with the system mechanical stages and with the candidate facility (IV10 at Sitael) have been also assessed.
When compared to traditional electric propulsion systems, the availability of an air-breathing engine would allow for significant cost and mass reductions of low-earth-orbiting spacecraft while enabling a whole spectrum of missions never thought possible before. The attractiveness of in-situ resource utilization for the propellant is associated with the removal of the main mission duration limiting factors. This will, in-turn, enable mission scenarios never thought possible before and change completely the paradigm of in-space propulsion for LEO, VLEO and low orbit interplanetary missions.
The AETHER project builds on the technological advantage of Europe in air-breathing propulsion, moving to a more advanced development stage compared to the international competition, while also protecting the relevant IPR. This will secure the market leadership on air-breathing, xenon-independent electric propulsion systems, employing a fully European supply chain. As part of AETHER, the RAM-EP engine will be developed to achieve TRL5 and thus will lead to an unprecedent technological advancement in air-breathing space propulsion.
Air-breathing electric propulsion will allow Europe to achieve a prime role in the exploitation of VLEO. The AETHER project, will achieve the development status required to address this market through collaboration of several European entities, from large companies to SMEs and academia, ensuring a reliable European supplier base while pushing the limit of what is currently achievable in the space industry.
The first prototype fired by Sitael in 2017 with atmopheric propellant
Typical Plasma Component Composition for 500 W of absorbed power
Image of a RAM-EP spacecraft (rendering)