Publications

Space missions in very low Earth orbit (VLEO) offer advanced capabilities for Earth observation, telecommunications, and security but are challenged by continuous orbit decay. Atmosphere-Breathing Electric Propulsion (ABEP), which uses atmospheric particles as propellant, provides a potential solution. Within the H2020 DISCOVERER, ESA ram-CLEP and ATLAS projects, IRS is developing a specular intake and helicon plasma thruster to advance ABEP systems. This study uses Direct Simulation Monte Carlo (DSMC) simulations to evaluate specular intake geometries, analyzing particle density, pressure, mass flow rate, and collection efficiency. The results indicate that reducing the focal length of the parabolic intake significantly improves efficiency and mass flow rate, while increasing the discharge channel diameter proves more effective for achieving these high values as well. As pressure follows an opposing trend to efficiency, and reaching the ignition pressure is crucial, the optimal configuration among the investigated for balancing efficiency and pressure is a discharge channel diameter of 25 mm with a focal length of 3 mm.

This study reports the performance comparison of the RAIJIN-66 TAL-type Hall thruster with argon propellant, using two hollow anode designs, one with a simple straight shape and another one with a sawtooth shape. Simulations of the rarefied gas in the sawtooth hollow anode region suggest a successful reversal of the direction of neutral particle flow, with an average increase in the neutral particle density by 15.5% when compared to the straight-shaped hollow anode. This contributes to the improvement in performance across a range of discharge voltages that was measured experimentally. When the thruster is operated with a discharge voltage of 150 V and a flow rate of 70 SCCM, the propellant utilization efficiency with the straight anode is 14%, while with the sawtooth anode it is 25.1%. The anode efficiency reaches in the vicinity of 15% with the sawtooth anode in high voltage conditions, exceeding the efficiencies achieved with the straight anode in the same operating conditions. The optimal magnetic field condition for argon operation and the tuning parameters of the sawtooth anode design for RAIJIN-66 are also discussed.

When rarefied gas flows through a channel exposed to vacuum, wall reflections and inlet velocity differences strongly affect the outlet velocity. This study uses the Direct Simulation Monte Carlo method, incorporating the Cercignani–Lampis–Lord wall reflection model, to analyze the injection method (parallel and perpendicular) and channel aspect ratio (AR = length of the walls/width between the walls) effects on the outlet density and velocity. The results demonstrate that AR determines the dominant physical mechanism governing the flow. In low-AR channels (AR  4), the flow thermalizes through particle–wall interactions, and the outlet velocity converges to the root-mean-square thermal velocity irrespective of the injection method. These findings establish a quantitative relation between channel AR and the effectiveness of injection-based flow control in rarefied environments.

Challenging space missions at very low altitudes face significant atmospheric drag, requiring efficient propulsion methods such as Atmosphere-Breathing Electric Propulsion (ABEP) to extend mission lifetimes. ABEP captures atmospheric particles and uses them as propellant for an electric thruster, reducing dependence on limited on-board propellant. This could extend missions in Very Low Earth Orbit (VLEO) and on celestial bodies with an atmosphere, such as Mars. The Institute of Space Systems (IRS), under the EU H2020 DISCOVERER, ESA Ram-CLEP, and CRC ATLAS projects, is developing a high-efficiency specular intake and a RF Helicon-based plasma thruster (IPT) for ABEP. This study uses the numerical tool PICLas and its Direct Simulation Monte Carlo Method (DSMC) to analyse the effect of solar activity and evaluate the validity of the hyperthermal assumption in VLEO for ABEP intake designs. Additionally, the effect of changing intake lengths on important key parameters, such as intake efficiency, mass flow rate, and pressure, is examined. The results show that efficiency decreases with higher solar activity, longer intakes, and higher altitudes, with particle temperature having the greatest effect on efficiency, due to its influence on thermal velocity and the molecular speed ratio. An almost linear relationship between efficiency and molecular speed ratio is shown, revealing that the hyperthermal assumption may not be valid for VLEO applications. To achieve the required pressure level for ignition, flexible ABEP operation is recommended to accommodate varying solar activity, suggesting lower altitude operation during low solar activity and higher altitude operation during high solar activity.

The propellant utilization efficiency of RAIJIN-66, a 2-kW class Hall thruster with anode layer, was investigated with varying anode temperature to evaluate ionization length, which is the length of the ionization region determined by the channel and magnetic field design. During RAIJIN-66’s thermally transient operation from the ignition, the ion beam current was monitored as a function of anode temperature using an ion collector plate biased negatively at 40 V. Two magnetic field profiles were examined with and without trim yokes. From the measured correlation between the propellant utilization efficiency and anode temperature, the ionization length was evaluated. As a result, the ionization length was 5.6 mm without the yokes, and 2.5 mm with the yokes. The ionization length of 2.5 mm was enough to achieve high propellant utilization efficiency with xenon, while it is too short to operate with argon because argon ionization mean free path is notably longer than xenon. This measured length was experimentally confirmed to be almost independent of discharge voltage and electron temperature. In conclusion, to achieve the high performance with argon propellant equivalent to that with xenon propellant, the ionization length as long as 14.5 mm is required in RAIJIN-66 size thrusters.

Cosmic dust transports information about the composition and evolution of distant realms over space and time. Dust sources may be in our local neighbourhood, such as the surfaces of moons and small bodies, or further away, in the galactic environment. The interior of moons like Io or Enceladus are well known dust sources in our solar system. Dust grains are therefore like probes, giving us the opportunity to investigate these objects at a distance. Thus, a new field of activity has been born: Dust Astronomy. The ultimate tool for Dust Astronomy is a dust observatory which was never been flown so far. Until today, all our knowledge is based on smaller individual dust detectors flown on various interplanetary spacecraft. Recently, a new generation of dust telescopes, which can be combined to a full dust observatory, became available. The scientific goal of such an observatory is to characterise our micrometeoroid environment with high precision and sensitivity and to record an inventory of various dust populations from asteroidal, cometary and interstellar dust sources. Two competitive studies on a Dust Astronomy mission were performed as part of a master’s course, including mission analysis and spacecraft design. The goal was to demonstrate the feasibility of an observatory reaching the main asteroid belt with a minimum spacecraft mass using electric propulsion. Additional secondary payloads supporting the primary objective were selected as well. The results prove that small probes with less than 700 kg mass are capable of placing an array of dust telescopes deep in the asteroid belt, leading to a huge leap in Dust Astronomy and our knowledge about the local dust environment.

Hall thrusters are widely used for efficient in-space propulsion, but their reliance on xenon presents challenges in terms of cost and availability. Alternative propellants such as argon or krypton exhibit lower propellant utilization efficiency, motivating thruster designs that increase plasma density within the ionization region. This work investigates such a scaling method using an analytical magnetohydrodynamic (MHD) framework to examine the effects of higher plasma density and magnetic field adjustments. Experimental Hall parameters and anomalous diffusion coefficients of existing thruster designs were estimated using the J × B force, highlighting differences between SPT and TAL configurations. A fluid-based MHD approach was then applied to identify the principal scaling parameters: mass flow density and magnetic flux density. The framework was demonstrated on the reference TAL-type thruster RAIJIN66. Reducing the anode cross-sectional area increased propellant utilization efficiency but also raised the discharge current and thermal load, which were mitigated by increasing the magnetic flux density. Importantly, while thrust remained essentially constant, the electron current was significantly reduced, illustrating the role of the magnetic field in controlling currents and thermal loads in high-density operation. These results highlight the importance of magnetic field adjustment in maintaining efficient thruster operation under high-density conditions and establish a first-order analytical tool for guiding the design of Hall thrusters using alternative propellants, with potential applications to future high-density, ion-magnetized regimes.

The Dedicated Infrastructure and Architecture for Near-Earth Astronautics (DIANA) is an autonomously deployable lunar base concept for a long-duration crewed mission on the Moon's surface. It will be robotically constructed in proximity to the De Gerlache crater ridge on the lunar South pole. The base, which accommodates four astronauts with a planned 2030 arrival, enables scientific operations and local sorties for human and robotic exploration. Furthermore, its self-sustainability will increase over its lifespan. The base will be transported in a compacted form and expanded to a habitable volume by autonomous deployment after reaching the lunar surface. The multilevel base encompasses all possible habitation needs including, but not limited to, dedicated private and communal spaces, technical support systems and a greenhouse. To establish and operate the base, the following subsystem concepts are crucial. The electrical power system consists of solar panels and a regenerative proton exchange membrane fuel cell using water electrolysis for power storage. Thermal insulation and adequate temperatures are provided through a closed water loop system, radiators and the use of regolith, the latter further providing radiation shielding. The environmental control and life support system initially relies on a high technological readiness level physico-chemical approach. Over time, it will progress towards a biologically closed loop system through the implementation of a greenhouse for food production and in-situ resource utilisation (ISRU) for water and oxygen harvesting. ISRU is essential in supplying astronauts not only with life support, but also with a large variety of construction material leading to increasing self-sustainability and long-term cost effectiveness. The communication system uses a Low Lunar Orbit communication relay satellite constellation and the Lunar Gateway. DIANA also offers a phased antenna array for radio interferometry on the far side of the Moon to perform observations of the universe.