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This article is devoted to the presentation of a numerical model of a Helicon Plasma Thruster (HPT) which relies on: 1) the 3-D adVanced fluId dRifT diffUsion plaSma solver (3D-VIRTUS) for the simulation of the plasma source and 2) an analytical model of the plume for the solution of the plasma acceleration and detachment, and in turn for the preliminary estimation of the propulsive performances (e.g., thrust and specific impulse). The results of the numerical model have been compared against experimental measurements performed with a thrust stand in order to evaluate the reliability of the code when dealing with real-life prototypes. Specifically, a dedicated combined numerical–experimental campaign has been conducted on a low power (50-W range) HPT prototype operated with argon propellant.

REGULUS is an Iodine-based electric propulsion system. It has been designed and manufactured at the Italian company Technology for Propulsion and Innovation SpA (T4i). REGULUS integrates the Magnetically Enhanced Plasma Thruster (MEPT) and its subsystems, namely electronics, fluidic, and thermo-structural in a volume of 1.5 U. The mass envelope is 2.5 kg, including propellant. REGULUS targets CubeSat platforms larger than 6 U and CubeSat carriers. A thrust T = 0.60 mN and a specific impulse Isp = 600 s are achieved with an input power of P = 50 W; the nominal total impulse is Itot = 3000 Ns. REGULUS has been integrated on-board of the UniSat-7 satellite and its In-orbit Demonstration (IoD) is currently ongoing. The principal topics addressed in this work are: (i) design of REGULUS, (ii) comparison of the propulsive performance obtained operating the MEPT with different propellants, namely Xenon and Iodine, (iii) qualification and acceptance tests, (iv) plume analysis, (v) the IoD.

REGULUS is a propulsion platform for CubeSats. It integrates the Magnetically Enhanced Thruster (MET) and its subsystems (i.e., fluidic line, electronics, and thermo-structural components) in a 2U envelope of weight lower than 3 kg. MET is a RF cathode-less thruster capable of providing thrust in the range 300 μN to 900 μN, with maximum specific impulse of 900 s and maximum operation power of 60 W. The performance has been measured with a dedicated thrust balance, when the thruster is operated with 0.1 mg/s of Xenon gas. REGULUS: (i) is compatible with thermal, mechanical and electrical interfaces of the CubeSat platforms available in the marked, (ii) it relies on COTS components to abate the recurrent costs, and (iii) it is based on a passive thermal control system. The main framework of application of the REGULUS platform is the propulsion of medium-to-large CubeSats (from 6U up to 27U). Such capability is here demonstrated by comparing MET with other thrusters for CubeSats offered in the market. The feasibility of two possible mission scenarios, namely drag compensation and constellation deployment, has been verified through preliminary orbit calculations. The REGULUS platform can compensate the effects of atmospheric drag on a 6U CubeSat in a 400 km altitude orbit for years. Besides, by exploiting the natural drift of the ascending node caused by the second zonal harmonic of the terrestrial gravity field, a CubeSat constellation can be deployed through several planes in some months employing small fractions of the onboard propellant.

A gaseous plasma antenna array (PAA) is an aggregate of plasma discharges and possibly conventional metallic radiating elements, and it constitutes a promising alternative to metallic antennas for applications in which fast reconfiguration of radiation pattern, and gain is desired; such properties can be achieved by exploiting the electronic switch on/off condition of plasma discharges, and tuning of the plasma parameters. Here, the authors present a reconfigurable PAA that features a central metallic half-wavelength dipole working around 1.45 GHz, surrounded by a planar circular lattice of cylindrical plasma discharges. Customised plasma discharges have been realised, and filled with argon gas at 2 mbar so as to have a complete control on the plasma discharge properties (e.g. plasma frequency, collisional frequency). The magnitude of the reflection coefficient, and the gain pattern on the H -plane have been investigated numerically and experimentally; numerical and experimental results exhibit a good agreement and show that the central intrinsically omnidirectional antenna can provide simple beamforming capabilities upon turning on a subset of plasma discharges; as these plasma discharges are turned on, the authors have observed a maximum gain of ~5 dBi, a half-power beam width of 80°, and an angular steering resolution of ~15°.

We have designed and tested a thrust stand for RF plasma thrusters characterization. The balance is employed in the development of small and medium size RF plasma thrusters; it allows for a high number of tests per day with an accuracy in the order of 10%. The balance relies on the counterbalanced-type pendulum concept, which allows adjusting the instrument sensibility without changing the overall pendulum size. The range of thrust which can be evaluated depends on the mass of the prototype under test; e.g. for a 0.5 kg prototype the thrust can vary from 20 μ N up to 50 mN. The system can be calibrated with both a calibration mass, and an electric calibrator. We have developed an algorithm which corrects the thermal drifts generated during thruster operation. We have compared the stand results against Faraday cup measurements, finding an agreement within 20%.

Gaseous plasma antennas are devices that exploit partially or fully ionized gas to transmit and receive electro-magnetic waves, in contrast with conventional antennas that are only made by metal and dielectric materials. Since plasma discharge parameters, e.g. plasma density, can be tuned, plasma antenna properties can be changed dynamically; this constitutes a promising alternative to conventional metallic antennas for applications in which reconfigurability is desired. In this work, we report on the first steps toward the realization, and the characterization in terms of radiation pattern, and magnitude of the reflection coefficient of an early prototype of a gaseous plasma antenna in the UHF frequency range. Numerical investigations have supported the design of the setup, and helped in the evaluation of the the role of plasma density profiles in affecting the antenna properties.

Gaseous plasma antennas constitute a promising alternative to conventional metallic antennas for applications in which reconfigurability is desired. By tuning the plasma discharge parameters, e.g., plasma density, antenna properties can be changed dynamically. In this work we report on recent numerical investigations into the characteristics of a plasma antenna as a function of the plasma discharge parameters, viz., plasma density, and magnetostatic field. In addition, the effect of different gasses has been examined. We have used ADAMANT (Advanced coDe for Anisotropic Media and ANTennas) — a full-wave numerical tool based on integral equations — to assess the role played by plasma discharge parameters in shaping the radiation pattern, which is mainly determined by the plasma current distribution. The experimental characterization of the plasma discharge to be used as plasma antenna is briefly presented.

In the framework of the ”Helicon Plasma Thruster for Space Missions AO7048” research program, a zero-dimensional numerical model is developed in order to assess the propulsive performances of the plasma thruster when fed with different molecular gases as propellants. The zero-dimensional model developed consists of detailed kinetic schemes for bulk plasma reactions and surface processes; particle in cell simulations are performed to properly describe the behaviour of the charged particles at the exhaust plume so to obtain exhaust parameters for the global model. Given a set of input parameters, such as geometry and mass flow rate, the model is able to follow the time evolution of plasma main physical quantities, such as neutral and charge densities and the electron temperature, and to calculate thruster performances. The model is then linked to the genetic algorithm optimization toolbox in Matlab environment in order to obtain high performance configurations. Propellants considered are H2, O2, N2 and N2O.

In this communication we report on a combined experimental-numerical activity thas was conducted to assess the antenna-plasma interaction within a Helicon plasma source for space thrusters. The experiment is based on a versatile, re-configurable set-up which allows testing mulitiple thruster configurations under different operating condtions, featuring a high-efficiency RF antenna. The numerical results were opbtained by means of various simulation tools for both RF circuit and antenna-plasma interface analysis; these tools were validated against experimental data. The results helped to improve our understanding of antenna-plasma coupling and the assessment/prediction of the RF system performance.

In this work we illustrate the design of a thrust balance, to be employed for the experimental characterization of low power helicon plasma thrusters developed at the Center for Aerospace Studies and Activities (CISAS) “G. Colombo” of the University of Padua. The nominal thrust level of the propulsive systems to be tested is estimated between 1 and 20 mN. The measurement of millinewton-range thrusts in presence of RF emissions magnetic fields from the thruster poses several engineering challenges as: (i) an highly sensible system is required, capable of detecting the low thrust levels produced by the thrusters with sufficient accuracy and stability; (ii) the necessity of feeding RF power to the thruster mounted on the balance imposes to deal with RF disturbances on the measurement systems and RF heating of the power line and of the mechanical structure of the balance; (iii) the magnetic field can interact with elements of the balance, hampering the measurement. We considered all these aspects with careful theoretical analyses, supported by experimental validation of the envisioned solutions. The work was thus structured as follow: (i) definition of the physical principles related to the measurement of millinewton-range thrusts in an RF environment; (ii) definition and preliminary characterization of the mechanical configuration of the system; (iii) definition of the measurement chain, in terms of mechanical interfaces, sensors, RF shielding and data handling, (iv) analysis of system criticalities; (v) design and experimental validation of the critical technologies involved in the system; (vi) detailed design of the thrust balance.

Radiofrequency (RF) magnetized Helicon plasma sources have been proposed for the development of space thrusters, whose thrust efficiency and specific impulse depend on the power coupled into the plasma by the RF antenna that drives the discharge. In this work we report on a set of numerical experiments specifically conceived to optimize Helicon sources in terms of plasma parameters (e.g., gas species, plasma density, external magnetostatic field, neutral pressure), and the RF antenna shape. Results concerning the power coupled into the plasma and the antenna impedance for different antenna configurations and plasma parameters are presented and discussed.

The non-intrusive density measurement of the thin plasma produced by a mini-helicon space thruster (HPH.com project) is a challenge, due to the broad density range (between 1016 m-3 and 1019m -3) and the small size of the plasma source (2 cm of diameter). A microwave interferometer has been developed for this purpose. Due to the small size of plasma, the probing beam wavelength must be small (λ=4 mm), thus a very high sensitivity interferometer is required in order to observe the lower density values. A low noise digital phase detector with a phase noise of 0.02° has been used, corresponding to a density of 0.5 × 10 16 m-3. © 2013 American Institute of Physics.

We have designed and tested a thrust stand conceived for the characterization of RF plasma thrusters. The balance has been employed in the development of small-medium size HPT prototypes, therefore it allows for an high number of tests per day with an accuracy within the 10%. The balance relies on the counterbalanced-type pendulum concept, which allows to achieve high sensitivity while maintaining a low overall size of the system; the displacement is measured by means of an high-accuracy laser interferometer put outside the vacuum chamber. The system can be calibrated with both a calibration mass, before the test, and an electro-magnetic device, during the test session. We have verified the linear behavior of the instrument and we have developed a dedicated algorithm in order to correct the thermal drifts of the balance. We have compared the stand measurements with the thrust estimations derived from Faraday probe measurements within the plasma plume, verifying that the two estimates are in agreement within 20%.