New concept of a low power plasma engine for in-space propulsion of small and medium size satellites
The offer concerns to a new concept of a plasma engine denominated ALPHIE for in-space propulsion of medium and small satellite. This simple and low cost plasma thruster is designed for the planned constellations of small satellites in low Earth orbit, such as OneWeb, LeoSat, Xinwei, etc. The weight of these satellites would range 100-200 Kg in order to accommodate the telecommunication equipment along with the small power plant based on solar panels.
The small sized ALPHIE (see Fig. 1) is a low budget, compact plasma engine. Its electrical system is rather simple and based only on three DC power supplies. The involved voltages are always below the kV range, which avoids sparking and to handle with high voltages under space conditions. This fact would reduce the cost of the electronic Power Processing Unit (PPU) that is the most expensive element of electric propulsion systems.
The plasma engine delivers a variable throttle between 0-5 mN controlled by a voltage signal. This allows flight formation of satellites and permits to optimize the mission profile. The discharge chamber is made of stainless steel avoiding complex ceramic materials that might be degraded or wear. The low propellant consumption is because of a highly efficient magnetic trap, made of permanent magnets thermally insulated.
The configuration of the internal magnetic field inside the discharge chamber confines the ionizing electrons which give rise to high ionization rates of propellant. The cathode and control grids have plane geometry. Few ALPHIE units could be clustered together using the same basic circuit. Hence, using different throttle control voltages the systems could provide non-axial thrust and/or rotational (spin) motion. The electric power needed by this plasma engine do not exceed 300 W with mass flow rates of the neutral gas (Argon or Xenon) employed as propellant below 10 sccm. The use of Argon (instead of Xenon) constitutes a key factor to reduce the costs of qualification tests.
The ALPHIE plasma engine has reached TRL-4 and is now currently tested in a vacuum chamber using laboratory power supplies. There exist commercial solutions (TRL- 9) for the neutral gas flow control subsystem as well as for the electron sources. The latter are employed for primary plasma production and ion beam neutralization. The design of a flexible electronic PPU would be one of the next landmarks.
Innovations & Advantages
Small size and weight with low electric power consumption (below 300 W) and neutral mass flow rates below 10 sccm.
- Variable throttle (0-5 mN) controlled by a voltage signal.
- Simple conception of the discharge chamber made of stainless steel avoiding dielectric coating that could be degraded by ion and/or electron bombardment.
- Simple design of the electrical system based only on three DC power supplies with voltages below the kV. This avoids sparking and simplifies PPU unit.
- Only one electron source is needed for either, primary plasma production and ion beam neutralization. This feature also reduces the thermal stresses.
- Grids are planar and parallel.
- The gas feed system uses only one valve.
The plasma engine is a cylinder of about 12 cm in diameter, 15 cm in length and weights below 2 Kg. The propulsion principle relies on accelerated ion populations that form a plasma jet, which up today has been characterized using four grids retarded potential analyzers. Direct measurements of thrust are still an issue we are addressing whereas the range of 0-5 mN is based on the measured ion currents and a reasonable estimate of the ion energy.
Contrary to gridded ion engines, the ions are not accelerated by the external grid 18, which is employed for the control of throttle. The applied voltage VCT to this grid provides of a maximum (VCT=0) ion outflow or inhibits the ion current over an onset value. Hence, the delivered throttle is controlled by the voltage signal applied to the grid (18). Additionally, few ALPHIE units could be clustered together connected to the same VAC voltage line but with independent throttle voltages VCT to provide non-axial thrust and/or spin. This is why we term this design as “adaptable” because ALPHIE is modular and could be configured with two or more controls signals to provide rotational motion.
Current and Potential Domains of Application
In-orbit electric propulsion of small/medium size satellites. Station keeping. Orbit drag compensation. Flight formation of satellites. End-of-life-satellite disposal.