The present disclosure relates generally to electric propulsion devices, and more particularly to such devices having improved efficiency and longer lifetimes.
There is an interest in efficient, high power space propulsion engines. Hall Effect Thrusters (HETs) produce thrust by ejecting ionized matter and are popular in orbit maneuvering and attitude control of many low earth orbit (LEO) and geosynchronous earth orbit (GEO) satellites.
Currently known HETs offer specific impulses over 2400 s, thrust over 1 N, and power exceeding 50 kW at efficiencies close to 60%. However, the commercial exploitation of Hall thrusters imposes a stringent constraint of trouble-free operation for more than 8000 hours.
The walls of the discharge chamber of a stationary plasma thruster (SPT) are commonly made of composite ceramic materials, for example, boron nitride, silicate oxide, and/or the like. Among many potential reasons limiting the efficiency and lifetime of a Hall thruster, an important reason is the wear of the surface layer of the discharge chamber walls. The wall erosion of the thruster occurs primarily due to plasma-wall interactions. If the ion impact energy is sufficiently large, the impact ions may cause relatively severe, undesirable sputtering of the discharge walls, the anode, and/or the hollow cathode walls. These surfaces may then develop non-uniformities (e.g. asperities) due to the sputtering, as well as to re-deposition, cracking, etc. Further, sputtered material may, in some instances, contaminate the plasma and potentially the spacecraft surface. This may significantly affect the performance of the HET, and may potentially affect the working parameter optimization.
Although the lifetime issues are important to its design and potentially critical for long duration mission applications, many physical aspects in thruster plasma are yet to be understood. The lifetime of an on-board Hall thruster is expected to exceed several thousand hours. This complicates the experimental investigation and numerical prediction of the wall wear as several parameters come into play during the operational lifetime of the thruster. This generally results in a lack of reliable data on the sputtering yield under operational conditions.
In choosing a thruster size, one generally balances efficiency against thruster lifetime. High-energy plasma in existing technology tends to adversely interact with the walls of the thruster, as stated above. Despite significant numerical and theoretical advances of the recent past, scientists lack an adequate design to operate the Hall thruster at high power for long duration missions.
Thus, it would be desirable to provide a high efficiency and long lifetime electric propulsion device which advantageously reduces the potential for device wall erosion.