Microdischarges for use as microthrusters: modelling and scaling

Abstract

Microsatellites with masses of tens of kilograms require only hundreds of micronewtons of thrust for station keeping and attitude control. Microdischarges (MDs) offer a compact way of generating such thrusts without using complex propulsion systems. In this paper, results from computational investigations of MDs sustained in Ar with tens of Torr back pressure are discussed with emphasis on conversion of discharge power into gas heating which can then be expanded in a nozzle to generate thrust. Typical cylindrical geometries have diameters of a few hundred micrometres and lengths of a few millimetres. We found that the gas temperature can exceed 1000 K for power densities of tens of kilowatts per cubic centimetre at back (upstream) pressures of tens of Torr. The nozzle length and location of the discharge in the MD channel are important from a gas dynamics viewpoint and so influence the incremental thrust (above that of the cold flow). Confining the discharge in the nozzle typically increases the peak gas temperature and the flow velocity, thereby potentially improving the performance of a MD used as a microthruster.

Self‐Consistent Simulations of Plasma and Gas Dynamics in Microplasmas with Metallic and Dielectric Electrodes

“…The discharge is initiated by releasing an electron swarm near the cathode, and the evolution is followed till the stage of particle over‐amplification. The initial cloud is consistent with values used in literature 32–34. It is interesting to note that the magnitude of the initial swarm may be important as it could govern the time scale of the evolution and inception of breakdown stages.…”

Spatiotemporal study of gas heating mechanisms in a radio-frequency electrothermal plasma micro-thruster

“…The neutral gas temperature is estimated using rovibrational spectroscopy of the N 2 second positive system (C 3 u →B 3 g ) between the wavelengths of 365 nm and 381 nm, capturing the (0,2), (1,3), (2,4), and (3,5) vibrational transition bands [14]. Simulated spectra are iteratively fitted to the experimental data to extract both vibrational temperature (T v ) and rotational temperature(T r ) using the same method as previously fully outlined in Greig et al [6].…”

“…Electrothermal micro-thrusters are a class of small thrusters designed for use on micro-or nanosatellites, based around propellant gas heating using electrical means [1][2][3]. Two common types of electrothermal thruster are the resistojet and arcjet, both variants having previously been deployed on satellite missions.…”

Direct Measurement of Axial Momentum Imparted by an Electrothermal Radiofrequency Plasma Micro-Thruster

“…As a result of the measurement procedure and the absence of a gas flow valve directly located at the plenum, it is expected that the measured value of F cold gas may be somewhat below the true cold gas thrust due to the residual gas trapped in the small diameter 4 m long teflon tubing gas line which requires hours to be effectively pumped out. This uncertainty may be combined with other effects related to the geometric details of the orifice/nozzle, its sonic surface, and the "free jet" expansion [18,19].…”