Application of the DSMC Method for Design of a Coaxial Microthruster Nozzle
The Direct Simulation Monte Carlo (DSMC) method is used to numerically simulate and design a micronozzle with improved performance. Thrust calculations using the DSMC method demonstrate that the coaxial micronozzles can achieve milli-Newton thrust levels with specific impulses on the order of 45 s using argon in a cold gas expansion. Improved micronozzle designs of coaxial microthrusters are also proposed. Coaxial micronozzles utilizing center-body geometries to exploit pressure thrust show about 140% increase in specific impulse at low Reynolds numbers compared to a traditional converging nozzle.
Microspike Based Chemical/Electric Thruster Concept for Versatile Nanosat Propulsion
††, * Small spacecraft that can be categorized as microsats, nanosats, and picosats has a strong potential for wide applications in communication, scientific experiments, and space exploration. In order to combine the advantages of both electric and chemical propulsion thrusters, a dual-mode microspike based thruster concept is proposed. For a fixed input power, it can operate in either a high-Isp mode or a high-thrust mode depending on the propulsive maneuver requirements. The hybrid thruster consists of a plug-annular cold or heated gas thruster in the chemical mode and a field emission thruster housed within the plug operating in the electric mode using a metallic propellant. The direct simulation Monte Carlo (DSMC) technique and the particle-in-cell technique are used to model the two different modes to estimate performance parameters of the thruster. The DSMC simulations show that the microspike nozzle can provide an improved specific impulse (Isp) at low Reynolds numbers when compared to a straight orifice or converging-diverging nozzle. The PIC simulations for the field emission thruster are shown to compute the current density, ion beam density, ion beam velocities and, hence, specific impulse and thrust accurately for conditions corresponding to earlier published experiments.
Effects of reservoir volume on performance of pulse tube cooler.
A pulse tube cooler has the advantages of long-life and low-vibration over conventional cryocoolers such as G-M and Stirling coolers because of the absence of moving parts at low temperature. On the other hand, the combination of a reservoir and orifice is indispensable to optimize the performance of pulse tube coolers. In order to make the pulse tube cooler compact for practical applications, the volume of reservoir should be minimized. This paper analyzes the effects of the reservoir volume on the thermodynamic performance of various components in a simple orifice and a double-inlet pulse tube cooler by combining a linearized model with a thermodynamic analysis. Expressions of entropy production for those components are presented. The results show that the reservoir volume has a significant influence on the entropy production in the various components when the reservoir to pulse tube volume ratio is smaller than about 5. The ratio is important to determine the minimum reservoir volume for a pulse tube cooler. Optimum settings for a double-inlet pulse tube cooler are also discussed.