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. Nomenclature Cdiv = correction factor dA = increment of area F = force or thrust g = standard gravity I = current Isp = specific impulse m = mass p = pressure q = charge R = specific gas constant R x = reaction force T 0 = stagnation temperature Tx = x-component of temperature u = axial velocity v e = effective velocity γ = ratio of specific heats ΔV = electrostatic potential ρ = density