Taylor Lilly

Performance testing of a microfabricated propulsion system for nanosatellite applications

Abstract : There is a growing interest in the use of micro and nanosatellites within the aerospace community. Constellations of small satellites may eventually replace much larger, single function spacecraft as a cheaper, more flexible alternative. Micro-technologies will be required to enable small satellite missions including efficient, low-cost propulsion systems for maneuvering. A MEMS fabricated propulsion system has been developed for maneuvers on an upcoming University nanosatellite mission. The Free Molecule Micro-Resistojet (FMMR) is an electrothermal propulsion system designed for on-orbit maneuvers of nanosatellites, which are defined as spacecraft with an initial mass less than 10 kg. The FMMR has been tested using a torsion force balance to assess its performance using a variety of propellants including helium, argon, nitrogen and carbon dioxide. The experimental performance results compare favorably with results obtained from gas kinetic theory, which were used in the design phase to estimate the thrusters performance. The measured performance of the FMMR in this study has proven to be adequate to perform attitude control maneuvers for the University nanosatellite mission.

Measurements and computations of mass flow and momentum flux through short tubes in rarefied gases

Gas flows through orifices and short tubes have been extensively studied from the 1960s through the 1980s for both fundamental and practical reasons. These flows are a basic and often important element of various modern gas driven instruments. Recent advances in micro- and nanoscale technologies have paved the way for a generation of miniaturized devices in various application areas, from clinical analyses to biochemical detection to aerospace propulsion. The latter is the main area of interest of this study, where rarefied gas flow into a vacuum through short tubes with thickness-to-diameter ratios varying from 0.015 to 1.2 is investigated both experimentally and numerically with kinetic and continuum approaches. Helium and nitrogen gases are used in the range of Reynolds numbers from 0.02 to 770 (based on the tube diameter), corresponding to Knudsen numbers from 40 down to about 0.001. Propulsion properties of relatively thin and thick tubes are examined. Good agreement between experimental and numerica...

Numerical and experimental investigation of microchannel flows with rough surfaces

A conical surface roughness model applicable to particle simulations has been developed. The model has been experimentally validated for channel flows using helium and nitrogen gases at Reynolds numbers from 0.01 to 10 based on inlet conditions. To efficiently simulate gas-surface interaction, molecular collisions with the actual rough surface are simulated by collisions with a randomly positioned conical hole having a fixed opening angle. This model requires only one surface parameter, average surface roughness angle. This model has also been linked to the Cercignani-Lampis scattering kernel as a required reference for use in deterministic kinetic solvers. Experiments were conducted on transitional flows through a 150μm tall, 1cm wide, 1.5cm long microchannel where the mean free path is on the order of the roughness size. The channel walls were made of silicon with: (i) polished smooth surfaces, (ii) regular triangular roughness, and (iii) regular square roughness with characteristic roughness scales of ...

Development of a Specific Impulse Balance for Capillary Discharge Pulsed Plasma Thrusters

tot mpropg0 (1) where Itot is the total impulse, mprop is the total propellant mass loss, and g0 is the gravitational constant. The thruster will be configured on the thrust stand such that the impulse generated by the discharge and the steady-state force generated by the propellant mass loss act in the same direction. The combined signal from these effects can then be decoupled to assess the ratio of the impulse to the weight of propellant expended, yielding the specific impulse.

Nozzle Plume Impingement on Spacecraft Surfaces: Effects of Surface Roughness

An experimental and numerical effort was undertaken to assess the effects of a cold-gas (To =300 K) nozzle plume impinging on simulated spacecraft surfaces. The nozzle flow impingement is investigated experimentally using a nanonewton resolution force balance and numerically using the direct simulation Monte Carlo numerical technique. The Reynolds number range investigated in this study is from approximately 2 to 350 using nitrogen propellant. The thrust produced by the nozzle was first assessed on a force balance to provide a baseline case. Subsequently, aluminum plates were attached to the same force balance parallel to the plume flow to simulate spacecraft surfaces in proximity to the thruster. Three plates were used, an electropolished plate with smooth surface and two rough surface plates with equally spaced rectangular and triangular grooves. A 15% degradation in thrust was observed both experimentally and numerically for the plate relative to the free plume expansion case. The effect of surface roughness on thrust was found to be small due to molecules backscattered from the plate to the nozzle plenum wall. Additionally, the influence of surface roughness in the diverging part of the nozzle on thrust was examined numerically and found to be significant at Reynolds numbers less than 10.

Development of a Thrust Stand Micro-Balance to Assess Micropropulsion Performance

Abstract : As proposed spacecraft and their associated thrusters have become smaller, technology has been developed to meet the demand for performance measurements for the extremely low force levels produced. For such thrusters, it is also desirable to measure the mass changes resulting from the utilization of propellant associated with either the steady state thrust or transient impulses. A thrust stand and novel data analysis method is presented to make both thrust (or impulse) and mass change measurements concurrently. It is shown that very accurate and repeatable measurements of mass can be made using an existing thrust stand system. Furthermore, it is shown that impulse and mass measurements can be resolved at the same time from a single thrust stand trace.

Experimental and Numerical Study of Nozzle Plume Impingement on Spacecraft Surfaces

An experimental and numerical effort was undertaken to assess the effects of a cold gas (To=300K) nozzle plume impinging on a simulated spacecraft surface. The nozzle flow impingement is investigated experimentally using a nano‐Newton resolution force balance and numerically using the Direct Simulation Monte Carlo (DSMC) numerical technique. The Reynolds number range investigated in this study is from 0.5 to approximately 900 using helium and nitrogen propellants. The thrust produced by the nozzle was first assessed on a force balance to provide a baseline case. Subsequently, an aluminum plate was attached to the same force balance at various angles from 0° (parallel to the plume flow) to 10°. For low Reynolds number helium flow, a 16.5% decrease in thrust was measured for the plate at 0° relative to the free plume expansion case. For low Reynolds number nitrogen flow, the difference was found to be 12%. The thrust degradation was found to decrease at higher Reynolds numbers and larger plate angles.

Experimental and Numerical Modeling of Rarefied Gas Flows Through Orifices and Short Tubes

Flow through circular orifices with thickness‐to‐diameter ratios varying from 0.015 to 1.2 is studied experimentally and numerically with kinetic and continuum approaches. Helium and nitrogen gases are used in the range of Reynolds numbers from 0.02 to over 700. Good agreement between experimental and numerical results is observed for mass flow and thrust corrected for the experimental facility background pressure. For thick‐to‐thin orifice ratios of mass flow and thrust vs pressure, a minimum is established. The thick orifice propulsion efficiency is much higher than that of a thin orifice. The effects of edge roundness and surface specularity on a thick orifice specific impulse were found to be relatively small.

Free Molecule Micro-Resistojet: Nanosatellite Propulsion

Constellations and platoons of small satellites can offer an assortment of benefits over larger, single function spacecraft. The strict mass, volume, and power limitations of small satellites will require unique micro-technologies to help develop efficient propulsion systems for maneuvering. The Free Molecule Micro-Resistojet (FMMR) has been analyzed and tested in this study to determine its applicability for an upcoming Texas A&M (TAM) nanosatellite mission. The nanosatellite mission will demonstrate the performance and survivability of a water propelled FMMR for attitude control maneuvers and could mark the first meaningful operation of a Microelectromechanical Systems (MEMS) fabricated thruster in space. The Mark 3.1 design of the FMMR heater chip uses a deposited serpentine heater pattern to resistively heat a gaseous propellant expanding through long (13 mm), narrow (100 µm) slots. Experimental data shows that the FMMR, with a heated wall temperature of 575 K, can attain a specific impulse of 65 seconds with a thrust level of 1.2 mN for a nitrogen gas propellant with a mass flow of 100 SCCM. The expected specific impulse when run on a water vapor propellant is expected to be 80 sec at similar thrust levels. Higher thrust levels can be achieved by increasing the temperature of the FMMR heater chip and / or the propellant mass flow through the expansion slots. The measured performance of the FMMR in this study has proven to be adequate to perform the attitude control maneuver for the TAM nanosatellite.

Neutral gas heating via non-resonant optical lattices

Energy deposition from high intensity pulsed optical lattices to a neutral gas was experimentally recorded for molecular nitrogen at 300/500 K and methane at 300 K. The magnitude of acoustic waves generated by the interaction was experimentally measured and simulated using the direct simulation Monte-Carlo method. The relationship between the lattice velocity and the measured acoustic wave magnitude was compared to numerical simulation which both exhibited dependence on lattice velocity, indicating that the detected pressure wave was the result of gas heating from the optical lattice and not from other forms of laser energy deposition.