Search

Theories for laser-atom interactions have been under development since the advent of laser technology. The theories have yet to be adequately integrated into kinetic flow solvers. Realizing this integration would greatly enhance the scaling of laser-species interactions beyond the realm of ultra-cold atomic physics. A representative numerical investigation was conducted using a custom collisionless gas particle trajectory code, demonstrating this goal in the present study. The investigation covered neutral atomic beam steering and collimation using near-resonant laser fields. In addition to the numerical investigation, a validating experiment was conducted. The experimental results showed good agreement with the numerical simulations when experimental parameters, such as finite laser line width, were taken into account. These simulations showed trends and some limitations associated with the use of a continuous-wave Gaussian laser fields for the steering and collimation of a geometrically skimmed cesium atomic beam using the photon scattering force and the near-resonant induced dipole gradient force. These simulations indicate possible integration of the resonant laser-atom interaction with other rarefied and collisional solvers for similar species such as alkali metals., For presentation at the International Symposium on Rarefied Gas Dynamics (27th), Monterey, CA, 10-15 July 2010. Prepared in collaboration with University of Colorado, Colorado Springs, CO and ERC Inc., Edwards AFB, CA. The original document contains color images. All DTIC reproductions will be in black and white.

A capillary discharge based pulsed plasma thruster is currently under development at the Air Force Research Laboratory. A torsion thrust stand has been developed to simultaneously measure the shot by shot total impulse and propellant mass loss of the thruster, yielding a per shot specific impulse. Competing design considerations affecting the performance of the thrust stand has lead to an optimized diagnostic tool capable of measuring total impulses up to 150 mN s with a resolution of 0.4 mN s and mass losses up to 18g with a resolution of 1 mg., Prepared in collaboration with ERC Inc., Edwards AFB, CA. For presentation at the AIAA Joint Propulsion Conference(44th), Hartford, CT, 20-23 Jul 2008. The original document contains color images. All DTIC reproductions will be in black and white. Document page chg per USAF AFMC AFRL/RZOI, Edwards AFB, CA on 1 Jun 2009.

The Direct Simulation Monte Carlo (DSMC) method was used to investigate the interaction between argon, nitrogen, and methane test gases and ten successive pulsed optical lattices. The one-dimensional lattices were formed by two 100 ps, 393 mJ, 532 nm, laser pulses and were assumed to be far from any electronic resonance. The sequential interaction represents multiple reflections within an optical cavity or the emission of high repetition rate pulsed lasers. The maximum centerline temperature was found as a function of the intervening time between the pulses. An optimum intervening time was found and related to the mean collision time and available unexcited energy modes. The optimum time shifted proportional to the change in gas pressure, thus collision time. During sequential pulses with intervening times near zero, subsequent pulses can act to cool the gas. For pulses with intervening times longer than the optimum, thermal diffusion carries energy away from the centerline, reducing the maximum temperature. The optimal intervening time was found to be 0.7, 1.0 and 0.25 ns for argon, nitrogen, and methane at one atmosphere respectively., Submitted for presentation at the International Symposium on Rarefied Gas Dynamics (26th), held in Kyoto, Japan, on July 21-25, 2008. Prepared in collaboration with University of Colorado at Colorado Springs; ERC, Inc., Edwards AFB; and Princeton University, Princeton, NJ. Sponsored in part by Air Force Office of Scientific Research (AFOSR).

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 150um 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: (1) polished smooth surfaces, (2) regular triangular roughness, and (3) regular square roughness with characteristic roughness scales of <1um, 11um, and 29um respectively. For the triangular roughness, mass flow reductions ranged from 6% at the higher stagnation pressures tested to 25% at the lower stagnation pressures tested when compared to the smooth channel., Published in the Jnl. Physics of Fluids, v19, p106101, 2007.

Advances in micro-technology manufacturing and capability have led to an increased interest in micro and nano-satellites. A propulsion system has been designed to meet the on-orbit attitude control requirements for nano-spacecraft. The Free Molecule Micro-Resistojet (FMMR), a low cost, low power, high propellant storage density, and green propulsion system, has been analyzed in this study to determine its ability to provide a slew maneuver for a typical 10 kg nanosatellite. Additionally, a FMMR technology demonstrator (TD) has been fabricated using traditional and Microelectromechanical Systems (MEMS) techniques. The TD has been analyzed and tested in this study to determine its performance characteristics while operating with water propellant. Experimental data shows that the FMMR, with a heated wall temperature of 580 K, can attain a specific impulse of 79.2 seconds with a thrust level of 129 micro-N. For a given mass flow, higher thrust levels can be achieved by increasing the temperature of the FMMR heater chip. The experimental results agree favorably with predicted values from kinetic theory. Applying the measured performance of the TD to an optimized setup, the FMMR system could provide a 45-degree slew of a typical nanosatellite in 60 seconds, which is acceptable for many nanosatellite applications., Submitted for publication in the Journal of Spacecraft and Rockets. Prepared in collaboration with University of Southern California, Los Angeles, CA.

A novel diagnostic technique has been developed, utilizing the Thrust Stand Mass Balance, to directly measure a time accurate mass flow from a solid-fuel thruster for systems where the mass flow rate is of the same order as the experimental error. The mass flow measurement technique has been verified using an idealized numerical simulation. Two calibration experiments have been performed to assess the dynamic response of the mass balance. First, a set of calibration weights were placed on the mass balance and removed in order to properly characterize the mass balance motion. Second, a known mass flow rate of water was deposited onto the test stand. As a proof of concept experiment, a 3.81cm diameter PMMA/GOx hybrid thruster core was burned and the propellant mass flow was measured. Variations in the GOx flow rate resulted in corresponding variations in the total propellant mass flow as expected, showing the utility of the Thrust Stand Mass Balance as a mass flow measurement device., Presented at the AIAA/ASME/SAE/ASEE Joint Propulsion Conference and Exhibit (43rd), paper no. AIAA-2007-5364, held in Cincinnati, OH, on 8-11 Jul 2007. Prepared in collaboration with University of Southern California (USC), Los Angeles, CA.

Advances in micro-technology manufacturing and capability have led to an increased interest in micro and nanosatellites. A propulsion system has been designed to meet the on-orbit attitude control requirements for nanospacecraft. The Free Molecule Micro-Resistojet (FMMR), a low cost, low power, high propellant storage density, and green propulsion system, has been analyzed in this study to determine its ability to provide a slew maneuver for a typical 10 kg nanosatellite. Additionally, a FMMR technology demonstrator (TD) has been fabricated using traditional and Microelectromechanical Systems (MEMS) techniques. The TD has been analyzed and tested in this study to determine its performance characteristics while operating with water propellant. Experimental data shows that the FMMR, with a heated wall temperature of 580 K, can attain a specific impulse of 79.2 seconds with a thrust level of 129 micro-N. For a given mass flow, higher thrust levels can be achieved by increasing the temperature of the FMMR heater chip. The experimental results agree favorably with predicted values from kinetic theory. Applying the measured performance of the TD to an optimized setup, the FMMR system could provide a 45-degree slew of a typical nanosatellite in 60 seconds, which is acceptable for many nanosatellite applications., Presented at the AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit (43rd) in Cincinnati, OH on 8-11Jul 2007. Published in proceedings of the same as paper AIAA 2007-5185.