Development of a pneumatic high-angle-of-attack flush airdata sensing (HI-FADS) system

A nonintrusive high-angle-of-attack flush airdata sensing system was installed and flight tested in the F-18 High Alpha Research Vehicle. This system consists of a matrix of 25 pressure orifices arranged in concentric circles on the nose of the vehicle to determine angles of attack and sideslip, Mach number, and pressure altitude. During the course of the flight tests, it was determined that satisfactory results could be achieved using a subset of just nine ports

Formulation of a General Technique for Predicting Pneumatic Attenuation Errors in Airborne Pressure Sensing Devices

Presented is a mathematical model derived from the Navier-Stokes equations of momentum and continuity, which may be accurately used to predict the behavior of conventionally mounted pneumatic sensing systems subject to arbitrary pressure inputs. Numerical techniques for solving the general model are developed. Both step and frequency response lab tests were performed. These data are compared with solutions of the mathematical model and show excellent agreement. The procedures used to obtain the lab data are described. In-flight step and frequency response data were obtained. Comparisons with numerical solutions of the math model show good agreement. Procedures used to obtain the flight data are described. Difficulties encountered with obtaining the flight data are discussed

Environmental influences on galaxy evolution

We investigate the role of mergers and interactions in the evolution of galaxies by studying galaxies in compact groups. Compact groups of galaxies have high spatial densities and low velocity dispersions making these regions ideal laboratories in which to study the effect of interactions and mergers. Based on a detailed spectroscopic and multi-color imaging study, we find that both the isophotal shapes and the stellar kinematics indicate that many of the elliptical galaxies in compact groups have been affected by tidal interactions. At the same time, however, we find that only a few elliptical galaxies in compact groups have evidence for the young stellar populations that would be expected if they are the result of recent merger of two spiral galaxies. Therefore, we conclude that tidal interactions affect galaxy properties at the current epoch, but the bulk of basic galaxy formation and transformation must have occurred at much higher redshift

Compensating for pneumatic distortion in pressure sensing devices

A technique of compensating for pneumatic distortion in pressure sensing devices was developed and verified. This compensation allows conventional pressure sensing technology to obtain improved unsteady pressure measurements. Pressure distortion caused by frictional attenuation and pneumatic resonance within the sensing system makes obtaining unsteady pressure measurements by conventional sensors difficult. Most distortion occurs within the pneumatic tubing which transmits pressure impulses from the aircraft's surface to the measurement transducer. To avoid pneumatic distortion, experiment designers mount the pressure sensor at the surface of the aircraft, (called in-situ mounting). In-situ transducers cannot always fit in the available space and sometimes pneumatic tubing must be run from the aircraft's surface to the pressure transducer. A technique to measure unsteady pressure data using conventional pressure sensing technology was developed. A pneumatic distortion model is reduced to a low-order, state-variable model retaining most of the dynamic characteristics of the full model. The reduced-order model is coupled with results from minimum variance estimation theory to develop an algorithm to compensate for the effects of pneumatic distortion. Both postflight and real-time algorithms are developed and evaluated using simulated and flight data

A preliminary look at techniques used to obtain airdata from flight at high angles of attack

Flight research at high angles of attack has posed new problems for airdata measurements. New sensors and techniques for measuring the standard airdata quantities of static pressure, dynamic pressure, angle of attack, and angle of sideslip were subsequently developed. The ongoing airdata research supporting NASA's F-18 high alpha research program is updated. Included are the techniques used and the preliminary results. The F-18 aircraft was flown with three research airdata systems: a standard airdata probe on the right wingtip, a self-aligning airdata probe on the left wingtip, and a flush airdata system on the nose cone. The primary research goal was to obtain steady-state calibrations for each airdata system up to an angle of attack of 50 deg. This goal was accomplished and preliminary accuracies of the three airdata systems were assessed and are presented. An effort to improve the fidelity of the airdata measurements during dynamic maneuvering is also discussed. This involved enhancement of the aerodynamic data with data obtained from linear accelerometers, rate gyros, and attitude gyros. Preliminary results of this technique are presented

Three-Dimensional Printing of Green Fuels for Low-Cost Small Spacecraft Propulsion Systems

This paper details the advantages of employing modern additive manufacturing methods to fabricate hybrid rocket fuels for intrinsically safe and green small spacecraft propulsion systems. Using additive manufacturing overcomes multiple issues frequently associated with hybrid propulsion, including poor volumetric efficiency, system ignitability, and low fuel regression rates. When certain three-dimensionally printed thermoplastics are subjected to a high-voltage low-wattage charge, electrostatic arcing along the surface pyrolizes a small amount of material that, with the introduction of an oxidizer, “seeds” combustion and produces immediate and reliable ignition. Thermoplastic fuel grains can be printed with port shapes that enhance burn properties and increase volumetric efficiencies. Embedded helical fuel ports significantly increase regression rates. The presented test results from several prototype systems using gaseous oxygen and printed acrylonitrile butadiene styrene demonstrate the various advantages of additive manufacturing, including low-power ignition, regression rate enhancement, and system scalability. The test results from both ambient and vacuum tests of a 25 N flight-weight small spacecraft thruster are presented. Multiple burn tests allowed statistical characterization of ignition timing and burn-to-burn thrust, as well as total impulse consistency. The test results demonstrating specific impulse values exceeding 295 s are presented. When fully developed, this propulsion technology has the potential for “drop-in” replacement of many hydrazine-based propulsion applications

Frequency Response of Pressure Sensor Configurations in Slip-Flow Conditions

The article of record as published may be found at http://dx.doi.org/10.2514/2.3823A dynamic model is presented for pneumatic tubing and pressure sensor configurations in rarefied slip-flow conditions. The model uses the linearized Navier–Stokes equations, with the boundary conditions extended to allow for rarefied conditions. At low pressure levels, the modified wall boundary condition allows fluid elements to slip when directly in contact with the tubing wall. This slippage effectively lowers fluid viscosity. Dynamic effects of the rarefied-flow extension are demonstrated by comparing rarefied-flow solutions to equivalent solutions generated using continuum-flow models. Lower viscosity resulting from rarefied flow causes the configuration response to be less damped than for similar conditions without molecular effects. Comparing steady-state response to data from a series of laboratory experiments validates the range of the rarefied-flow model. When pneumatic tubing is heated unevenly, rarefied flow forces the tube hot end to have higher pressure than the cold end, with no net flow along the tube. This pressure difference results in a dc offset in the measured pressure reading. Comparisons of the steady-state model to experimental data show that the slip-flow model is generally applicable for Knudsen numbers up to approximately 0.65. Beyond 0.7 Knudsen number, molecular effects dominate, and the model is no longer applicable to the problem physics

Nytrox as “Drop-in” Replacement for Gaseous Oxygen in SmallSat Hybrid Propulsion Systems

A medical grade nitrous oxide (N2O) and gaseous oxygen (GOX) “Nytrox” blend is investigated as a volumetrically-efficient replacement for GOX in SmallSat-scale hybrid propulsion systems. Combined with 3-D printed acrylonitrile butadiene styrene (ABS), the propellants represent a significantly safer, but superior performing, alternative to environmentally-unsustainable spacecraft propellants like hydrazine. In a manner analogous to the creation of soda-water using dissolved carbon dioxide, Nytrox is created by bubbling GOX under pressure into N2O until the solution reaches saturation. Oxygen in the ullage dilutes N2O vapor and increases the required decomposition energy barrier by several orders of magnitude. Thus, risks associated with inadvertent thermal or catalytic N2O decomposition are virtually eliminated. Preliminary results of a test-and-evaluation campaign are reported. A small spacecraft thruster is first tested using gaseous oxygen and 3-D printed ABS as the baseline propellants. Tests were then repeated using Nytrox as a “drop-in” replacement for GOX. Parameters compared include ignition reliability, latency, initiation energy, thrust coefficient, characteristic velocity, specific impulse, combustion efficiency, and fuel regression rate. Tests demonstrate Nytrox as an effective replacement for GOX, exhibiting a slightly reduced specific impulse, but with significantly higher volumetric efficiency. Vacuum specific impulse exceeding 300 s is reported. Future research topics are recommended

Effects of Radiation Heating on Additively Printed Hybrid Fuel Grain Oxidizer-To-Fuel Ratio Shift

Utah State University has researched and developed a hybrid rocket system that uses a non-toxic, simple, and 3D printed plastic as the fuel. This plastic is ABS (acrylonitrile butadiene styrene) which is a common material used in pipe systems, automotive components, and toys such as Lego bricks. As a fuel, ABS has structural properties that outweigh other polymer fuels; has matching or better performance than most commonly used propellants; is an environmentally-friendly fuel; and is easily manufactured and assembled. Furthermore, Utah State University has developed a novel ignition technology for hybrid rocket systems that involves pyrolyzing a marginal portion of the ABS fuel into a vapor rich in hydrocarbons which, when introduced to an oxidizer, initiates rapid combustion. Thus, the system simply requires a valve and spark command which grants restart and throttle capability. Although this technology has the potential to become a game-changing propulsion system for both the launch vehicles and small satellite communities, its performance and stability are still relatively uncharacterized. Many tests have been implemented at Utah State University and the performance model continues to be improved still. Recently, we have conducted tests on smaller-scale motors suited towards small spacecraft and have noticed a surprising trend in the oxidizer-to-fuel (O/F) ratio. Most results for hybrid rocket performance indicate that this ratio increases as the fuel is burned away, meaning that the combustion product becomes more oxidizer-rich as the motor is being fired. However, the results from the smaller-scale motors indicate that the oxidizer-to-fuel ratio decreases as the fuel is burned away. We believe that this trend towards a more fuel-rich burn is due to a neglected radiation effect that enhances the fuel regression rate. The goal of this research is to investigate this phenomena through running extensive tests as well as redevelop the equations describing fuel regression rate