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Jung T.P.,University of Colorado at Boulder | Starkey R.P.,University of Colorado at Boulder | Argrow B.,University of Colorado at Boulder | Argrow B.,Research and Engineering Center for Unmanned Vehicles
Journal of Aircraft | Year: 2012

As a sonic boom pressure signal propagates through the atmosphere, the age variable that quantifies nonlinear distortions approaches an asymptotic limit. As this limit is approached, distortion of the pressure signal decreases until it is "frozen." For an aircraft at 51,000 ft and Mach 1.7, the age variable is still 24% away from this limit. Alternatively, a sonic boom may be frozen by balancing lobes in the F function. Software, based on modified linear theory, is used to design an supersonic business jet that uses lifting components to create a lobe-balanced sonic boom. Leading and trailing shock pressure rise, peak overpressure, and perceived level of loudness are evaluated for a several configurations. In one case, the leading shock is reduced from 1.4 to 0.83 psf, and in another, the trailing shock is reduced from 1.2 to 0.87 psf. The software also calculates performance metrics to ensure reasonable longitudinal stability and performance. Off-track signatures demonstrate multishock sonic booms to the sides. Sonic booms are compared with computational fluid dynamics to demonstrate the accuracy of the method. Source

Roadman J.,University of Colorado at Boulder | Elston J.,University of Colorado at Boulder | Argrow B.,University of Colorado at Boulder | Argrow B.,Research and Engineering Center for Unmanned Vehicles | Frew E.,University of Colorado at Boulder
Journal of Aircraft | Year: 2012

The Tempest unmanned aircraft system was developed to demonstrate the feasibility of sampling severe convective storms with small unmanned aircraft. The unmanned aircraft system, including its ground support vehicles, was deployed during the Spring 2010 VORTEX2 (second Verification of the Origins of Rotation in Tornadoes Experiment) field experiment. The purpose was validation and verification of the systems, capabilities, and effectiveness of a small unmanned aircraft system to operate in a supercell thunderstorm, within current airspace regulatory constraints. The mission concept of operations that determined the performance requirements for the airframe, and command, control, and communications systems, is presented. The airframe design process is described, with emphasis on design solutions unique to a low-cost, portable storm-penetrating unmanned aircraft system. Results from test flights and from the Spring 2010 VORTEX2 deployment are compared to evaluate the performance of the airframe subsystems, particularly the autopilot. A preliminary analysis of the local atmospheric turbulence spectrum is also presented. Finally, conclusions are presented with a discussion of the engineering and science needs for the next-generation storm-penetrating unmanned aircraft system. Source

Argrow B.M.,Research and Engineering Center for Unmanned Vehicles | Palo S.E.,Colorado Center for Astrodynamics Research
Journal of Spacecraft and Rockets | Year: 2010

The energy-accommodation coefficient is an important parameter affecting satellite drag and orbit predictions. Previous estimates of this coefficient have been based on interpolation from values tabulated at several altitudes and solar conditions. In an effort to improve drag coefficient accuracy and to compute values of the accommodation coefficient that respond to the real variability of the atmosphere, a first-principles approach is desired. The present work combines the theory that gas-surface interactions in low Earth orbit are driven by adsorption of atomic oxygen, with observations of satellite accommodation collected during solar cycle 22. The result is a semiempirical model based on Langmuir's adsorption isotherm, which agrees with the data to within 3%. This model can be used to improve drag predictions during a wide range of space weather conditions, as well as to improve the accuracy for atmospheric densities derived from satellite drag. © 2010 by the American Institute of Aeronautics and Astronautics, Inc. Source

Moe K.,Space Environment Technologies, LLC | Palo S.E.,Colorado Center for Astrodynamics | Argrow B.M.,Research and Engineering Center for Unmanned Vehicles
Journal of the Astronautical Sciences | Year: 2011

The first absolute measurement of thermospheric density was made by combining simultaneous observations of spin and semimajor axis decay of Explorer VI. Providing two independent measures of the interaction with the airstream enabled the determination of both air density and drag coefficient. Then by using a realistic model of the gas-surface interaction, the energy accommodation coefficient was determined. Only four such measurements were made prior to the time of writing. In this paper, we review the history of paddlewheel measurements and explain their importance to ongoing work in satellite drag. Next, a novel concept for paddlewheel satellites based on the CubeSat platform is discussed along with the relevant design parameters. A rudimentary error analysis for paddlewheel measurements evaluated the feasibility of these designs and it was found that the drag torques generated on a three-kilogram paddlewheel are within the measurement capabilities of today's technologies. For certain types of paddlewheel configurations, the use of direct simulation methods is important for accurately analyzing the data. This is because a paddlewheel with the spin axis oriented in the orbit normal direction undergoes significant flow-shadowing and this is not easily represented by analytical methods. Increasing the availability of accommodation measurements via the paddlewheel method represents an improvement in the accuracy of Earth's total density models as well as the understanding of gas-surface interactions in low Earth orbit. This is of profound importance in the prediction of satellite orbits as well as the understanding of atmospheric phenomena. Source

Pilinski M.D.,University of Colorado at Boulder | Pilinski M.D.,Research and Engineering Center for Unmanned Vehicles | Argrow B.M.,University of Colorado at Boulder | Argrow B.M.,Research and Engineering Center for Unmanned Vehicles | And 3 more authors.
Journal of Spacecraft and Rockets | Year: 2013

Orbits of launch-vehicle upper stages and spheres were observed by U.S. Air Force Space Command, and the resulting observations were converted by the Space Analysis Office to fitted ballistic coefficients by comparing the observed orbit with an orbit predicted by an atmospheric-drag model. The ballistic coefficients contain signals that result from atmospheric variability not captured by the model as well as signals that correspond to changes in the satellite-drag coefficient. For objects in highly elliptical orbits with perigee altitudes below 200 km a 50% change in ballistic coefficient can be observed. This drastic change is associated with both changes in the energy accommodation coefficient driven by atomic-oxygen adsorption and entry into a transition flow region where a diffuse shock forms ahead of the satellite near perigee. Furthermore, the observed ballistic coefficients for objects in near-circular orbits (7.5 km/s speeds) do not match those of objects in highly eccentric orbits (10 km/s speeds near perigee). This difference is attributed to a decrease in adsorption efficiency postulated by previous researchers that is formalized in this work into a semi-empirical model. The model parameters suggest that the average binding energy of atomic oxygen on satellite surfaces is about 5.7 eV. Copyright © 2012 by the American Institute of Aeronautics and Astronautics, Inc. Source

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