Pacific Palisades, CA, United States
Pacific Palisades, CA, United States

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Moe K.,Space Environment Technologies, LLC | Wu Q.,High Altitude Observatory
Journal of Geophysical Research: Space Physics | Year: 2014

The recent HIWIND (High-Altitude Interferometer Wind Observations) balloon measurements have revealed persistent equatorward winds in the dayside thermosphere during geomagnetically quiet times. Although this result does not agree with some current thermospheric density models, it is consistent with an earlier thermospheric density model (M1975) which includes the energy input through the magnetospheric dayside cusps during geomagnetically quiet times. We show the thermospheric density distribution with and without the magnetospheric input to illustrate the effect of the density gradient on the winds at high latitudes. We review the early history of the development of our understanding of the energy input to the high-latitude thermosphere. Future HIWIND measurements can add to our understanding and lead to improved models of thermospheric densities and winds. Key Points Recent HIWIND measurements disagree with most thermospheric density models They do agree with a model which includes energy from the magnetosphere More HIWIND measurements are needed ©2014. American Geophysical Union. All Rights Reserved.


Pardini C.,CNR Institute of Information Science and Technologies Alessandro Faedo | Moe K.,Space Environment Technologies, LLC | Anselmo L.,CNR Institute of Information Science and Technologies Alessandro Faedo
Planetary and Space Science | Year: 2012

Uncertainties in the neutral density estimation are the major source of aerodynamic drag errors and one of the main limiting factors in the accuracy of the orbit prediction and determination process at low altitudes. Massive efforts have been made over the years to constantly improve the existing operational density models, or to create even more precise and sophisticated tools. Special attention has also been paid to research more appropriate solar and geomagnetic indices. However, the operational models still suffer from weakness. Even if a number of studies have been carried out in the last few years to define the performance improvements, further critical assessments are necessary to evaluate and compare the models at different altitudes and solar activity conditions. Taking advantage of the results of a previous study, an investigation of thermospheric density model biases during the last sunspot maximum (October 1999 - December 2002) was carried out by analyzing the semi-major axis decay of four satellites: Cosmos 2265, Cosmos 2332, SNOE and Clementine. Six thermospheric density models, widely used in spacecraft operations, were analyzed: JR-71, MSISE-90, NRLMSISE-00, GOST-2004, JB2006 and JB2008. During the time span considered, for each satellite and atmospheric density model, a fitted drag coefficient was solved for and then compared with the calculated physical drag coefficient. It was therefore possible to derive the average density biases of the thermospheric models during the maximum of the 23 rd solar cycle. Below 500 km, all the models overestimated the average atmospheric density by amounts varying between 7% and 20%. This was an inevitable consequence of constructing thermospheric models from density data obtained by assuming a fixed drag coefficient, independent of altitude. Because the uncertainty affecting the drag coefficient measurements was about 3% at both 200 km and 480 km of altitude, the calculated air density biases below 500 km were statistically significant. The minimum average biases were obtained with JB2008, NRLMSISE-00 and GOST-2004. Above 500 km, where only one satellite was analyzed (at 630 km), and errors tend to increase with altitude, it cannot be asserted that the calculated biases are significant. Nevertheless, they are presented to show how the various models diverge at higher altitudes. Around 630 km, NRLMSISE-00 had a negligible average bias, while the other models underestimated (GOST-2004) or overestimated the average density, by amounts varying between 6% and 16%. However, in terms of semi-major axis root mean square residuals, JB2006 and JB2008 were the best in any case. Below 500 km, the short-term behavior of the models was also investigated by fitting the semi-major axis decay over 30-day arcs. The resulting fitted drag coefficients displayed a significant variability, probably associated with mismodeled density variations, but JB2008, followed by JB2006, provided the smallest semi-major axis residuals and a reduced short-term variability of the density bias at just a few frequencies, having been probably successful in removing a significant fraction of the mismodeling sources. © 2012 Elsevier Ltd. All rights reserved.


Weimer D.R.,Virginia Polytechnic Institute and State University | Bowman B.R.,U.S. Air force | Sutton E.K.,Air Force Research Lab | Tobiska W.K.,Space Environment Technologies, LLC
Journal of Geophysical Research: Space Physics | Year: 2011

The total Poynting flux flowing into both polar hemispheres as a function of time, computed with an empirical model, is compared with measurements of neutral densities in the thermosphere at two altitudes obtained from accelerometers on the CHAMP and GRACE satellites. The Jacchia-Bowman 2008 empirical thermospheric density model (JB2008) is used to facilitate the comparison. This model calculates a background level for the "global nighttime minimum exospheric temperature," ΔTc, from solar indices. Corrections to this background level due to auroral heating, ΔTc, are presently computed from the Dst index. A proxy measurement of this temperature difference, ΔTc, is obtained by matching the CHAMP and GRACE density measurements with the JB2008 model. Through the use of a differential equation, the Tc correction can be predicted from IMF values. The resulting calculations correlate very well with the orbit-averaged measurements of ΔTc, and correlate better than the values derived from Dst. Results indicate that the thermosphere cools faster following time periods with greater ionospheric heating. The enhanced cooling is likely due to nitric oxide (NO) that is produced at a higher rate in proportion to the ionospheric heating, and this effect is simulated in the differential equations. As the ΔTc temperature correction from this model can be used as a direct substitute for the Dst-derived correction that is now used in JB200, it could be possible to predict ΔTc with greater accuracy and lead time. Copyright 2011 by the American Geophysical Union.


Moe K.,Space Environment Technologies, LLC | Moe M.M.,Space Environment Technologies, LLC
AIP Conference Proceedings | Year: 2011

When the space age began, some aerodynamicists expected that the surfaces of spacecraft would be cleaned by desorption in the high vacuum of space; while others, familiar with experiments on engineering surfaces, believed that satellite surfaces would be contaminated. During subsequent decades, satellite evidence has accumulated, showing that surfaces in low-Earth orbit are contaminated by adsorbed atomic oxygen and its reaction products. These contaminants cause accommodation coefficients to be high, and the angular distribution of reemitted molecules to be nearly diffuse. These surface conditions must be considered in calculating satellite drag coefficients in free-molecular flow. We describe the experimental and theoretical developments which have led to these conclusions. © 2011 American Institute of Physics.


Moe K.,Space Environment Technologies, LLC | Moe M.M.,Space Environment Technologies, LLC
Space Weather | Year: 2011

Improvements in knowledge of satellite drag coefficients confirm current reports of a long-term decline in thermospheric density. Operational thermospheric models, though highly sophisticated, did not predict the extent of the decline, posing a problem for orbit control and maintenance. Evidence is presented that current models could not predict the magnitude of the decline for two reasons: (1) they do not realistically describe the highly variable energy entering the thermosphere from the solar wind at all times, especially at geomagnetically quiet times, and (2) they overestimate the less volatile ultraviolet contribution by ignoring eddy diffusion which transfers energy from the thermosphere to the mesosphere. The historical background of operational thermospheric models and suggestions for improvement are provided. Copyright 2011 by the American Geophysical Union.


Grant
Agency: NSF | Branch: Standard Grant | Program: | Phase: PLANETARY ASTRONOMY | Award Amount: 382.97K | Year: 2015

The goal of this program is to determine limits for the rate of atmospheric escape from the moon Europa into Jupiters plasma sheet. The research will constrain important properties of Europas atmosphere, including the presence of H2O vented from a subsurface ocean. To accomplish its goals, the project will model the Europa plasma sheet to determine plasma diffusion probabilities, lifetimes and mass loading rates.

Broader impacts of the work include training of undergraduate and graduate students. The work could inform future decisions on whether a dedicated space mission to Europa is warranted.


Grant
Agency: National Aeronautics and Space Administration | Branch: | Program: SBIR | Phase: Phase II | Award Amount: 774.94K | Year: 2012

The existing state-of-the-art for physics-based, data-driven, climatological specification of the global radiation environment is the capability embodied by Nowcast of Atmospheric Ionizing Radiation for Aviation Safety (NAIRAS) and supported by the validation activity in the Automated Radiation Measurements for Aviation Safety (ARMAS) project Phase I. In Phase II the ARMAS team will: i) integrate, fly, and operate two micro dosimeters on aircraft; ii) validate and calibrate the micro dosimeters with a tissue equivalent proportional counter; iii) retrieve the micro dosimeter dose and dose rate data in real-time via an automated downlink system; iv) use the dose and dose rate measurements in a data assimilation algorithm to correct the NAIRAS model dose and dose rate output along the flight track; and v) report the corrected dose and dose rate via server, web, Google Earth, and smart phone apps for aviation safety.


Grant
Agency: National Aeronautics and Space Administration | Branch: | Program: SBIR | Phase: Phase I | Award Amount: 100.00K | Year: 2011

Commercial aircrew members and frequent flyers face radiation hazards from the effects of cosmic rays and solar energetic particles. During significant solar events, dose rates can exceed safety thresholds. To mitigate the radiation dose rate and total dose hazards, a unique, state-of-the-art system of physics-based models and real-time data characterizing the aviation radiation environment called Nowcast of Atmospheric Ionizing Radiation for Aviation Safety (NAIRAS) is undergoing development. However, validation of the NAIRAS system must occur to provide confidence that accurate nowcasts, and eventually forecasts, can be made for the aviation radiation environment. The Automated Radiation Measurements for Aviation Safety (ARMAS) project will provide that validation in a cost-effective manner. The Tissue Equivalent Proportional Counter (TEPC) radiation detector measures the rate and total quantities of absorbed dose and dose equivalent during aircraft flights. These measurements help estimate the biological risk associated with radiation exposure to humans. Up to three flights of TEPC will be flown during the first half of the performance period. The flight regimes are designed to test a range of representative radiation environments. TEPC results will be analyzed in the second half of the performance period and compared with NAIRAS to validate modeled flight profile results.


Shemansky D.E.,Space Environment Technologies, LLC | Liu X.,Space Environment Technologies, LLC
Canadian Journal of Physics | Year: 2012

Stellar occultations of the Saturn atmosphere using the Cassini ultraviolet imaging spectrograph (UVIS) experiment have provided vertical structure at a range of latitudes. The transmission spectra in the extreme-far ultraviolet (EUV-FUV) range allow extraction of vertical profiles of H 2 and hydrocarbon abundances from the top of the atmosphere to about 300 km above the 1 bar (1 bar = 100 kPa) pressure level. A reanalysis of the Voyager 2 δSco occultation in 1981 is consistent with the original report. The hydrocarbon homopause is near a pressure of 0.2 μbar in the UVIS analysis, compared to ∼0.01 μbar obtained from the Voyager occultation. Measured hydrocarbon abundances are obtained in the pressure range 600-0.1 μbar in the Cassini UVIS experiment. The combined UVIS results provide evidence for significant latitudinal dependence of vertical temperature profile. The confinement of the hydrocarbons in the current observations compared to published models and the Voyager ultraviolet spectrograph (UVS) results at solar maximum, infer smaller eddy diffusion coefficients in this epoch. Model calculations indicate that the latitudinal dependence of H 2 vertical displacements is caused primarily by the combined effects of gravitational potential and evident differences in electron energy deposition at the top of the atmosphere affecting the temperature profile. The derived H 2 density profiles from ∼-40° latitude and others close to the equator, are found to be nearly identical on a pressure scale below the exobase. The inference is that that the pressure profile of H 2 density at Saturn is unchanged over a broad range of latitudes. © 2012 Published by NRC Research Press.


Grant
Agency: Department of Defense | Branch: Air Force | Program: SBIR | Phase: Phase II | Award Amount: 750.00K | Year: 2010

The USAF requires accurate specification and forecast of thermospheric densities for LEO satellite orbit calculations. The JB2008 thermospheric density model provides the high accuracy densities, partly made possible by using the Dst index. Dst characterizes the energy input during geomagnetic storms and substorms. Because of JB2008''s advantages the USAF plans to operationally implement this model. Unfortunately, Dst is not provided with the operational robustness required for Air Force operations. In addition, Dst is produced outside the U.S. at the World Data Center Kyoto University facility. The USGS has recently developed an excellent comparative Dst index based on the same network of magnetic observatories as the ones used by the Kyoto Dst. This Phase II project will provide a real-time, fully redundant Dst production system demonstrated with 1-minute time granularity at the current epoch, with latencies of no more than 5 minutes, and with cadences of no more than 5 minutes. The system also has the goal of providing an accurate Dst forecast with time granularity of 1-minute up to 1 hour and 1-hour to 72-hours. The project team will develop, implement, and demonstrate this system at TRL 8 for the AFRL customer and the AFSPC JB2008 end user. BENEFIT: The Phase II project will provide a real-time fully redundant Dst production system demonstrated with 1-minute time granularity at the current epoch, with latencies of no more than 5 minutes, and with cadences of no more than 5 minutes. The system also has the goal of providing an accurate Dst forecast with time granularity of 1-minute up to 1 hour and 1-hour to 72-hours. The project team will develop, implement, and demonstrate this system for the AFRL customer and the AFSPC JB2008 end user. The system and data provision that we accomplish during Phase II and the TRL 8 demonstration will allow transfer of technology to other Air Force and military entities and to the commercial market. For example, the system would have significant application for improving high latitude accuracies in radar, radio communications, and navigation systems as a result of use by the GAIM system that has been implemented at AFWA. At the conclusion of Phase II the project will immediately roll over into Phase III activity, including the operational provision of the real-time and forecast Dst indices to AFSPC for use by JB2008. In Phase III, SET plans to market the real-time and forecast Dst to radio communications and navigation systems users through inclusion in the Utah State University (USU) GAIM system that is being commercialized under the USU USTAR initiative. The Phase II development and implementation is crucial to achievement of such commercialization goals.

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