Absolute total density and density fluctuations in the thermosphere, on time scales as small as two hours, are measured using precision satellite orbit ephemeris data and satellite laser ranging. High precision data are retrieved from two satellites with very precise accelerometer information on board, and from modern Kalman filtering analyses within the optimal orbit determination technique applicable to hundreds of satellites. The precise determination of atmospheric density between 200 km and 1400 km and its temporal variation is useful for validation of atmospheric density models and for accurate quantification of satellite drag. Correlation of derived density fluctuations with solar flux proxies and magnetic indices are used to investigate the sensitivity of temporal and global density changes to solar and geomagnetic forcing. The research is brought into the classroom by creation of an orbital mechanics and upper atmospheric physics class for graduate students. That course is offered with the option of distance learning participation. Engineering design projects are developed for undergraduate research participation, and a formal collaboration with the Turtle Rock Community College brings Native Americans directly into the research program through graduate assistant participation and lectures at the College.
Atmospheric density modeling has long been one of the greatest uncertainties in the dynamics of low Earth satellite orbits. Accurate density calculations are required to provide meaningful estimates of the atmospheric drag effects on satellite motion. These effects increase with lower altitude orbits and also with higher effective area and lower mass satellites. This research used precision satellite orbits (produced using GPS and satellite laser ranging measurements) to produce a new data source for upper atmospheric density. The density data sets will help atmospheric modelers validate and improve their neutral density models, and provide a data source for researchers studying both long and short term changes in the upper atmosphere. The long term objectives of the PI are to better understand the density fluctuations in the thermosphere, to improve orbit estimation and prediction for low Earth orbit (LEO) satellites, to improve the transfer of knowledge between the aeronomy and orbital mechanics communities, and to educate a broad audience about space weather and orbital mechanics. Progress toward achieving these long term goals will be furthered by the specific objectives of research. 1. Develop a series of upper atmospheric density data sets using precision orbit ephemeris (POE) data and satellite laser ranging (SLR) data. 2. Examine the fluctuations in atmospheric density over time scales ranging from two hours to one day and correlate these fluctuations with specific upper atmospheric phenomena. 3. Present research results and increase awareness of space weather at a variety of levels and to a variety of audiences, train future researchers, and improve interaction among researchers in both the aeronomy and orbital mechanics communities. Highlights of the research include using the CHAMP and GRACE satellites to perfect the technique and showing the POE derived densities are better than those found using existing atmospheric models. POE derived neutral density data sets were derived for the life of the CHAMP and GRACE satellite missions, and for the TerraSAR-X and ICESat satellites. All of this data is available for further research including model validation or for assimilation into models. Five students have completed Master of Science degrees in Aerospace Engineering while working on this research. Three undergraduate students were involved with the research. Projects and lectures related to this research were incorporated into four classes and several public presentations related to aeronomy and satellite drag have been made. A collaboration with Haskell Indian Nations University was begun with hopes to further develop this relationship in the future.
