National Aeronautics and Space Administration

Living With A Star

Targeted Research and Technology

Application of New Solar and Atmospheric Variability Models for Forecasting Thermospheric Drag on Spacecraft: Starshine and Yohkoh Case Studies

ROSES ID: NRA-00-OSS-01      Selection Year: 2001      

Program Element: Independent Investigation: LWS

Principal Investigator: Michael J, Picone

Affiliation(s): Naval Research Laboratory


The overall goal of the proposed work is to study and specify accurately the response of the neutral upper atmosphere to solar irradiance variations. A direct application of this work is improved forecasting of atmospheric drag on low earth orbiting (LEO) spacecraft, notably the International Space Station (ISS) and the debris which threatens the ISS. Varying solar energy inputs cause significant fluctuations in upper atmospheric temperature and density that impede the motions of earth-orbiting spacecraft. Knowledge of the instantaneous locations of orbiting spacecraft (and debris) is essential to support societal needs that include national defense, communications, spacecraft and space shuttle mission planning and astronaut safety.
The largest source of error in precision LEO orbit determination is the estimation of drag, primarily due to errors in the density model. Past studies indicate that the driver of these errors is inaccuracy of the F10.7 cm radio flux in representing the solar driver of the thermosphere. We will combine, for the first time, (1) new models of EUV irradiance variability developed recently at NRL (NRLEUV and the SOL-C index) and (2) NRLMSIS, an improved upper atmospheric composition and temperature model also developed recently at NRL. We will test and validate the new capability by comparing predicted and actual locations of the Starshine and Yohkoh spacecraft and by comparing the NRLMSIS atmospheric density values with those derived from the spacecraft orbits. A product of our work - an improved density model for predicting LEO spacecraft locations - has immediate relevance, for example, in reducing the time spent in collision avoidance maneuvers by the ISS. The more accurate empirical atmospheric model will also improve analysis of observations by important science missions (e.g., TIMED) and will embody a clearer picture of the Sun's effect on the near-Earth space environment.
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