Marcin Pilinski, University of Colorado at Boulder / Laboratory for Atmospheric and Space Physics; Geoff Crowley, ASTRA LLC.; Matt Seaton, ASTRA LLC.; Eric Sutton, University of Colorado / SWx TREC
Keywords: Conjunction Analysis, Satellite Drag, Low Earth Orbit, Space Environment, Data Assimilation
Abstract:
Much as aircraft are affected by the prevailing winds and weather conditions in which they fly, satellites are affected by the variability in density and motion of the near earth space environment. Drastic changes in the neutral density of the thermosphere, caused by geomagnetic storms or other phenomena, result in some of the most significant perturbations of LEO satellite motions through drag on the satellite surfaces. This can lead to difficulties in accurately locating satellites, temporarily losing track of satellites, and errors when predicting collisions in space. As the population of satellites in Earth orbit grows, higher space-weather prediction accuracy is required for critical missions, such as accurate catalog maintenance, collision avoidance for manned and unmanned space flight.
The Dragster assimilative atmospheric tool was developed by ASTRA LLC. in conjunction with university and government partners to address this critical need. The main objective of the Dragster tool was to reduce conjunction analysis errors through better aerodynamic force modeling along the satellite orbit. Dragster assimilates orbital data from 70-100 LEO space objects into an ensemble of atmospheric models. Solar and geomagnetic forcing parameters are included in the state vector as they are critical to determining the atmospheric state. Currently, ASTRA LLC. is working with the University of Colorado, Boulder on several significant updates to the Dragster tool that will help build an enhanced, comprehensive, nowcast and forecast of the satellite drag environment.
To date, Dragster has primarily used two-line element (TLE) orbit data and empirical atmospheric models for its validation and testing. Recent developments have added the capability to assimilate orbital data based on special-perturbation (SP) orbit solutions which have higher-cadence and accuracy than TLEs. Furthermore, the ensemble management system has been upgraded to include multiple parallelized ensembles of Global Circulation Models (GCMs) running across an arbitrary number of processing cores and computers. Unlike empirical models of the atmosphere, the GCMs solve for the coupled fluid motions in the upper atmosphere providing a more spatially resolved picture of the satellite drag environment.
In this paper, we will first review the Dragster architecture and design. Next, we present validation results of the Dragster assimilation when using high cadence SP-based data as well as ensembles of Global Circulation Models. Finally, we compare these validation results to previous results that used empirical atmospheric models and TLEs. As part of the validation, we compare the drag observed by a variety of satellites which were not used as part of the assimilation-dataset and whose perigee altitudes span a range from 200 km to 700 km. We also compare Dragster results with remote sensing observations of the atmosphere which are independent of satellite drag entirely. The performance of Dragster atmospheric specification will be compared with several leading atmospheric models.
Date of Conference: September 17-20, 2019
Track: Astrodynamics