An Innovative Method for Measuring Drag on Small Satellites

The need to accurately predict satellite positions is a leading aspect of space situational awareness and presents increased challenges in the specification of the spacecraft environment in low earth orbit. Atmospheric drag is the most important environmental perturbation for low orbiting spacecraft and the most difficult one to model and predict precisely. The author will present a method for the characterization of satellite drag through the use of a dual-instrument in-situ approach. The elements of this method include a novel acceleration measurement suite and a small Wind and Temperature Spectrometer in order to measure both atmospheric density and wind. A sophisticated error model has been developed to evaluate this method and the results show that it is possible to improve our ability to characterize satellite drag by at least 10-14%. Furthermore, ground testing indicates that the instrument hardware will meet the requirements necessary to produce an improved data product. In order to evaluate this approach in orbit, students at the University of Colorado at Boulder have developed a small spacecraft called the Drag and Atmospheric Neutral Density Explorer. This small (under 50 kg), spherical satellite addresses important needs of the defense and civilian community by measuring quantities which are crucial to the determination of atmospheric drag on spacecraft. This paper describes the measurement process, as well as a method of computing the satellite drag coefficient. We then present the design and testing of the instruments and summarize the results of the error model.