Neutral Density Measurements from the Gravity Recovery and Climate Experiment Accelerometers

Predicting the orbits of space objects in low-altitude orbits requires an accurate model for the atmospheric neutral density. The current accuracy of semi-empirical models limits the prediction accuracy and impacts a number of operational decisions. The current models are based on sparse measurements of the neutral density, collected over an extended period. One of the problems is observing the thermosphere density changes in response to the solar and geomagnetic variability on short temporal scales, such as those characterized by geomagnetic storms. The stochastic behavior of the solar forcing represents one of the major challenges in predicting satellite orbits. In situ measurements of the density can play a significant role in improving the structure of the neutral density models and in providing a timely measurement for enhancing the accuracy of the satellite predictions. Measurements from orbiting accelerometers carried by the twin Gravity Recovery and Climate Experiment satellites have the potential for providing accurate and timely measurements to improve the satellite prediction accuracy. The objective of this paper is to describe the procedure for using the Gravity Recovery and Climate Experiment accelerometer measurements for determining accurate density measurements.