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The accuracy of global atmospheric models used to predict the middle/lowerthermosphere characteristics is still an open topic. Uncertainties in theprediction of the gas properties in the thermosphere lead to inaccuratecomputations of the drag force on space objects (i.e. satellites or debris).Currently the lifetime of space objects and therefore the population ofdebris in low Earth orbit (LEO) cannot be quantified with a satisfactorydegree of accuracy. In this paper, the Global Ionosphere Thermosphere Model(GITM) developed at the University of Michigan has been validated in order toprovide detailed simulations of the thermosphere. First, a sensitivityanalysis has been performed to investigate the effect of the boundaryconditions on the final simulations results. Then, results of simulations havebeen compared with flight measurements from the CHallenging MinisatellitePayload (CHAMP) and Gravity Recovery and Climate Experiment (GRACE)satellites and with existing semi-empirical atmospheric models (IRI andMSIS). The comparison shows a linear dependency of the neutral density valueswith respect to the solar activity. In particular, GITM shows anover-predicting or under-predicting behaviour under high or low solaractivity respectively. The reasons for such behaviour can be attributed to awrong implementation of the chemical processes or the gas transportproperties in the model

Effect of the solar activity variation on the Global Ionosphere Thermosphere Model (GITM)