DFG-TIPOD

Satellites and space debris in low orbits are strongly dragged by Earth's atmosphere. The atmospheric drag is generally larger at lower altitudes. In fact, for low Earth orbiting satellites (LEOs) below 1000 km, the atmospheric drag
acceleration is the largest non-gravitational perturbation that has to be considered for precise orbit determination (POD). Precise orbits are crucial for a number of satellite-related geodetic applications, e.g.,  altimetry missions like Jason-3 measuring the surface height of the Earth's ocean or gravity missions like GRACE—FO determining the time variable gravity field of the Earth. Another important application is to determine if and where space debris crashes on the Earth. 

Satellites without an accelerometer  can not measure the atmospheric drag acceleration. Thus, this acceleration has to be modeled for POD. The atmospheric drag acceleration acting on a satellite depends mainly on the thermospheric neutral density. There are several atmospheric density models. However, there are significant differences between the densities computed with those models. Thus, the TIPOD project aims for improving LEO—POD based on high-precision thermosphere models.