The upper atmosphere (aka as D-region, mesosphere or middle atmosphere) is only accessible for in-situ measurements with the help of sounding rockets. Data from the height region 50 to 100 km are therefore scant and theoretical models describing the chemical, physical and dynamic properties of this region are in need of more data to ascertain their validity. Experimentally the main emphasis has traditionally been on the determination of plasma densities (electrons, ions, ratio between the two etc.), but due to the co-operation with other institutions aboard the same sounding rockets and a wide variety of scientific topics (e.g. dynamics, distribution of trace constituents, etc.) have been and are being addressed. Ultimately the aim is a convergence of the outcome of theoretical modelling with results of empirical/statistical models.