Thesis defence T. Visser: GOCE

27 November 2019 12:30 - Location: Aula, TU Delft - By: webredactie

Cross-wind from linear and angular satellite dynamics - The GOCE perspective on horizontal and vertical wind in the thermosphere. Promotor 1: Prof.dr.ir. P.N.A.M. Visser (LR).

The decay of satellite orbits has been used extensively in the past to determine the density of the highest layer of our atmosphere, the so called thermosphere. The air particles cause drag on the satellite, thus causing it to decelerate and lower its orbit. Due to the introduction of extremely sensitive accelerometers, we have seen the rise of an additional measurement opportunity: deriving the wind at the satellite location from the aerodynamic forces acting on the satellite. Validating these new wind measurements is however difficult. The measurements often only partly agree with ground measurements and existing atmosphere models. Errors in the aerodynamic model of satellites could explain these differences, but density measurements suggest otherwise.

Therefore in this work an attempt is made to derive the wind not only from aerodynamic forces, but also from the aerodynamic moments acting on a satellite. For this investigation, the GOCE satellite (of the space organization ESA) was selected, that carried unrivaled accelerometers and flew at the exceptionally low altitude of 250 kilometers. Indeed, it turns out to be possible to derive the wind from the aerodynamic moments. On top of that, by combining both measurements not only the horizontal, but also the vertical flows could be validated. However, due to its slim, symmetric shape, it was not possible to validate the aerodynamic model of this satellite by comparing the two wind measurements. The forces and moments turned out to react nearly identically to changes in the attack angle of the flow, causing the measurements to be inter-dependent. Changes in the aerodynamic model did therefore not improve the consistency between the two measurements. It is probably possible to improve the aerodynamic model if the same method is applied to other satellites with a less symmetric shape, such as Swarm, CHAMP, or GRACE.

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For access to theses by the PhD students you can have a look in TU Delft Repository, the digital storage of publications of TU Delft. Theses will be available within a few weeks after the actual thesis defence.