Simulation and parameter studies for the conceptual design of a combined thermal and mechanical penetration mechanism for icy planetary bodies

Kurzfassung

The search for traces of life on other planets has been one of the perspectives of science ever since. The water ice in the polar regions on Mars and the icy Jovian moon Europa or the subglacial lakes in the Antarctica are places of interest for astrobiological research. Melting probes are an effective way to bring research instruments to an operational depth, where it is guaranteed that the overburden soil or ice protects the traces of life from galactic rays. However, these probes get stuck if soil accumulates in front of the probe. For this reason a combination of a melting probe and a Mole mechanism for soil Penetration is investigated in this thesis. The combination of these two promising concepts is named Cryomole. The Mole mechanism is supposed to displace the accumulated soil into the small gap between the housing and the ice and prevent the shaft of the Cryomole from refreezing by ist movement. In order to find a prototype design, the theory of melting (very cold) water ice, the theory of the hammering mechanisms and the theory of soil resistance forces is discussed intensively. The existing theory of melting ice has been expended by the influence of a melting water layer. Based on these theories a simulation framework has been proposed developed and implemented in MATLAB. This simulation allows to predict the hammering performance of a Mole mechanism and the melting performance of a Mole shaped melting probe. The Simulation of existing Mole designs is included in the simulation as well. Moreover, different semi-empirical soil models are implemented. Secondary to soil models for Mars and Moon, a model of quartz sand under earth gravity is included in the simulation, for validation pupose. The thermal environment for the three areas of application is considered as well. In the end a parameter study for the mechanical and thermal penetration is performed. The study includes a discussion of the length to diameter ratio, the cone angle of the tip, the surface roughness of the housing, the mass of the housing and the ice temperature. The results of the parameter studies, for example, confirm a optimal performance for a cone angle of 60�° and suggest to increase the length of the Mole rather than the diameter to enlarge the volume. Finally some more guidelines for a first prototype design are summarized and some perspectives for the future of the Cryomole are stated.