P. Hager, R. Haber, D. Kraus, S. Nogina, A. Sievers, T. Tattusch, U. Walter

For surface-craft such as rovers, the lunar surface provides a challenging thermal environment. Environmental temperatures between 40 K and 400 K are encountered. Spatial temperature gradients of about 200 K within a few centimeters are possible. Heat transfer is dominated by radiation and no atmosphere dampens the incoming solar heat flux. Future lunar rovers will have to move through this demanding environment and are subject to varying heat loads. This scenario is the focus of the Thermal Moon Simulator (TherMoS) of which we present the current status in this paper. Today's thermal designs for rovers to be used on the Moon are traditionally based on worst case scenarios. These minimum/maximum designs are either heavy or restricted to certain selenographical regions. Commercial thermal tools like ESATAN-TMS®, Thermal Desktop® or Thermica® are well suited to account for the thermal design questions arising for spacecraft in orbits and for static objects such as bases on the Moon. They are not suited to simulate the dynamic temperature behavior caused by rover movement and large environmental heat flux from multiple directions. The Institute of Astronautics at the Technische Universität München investigates the question in which cases and on which scales the dynamic behavior of thermal problems in space applications are necessary in contrast to the worst-case approach. Target groups for this tool are thermal engineers, systems engineers, and project managers. In this context the TherMoS - computer simulation tool is being developed. The TherMoS tool is composed of a topographic module, a regolith module, a module for craters and boulders, a module for orbit propagation and lunar orientation, a ray tracing module, a geometry assembly module, a thermal solver module and a post-processing module. All but the ray tracing module are implemented in MATLAB® and the ray tracing algorithm uses NVIDIA OptiX®. The global topography is based on a publicly available dataset measured by the LALT (Laser ALTimeter) instrument onboard the Japanese probe Kaguya. The regolith model improves on older models by integrating temperature dependent values and a depth dependent regolith density profile. The orbit propagator is based on the VSOP2000A, a semi-analytical power-series approximation. The TherMoS simulation allows importing and manipulating geometric models from other software. The ray tracing algorithm determines the radiative heat transfer between the lunar surface and the surface craft. It takes into account the solar fluxes, the IR radiation and their diffusive reflections. The ray tracing functionality runs on a graphics processor and is called from MATLAB®. In MATLAB® the thermal calculations are performed; temperatures and temperature dependent material properties are recalculated. The orbit propagator alters the local Sun vector during the simulation. Manipulation of the geometry between calculation steps allows for the movement of the surface-craft. The thermal solver and the post-processing module are not discussed in this paper. Within this paper we present results for the modules and preliminary results for a generic rover in a lunar environment. Besides we discuss the general outline and point out the next steps in the development of the TherMoS tool.

Deutscher Luft- und Raumfahrtkongress 2012, Berlin

Deutsche Gesellschaft für Luft- und Raumfahrt - Lilienthal-Oberth e.V., Bonn, 2013

Conference Paper

englisch

21,0 x 29,7 cm, 10 Seiten

urn:nbn:de:101:1-2013052411098

ray tracing, roving vehicles, Exploration, Thermalanalyse

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24.05.2013