Wind and Surface Roughness Considerations for Seismic Instrumentation on a Relocatable Lander for Titan

The influence of terrain and the atmosphere on seismic measurements to be made by the Dragonfly rotorcraft lander on Saturn’s moon Titan are examined. The need to relocate the vehicle leads to rather different deployment considerations from a fixed lander. Surface texture affects both the steady-state tilt that the instrument must tolerate on deployment, and it affects (via aerodynamic roughness) the wind load on the instrument body, or on a windshield around it: a tolerance of 5-10° and legs of 1-3 cm should eliminate the need for leveling mechanism at most sites. Wind models suggest a characteristic velocity noise of ~1 um/s may be expected on the lander skids on loose ground. The tilt noise caused by ground deformation means the horizontal axes of an instrument deployed between the skids may be at a similar level, so exquisite sensitivity in these axes may not be justified. Wind loads directly on a streamlined seismometer housing, on the tether, and on the lander via the ground all give comparable vertical noise (~10 nm/s) at the instrument, and thus the mechanical complexity of a separate windshield, which would need to be massive to not itself blow away, is not justified.