Strategies for Safely Landing on Venus Tesserae
Magellan-derived information, including stereo topography, imaging, and altimeter products (roughness, rms slope) suggest generally low slopes and sufficiently smooth surfaces, but these data represent average properties over kms of scale. A lander system capable of identifying and avoiding meter-scale hazards is required.
We identified 5 primary issues which the lander’s HD&A system must accommodate: a monochromatic surface, near-isotropic lighting, atmospheric scattering, atmospheric turbulence, and the need for autonomy. Several of these issues have already been partially addressed (e.g., Chang’e-3 successful landing on the monochromatic surface of the Moon’s far side). The VFM lander design includes a NIR descent imager that is used at relatively high altitudes (~15 km) for broad scale hazards and a LIDAR system used at relatively low altitudes (~2 km) for small scale hazards. Early work on the problem of the near-isotropic lighting suggests that texture analysis may solve problems with reliable feature tracking. If these issues can be addressed, autonomous neural networks capable of dealing with uncertainty are the best option to allow efficient prioritization and guidance to a low hazard, high science value location. Identification of meter-scale hazards is only possible in the last few km of descent with avoidance maneuvers only in the final 2.5 km, providing ~3-6 minutes to divert the spacecraft. Goddard LIDAR experts are working on increasing the effective range up to 9 km, which would provide ~11-20 minutes to divert the spacecraft. We considered different options for horizontally maneuvering the spacecraft in the dense atmosphere and identified using fans as the most SWaP-efficient method. A fan system with 20 cm propellers and ~17 W can divert the lander up to 50 m if activated by 2 km altitude.