Flyover Modeling of Planetary Pits

Introduction: On the surface of the moon and Mars there are hundreds of skylights, which are collapsed holes that are believed to lead to underground caves. This research uses Vision, Inertial, and LIDAR sensors to build a high resolution model of a skylight as a landing vehicle flies overhead. We design and fabricate a pit modeling instrument to accomplish this task, implement software, and demonstrate sensing and modeling capability on a suborbital reusable launch vehicle flying over a simulated pit. Future manned colonies on other planets and moons will start in caves for their protection from the harsh space environment, led by the technology developed by this research. While planetary caves have been hypothesized for decades, they have not been plausible exploration candidates due to lack of surface access, difficulty of operation, and obscurity from orbit. Newly discovered planetary pits might be key to accessing subsurface voids, caves, and lava tubes. While the existence of pits is now unambiguous, how to explore them and whether any lead to extended caves is unknown. Pits represent an unparalleled opportunity to access enigmatic subterranean spaces, but their complex geometry makes them impossible to fully observe from orbit. Future robotic exploration missions will target one of these pits[3]. As a spacecraft is about to land, it flies at an altitude under a few hundred meters, traveling at a speed under tens of meters per second. As it flies over a pit during this time, it can collect high quality visual, inertial, and LIDAR data at unprecedented viewing angles from which to model the pit. This same sensor suite is used for precision navigation and terrain hazard avoidance. Reconnaissance from flyover modeling will be used to inform approach and entry paths for rovers[4]. It will be used to characterize geology, select likely locations for inhabitation, and inform follow on exploration. Instrument Design: The pit modeling instrument design accounts for pit geometry, vehicle dynamics during scanning, and required data precision and resolution. The geometry of planetary skylights drives range and field of view of the sensors. Our work specifically studied lunar skylights, which are the best characterized and of high interest. Wagner and Robinson[5] used automated computer vision to detect 200 candidate skylights that are evenly distributed in both location and size. Based on these statistics, the sensor is designed to survey an area that is nominally 50m in radius and 50m in depth. This can model the majority of lunar pits. The dynamical parameters of the landing phase determine sensor range and rate requirements. One example with publicly available data is the NASA ALHAT free flight campaigns on the Morpheus vehicle, which commanded an apogee of 245 meters and a 30-degree glide slope at 12.5 meters per second[1]. This trajectory has been designed to simulate the final landing portion of a robotic lunar mission and can be used as the nominal profile for a skylight scanning mission. From this nominal trajectory, we defined the maximum sensing range to be 260m. This is corresponds to a 45 degree pointing angle above vertical at 180m altitude.