PRELIMINARY RESULTS OF HYDROGEN PROSPECTING WITH A PLANETARY

Introduction: High resolution hydrogen deposit mapping is central for a detailed understanding of lunar water ice deposits in permanently shadowed lunar craters. This becomes especially relevant in the context of potential in-situ resource utilization (ISRU). Although orbital remote sensing can provide much information, prospecting for subsurface resources can only be performed directly on the surface. The long acquisition time required as well as the extreme conditions within permanently shadowed craters require robotic execution of such a task. The small HYDRA neutron spectrometer has been successfully integrated onto the K10 Black planetary rover operated by the IRG [1,2]. In September 2007, the system was used to assess hydrogen content in an initial set of field tests at NASA Ames (ARC). During these tests, we attempted to detect and map targets of various hydrogen contents and burial depths. Test Objectives: The purpose of the rover test was to demonstrate the utility of HYDRA in a robotic prospecting task for near-surface hydrogenous deposits. Thus the objectives of the exercise were: (1) Acquire HYDRA data as the rover navigates a grid of GPS way-points chosen without prior knowledge of the target locations; (2) Detect and localize near-surface enhanced hydrogen deposits within the rover test area; (3) Validate the Haughton site-survey architecture and visualization tools in a small footprint sensor test with scientists in the loop. Test Location and Setup: The K10/HYDRA rover tests were carried out at a relatively level, unvegetated pad of fill dirt, at ARC that served as a proxy for the lunar surface. The extent of the test area was approximately 50 meters in the north-south direction, and 20 meters in the east-west direction. Within this area holes were excavated. One set of targets consisted of 3x3 foot polyethylene slabs (each 0.5 in thick, stacked 8 deep for an overall thickness of ~10 cm), buried at depths of 0, 5, 15 and 30 cm. Another set of targets consisted of stacks of cut 0.5-inch thick drywall (gypsum, 21 wt% H2O). Finally, some excavations were simply back-filled with the excavated material to act as decoys for the test. The locations of the targets were known only to three personnel involved in the exercise, in order to provide a single-blind test. On the lunar surface, cosmic rays constantly impinge on the regolith, but for terrestrial testing, a Californium-252 neutron source (activity of ~2x10 neutrons/s) was used to interrogate the soil beneath the rover. The source was co-located with the HYDRA instrument, to provide a fixed geometry and to minimize the effects of variations in soil-to-source distance (approx. 15 cm). Figure 1 shows HYDRA and the source mounted on the front of K10 Black. When the energetic neutrons from the source encounter hydrogenous materials, HYDRA measures an enhanced backscatter “albedo” flux of thermal and epithermal neutrons as the robot traverses the site.