A prototype cryobot for clean subglacial access and sampling
VALKYRIE is an ice-penetrating robot, also known as a cryobot, developed at Stone Aerospace under a NASA ASTEP grant to test new strategies and technologies for descending through the thick ice shell on Europa and other outer-planet icy moons. VALKYRIE uses a unique power source: a high-power industrial laser transmits infrared light to the robot via glass fiber. Upon reaching the cryobot, the light beam is expanded onto a dispersion mirror, which redirects the light to strike the sidewalls of a cylindrical heat exchanger attached to the vehicle nose cone. As the sidewalls warm up from the infrared light, water cycling through the heat exchanger is also heated. The robot can descend either “actively,” jetting hot water out of the nose cone or “passively,” using just the heated nose cone. The nose cone design incorporates a primary water jet on the centerline and secondary off-center jets that can be activated for turning. In active jetting mode, intake ports in the nose pull water into the heat exchanger and the warmed water is pumped out the nose cone jets. In this fashion the cryobot becomes a closed-cycle hot water drill.
To identify, and thus possibly avoid, obstacles in the ice a novel end-fire Synthetic Aperture Radar was designed and built at University of Colorado, Boulder, and incorporated into the robot design. VALKYRIE also carries a science payload to investigate microbial activity in the ice column. The payload consists of a fluorescence-based multi-channel flow cytometer from Leiden Measurement Technology and water and filter sample collection systems. Autonomous sample collection algorithms were developed which use real-time data streams from the flow cytometer to determine optimal triggering and timing of sampling routines. The samples were subsequently processed by the Christner lab at Louisiana State University.
VALKYRIE was tested over the course of two month-long field seasons on the Matanuska Glacier in Alaska in 2014 and 2015. The initial prototype measured 25 cm in diameter by 2.5 m in length and the first season tested the vehicle’s descent speed and turning capability. Using active jetting the robot descended to 30.52 m depth at an average rate of 0.9 m/hr and, using turning jets, achieved a 7-degree diversion angle off dead vertical. Tests were terminated, due to time constraints, with the cryobot fully functioning and all systems go. In the second field season the science payload was integrated into the vehicle. Sample collection algorithms were tested and the cryobot collected filter and water samples for subsequent laboratory analysis. The SAR system was tested on the glacier independently and showed ability to detect, and model for obstacle avoidance behaviors, a 1 m object 80 meters in advance.
In addition to helping us learn about how to penetrate ice on other ocean worlds, the technology developed on VALKYRIE may provide alternative access to deep subglacial lakes on Earth with minimal contamination. The robot can be sterilized and the melt hole allowed to refreeze behind it, minimizing forward contamination. Successful completion of VALKYRIE has led to the development of advanced cryobot concept designs for the NASA-funded SPINDLE project, which will utilize Antarctic ice sheets as planetary-analog testbeds.