The future in-situ exploration of small Solar System bodies such as asteroids, comets or small icy moons, requires robotic platforms capable of controlled surface mobility. In the microgravity environment of small bodies, conventional wheeled rovers are quite ineffective due to the low frictional forces on the ground. Accordingly, we have been developing a minimalistic, internally-actuated rover, called Hedgehog, which is capable of achieving large surface coverage (by attitude-controlled hops), fine mobility (by tumbling), and coarse instrument pointing (by changing orientation relative to the ground). Specifically, Hedgehog uses motors and mechanical brakes to apply torques to three internal flywheels, which transfers angular momentum to the external structure. For a grounded rover, this gives rise to controllable ground reaction forces that propel it along desired trajectories. This type of hopping mobility is critically enabled by the microgravity environment of small bodies, whereby small surface contact forces can produce long-range ballistic flight. We have demonstrated this locomotive capability in simulations, experiments in microgravity test beds, and on reduced gravity parabolic flights.
In this talk we describe a mission architecture that allows for systematic and affordable in-situ exploration of small bodies with one or many Hedgehog rovers. The Hedgehogs would be deployed from a mother spacecraft, which would then act as a communication relay to Earth and aid with tasks such as localization and navigation. Power would be provided by primary batteries, and/or secondary batteries with solar panels for recharging. Due to its small, cube-shaped form factor, Hedgehog could leverage many subsystems being developed for interplanetary CubeSats. Since this mobility concept is scalable, the platform can be sized accordingly to accommodate a suite of scientific instruments such as cameras, microscopes, and XRS.
Collectively, our study aims to demonstrate that exploration via controlled mobility in low-gravity environments is technically possible, economically feasible, and would enable a focused, yet compelling set of science objectives aligned with interests in planetary science and human exploration. After three years of maturation under the NIAC program (as well as support from NSF, CIF, SURP, FOP), Hedgehog rovers will become available for infusion into space missions in the 2017-2018 time-frame.
This is a joint project between Stanford University, the Jet Propulsion Laboratory, and the Massachusetts Institute of Technology, and is performed under the NASA Innovative Advanced Concepts program. Government sponsorship acknowledged.