Robotic exploration of planetary surfaces is restricted by the availability of solar power and implications of thermal conditioning to survive extremes of hot and cold, of midday sun and overnight hibernation. Power and thermal cycling are fundamental reasons why exploration ambitions and accomplishments are compromised. With a constant energy source and moderate ambient temperatures, surface exploration missions could last for months or years. The number of daily accomplishments would be multiplied by remaining longer in sunlight and, in some cases, never experiencing nightfall. New mission concepts that dramatically expand operational goals and time frames will revolutionize planetary surface exploration.
We advocate sun-synchronous circumnavigation as a mission concept for planetary surface exploration. With the robotics technologies necessary to enable it, sun-synchronous circumnavigation will provide the capability of persistent, in some cases perpetual, presence to explore, dwell in, and develop resource-rich regions near the poles of planets and moons.
Sun-synchronous navigation is accomplished by traveling opposite to planetary rotation, navigating with the sun, to remain continually in sunlight. At appropriate latitude and speed, rovers can maintain continual exposure to solar insolation sufficient for sustained operation. Furthermore by lagging the night-to-day terminator by the appropriate phase angle, these rovers can regulate their temperature, seeking the transient region between nighttime cold and daytime hot. Power and thermal limitations can thus be overcome on destinations like the Moon and Mercury.
At mid-latitudes sun synchrony results in global circumnavigation but at polar-latitudes, during periods of continual sunlight, the sun synchronous route is a circum-feature circuit. Energy-efficient, solar-powered rovers can operate, even on Earth, in the persistent sunlight of the polar summer by tracking the sun with the orientation of their vertically-oriented solar panels. They must navigate around terrain features to avoid shadowing or seek locations of unobstructed sunlight.
Sun-synchronous navigation makes possible an innovative class of planetary rovers notable for their lower mass, reduced complexity and cost, and freedom from nuclear power and overnight hibernation. These rovers will manage the collection of solar power, so that power storage requirements are minimized. This translates into further reduced rover mass, complexity, and cost.
The objective of this research is to discover, express, and exhibit the importance of reasoning about sunlight as it pertains to robotic exploration. At the Robotics Institute of Carnegie Mellon University we are developing the algorithms, technologies, and experiments that will fulfill the vision of sun-synchronous navigation.
The great explorers of history went beyond their own backyard, to follow rivers, cross mountain ranges, reach the poles, and circumnavigate the globe. The ambition then and now is to discover the unknown: to explore regions, not just sites; to analyze, not just observe; and to operate effectively and reliably without excessive support. Robotic explorers capable of sustained operation will perform rigorous in situ science, detailed surveys, resource characterization, and exploration on a vast scale.
