Carnegie Mellon's Hyperion demonstrates sun-synchronous navigation

Citation

(2002), "Carnegie Mellon's Hyperion demonstrates sun-synchronous navigation", Industrial Robot, Vol. 29 No. 3. https://doi.org/10.1108/ir.2002.04929cab.005

Carnegie Mellon's Hyperion demonstrates sun-synchronous navigation

Carnegie Mellon's Hyperion demonstrates sun-synchronous navigation

Keywords: Carnegie Mellon, Navigation

Carnegie Mellon University's Robotic Institute has developed, with support from NASA, a prototype solar-powered robot named Hyperion (Plate 4), which made history last July by successfully circumnavigating the Von Braun Planitia, an area near Devon Island's Haughton Crater in the Canadian Arctic that is considered to be analogous to the terrain on Mars.

Hyperion tested the concept of sun-synchronous navigation, a technique that involves tracking the sun while exploring terrain. It is accomplished by traveling opposite to planetary rotation, navigating with the sun, to remain continually in sunlight. Hyperion performed navigation experiments during a period of 24-hour sunlight, exploring the terrain it encountered while simultaneously monitoring its solar panels to ensure that they collected enough energy to complete each segment of its planned traverse.

Plate 4 The Hyperion rover navigates Devon Island, the largest uninhabited island on Earth (^©Carnegie Mellon University, 2001)

Hyperion represents a class of polar rover notable for reduced mass, reduced complexity, and vertically-oriented solar panels. It gets its name from a Titan in Greek mythology who fathered the sun, moon, and dawn. The word Hyperion roughly translates to: he who follows the sun. The Hyperion rover weighs 156kgs, is 2m long by 2m wide, and is almost 3m tall with a near-vertically mounted solar panel of 3.5 square meters. It carries this panel mounted upright to catch the low-angle sunlight of the polar regions. Its chassis is fabricated of aluminum tubing and has four wheels on two axles. Hyperion is driven by four motors, one for each wheel. It has a passive (unactuated) joint at the front axle that can roll and yaw relative to the back end – similar to a wagon. It steers by driving the wheels at different speeds, but instead of skidding like a bulldozer, the passive joint turns and the robot smoothly follows arcs. The advantage is that the number of actuators is minimized (there are only four motors) but energy is not wasted skidding the wheels when turning. Hyperion measures speed, voltage and current on all its motors so that it can monitor their performance, and it has roll and pitch inclinometers for determining motions. The robot has numerous sensors to monitor power generation and consumption. There are temperature sensors spread throughout to monitor critical components. On the front axle an A-frame stands 1.5m high to support the stereo cameras and laser line scanner at a proper height to see the surrounding terrain. All of Hyperion's computers, electronics and batteries are enclosed in a single sleek body mounted between the axles.

All of Hyperion's energy comes from the sun. Its solar cells supply its power bus, which runs computers and sensors, drives the wheels and charges its batteries. The output of the solar panels depends on the solar flux, which is a function of the orientation of the panel and atmospheric conditions. The overall power tracking system is 11 percent efficient, so if 600W/m² of solar energy (a typical value) falls on the 3.5m² panels then Hyperion will have about 200W to use. Any excess power is put into a bank of lead-acid batteries so that Hyperion has capacity to climb a steep slope, drive over an obstacle, or take a shortcut through a shadow or away from the sun when necessary. Its battery capacity is 32Ahr at 24V.

According to project manager David Wettergreen, a Robotics Institute research scientist, about 95 percent of Hyperion's initial 6.1km circuit on Devon Island was completed autonomously, with the remainder under remote supervision. The initial experiment began and ended with the robot's batteries charged and ready to continue operation. As it encountered the unknown terrain, Hyperion at times fell behind its scheduled plan, but each time it caught up when it emerged in a more easily navigable region. "The ability of the robot's perception and navigation systems to find routes was very impressive", said Wettergreen. "Analysis of telemetry recorded from Hyperion will reveal the thousands of obstacles Hyperion detected and evaluated, the tens of thousands of steering corrections, and the statistics of planned versus actual navigated distance and power. Qualitatively, Hyperion wiggled through some pretty tight spots."

In the extended experiment, which was a few days after the initial one, Hyperion covered a greater distance – 9.1km – and traversed rougher terrain including scree slopes and mud flats, and was challenged with a mission plan that at times put desired goal locations in conflict with the position of the sun. Wettergreen said that the extended experiment, by design, pushed the limits of Hyperion's capability to find where further research was necessary. In this experiment Hyperion had greater difficulty due to communication drop-outs, areas of extremely rugged terrain, and dazzling of its stereo cameras by the sun, but in the end it arrived at its final destination on schedule with charged batteries. One instance of manual intervention was required to correct a steering problem. There is more work to do to move new technologies from research into development but the fundamental ideas have been proven.

For more detailed information about Hyperion and the sun-synchronous navigation experiments successfully performed in the Canadian Arctic, see http://www.frc.ri.cmu.edu/sunsync.