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Hyperion is two meters long and two meters wide with a panel of silicon solar cells
of 3.5 square meters. It can be configured for polar or equatorial operation.
In polar regions it carries its solar array near vertically to catch the low-angle
sunlight; when operating closer to the equator its panel lays flat in a level
deck for the sun overhead. Hyperion is fabricated of lightweight aluminum tubing
and has four wheels on two axles. On the front axle an A-frame stands 1.5 meters
high to support the stereo cameras and laser scanner at a proper height to
see the surrounding terrain. All of Hyperion’s computers, electronics
and batteries are enclosed in a single body mounted between the axles. The
robot weighs 156 kilograms.
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 of this design is that the number of actuators is minimized (there
are only four motors) but energy is not wasted skidding the wheels when
turning.
Hyperion uses a pair of digital cameras to image the terrain in front of it
and a laser line scanner to detect close in obstacles. It carries a third camera that can produce panoramic images so that remote observers can view its
complete surroundings. Hyperion’s laser scanner sweeps a line in front
of it looking for obstacles, either rocks or drop-offs. Hyperion measures speed,
voltage and current on all its motors so that it can monitor their performance
and determine its motion. 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.
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
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% efficient so if 600 W/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. It’s
battery capacity is 32Ahr at 24V.
Hyperion operates sun-synchronously, meaning it tracks the sun and determines
its actions to maintain sufficient power to complete its mission. To navigate
Hyperion must have a map of the terrain, an estimate of where it is located,
and a measurement of the current time. Digital elevation maps at 100m resolution
or better are available for most of the Earth. Maps of this resolution or better
are, or will soon be, available for interesting areas of the Moon and Mars. Hyperion
uses a combination of inertial sensing and odometry to determine its location
and an accurate onboard clock to know the current time. With a map and a clock
Hyperion can determine the relationship between the sun and terrain to compute
where shadows will fall. By knowing its location relative to the map it can
determine where the shadows are and how they will move over time. The difficult
problem is then to make decisions that optimize the efficiency and safety of
the path while reconciling the need to maintain adequate power all the time.
To travel through terrain Hyperion uses a pair of cameras, like eyes, and computer
algorithms to see, measure and model obstacles in its immediate surroundings.
It then evaluates multiple possible paths that avoid the obstacles, selecting
a path that heads toward its goal while collecting sufficient solar energy
to proceed. Hyperion can miss seeing an obstacle under certain conditions so
it also carries a laser scanner to act as a “virtual bumper”. If
something, like a dirt-covered rock, appears in front of it, Hyperion stops
immediately and sends a message indicating that it has been surprised and may
have a problem.
The answer is sometimes yes and sometimes no. Hyperion’s control system
is designed for what is sometimes called “sliding autonomy.” It
can smoothly slide from direct teleoperation where a human operator tells it
everything to do, through modes of control where the operator and robot share
decision making, to full autonomy where Hyperion decides for itself how to
perform a given mission, where to go and when. Hyperion has a health monitoring
capability that enables it to decide when it needs help. If it can’t
find it’s way, thinks the mission is impossible, or detects strange behavior
from its sensors, it sends a message to human operators about what has happened
and if it has decided to stop and wait for instructions. When everything is
okay it can decide to pick up and continue on its own.
Hyperion must move with the sun to collect the energy that it needs to survive.
As it explores it can conduct science investigations on the fly, collecting
data and seeking evidence of specific phenomena: biological, hydrological or
geological, while it is traveling. Exploration is complicated by the sometimes
conflicting goals of scientific interest and power consumption but ultimately
the advantage is that Hyperion can cover great distances and survive for a
long time. In exploration both of these factors increase the chance of finding
something interesting.
- Devon Island Expedition 2000
- Atacama Desert Expedition 2002
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