ROBOTIC SPACE MISSIONS
Space robots come in all
shapes and sizes, and have a wide variety of functions. These include
planetary flyby probes (e.g. Voyagers 1 and 2), orbiters (e.g. Galileo,
Cassini), atmospheric probes (e.g. Huygens Titan probe), landers (e.g.
Mars Pathfinder), rovers (e.g. Sojourner), robot arms (e.g. the Space
Shuttle Remote Manipulator System), and robots currently under development
for the International Space Station.
All space robots are basically quite similar, in that each has a controller, sensors, actuators, radio communications and a power supply. The sensors provide information about the robot and its environment. The controller processes the information from the sensors, along with instructions radioed from ground control, and sends appropriate command signals to the actuators. The actuators and drive convert the command signals into actions.
The long transmission times for radio waves over interplanetary distances preclude “real-time” remote control of distant space robots from Earth, so such robots must be capable of operating independently (autonomous control). This is particularly important for rovers, which are likely to encounter rocks, cliffs, craters and other hazards as they move around.
Many mobile robot
(“mobot”) controllers use a layered system of control modules based
on insect behaviour. In the development of the software, layers of behaviour
generating modules are added one at a time, each of which connects sensing
to action. The modules all run in parallel whenever triggered by the
relevant sensors. To prevent conflicts arising between behaviours that
could be triggered at the same time, the modules are organised into a
“pecking order” (hierarchy). Higher-level behaviours have the power to
temporarily suppress lower-level ones, but when the higher-level behaviours
are no longer being triggered, the lower-level ones resume control.