Robot Astronauts Help
The American space program reached a turning point in 1969 when Apollo 11 landed on the Moon, and for the first time, a creature from Earth walked on another world. Some people think the visitor from Earth should have been a robot. Some scientists argue that there is no need to risk people’s lives by sending them into space. Robotic space probes have been sent near planets in the Solar System. Robotic spacecraft have landed, as of this writing, on Venus and Mars, and comets have been explored up close. Why not have robotic spacecraft do our cosmic wanderings?
Almost Like Being There
Robots could, in theory, be used to explore outer space while people stay safely back on Earth and work the robots via remote control. A human being can wear a control suit and have a distant humanoid robot, called a telechir , mimic all movements. The robot can be some distance away. The remote-control operation of a robot is called teleoperation . When the remote control has feedback that gives the operator a sense of being where the robot is, the system is called telepresence (Fig. 19-1).
With high-end virtual reality , it is possible to duplicate the feeling of being in a place to such an extent that the person can imagine that he or she is really there. Stereoscopic vision, binaural hearing, and a crude sense of touch can be duplicated. Imagine stepping into a gossamer-thin suit, walking into a chamber, and existing, in effect, on the Moon or Mars, free of danger from extreme temperatures or deadly radiation! With remote control, virtual reality can have its basis in actual reality.
Despite the assets of robotic space travel, some people say that it defeats the ultimate reason for having a space program: the romantic adventure of living beings roaming the Cosmos. There is another problem too: Communications signals don’t travel very fast on an interstellar or intergalactic scale.
The Light-speed Problem
If robots are used in space travel with the intention of having the machines replace human astronauts, then the distance between a robot and its operator cannot be very great. The reason is that the control and response signals propagate through space at only 299,792 km/s (186,282 mi/s).
The Moon is 1.3 light-seconds from Earth. If a remotely controlled robot, rather than Neil Armstrong, had stepped onto the Moon on that summer day in 1969, its Earthbound operator would have had to deal with a delay of 2.6 seconds between command and response. It would take each command 1.3 seconds to get to the Moon and each response 1.3 seconds to get back to Earth. True telepresence is impossible with a delay like this. Experts say that the maximum delay for realistic telepresence is a tenth of a second (0.1 s). Therefore, the distance between the robot and its controller cannot be more than 0.5, or 1/20, light-second. This is about 15,000 km or 9,300 mi, slightly more than the diameter of the Earth.
Suppose that astronauts are in orbit around a planet whose environment is too hostile to allow an in-person visit. Then a robot might be sent down. An example of such a planet is Venus, whose crushing surface pressures would kill an astronaut clad in even the most advanced pressure suit. It would be easy to sustain an orbit of less than 15,000 km above Venus, so telepresence would be feasible.
Practice problems of this concept can be found at: Traveling and Living in Space Practice Problems
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