Table of Contents

Satellite Communications

Tele-Robotics, Tele-Medicine and Time Delay

Teacher Background

With the increase in the sophistication of telecommunications satellites, the opportunity exists to transmit and receive not only images and voice but also command and control functions for machines. The machines may be mining equipment working in harsh environments (coal or uranium mines), may be rovers or other vehicles on remote location on Earth (Antarctica) or exploring distant planets, or may be laboratory or medical equipment in remote regions of Earth.

Another example might be the use of tele-medicine to combat doctor shortages in remote areas. Transportation on short notice of highly trained individuals (such as doctors) into remote communities to carry out a surgical procedure is not practical. Through telecommunication and tele-robotics surgery can be performed efficiently and at reduced cost, while bringing a better quality of life to individuals in remote communities.

Time Delay for Telecommunications Satellites

Telecommunication satellites typically orbit the Earth in a geostationary orbit – one whose orbital period is equal to the rotation of the Earth (24 hrs). This allows the satellite to always be visible at the same point in the sky. The height of this orbit (from the centre of Earth) is 42,200 km, or 35,800 km from Earth's surface directly below the satellite. Telecommunication signals travel at essentially the speed of light (300,000 km/s) so that the minimum time delay expected in an area that is serviced by a single satellite will be no shorter than 0.24 seconds. Since this is a one-way trip – for a command to go to a robotic system, the return trip (e.g. the visual confirmation of the command) is also 0.24 seconds. From commanding an action to receiving the acknowledgement of the action, then, is no less than about 0.5 seconds. For most applications this time delay is insignificant. For very fine and precise experiments or operations, this delay may be critical.

Consider telecommunications with rovers on other planetary bodies. The Moon is approximately 384,000 km away from Earth. The time delay, one-way, to the Moon is about 1.28 seconds. Although this is not overly significant, remote control, robotic exploration of the Moon would require safeguards (such as speed limitation) to ensure the rover does not collide with surface objects or fall into lunar craters. When Apollo astronauts were televised lifting off from the moon, cameras left on the moon were operated from Earth. Because of the time delay, capturing the launch and the ascent of the lunar module required the camera operators to anticipate the launch by zooming the television camera back and tilting it up before liftoff. Had there been a launch incident, the camera operator would be "behind the action" by about 2.5 seconds, potentially losing valuable data associated with the incident. They avoided this by ensuring that the field-of-view of the camera would be large enough to cover such contingencies.

Should we wish to carry-out remote control exploration of Mars using rovers then the time-delay will be very significant. The time delay to Mars when Mars is closest to Earth is about 4 minutes, while at its furthest the time delay is approximately 20 minutes. This type of exploration would proceed very slowly.

Current State of Tele-Robotics / Tele-Medicine

The following is a brief summary of the current activities associated with tele-medicine and tele-robotics. Projects to link North America and Europe with developing countries to aid in training doctors in those areas, as well as projects to provide adequate healthcare to individuals working in areas where access is limited are becoming a common occurrence, with satellite stations found throughout several poorer nations. Major players (on the provider side) are Canada (World leader), the United States, Australia and Europe (UK, Germany, and France). The United States seems to have taken the forefront in the development of robotic surgical equipment with Canada taking the forefront in its application, use, and the development of the satellite technology required for implementation.

Appropriate Links

• Telemedicine – Memorial University, http://www.med.mun.ca/telemed/
• Center for Medical Robotics and Assisted Surgery – Pennsylvania: http://www.mrcas.ri.cmu.edu/