The possibility of communicating over thousands of miles using a transmitter in space was proposed by Arthur C. Clarke in a 1945 article in Wireless World, in which he described a system of “extraterrestrial relays” or repeaters in space. Clarke calculated that an object put into orbit 22,300 miles (36,000 km) above the earth would revolve around the planet in 24 hours, the time it takes the earth to rotate on its axis. Thus, the repeater would appear motionless or “geostationary” from the earth. He noted that three such repeaters located 120 degrees apart above the equator would cover the entire globe.
Only 12 years later, the Soviets launched the Sputnik satellite. However, Sputnik was not a geostationary satellite; it was in low earth orbit and had to be tracked across the sky, and it simply beeped. But it spurred US scientists and engineers to develop more sophisticated satellites for commercial use. In 1963, the world saw the results as the Syncom 3 satellite transmitted television coverage of the Tokyo Olympics. In 1965, just 20 years after Clarke’s article was published, the first commercial international satellite, known as Early Bird or Intelsat I, was launched to link North America and Europe.
Today, there are numerous geostationary (or GEO) satellites that can provide global, regional, or national coverage. The first global system was Intelsat, still in existence today. Other global systems include Intersputnik, a system comparable to Intelsat that was built and operated by the Soviet Union, PanAmSat, Intelsat’s first global commercial competitor, and now acquired by Intelsat, and Inmarsat, used for global maritime communications. However, single geostationary satellites can also be used to cover large nations such as Australia, Brazil, Canada, China, India, Indonesia, Russia, and the US, and regions such as North America, Europe, East Asia, Southeast Asia, and South Asia.
Satellite technology has evolved dramatically since the early 1960s. Early Bird had only 240 telephone circuits, while today’s geostationary satellites have 24–72 transponders, each capable of carrying a high definition TV channel, or multiple television channels, or thousands of telephone calls, text, and data messages. Early experimental satellites were designed for a lifetime of 2 years; today’s satellites are designed to last from 10 to 15 years. (The limitation on the satellite’s life is not the reliability of the electronics, which are fully redundant, but the weight, which limits the amount of station-keeping fuel that can be carried to nudge the satellite back into position when it begins to drift.)
Satellites have several properties that make them particularly appropriate for many communications applications. Geostationary satellites can cover as much as one-third of the Earth’s surface. Earth stations placed anywhere in the satellite’s beam are linked with each other through the satellite. As a result, the cost of communication via satellite is independent of distance – the cost of communicating across 500 or 5,000 miles is the same. In contrast, the cost of building and maintaining terrestrial networks is directly proportional to the length of the transmission route.
In addition to covering very large regions, geostationary satellites offer several advantages for providing communications to rural and remote areas. Earth stations can be installed virtually anywhere, whether a remote village, an offshore oilrig, a high-rise building, or a disaster site. Thus, communication can be provided wherever it is needed, without waiting to extend terrestrial facilities, for example, from cities to remote villages. Satellite networks are highly reliable; a problem with an earth station affects only that location, whereas a damaged terrestrial microwave repeater or cut fiber optic cable can knock out the entire network beyond that point. Satellite capacity is also flexible; the technology can be used for voice, data, and video, and it is simple to allocate additional bandwidth where needed. For example, a community can begin with a few voice circuits, and then add more circuits and television reception.
A disadvantage of GEO satellites for interactive services (such as telephony) is that there is a quarter second delay in each direction (to and from the satellite) because of its distance above the earth. Also, this distance means that the signals are weak, and devices must be large enough (typically with an antenna of half a meter or more in diameter) to amplify the signals from the satellite.
Low earth orbiting (LEO) satellites have no noticeable delay because they are located only about 600 miles above the earth. At this altitude, the satellites pass much faster overhead, and numerous satellites in various orbits must be used to provide continuous coverage. However, current generations of LEOs have very limited bandwidth, making them suitable only for voice and text or simple email. Two LEO systems, Iridium and Globalstar, provide portable voice and limited data communications with handheld devices about the size of early “brick” mobile phones. They can be used where mobile phone service is not available, such as at oilrigs and mining sites, mountain-climbing camps, other isolated regions, and war zones. However, the price of their service and their limited bandwidth make them unsuitable for providing basic communications in developing countries.
The most common use of satellites is for television transmission. Satellites transmit news feeds from around the world, and major sporting events such as the Olympic Games and the World Cup. Global and regional satellites transmit television signals across oceans and continents; domestic satellites transmit television channels to local television stations for terrestrial rebroadcast or to cable headends for distribution through local cable networks. High-powered GEO systems transmit satellite signals directly to end-users, who install a small antenna on the outside of their house or apartment.
Specialized GEO satellites also transmit radio programs to small receivers. The WorldSpace satellite system delivers digital audio directly to portable radios in Asia and Africa. While one target audience is people who can afford to subscribe to digital music and ethnic channels, the system can also be used to transmit educational programs in a variety of languages for individual reception or community redistribution over small local radio stations for listeners with inexpensive transistor radios. In North America, similar satellite systems transmit commercial-free radio primarily to built-in automobile receivers for commuting drivers.
LEO satellites operated by Iridium and Globalstar provide telephone service almost anywhere in the world to handheld receivers. These systems provide voice and low-speed (typically 2.4–9.6 kbps) data connectivity that could be used for email, but is too slow for web access. The price per minute for these services is typically much higher than national terrestrial services. Thus, while they may be used by reporters and adventurers, and by relief agencies to coordinate aid and logistics for natural disasters, they are far too expensive for residents of developing countries. A somewhat less expensive option for the Middle East and much of Asia and Africa is phone service using Thuraya, a GEO satellite with operations headquartered in Abu Dhabi. GEO satellites can also be used for telephony using community earth stations. In Alaska, village telephone service is by satellite, with a local telephone network connected to a satellite terminal. The signal delay is an inconvenience, but the system is very reliable, and definitely preferable to the old two-way radio systems.
Internet gateways can be accessed via geostationary satellites. For example, Alaskan villagers and residents of the Canadian Arctic are connected to the Internet via US and Canadian domestic satellites. A Mongolian Internet service provider (ISP) and some African ISPs access the Internet in the US via Intelsat. However, these systems are not optimized for Internet use, and may therefore be quite expensive. GEO satellites designed for Internet access are now available in the US and Canada, and are planned for other regions without terrestrial broadband. Canada’s Anik F2 provides Internet access in rural and remote parts of Canada; in the US, WildBlue and Directnet offer Internet access via satellite for households and small businesses without terrestrial broadband service. The price of Internet access is likely to decline as new protocols are being developed to make more efficient use of satellite bandwidth and thus lower transmission costs for users.
GEO satellites designed for interactive voice and data can also be used for data broadcasting. For example, China’s Xinhua news agency transmits broadcasting news feeds to subscribers equipped with very small aperture terminals (VSATs). WorldSpace’s digital radio system can also be used for delivery of Internet content; schools or telecenters can identify which websites they want to access on a regular basis, and WorldSpace broadcasts the data for reception via an addressable modem attached to the radio. WorldSpace has donated equipment and satellite time for pilot projects at schools and telecenters in Africa.
Many of the innovations in satellite technology were originally designed for military or for government research, and then made available for commercial applications. NASA’s Applied Technology Satellites in the 1980s and joint US–Canadian Communication Technology Satellite tested new frequencies and antennas, and were made available for public experiments in telemedicine, distance education, and community networking. Spread spectrum technology was developed for the US military as a very secure means of transmitting by satellite to avoid interception. Spread spectrum is now used for VSATs and in wireless mobile systems with code division multiple access (CDMA). Global positioning systems (GPS) using multiple satellites enable the US military to identify the location of targets on the ground with great accuracy. Initially, GPS systems for consumer use were “dumbed down” to limit precision, but now the most accurate versions are commercially available for use with handheld devices for hikers and for pinpointing the location of mobile phone users in emergencies.
Remote sensing by satellite was developed for geological research and mapping of terrain. Now farmers in the US midwest download remote sensing data to ascertain which parts of their fields need fertilizer, and with GPS transceivers in their tractors, can apply the fertilizer exactly where it is needed. Public online tools such as Google Earth use satellite imagery to enable the public to view their neighborhood or sites around the globe. Specialized satellite systems gather information that can be used for a variety of purposes. Remote sensing satellites are used to map the earth and to identify mineral deposits and various forms of soil and vegetation. This information can be used to identify promising areas for mining, to monitor flooding and desertification, and to plan land use for agriculture, forestry, and human settlements. Weather satellites transmit images that are used to monitor storms and forecast weather conditions. GPS systems calculate distances to three or more satellites to determine the location of the user within a few meters on the earth’s surface. Standalone GPS systems are used for navigation, exploration, and outdoor recreation, and are being built into mobile phone handsets so that callers can be precisely located in emergencies.
Satellite Applications In Developing Regions
Business And Consumer Services
Small satellite earth stations operating with GEO satellites can be used for interactive voice and data, as well as for broadcast reception. VSATs have been used for interactive services such as video conferencing and for broadcasting in the Australian outback. VSATs are also used for telephony and Internet access in Alaska. Banks in remote areas of Brazil are linked via VSATs; the National Stock Exchange in India links brokers with rooftop VSATs. VSATs for television reception (known as TVROs, for “television receive only”) deliver broadcasting signals to viewers in many developing regions, particularly in Asia and Latin America.
Rural Health-Care Delivery
In Alaska, community health aides are the frontline providers in village health-care. A satellite network links the villages with regional hospitals, which in turn are linked to a major medical center in Anchorage. The village health aides are in daily communication via satellite with physicians at the regional hospitals. The Alaska Federal Health Care Access Network (AFHCAN) project is extending the use of the Internet for telemedicine throughout rural Alaska, using the satellite network. Equipment provided in village clinics is designed to be simple and cost effective, consisting of a personal computer and peripherals including electrocardiograms (for heart monitoring), electronic otoscope for observing otitis media (ear infections common in village babies), and a digital camera to send still images of patients. Much of this communication can be done in store-and-forward mode; for example, the digital photos can be sent as email attachments. Doctors at the regional hospitals, in turn, can transmit X-rays and other medical data to specialists in Anchorage. AFHCAN may now be the world’s largest telemedicine project, serving more than 235 sites, including 198 native clinics.
SatelLife of Cambridge, Massachusetts, operates a store-and-forward satellite system, using a LEO satellite, HealthSat-2. The satellite’s unique polar orbit allows ground stations to transmit and receive data from any point on earth daily. SatelLife’s HealthNet network enables medical practitioners to seek advice on treatment of unusual cases from colleagues in other parts of Africa, and to download articles from medical libraries. Burn surgeons in Mozambique, Tanzania, and Uganda have used HealthNet to consult with one another on patient treatment and reconstructive surgery techniques. In response to a cholera epidemic in Zambia, the medical librarian at the university obtained literature from her “partner library” at the University of Florida, and then disseminated the information to all HealthNet users in the region. SatelLife has also evolved to become an Internet gateway, providing public health and environmental workers with an inexpensive “on ramp” to the global information superhighway.
Distance Education And Training
The Rural Communication Services Project (RCSP) was designed to use satellite communications via Intelsat to provide basic telephone service and teleconferencing to support development activities in an isolated region of Peru. The RCSP provided public telephone service and audio conferencing facilities to seven communities in the Department of San Martín, a high jungle area east of the Andes. The conferencing activities were developed in cooperation with Peruvian agriculture, health, and education ministries, and incorporated a wide variety of administrative, training, diffusion, and promotion strategies. More than 650 audio teleconferences were carried out during the project. At the end of the two-year period, the telecommunications operator, ENTEL, transferred responsibility for teleconferencing development to its commercial sector, with plans to promote teleconferencing among government agencies and private businesses.
The University of the South Pacific uses a satellite-based network called USPNet to provide tutorials to correspondence students scattered in 12 island nations of the South Pacific from its main campus in Fiji. USPNet enables distance students to participate in audio tutorials conducted from any campus, communicate by email with lecturers/tutors or other students, access the world wide web, watch live video broadcasts of lectures from any of the three campuses (in Fiji, Samoa, and Vanuatu), and take part in interactive video conferences and tutoring with the main campus. Also, the network’s communication facilities are important in saving time and travel for the staff of the correspondence program and the extension centers scattered across several time zones (and both sides of the International Date Line) and thousands of miles of ocean. General university administration has also become more efficient with email communication via USPNet to all USP locations.
In the Caribbean, the University of the West Indies established a teleconferencing network called UWIDITE (UWI Distance Teaching Experiment – later Enterprise) to link its campuses in Jamaica, Barbados, and Trinidad with extension centers throughout the Commonwealth Caribbean. This initiative has evolved into UWIDEC (for UWI Distance Education Center) headquartered at the Trinidad campus, and with facilities at the main Jamaica campus and a smaller unit at the Barbados campus. The audio conferencing network links the three campuses with university centers in 15 other Caribbean nations. The network may be used for lectures, tutorials, and meetings, enabling students to complete certificates and to participate in outreach programs, as well as to listen to lectures in regular UWI courses in preparation for taking exams to complete the first part of their degrees from their home countries. UWIDEC now provides additional materials and support for distance education in the region.
Canadian Inuit have established the Inuit Broadcasting Corporation (IBC), which transmits TV programs via satellite across the north. Inuit communities are separated by huge distances in Nunavut, a region that makes up one third of Canada’s landmass. Most have no road access, and can be reached only by airplane or boat. As IBC notes: “The only roads connecting communities are electronic.” IBC programming is distributed by satellite over the Aboriginal Peoples Television Network (APTN), an indigenous network featuring native programming from across Canada and around the world.
Impact And Future Of Communication Satellites
Satellite communications have had dramatic impacts in ending isolation and creating a truly global village. News flashes around the world and across regions in seconds. People living in countries where media choices are few or heavily controlled get programs from outside their countries by installing small satellite dishes. While we think of satellites as primarily bringing content to end-users, their interactive applications are perhaps more significant. People in remote settlements can now make phone calls and access the Internet via satellite, as well as watch television. They can get medical help in emergencies, get access to education not available locally, and transmit their own information, as email messages, web pages, or radio programs.
Will satellites survive, as companies install more optical fiber, and terrestrial wireless networks link computers and mobile phones? Satellites will still have roles to play, particularly for broadcasting and in developing regions. As broadcasters introduce high definition TV, they need enormous bandwidth to carry the signals to all of their local outlets or cable headends. Fiber is not likely to be available for this form of point-tomultipoint distribution. Satellites will also be used instead of local cable or over-the-air transmission to deliver digital television directly to households. Satellites will remain an important means of transmitting video and high bandwidth content across oceans and between continents. Where submarine fiber optic cables have been installed, they will serve as a backup to prevent loss of service if cables are cut or circuits are overloaded. In the developing world, satellites will be important to deliver television and radio signals where no terrestrial network exists, and to provide broadband Internet access. They will become less important for telephony as mobile wireless networks are built out, but will still be the only means to reach isolated communities.
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