What is Satellite Communication?Saman
We rely heavily on satellite communication in our modern world, but that reliance does not necessarily transfer into an understanding of how satellite communication works or an appreciation for the range of applications it has. While not comprehensive by any means, this article delves into both of these topics.
Learning more about what satellite communication is begins with the dictionary. Dictionary.com defines satellite communication as “an artificial earth satellite that facilitates communications, as radio, television, and telephone transmissions, by means of the reflection or the amplification and retransmission of signals between stations on earth or in space.”[i] These signals come in the form of electromagnetic waves, but because of how these waves travel, they require line-of-sight. The earth’s curvature prevents this, so the satellite relays the signals to enable communication between very disparate places.[ii] The original idea for communications satellites came from noted scientist and science-fiction writer Arthur C. Clarke in his 1945 article “Extra-terrestrial Relays: Can Rocket Stations Give World-wide Radio Coverage?” published in Wireless World.[iii] He included a figure to represent how that communication would work.
While Clarke observed that his idea would seem fantastical, he argued that it would come to pass. From our vantage point in the 21st century, we can easily agree with Clarke. Satellites are placed at different orbital levels. Geostationary satellites have a geostationary orbit (GEO) and are the farthest away at about 22,000 miles from earth. Medium Earth Orbit (MEO) satellites are closer but still at least about 1,000 miles from earth. Low Earth Orbit (LEO) satellites are the closest and also the most common kind of satellite.[iv] A single GEO satellite can cover about 1/3rd of the Earth’s surface, accounting for 99% of the population. MEO and LEO satellites cover much less area.[v] Satellites all use different frequencies for their transmissions, and as satellite communication has become more common, congestion, especially in lower-frequency bands, has become a problem. The frequencies that satellites use are divided into seven groups: L, S, C, X, Ku, K, and Ka. L has the lowest frequencies and Ka the highest.[vi] Satellites are often referred to using these bandwidth designations because different frequencies often carry different kinds of channels, as one example. Websites like LyngSat.com provide lists of channels based on satellite. The International Telecommunication Union handles the allocation of bands.[vii]
Passive and active satellites
There are two main types of satellites, passive and active. Passive satellites reflect the signal from the source to the receiver, but active satellites amplify the signal. Most satellites used now are active.[viii] A subset of these two types of satellites is the Molniya satellite, which was pioneered by the Russians to deal with the problem of satellite placement near the poles. The curvature of the Earth makes regular geosynchronous satellites largely nonfunctional, but the Molniya satellite enables communication even at high latitudes.[ix] The earth-bound receivers vary in size. Technology has advanced to the point that receivers can be as small as roughly the size of a cell phone. These very small aperture terminals (VSATs) make satellite communication more affordable and available.[x] For information to be transmitted efficiently, a satellite network requires many receivers.[xi]
The main purpose of satellite communication is to make communication easier and faster. Using a satellite network, the same broadcast can reach billions of people, and satellite communication can provide access to phone, internet, and television services to people in remote or rural areas when traditional land-based technologies fail.[xii] Satellite communication presents rewarding business opportunities. Gross revenues in 2000 reached $60 billion,[xiii] and that number more than tripled with 2014 global revenue of $203 billion.[xiv] Industry leader SES offers both civilian and military options for mobile voice and data, television programming, internet access, and earth observation services.[xv] The most profitable and common use of satellite communication is satellite TV services, which for 77% of all satellite services revenues in 2014.[xvi] Amateur satellite radio groups have a long history of using satellite communication for radio broadcasts, and groups like the Radio Amateur Satellite Corporation (AMSAT), which was first formed in 1969 continue to provide opportunities for people outside the industry to use satellite technology.[xvii] Militaries rely on satellite communication for world-wide broadband Communications-On-The-Move (COTM) so that soldiers, commanders, and military leadership can access and share high-definition video, voice, and data from anywhere in the world almost instantaneously.[xviii]
Given the increase in use of satellite communication, it promises to be an industry that will continue to grow and provide more options for users. When companies like COMSAT decided to venture into the new area of satellite communication in the mid-1960s, it was unclear whether the risk would be worth it, but over a half century later, Clarke’s prediction that satellite communication would be invaluable has clearly come true.
[i] “Communications satellite.” Dictionary.com.
[ii] “Satellites-Communication Satellites.” Satellites.spacesim.org.
[iii] Clarke, A. C. ““Extra-terrestrial Relays: Can Rocket Stations Give World-wide Radio Coverage?” Wireless World (October 1945): 305-8.
[iv] “Types of Orbits.” Polaris Project Evening Star. Iowa State University. http://www.polaris.iastate.edu/EveningStar/Unit4/unit4_sub3.htm
[v] Elbert, B. Satellite Communication Applications Handbook. 2nd. Ed. Artech House, 2004.
[vi] “Satellite Frequency Bands.” Telecommunications and Integrated Applications. European Space Agency. http://www.esa.int/Our_Activities/Telecommunications_Integrated_Applications/Satellite_frequency_bands
[vii] “ITU Radiocommunication Sector.” International Telecommunication Union. http://www.itu.int/en/ITU-R/Pages/default.aspx
[viii] “Military Satellite Communications Fundamentals.” Crosslink 11.1 (2010).
[ix] “Molniya.” Global Security.org. http://www.globalsecurity.org/space/world/russia/molniya.html
[x] Elbert, B. The Satellite Communication Ground Segment and Earth Station Handbook, Second Edition. Artech House, 2014.
[xi] Elbert, 2004.
[xii] Elbert, 2004.
[xiii] Elbert, 2004.
[xiv] Tauri Group. 2015 State of the Satellite Industry Report. Satellite Industry Association, September 2015. http://www.sia.org/wp-content/uploads/2015/06/Mktg15-SSIR-2015-FINAL-Compressed.pdf
[xv] “About Us.” SES. https://www.ses.com/about-us/why-satellites
[xvi] Tauri Group. 2015 State of the Satellite Industry Report. Satellite Industry Association, September 2015. http://www.sia.org/wp-content/uploads/2015/06/Mktg15-SSIR-2015-FINAL-Compressed.pdf
[xvii] “About Us.” http://www.amsat.org/
[xviii] ViaSat. https://www.viasat.com/services/airborne-mobile-broadband