TECH TALK TYPE/DESCRIPTION
GEO: A geostationary satellite is in orbit around the Earth at an altitude where it orbits at the same rate as the Earth turns. An observer at any place where the satellite is visible will always see it in exactly the same spot in the sky, unlike stars and planets that move continuously.
MEO: Medium Earth orbit. The region of space around Earth above low Earth orbit (altitude of 1,243 mi) above sea level) and below geosynchronous orbit (altitude of 22,236 mi) above sea level).
LEO: Low Earth orbit is an altitude of 1,200 mi or less. Most of the manmade objects in outer space are in LEO.
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USES
Global communications, television broadcasting and weather forecasting, and have a number of important defense and intelligence applications.
PRO’S
Geostationary satellites appear to be fixed over one spot above the equator. Receiving and transmitting antennas on the earth do not need to track such a satellite. These antennas can be fixed in place and are much less expensive than tracking antennas. Less satellites needed to cover more area.
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The most common use for satellites in this region is for navigation, such as the GPS; and also deployed to provide broadband connectivity as of late. Communications satellites that cover the North and South Pole are also in MEO.
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The International Space Station conducts operations in LEO. All crewed space stations to date, as well as the majority of satellites, have been in LEO. The altitude record for human spaceflights in LEO was Gemini 11 with an apogee of 853.8 mi. Apollo 8 was the first mission to carry humans beyond LEO in December 1968. Since the Apollo program ended in 1972 there have been no human spaceflights beyond LEO. Earth observation satellites and spy satellites use LEO as they are able to see the surface of the Earth clearly by being close to it.
Closer distance provides low latency broadband delivery, with levels similar to the performance of fiber transmission. Fewer satellites needed to cover the planet compared to LEO.
LEO requires the lowest amount of energy for satellite placement. It provides high bandwidth & low communication latency. Satellites and space stations in LEO are more accessible for crew and servicing. LEO requires the lowest amount of energy for satellite placement. It provides high bandwidth & low communication latency. Satellites and space stations in LEO are more accessible for crew and servicing.
LEO satellites need less powerful amplifiers for successful transmission, LEO is used for many communication applications, such as the Iridium phone system. Some comm satellites use much higher geostationary orbits.
CON’S
A disadvantage is the incomplete geographical coverage. Another is that radio signals take approximately 0.25 of a second to reach and return from the satellite, resulting in a small but significant signal delay.
MEO satellites deliver low latency compared to GEO, their higher orbit means they may not reach quite the same levels planned by the new LEO sats.
Satellites in LEO have a small momentary field of view, only able to observe and communicate with a fraction of the Earth at a time, meaning a constellation of satellites is required to in order to provide continuous coverage. Satellites in lower regions of LEO also suffer from fast orbital decay, requiring either periodic reboosting to maintain a stable orbit, or launching replacement satellites when old ones re-enter.
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DOMmagazine.com | nov 2019
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