Satellite communications, which appeared in 1958, became widely developed all over the world in the early 1990s. Nowadays, even in countries with developed communication infrastructure, about 35% of services are provided by low-orbit satellite systems, which is the largest figure in the telecommunications market.
Message transmission via satellite to several thousand stations, which are within the limits of the “broadcast spot”, costs the same amount as the message transmission to one station.
Spacecraft are divided into three types – by their altitude above the Earth. The types of services of the spacecraft listed below may differ, but their set necessarily includes data transmission and communication support. The most important differences between satellites are in the area of communication coverage and the cost of launching into orbit.
Geo-stationary satellites (36 thousand km)
The system of three satellites allows covering the whole Earth surface except for high-latitude areas (e.g. northern).
No interruptions in communication due to the mutual movement of the satellite and the Earth station during the day.
There is no need to organize inter-satellite communication (as opposed to low-orbit systems, for example).
Long service life: 10-15 years.
High-capacity equipment requires high costs.
Long delays in signal distribution are possible.
The total number of satellites in geostationary orbit is limited.
Expensive launch into orbit.
Medium-orbit satellites (10-20 thousand km).
About 20 medium-orbit satellites will be required to cover the whole territory of the Earth.
Long service life (up to 10 years).
A small number of satellites is sufficient to ensure reliable communication in most regions (compared to low-orbit satellite systems).
The signal from such satellites is distributed with a delay – up to 140 msec – but it is invisible to the human ear.
The launch of a satellite into an average high-altitude orbit is much more expensive than a low one.
Low-orbit satellites (500-2000 km)
The system of low-orbit satellites should consist of at least 50 satellites to cover the whole territory of the Earth.
Biological factor: Unlike others, low-orbit satellites pose a lower radiation threat.
Satellites require less cost to put into orbit (compared to geostationary and medium orbiting satellites).
They allow to provide uninterrupted communication with terminals located at any point of the Earth and help to organize communication in regions with underdeveloped infrastructure.
They have improved energy characteristics in comparison with systems on high orbits.
Shortcomings of low-orbit satellites are mainly limited only by the large number of satellites that are put into orbit, and a shorter period of their active operation (in comparison with other satellite systems). It is also necessary to take into account that all the satellites must be launched before commercial operation of the system (at least one of them is excluded and communication is not established).
In addition to the orbit altitude, the satellites are also estimated by a number of other parameters, such as mass, solar panel capacity and cost.