General information about satellite technology

History of satellite technology
The satellite age began with the launch of Sputnik 1 on October 4, 1957. Although Sputnik 1 burnt up on re-entry into the earth’s atmosphere after 3 months in orbit, the first telecommunications and TV transmitting satellite was launched soon after in 1962. In 1983, the first directly receivable TV satellite was put in service over Europe. Direct satellite reception only became popular in the early 1990’ies. Today, approximately 50 satellites provide Europe with TV and radio channels. Modern
satellites weigh up to 5 tons and have huge solar panels to generate the power for their up to 36 transponders. New satellites have a transmitting power of up to 150 W per transponder. In addition to the solar generators, the satellites are equipped with batteries which ensure uninterrupted operation during eclipses (i.e. when the satellite passes through the earth‘s shadow). The lifecycle of a satellite is designed to be approximately 12 years. At the end of this period, the solar cells, batteries and the transmission booster will have deteriorated to a point where they can no longer be used. Usually, the fuel for the steering jets has also been depleted by then, and the satellite can no longer be kept in position. The last bit of fuel is then used to propel the satellite from its orbit in order to make space for a successor.

ASTRA
ASTRA I is a satellite constellation positioned at 19.2° east and is the most important satellite system for the German-speaking part of Europe. Since the launch of ASTRA 1A in December 1988, 10 individual satellites have been grouped directly side-by-side in this position, with 6 satellites still being in operation today. All ASTRA satellites are privately owned by SES in Luxembourg. In the beginning all signals to the satellites were transmitted via the headquarters of SES in Betzdorf, Luxembourg, nowadays many TV companies maintain their own uplink stations. The signals transmitted from earth are converted to another frequency, amplified and then sent back to earth. Since 1998, SES has been operating a second orbital position at 28.2° east, known as ASTRA II. At the moment it comprises 4 satellites. This position mainly broadcasts channels for the British market. Meanwhile, SES is operating the satellites Astra 3 and Astra 4 in different orbital positions and for different target groups.

EUTELSAT
EUTELSAT is a multinational organisation which was established in 1977. The first EUTELSAT I F1 satellite was launched into orbit in June 1983. Today, the EUTELSAT organisation operates numerous satellites in different orbital positions. The most commonly known position is 13° East, where 3 brand-new satellites are co-positioned under the name HOTBIRD. EUTELSAT also operates several satellites under the name AtlanticBird serving the Frenchspeaking region.

Co-Positioning
Today, it is common practice to position several satellites in close proximity, appearing from earth as a single satellite. These satellites are operated under one common name such as ASTRA I or HOTBIRD and are identified by index numbers or letters. The co-positioned satellites are located in a cube with an edge length of only 40 km. Of course, the satellites must not collide with other,
as this would cause terminal damage and effectively destroy them. This is why the exact position of each satellite is constantly monitored and adjusted with the aid of steering jets.

Footprint
From their position in orbit, geostationary satellites have a „view“ of almost half of the earth, but the available energy is not sufficient to completely cover this area with receivable signals. In accordance with economic considerations, the signals are focussed on certain regions, forming what is called the satellite‘s „footprint“. Satellite operators are often quite cautious about the official footprint data they publish, which is why it is often possible to receive a good signal well beyond the limits of the indicated footprint with the aid of a high quality reception system. In reality, the footprints are not
as uniform as shown in the graphics, especially not along the edges, which can be rather „ragged“. In such areas, trial and error is the only way to determine if signals can be received.

Orbital position or satellite position
The satellites are positioned in geostationary or geosynchronous orbit at an altitude of approx. 36,000 km precisely over the equator. At this specific altitude, they permanently retain their position above the same spot on earth. The longitude of this position is hence used to differentiate between the satellites. ASTRA I at 19.2° East is hence approximately right over the town of Mbandaka in Congo. However, the degree value does not directly relate to the orientation of the antenna toward the satellite.

Transpondera
Modern satellites have up to 36 transponders. One transponder can either carry one analogue or up to 12 digital TV channels. The output of current transponders is up to 23 Glossary 150 W, but does decrease over the years. The transponder outputs of older satellites is sometimes less than 50 W.
In principle, “old“ analogue transponders can still be used digitally, but their range of channels is generally smaller than that of newer transponders, and their footprint is narrower.